View Full Version : Oxford Crystal Reference restoration
Here is a picture of my very sad looking Oxford Crystal Reference TT, in need of restoration. It's not been used since my Premier 4 (also pictured) blew up over 10 years ago.
I would now like to play vinyl again, but the TT has many design issues and I need help from anyone who has some experience with this product to help me get it working properly.
Oh yes, and hello to everyone!
Peter.
http://www.saabphotos.com/gallery/albums/hpr_saab9k/Oxford0001.jpg
chris@panteg
12-08-2010, 12:52
Hi Peter
pop into the welcome area and introduce yourself , if you could .
i remember this deck very well , sounded amazing at the time i heard it (1988)
i think Guy Sergeant might know something about these ? not sure or perhaps Mark (ynwan) , the arm is the Air Tangent (air bearing) i believe , and uses some kind of pump ? is that still working .
Hi Chris,
Indeed the Airtangent is the original (Mk1) version with the heavy counterweight fitted. Just turned the pump on and it still runs, no cartridge fitted ATM so air bearing may or may not be ok but it seems to slide nicely. Also the turntable powers up and goes around (which considering the tiny 22 year old rubber belt used is a minor miracle!).
Turntable serial number is CR-059, and was made for me in Q1 1988.
The main problems are
(1) The sorbothane isolation disks cannot support the weight of the sub-chassis and after multiple failures (from day 1 really) have since been lost/discarded. Need to obtain an effective replacement that does not inject any sonic signature (my own attempts all seemed to colour the sound).
(2) The platters/bearing, something causes the TT to "wobble" when correctly set up, If you set the TT to eliminate the wobble it effectively becomes a swinger. In both cases there is a subtle wow. Could be a symptom of problem (1).
(3) The top platter has a dish machined into the top surface so the weight holds the record in contact. However this slope causes the arm to skate inwards and IMO effects tracking. IIRC the air-tangent is set up so that it neither skates in or out when correct on a flat/level TT. The slope also means the cartridge is not perpendicular to the record surface and the arm also appears to "run down hill" because the headshell is not parallel to the surface of the platter which means that the tracking force varies according to the music in more ways than you can think of!
(4) Lots of dust, obviously :)
It seems that however you set up the TT something is not right. At this stage it would be nice to know if mine is the only one with these problems.
I had borrowed a Koetsu Platinum Signature and this was the only time I remember it being right, as if the cartridge didn't really care about its alignment. When I found out how much that cartridge would cost I gave up the challenge. I took the cartridge out and forgot about it. Next time I turned the system on there was a loud crackle when my fingers brushed against the bare cartridge wires and that was that.
Peter.
Hello :). I remember the Oxford Crystal but never studied the specifics closely I'm afraid.
You can actually buy Sorbothane in lots of different grades depending on the weight it will carry; have a look on-line. To experiment (don't laugh) you could try buying posh insoles for running shoes - these are often made from layers of different density sorbothane and can be cut up with a pair of scissors.
Not sure about the 'wobble' issue - you will have to be more specific in your description.
Pics of the whole thing taken to bits would help.
The platter really needs to be taken to a machine shop and have the concave surface machined off IMHO. There was a definate fad amongst manufactures for this solution but, whilst superficialy a good idea, it didn't work very well.
I will take it apart this w/e as I have to relocate it anyway and take pictures.
>> have the concave surface machined off IMHO
Interesting. Do you think the top platter surface should be polished or rough?
I have thought about flipping the top part upside down, and putting some kind of mat in the space between the two sections. But then there is no central cutout where the LP label is. Hmm.
Another manufacturing flaw with the TT is that the two platter parts actually have a tiny gap (you can get a bit of paper beween them in places so there are areas where there is no contact). I don't know the theory behind a two section platter so don't know what the ideal material would be (if any). Perhaps an air gap all the way around is even desirable.
By "wobble" I mean that you can see the cartridge move up and down a mm or two (from memory) as the platter rotates when playing a flat record. It is very obvious at 45 rpm. This means that the spindle is not actually pointing perpendicular to the reference plane. and the whole bearing/platter assembly is precessing (?) a little. The bottom part of the bearing housing can be adusted so that the wobble is reduced to zero, but the centre of rotation is then effectively offset so you get the same effect as a "swinger" like an LP with the hole slightly in the wrong place. But of course the centre of inertia is then not in the right place either, and the belt tension varies during the revolution, etc. It's clearly preferable to put up with the wobble.
I should point out that this not a new phenomena. The TT did this from day it was installed. At the time I looked at other Crystal turntables and they all did this to some degree or other. I was told that it wasn't significant, but I believe it is why the next killer turntable on the block (the first Basis ?) buried the Reference sonicly without all the fuss and weight, because it was rotationally utterly stable.
A big irony is that one feature of this turntable is that you can remove the centre spindle and position a real swinger so that it does not swing! :doh:
I have seen sorbothane turntable feet as well as bushes and all kinds in varous grades. I'm spoiled for choice really. I am hoping someone knows the right one for this TT. This needs to be sorted before investigating anything else really as the sorbothane supports sets the level of the TT. again :doh:
Peter.
This deck was suposed to have superb machining and it sounds to me as if there's dirt of grit in between the platters preventing them from mating properly (?)
The dished platter may not be a huge problem with conventional tonearms as increasing the bias slightly would be enough to counter things (and possibly tilting the headshell ever so slightly too, to maintain channel separation). Obviously with a linear tracker, the dishing will cause some artificial "bias."
I only saw one of these once and at first I was confusing it with memories of "The Source." Try Oxford Audio Consultants, West Midlands Audio and Acoustic Arts (if he's still trading from home) - and other Absolute Sounds dealers of long-standing and see if any of them know about this deck. They're the kind of people with rich clients for these
Good luck :)
Spectral Morn
12-08-2010, 18:19
This deck was suposed to have superb machining and it sounds to me as if there's dirt of grit in between the platters preventing them from mating properly (?)
The dished platter may not be a huge problem with conventional tonearms as increasing the bias slightly would be enough to counter things (and possibly tilting the headshell ever so slightly too, to maintain channel separation). Obviously with a linear tracker, the dishing will cause some artificial "bias."
I only saw one of these once and at first I was confusing it with memories of "The Source." Try Oxford Audio Consultants, West Midlands Audio and Acoustic Arts (if he's still trading from home) - and other Absolute Sounds dealers of long-standing and see if any of them know about this deck. They're the kind of people with rich clients for these
Good luck :)
These are the people who had involvement in Oxford Acoustics at the time though if I remember right the main guy moved on John something or other :scratch: I can't remember sorry.
The deck needs to be taken to pieces and each section cleaned. The platter is probably not responsible for the arm problem.
My gut feeling is it is an issue with a part or parts not being level. Dirt under the platter could cause this slight rise and fall as could damage to the bearing. However it is hard to say with certainty without seeing the TT in the flesh.
Air bearing arms are exceptionally fussy about every part being level and the arm tube being clean (use isopropanol). Each part of the TT must be level and the deck must be set up on a concrete floor. Once the TT is level then check the arm mounting and arm are fully level. Then you go about setting up the arm cart etc, VTA, HTA etc must be 100% right.
The sorbothane is an issue as if I remember right I think different types were used in different areas to compensate for weight distribution and these had to be placed in the right spots.
This was a fantastic TT in its day and I would love one but I can't afford it. It is imho worth working on this to get it right as this TT and the NA Mentor Reference are seminal memories of mine, as to what at the time I thought was fantastic in TTs
Snoopdog (an AOS member) owned an Oxford (up until recently) so he should be able to help a bit....I wanted to buy his at the time he was selling but he would not sell without the SME 5 arm on it and I did not need another one.
Don't give up on this.
I would love an Air Tangent arm too. I have an Oracle Delphi and I remember seeing photos of them with AT arms on them at the time 20 years ago or so.
PS Can you pop into the welcome section and say hello, tell us a bit about yourself, taste in music and current system.
Additional info it was Jon Harker and the dealers that DSJR mention were the main dealers for the TT. If I remember right Oxford Audio Consultants came out of the ruins of Oxford Acoustics when they went tits up.
Regards D S D L
You guys are pretty spot on. I'm not sure if I should name names but yes, the turntable came from Acoustic Arts. I had booked their rooms in Watford to audition valve amplifiers over the christmas period. I had moved my entire system down there and as we were running out of time decided to leave it all there for the holiday. Later on a van reversed through the plate glass window toppling an equipment rack which had an Oracle Delphi and Airtangent on top. The arm was literally bent through 90 degrees. My turntable (then an Oracle Alexandria) was stolen (later recovered). Given that the air tangent was unsellable it became part of a deal which included a new Oxford Crystal Reference TT (which was the latest thing at that time), the Air tangent is designed for easy arm/cart swapping so the broken arm was easily replaced.
When the Oxford folks (Fraser Shaw & Jon Harker of Oxford Audio Consultants) put the system together prior to delivery they found that the Air Tangent Air Beam was also very slightly bent causing it to stick, so they arranged to have the arm shipped to Sweden to be repaired by the Stig himself. Meanwhile they installed the turntable at my old house with a well-tempered arm to keep me in business.
Unfortunately there was a problem with the top platter rotating against the bottom platter due to manufacturing defects. This causes scoring of lacquer on the bottom platter when small bits of dust gets trapped between (it gets in through the gap) and when you clean the metal section the polish can enter if you're not careful. So they took the TT away and reground/relaquered the various parts and when the airtangent returned they re-installed the turntable with it at my new house.
I mention this because these guys really did bend over backwards to get the TT going to my satisfaction, I don't think the Airtangent is a good match for the deck and the SME V would be a better choice for the alignment reasons given already. If it had worked then maybe the other problems would have been overlooked. My ultimate choice of Cartridge was also a factor in it not working. In the end Oxford Acoustics where not successful and it became impossible to get support, and I don't want to hassle them any further.
At the moment I would certainly consider exchanging the turntable (assuming it can be restored) for an Oracle Delphi so you never know. You must understand that it is high maintenance, requiring constant polishing, cleaning and removal of dust.
I cannot in all conscience let the Air-tangent go though as it has been in the wars. It is also a Mk1 and I am told quite inferior to the Mk2.
peter.
Spectral Morn
12-08-2010, 20:20
You guys are pretty spot on. I'm not sure if I should name names but yes, the turntable came from Acoustic Arts. I had booked their rooms in Watford to audition valve amplifiers over the christmas period. I had moved my entire system down there and as we were running out of time decided to leave it all there for the holiday. Later on a van reversed through the plate glass window toppling an equipment rack which had an Oracle Delphi and Airtangent on top. The arm was literally bent through 90 degrees. My turntable (then an Oracle Alexandria) was stolen (later recovered). Given that the air tangent was unsellable it became part of a deal which included a new Oxford Crystal Reference TT (which was the latest thing at that time), the Air tangent is designed for easy arm/cart swapping so the broken arm was easily replaced.
When the Oxford folks (Fraser Shaw & Jon Harker of Oxford Audio Consultants) put the system together prior to delivery they found that the Air Tangent Air Beam was also very slightly bent causing it to stick, so they arranged to have the arm shipped to Sweden to be repaired by the Stig himself. Meanwhile they installed the turntable at my old house with a well-tempered arm to keep me in business.
Unfortunately there was a problem with the top platter rotating against the bottom platter due to manufacturing defects. This causes scoring of lacquer on the bottom platter when small bits of dust gets trapped between (it gets in through the gap) and when you clean the metal section the polish can enter if you're not careful. So they took the TT away and reground/relaquered the various parts and when the airtangent returned they re-installed the turntable with it at my new house.
I mention this because these guys really did bend over backwards to get the TT going to my satisfaction, I don't think the Airtangent is a good match for the deck and the SME V would be a better choice for the alignment reasons given already. If it had worked then maybe the other problems would have been overlooked. My ultimate choice of Cartridge was also a factor in it not working. In the end Oxford Acoustics where not successful and it became impossible to get support, and I don't want to hassle them any further.
At the moment I would certainly consider exchanging the turntable (assuming it can be restored) for an Oracle Delphi so you never know. You must understand that it is high maintenance, requiring constant polishing, cleaning and removal of dust.
I cannot in all conscience let the Air-tangent go though as it has been in the wars. It is also a Mk1 and I am told quite inferior to the Mk2.
peter.
They were Oxford Acoustics.
Hi Peter sorry to read of all your disasters :doh::(
To be honest I would not want to sell or swap my Oracle however if the Airtangent works fully (and the price were right) I might be interested in it even if it is perhaps not cosmetically perfect.
What kind of mounting does it need ?
Yes the MK2 was better.
Regards D S D L
Snoopdog
12-08-2010, 20:24
Hi Peter
Oxford Acoustics was started by Jon Harker (owner/operator of Oxford Audio Consultants since 1990) and Fraser Shaw (a surgeon by profession) in 1986.
I purchased an Oxford Acoustics Crystal Reference tt with SMEV from Subjective Audio (Howard Popeck) in 1987 following a demo conducted at my home with Howard, Jon, Fraser and a very nice curry.
I owned that turntable until I sold it last year to Bob (It Costs How Much? - on HifiWigwam).
If you pm me your home email address I can send you a very comprehensive setup document that I compiled for Bob which also contains many tips I picked up over my 21 years of ownership.
I only sold the Oxford because it took up such a large footprint and I wanted a smallish tt I could site on the top shelf of my equipment rack.
The early sorbothane 'walnut whips' were soon superceded by a better design which did not sag over time (sounds like you have the early design).
I did have a plan to replace these with 3 X Stillpoints and I would be happy to discuss with you further how you might go about incorporating these into the Oxford design.
Oxford Acoustics were very much ahead of the game back in 1987 when the popular view was that only a suspended sub-chassis turntable would cut the sonic mustard. Jon and Fraser had some ambitious plans which included incorporating a mc phono stage in the top of the plinth. DIN sockets on the outside rear were installed for this purpose and to link to the power supply for the turntable.
Ultimately, Oxford Acoustics ceased to be when Fraser returned to medicine and Jon became a hi fi dealer.
In the meantime, a nostalgic pic to ponder:)
http://i3.photobucket.com/albums/y76/crystalref/IMG_0167.jpg
Neil,
I know, I really liked my Oracle Alexandria too, one of the best audio buying decisions I ever made after my first bit of hi-fi (which was a PL12D).
I don't rate the experience a disaster at all! At the time it was a real opportunity to aquire some serious high end gear at cost price. I also always assumed that the hassle came with the territory, a bit like sports cars?
Never experienced such customer service before or since, which was nice.
The Air-Tangent has been squashed by a flying van propelled Oracle Delphi and rebuilt. It is cosmetically fine, albeit dusty. Not sure if it works yet. I have all the accessories. It would be fitting for it to adorn another Delphi.
I might consider exchanging it for an SME V, if you happen to have a spare one.
:lolsign:
Seriously though, I need it to get the turntable to work, a tonearm exchange would be the only option for me.
Snoopdog
12-08-2010, 21:34
Found some more pics from my archives.
This shows the top of the 45kg sand-filled plinth/stand which sits on 4 x adjustable spikes for levelling. The void beneath the top plate houses the turntable power supply which is connected to the motor/speed switch via a DIn socket on the rear.
http://i3.photobucket.com/albums/y76/crystalref/392.jpg
Next up, the top steel plate in position with the three sorbothane suspension housings which have inset threads and bolts to engage and support the three downward pointing spikes on the sub-chassis.
http://i3.photobucket.com/albums/y76/crystalref/386.jpg
The top plinth with motor housing and speed switch is then bolted to the steel plate. Three holes allow the spikes on the sub-chassis to engage with the adjustable bolts on the suspension housings.
http://i3.photobucket.com/albums/y76/crystalref/387.jpg
Views of the MDF/steel sub-chassis showing the inverted bearing housing and the underneath with the protruding spikes.
http://i3.photobucket.com/albums/y76/crystalref/407.jpg
http://i3.photobucket.com/albums/y76/crystalref/406.jpg
The component parts.
http://i3.photobucket.com/albums/y76/crystalref/401.jpg
The assembled product playing a record (the 15kg phosphur bronze two-piece platter and weight buffs up nicely with some Solvol Autosol).
http://i3.photobucket.com/albums/y76/crystalref/381.jpg
Spectral Morn
12-08-2010, 21:43
Neil,
I know, I really liked my Oracle Alexandria too, one of the best audio buying decisions I ever made after my first bit of hi-fi (which was a PL12D).
I don't rate the experience a disaster at all! At the time it was a real opportunity to aquire some serious high end gear at cost price. I also always assumed that the hassle came with the territory, a bit like sports cars?
Never experienced such customer service before or since, which was nice.
The Air-Tangent has been squashed by a flying van propelled Oracle Delphi and rebuilt. It is cosmetically fine, albeit dusty. Not sure if it works yet. I have all the accessories. It would be fitting for it to adorn another Delphi.
I might consider exchanging it for an SME V, if you happen to have a spare one.
:lolsign:
Seriously though, I need it to get the turntable to work, a tonearm exchange would be the only option for me.
Hi Peter
Only arm I have sort of spare is a Graham 2.2 with spare ceramic arm wand.
Its on my Oracle at the moment as my SME 5 will be going onto a Technics 1200 as part of a wee experiment to see if the Technics is as good as many folks round here think. So far just with the standard arm it is showing huge bags of potential. What it will be like with a SME 5 on it I will just have to try to see.
I wonder what an Airtangent would be like on a Technics 1200 ?
Regards D S D L
Steve,
Ah, you have a proper lid on yours, the one they made for me really lets the side down IMHO. I'd rather have an effective lid than a M.C. preamp frankly. Also a box or way of transporting it would have been good idea. You'd think this would be a prerequisite for dealers. They did seem to have an odd sense of priorities, but thoroughly decent fellows, absolutely.
I very much look forward to studying your setup docs and see if I can get this one going again. And some nice progress pics for this gallery, of course.
peter
Snoopdog
12-08-2010, 22:42
My Crystal Reference was serial number CR-052 and came with two packing boxes, one for the plinth/stand and the other for the platter and sub-chassis. I always keep all boxes (something I was advised to do many years ago) and was able to pack it securely when I sold it.
I never opted for the Oxford lid which was an odd-looking open plan acrylic design.
The one in the picture I bought from a firm on Ebay who manufactured to the customer's specific dimensions.
Your'e right about Jon and Fraser being decent guys. Jon even made the journey down to Basingstoke when I moved house in early 1989 to help me unpack and set up the turntable in it's new location.
I think that using three Stillpoints as the 'suspension' medium with their mini inverse risers on adjustable threaded rods replacing the spikes in the sub-chassis is worth exploring.
http://stillpoints.us/Stillpoints/applications.html
Neil,
Of course the AT might be available for loan in the interests of such research.
To adress an earlier question. According to the mounting instructions you need to drill two 10mm holes through the mount of the TT spaced at 41mm apart. (the second hole is for the wires and airtube) the arm has spikes that keep it in place on the armboard even though it has only one mount hole.
The distance of the mount hole from the spindle varies such that the arm is neatly perpendicular to the edges of the TT, I think that you can use an existing hole if you are prepared to have the arm at a radical angle to the edges, and in some cases on smaller units you have no choice IIRC.
peter.
Spectral Morn
12-08-2010, 22:50
Neil,
Of course the AT might be available for loan in the interests of such research.
To adress an earlier question. According to the mounting instructions you need to drill two 10mm holes through the mount of the TT spaced at 41mm apart. (the second hole is for the wires and airtube) the arm has spikes that keep it in place on the armboard even though it has only one mount hole.
The distance of the mount hole from the spindle varies such that the arm is neatly perpendicular to the edges of the TT, I think that you can use an existing hole if you are prepared to have the arm at a radical angle to the edges, and in some cases on smaller units you have no choice IIRC.
peter.
That is a very kind offer that I may well take you up on.
Thank you
Regards D S D L
Snoopdog
12-08-2010, 23:02
Neil,
Of course the AT might be available for loan in the interests of such research.
To adress an earlier question. According to the mounting instructions you need to drill two 10mm holes through the mount of the TT spaced at 41mm apart. (the second hole is for the wires and airtube) the arm has spikes that keep it in place on the armboard even though it has only one mount hole.
The distance of the mount hole from the spindle varies such that the arm is neatly perpendicular to the edges of the TT, I think that you can use an existing hole if you are prepared to have the arm at a radical angle to the edges, and in some cases on smaller units you have no choice IIRC.
peter.
Peter
As your picture shows, a nice touch by Oxford Acoustics was to mount a bespoke control switch on the front right hand side of the deck for the Air Tangent arm.
As to your reference about the 'gap' between phosphur bronze platter and bearing housing, it was my understanding that this was intentional and part of the design in avoiding transmission of vibration from the bearing to the platter. I know Jon always was very careful to align the reference markings on the top of the bearing and inside the hole in the platter and then lower the assembly carefully so that the slight gap was equal around the seated bearing housing. Another design consideration in reducing vibration transmission to the record/stylus was the detachable phosphur bronze spindle with sorbothane film contacting the bearing housing.
Actually the gap I was referring to was between the platters, we are talking about a cigarette paper passing freely. A Tesco till receipt will go with a little encouragement. The first top platter resulted in a platter/platter gap that would acommodate 3 sheets of photocopy paper at some points before I complained.
I now hazily recall the bronze platter gap. I think I once saw Jon turn the bronze platter over the bearing until it hit a pin of some kind, but I don't see any pin in your pics.
To be clear, there is no gap and no play between the acrylic platter and the bearing housing on my unit.
So, did your turntable wobble at all?
The arm switch was a very good idea that sadly wasn't supported on the Mk1 AT. The arm lift is particularly frightning on a large TT when you can't rest your hand on anything and the lift arm is as rigid as a length of spagetti. takes a while to find the right action.
Snoopdog
13-08-2010, 08:52
The junction between the two part phosphur bronze and acrylic platters on my Oxford deck were closely coupled and no gap of the kind you describe existed. My platter did not wobble at all and speed stability was exemplary.
athe idea behind the two part platter and record weight was down to impedance matching of the materials. Oxford Acoustics argument was that acrylic was a better impedance match for the vinyl LP and so this material comprised the top of the platter and the corresponding bottom of the applied record weight. The phosphur bronze provided mass to create a flywheel effect for speed stability.
As I recall, the gap between phosphur bronze sub-platter and bearing housing was intentional and when fitting, two reference lines in pencil were aligned. There was no 'pin' of any kind on my turntable.
The acrylic platter was a close fit to the bearing housing and there was no intention to create a gap at this point.
I have given some thought to your wobbling issue and suggest that the inverted bearing be examined.
When the outer housing is removed (lift off carefully) it will reveal a lubricated stem which has tiny ball bearing sitting in a recess at the top. It is very easy to dislodge the ball bearing during disassembly so it is worth checking that this is still in place.
The ball bearing contacts a PTFE thrust pad located inside the inverted bearing housing. Again, it is worth checking to see if this is seated correctly and not worn.
I discovered during routine maintenance and refurbishment of the oil (I used a good oil of the correct consistancy obtained from Audio Origami) that the bearing housing can be pivotted slightly but when the mass of the platter is applied, the bearing is centered and sits straight without any lateral movement.
If you require a new drive cord, the one supplied by Mitchell for the Gyrodeck was recommended by Oxford Acoustics.
Pics:
Can't get the papers in any furthar than this: The spindle points in the same direction as the bearing marker line. The damping material has come away from the spindle and attached to the top of ther bearing
http://www.saabphotos.com/gallery/albums/album1330/DSCN0674.jpg
underneath the clamp. will need to disassemble to clean later
http://www.saabphotos.com/gallery/albums/album1330/DSCN0675.jpg
Motor spindle, boltheads showing signs of rust
http://www.saabphotos.com/gallery/albums/album1330/DSCN0678.jpg
Ok see where the spindle points, between platter and bearing there is contact at the top on this side...
http://www.saabphotos.com/gallery/albums/album1330/DSCN0680.jpg
and on the bottom on the opposite side, fishy?
http://www.saabphotos.com/gallery/albums/album1330/DSCN0681.jpg
I'm try to show here how the armboard is not square to the corner of the TT
http://www.saabphotos.com/gallery/albums/album1330/DSCN0683.jpg
top surface of bronze platter, starting to score again,
http://www.saabphotos.com/gallery/albums/album1330/DSCN0685.jpg
but that gap is *tiny*
http://www.saabphotos.com/gallery/albums/album1330/DSCN0686.jpg
taken it off now
http://www.saabphotos.com/gallery/albums/album1330/DSCN0687.jpg
Bearing assembly and armboard removed, you can see the heads of the bolts that screw into the sorbo supports underneath, the Bearing assy spikes are supposed to locate in them.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0689.jpg
Bearing assembly, pin on left opposite reference mark, signs of scuffing at the rim
http://www.saabphotos.com/gallery/albums/album1330/DSCN0690.jpg
trying to show "play" in bearing you have to switch between photos
http://www.saabphotos.com/gallery/albums/album1330/DSCN0691.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0692.jpg
Underneath
http://www.saabphotos.com/gallery/albums/album1330/DSCN0715.jpg
Where the arm is fixed and wired, the cable fixture has come away - careful
http://www.saabphotos.com/gallery/albums/album1330/DSCN0716.jpg
Bearing end
http://www.saabphotos.com/gallery/albums/album1330/DSCN0717.jpg
The cable is VDH D502 apparently
http://www.saabphotos.com/gallery/albums/album1330/DSCN0718.jpg
I need to lie down for a while now..
peter
Spectral Morn
13-08-2010, 13:07
Boy you have been busy Peter.
The movement in the bearing from the photos looks to be quite a lot and yet form below it looks like it is mounted square but from above its not :scratch: + there are signs of damage here and there.
You will need to clean a fair amount before fitting it all back together.
Its amazing though that bolts will rust a tad even when kept in a modern house (assuming you did store it in your house).
Snoopdog can no doubt offer further info on what he sees in the photos but I must say that I don't envy you the task ahead. Though it is imho worth it.
Getting the tone arm block square should be easy assuming all the holes can be lined up to make it square. Looking at it I can't help but think "made on a Friday" which is probably not fair as the two Oxfords, one Cyrstalette and their later black two layer TT were very well made, or at least the ones I saw (at the time) looked very well made.
I would once you get things sorted and assuming you keep the AT (Graham 2.2 is a very nice arm;)by the way) get rid of the VDH 502 wiring if you can as its not up to much imho.
Looks from the photos that the AT has only the one mounting bolt. Is there another locator stud etc below, that is hidden? If you had the AT arm mounting (or dimensions) jig then making an armboard would be easy I think.
Regards D S D L
Hmm..very intersting indeed - great photo's guys :).
The bearing movement concerns me though. Peter, you mentioned earlier that the bearing could be adjusted - how is this achieved?
Spectral Morn
13-08-2010, 13:33
Hmm..very intersting indeed - great photo's guys :).
The bearing movement concerns me though. Peter, you mentioned earlier that the bearing could be adjusted - how is this achieved?
You really could not ask for better photos...Its almost as good as being there.
Regards D S D L
The flash photography tends to magnify the defects, which is good for our purposes, and I have made no attempt to clean anything.
It is located near to a window (not double glazed), you can also just see how the sunlight has bleached the wood finish at the rear over the years. A useful caution to others, I hope.
I think the Friday effect is right. Even the finest craftsperson has good days and bad days, everyone makes a mistake. This is the cost of making things by hand as opposed to by machine. Things then get worse when you try and fix a mistake instead of either accepting it or binning the thing, and starting from scratch and doing it properly. I think pressure to deliver was pretty high for the Oxford folks during that period.
To fix the armboard squareness propably requires fileing two of the holes into slots, accepting it as a quirk, or getting a new armboard and starting from scratch.
When the turntable is polished and clean it really looks fantastic, the mind then helps it to sound fantastic, for a while at least.
It was designed to stay in one place and not be moved. Give this to an audiophile and he is going to tinker and fiddle and tweak and try it here move it there etc, etc. We audiophiles are never finished. I have to put my hand up and admit that a most of the wear was probably inflicted by me.
Steves excellent info and advice will be a tremendous help, no question.
Spectral Morn
13-08-2010, 13:56
At the time the recommendation was to use it on a concrete floor (weight and stability + sounding better). I only had a suspended floor at the time and the idea of wall mounting it on a large target wallshelf + granite shelf put me off (+lack of money) When the wall mount version (which did not look as nice to me) came out I had bought the Oracle Delphi mk4 so I was happy enough and didn't look after getting an Oxford any more until Snoopdog put his up for sale awhile ago then the memories all came flooding back.
Regards D S D L
If you look the photo where I mention that gap is *tiny*, you can see the holes (there are three) that have little grubscrews in them that you can adjust that sets the bearing axis and level.
The bearing movment may be ok, not sure. It may be like a unipivot arm where you think it has too much play but actually it is fine.
Thanks for the nice photo comments guys. :blush:
Spectral Morn
13-08-2010, 14:07
If you look the photo where I mention that gap is *tiny*, you can see the holes (there are three) that have little grubscrews in them that you can adjust that sets the bearing axis and level.
The bearing movment may be ok, not sure. It may be like a unipivot arm where you think it has too much play but actually it is fine.
Thanks for the nice photo comments guys. :blush:
Because of the amount of weight in the platter I don't think any play is what you would want, as that would translate into a pronounced rocking as it spun. Level and solid would be my though on it as otherwise you would end up with excessive wear on the bearing.
However I am not Jon so only he and his colleague of the time know what was the end goal of each part of their design.
Regards D S D L
I have used the TT on both types of floor. The effect is subtle compared to diferences in the actual room acoustics. The room with the suspended floor is much more "dead" acoustically than the "live" concrete room. In the end the LF resonances in the live room mean that the system sounded better in the dead room. It also depends on the music. The turntable has no problem with percussive music but with classical the speed instability and mistracking are just impossible to ignore after a while.
For proper TT performance though the hard floor is right and fortunately that is where it is going.
peter.
Because of the amount of weight in the platter I don't think any play is what you would want, as that would translate into a pronounced rocking as it spun. Level and solid would be my though on it as otherwise you would end up with excessive wear on the bearing.
However I am not Jon so only he and his colleague of the time know what was the end goal of each part of their design.
Regards D S D L
When I say "play" I don't mean to imply it is loose and rattling about. It has one natural resting position (probably the wrong one), and the platter weight tends to keep it in that position. However it is not rigid like a tonarm bearing and can move.
I will probably have to take it apart eventually, but I am a little nervous as this is a critical component that up to now I have been careful not to disturb or even invert. I remember the first time Jon assembled it he did it in such a way as to suggest "don't mess with this" and there was an audible sigh from both of them that indicated a critical assembly milestone has been reached and it was plain sailing from there.
Or they could just have been messing with my head :) I wouldn't put it past them.
Spectral Morn
13-08-2010, 14:42
When I say "play" I don't mean to imply it is loose and rattling about. It has one natural resting position (probably the wrong one), and the platter weight tends to keep it in that position. However it is not rigid like a tonarm bearing and can move.
I will probably have to take it apart eventually, but I am a little nervous as this is a critical component that up to now I have been careful not to disturb or even invert. I remember the first time Jon assembled it he did it in such a way as to suggest "don't mess with this" and there was an audible sigh from both of them that indicated a critical assembly milestone has been reached and it was plain sailing from there.
Or they could just have been messing with my head :) I wouldn't put it past them.
Ahhhh ! Okay yes if it was not perpendicular it would rise up and down as it turned. The bearing housing needs to be level and would appear not to be. Perhaps the three bolts holding it in place allow it to be adjusted/re-leveled.
I once had awful problems setting up a Roksan TT as there are three set screws underneath the bearing, which you can adjust to level the bearing. It took me hours to get this just right. At one point I nearly launched the TT out the open door of the shop I worked in at the time. You thought you had it right but looking at the side profile of the platter you could see it rising and falling. This rise was on the side where the bearing housing was off :doh: I got it done eventually but at that point I swore I would not do a Roksan again. Even my mana spirit level was of little help to me.
Regards D S D L
Oops, Steve covered this a few messages ago:
Steve >> I discovered during routine maintenance and refurbishment of the oil (I used a good oil of the correct consistancy obtained from Audio Origami) that the bearing housing can be pivotted slightly but when the mass of the platter is applied, the bearing is centered and sits straight without any lateral movement.
I think that agrees with my "play" comment.
Ahhhh ! Okay yes if it was not perpendicular it would rise up and down as it turned. The bearing housing needs to be level and would appear not to be. Perhaps the three bolts holding it in place allow it to be adjusted/re-leveled.
I once had awful problems setting up a Roksan TT as there are three set screws underneath the bearing, which you can adjust to level the bearing. It took me hours to get this just right. At one point I nearly launched the TT out the open door of the shop I worked in at the time. You thought you had it right but looking at the side profile of the platter you could see it rising and falling. This rise was on the side where the bearing housing was off :doh: I got it done eventually but at that point I swore I would not do a Roksan again. Even my mana spirit level was of little help to me.
Regards D S D L
That's exactly it, but in my case when it *is* level it does not turn about the centre, which causes the arm to swing in and out. It is as if the other end of the shaft from the one you can adjust is not correctly set (as if there were three screws at both ends, and the 3 that you cannot get at are set wrong). Possibly the large fixing beneath the subchassis is mis-positioned.
I am hoping that in reality the bearing is off because the sorbothane supports are not supporting the sub-chassis level, because fixing the supports would resolve that.
But I have Steves notes now so I will stop guessing and see what he has to say.
peter
Spectral Morn
13-08-2010, 15:09
That's exactly it, but in my case when it *is* level it does not turn about the centre, which causes the arm to swing in and out. It is as if the other end of the shaft from the one you can adjust is not correctly set (as if there were three screws at both ends, and the 3 that you cannot get at are set wrong). Possibly the large fixing beneath the subchassis is mis-positioned.
I am hoping that in reality the bearing is off because the sorbothane supports are not supporting the sub-chassis level, because fixing the supports would resolve that.
But I have Steves notes now so I will stop guessing and see what he has to say.
peter
you have my best wishes....
Regards D S D L
Try getting everything level (the base support chassis and platter) You probarly doing this but worth checking If not then a question of eliminating the cause
Best of luck
I just looked under the bronze platter, the platter does not rest directly on the bearing housing, there are in fact 3 allen bolts near the hole that rest on the housing. One of these engages with the pin or butts up to it.
Now, the tiny gap between the bronze platter and the bearing (as viewed from above means that the point of contact is just the three allen bolts. It also suggests that the bolts need to be very accurately machined or be adjustable if the platter is to rest concentric to the bearing shaft.
It's starting to make sense.
I need to take a picture to show this but the camera battery is flat cos I forgot to unplug the usb cable, again :doh:
More information:
I have located the original installation instructions. One point made is that not all the sorb mounts are the same. One has to bear a greater weight due to the tonearm, and is of differnt type. Its setting depends on the type of arm used as well and it is necessary to remove the platters adjust, replace platters, measure, repeat intil the arm weight bias is correctly nulled out.
Steves includes a tip that simplified this, as you can adjust the spike pentration without having to remove the sub-chassis, which I did not realise.
I can scan the instructions for future reference if that is helpful. It is an interesting read from the design perspective, and interesting to compare with Steves instructions/tips. There is also a detailed instruction on how to replace the bearing oil, with more description of the materials used.
The bottom line as everone has said is level, level, level (three times for stability!)
that means:
1) Top base plate must be level (4 feet/spikes at the bottom)
2) sub-chasses must be level (sorb bolts/chassis spikes) according to arm weight
3a) bronze platter is level (and concentric to bearing) by 3 hidden bottom platter bolt heads and upper 3 grub screws (very tricky, 6 degress of freedom, not including angle of platter wrt bearing.
4) Upper acrylic platter has to be level (concentric) so there is no gaps to the bottom platter. Note that if 3 is wrong, this is impossible. The only way to adjust this is to turn the platter through various angles and use the cig-paper test to find the best angle with optimum gap, OR, if its not level then repeat 3 until it is.
Perform wobble checks
Install arm/cart.
I had a problem with the sorbothane deforming in a no time. It occurs that I tend to have the turntable powered up 24/7 so the heat from the power-supply board could have accelerated the deformation, so the moral is "turn it off when not in use".
Sincere thanks to everyone for contributing so far.
Peter.
Spectral Morn
13-08-2010, 17:51
More information:
I have located the original installation instructions. One point made is that not all the sorb mounts are the same. One has to bear a greater weight due to the tonearm, and is of differnt type. Its setting depends on the type of arm used as well and it is necessary to remove the platters adjust, replace platters, measure, repeat intil the arm weight bias is correctly nulled out.
Steves includes a tip that simplified this, as you can adjust the spike pentration without having to remove the sub-chassis, which I did not realise.
I can scan the instructions for future reference if that is helpful. It is an interesting read from the design perspective, and interesting to compare with Steves instructions/tips. There is also a detailed instruction on how to replace the bearing oil, with more description of the materials used.
The bottom line as everone has said is level, level, level (three times for stability!)
that means:
1) Top base plate must be level (4 feet/spikes at the bottom)
2) sub-chasses must be level (sorb bolts/chassis spikes) according to arm weight
3a) bronze platter is level (and concentric to bearing) by 3 hidden bottom platter bolt heads and upper 3 grub screws (very tricky, 6 degress of freedom, not including angle of platter wrt bearing.
4) Upper acrylic platter has to be level (concentric) so there is no gaps to the bottom platter. Note that if 3 is wrong, this is impossible. The only way to adjust this is to turn the platter through various angles and use the cig-paper test to find the best angle with optimum gap, OR, if its not level then repeat 3 until it is.
Perform wobble checks
Install arm/cart.
I had a problem with the sorbothane deforming in a no time. It occurs that I tend to have the turntable powered up 24/7 so the heat from the power-supply board could have accelerated the deformation, so the moral is "turn it off when not in use".
Sincere thanks to everyone for contributing so far.
Peter.
No problem Peter, it has been fun and a real blast from the past......I did mention the different types of sorbothane early on....I just could not remember how many there were....old age creeping in.
I look forward to reading your post were you say its working and amazing.
Regards D S D L
Gawd, it reminds me of the far more humble Manticore Mantra turntable. The glass top platter sat on three little adjustable studs and one was severely warned not to touch these when setting up...
Snoopdog
13-08-2010, 20:53
Hmmmmm! Interesting read!
It's quite obvious comparing the photos of the Oxford I owned and the one Peter has (seperated by just seven on the serial numbers!) that there are slight but significant design changes.
First the bearing housing. There was no 'pin' on the lip of my bearing housing and the bottom of the phosphur bronze platter sat flush on the lip of the bearing housing. No Allen bolt heads for contact with the model I owned!
Secondly, comparing the two photos of the underneath of the sub-chassis showing the base of the bearing housing. There are differences in the design and fitting of this component.
I am quite alarmed at the pictures showing the paper wedged between the two part platter. Mine was almost a gas-tight seal!
I do recommend Peter, that you carefully disassemble the bearing to examine the tiny ball bearing and thrust pad interface as I described in an earlier post.
You are correct that the thrust pad (which can be turned over when worn on one side) is held in place by three grub screws and can be adjusted.
Glad the notes I emailed you helped. I look forward to following this restoration project further.
Underneath the platter, its only contact with the bearing is the socket heads.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0760.jpg
Trying to measure the head depth this way is inconclusive, will have to think of a better way
http://www.saabphotos.com/gallery/albums/album1330/DSCN0763.jpg
Ok lets do some polishing. This is part of the joy of Oxford TT ownership, and one reason for selecting it.
test a small area before trying it on the main thing, so will do the clamp, here it is again
I would normally spend more time on the bronze part but am more interested in the acrylic section as it is softer and more prone to scratches.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0723.jpg
I have disassembled it so the polish does not seep between components and each can be done individually.
The bronze top section has an annular ring of dust on the top side, (the centre is dust free but still needs polishing). The seepage is clear on the top of the bronze part
http://www.saabphotos.com/gallery/albums/album1330/DSCN0729.jpg
Underneath the bronze section we see the marks as before
http://www.saabphotos.com/gallery/albums/album1330/DSCN0730.jpg
a quick polish and ting!
http://www.saabphotos.com/gallery/albums/album1330/DSCN0731.jpg
clean the aluminum handle with Cif
http://www.saabphotos.com/gallery/albums/album1330/DSCN0732.jpg
And assemble thus:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0733.jpg
We are really interested in this bit. It is the same as the top platter and that must be spotless with no dust or that will score the soft bottom platter lacquer surface. You can see it is rather scratched as this is the bottom surface of the clamp. At this stage I've already cleaned the dust off with Cif
http://www.saabphotos.com/gallery/albums/album1330/DSCN0734.jpg
Next we apply some rubbing compound, just experimenting really to see what works
http://www.saabphotos.com/gallery/albums/album1330/DSCN0735.jpg
After much rubbing we get this
http://www.saabphotos.com/gallery/albums/album1330/DSCN0736.jpg
after polishing off, looks cleaner to me, now I am adding T-Cut
http://www.saabphotos.com/gallery/albums/album1330/DSCN0737.jpg
as before, love the smell of T-Cut.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0739.jpg
I think this is better, the deep scratches are still present with the right light, but it seems really clean.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0740.jpg
And finally re-assemble:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0744.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0741.jpg
Before and after
http://www.saabphotos.com/gallery/albums/album1330/DSCN0745.jpg
Want to get the cleaning covered and out of the way. So here we go again. We have the platter spindle and the Motor Housing Cover. The top section of the deck is made of this, as are the buttons and the armboard.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0750.jpg
First I add the stuff that "cleans baths without scratching"
http://www.saabphotos.com/gallery/albums/album1330/DSCN0751.jpg
Not sure about the scratching, still I am trying hard to show it
http://www.saabphotos.com/gallery/albums/album1330/DSCN0752.jpg
Now lets try automotive Turtle Wax
http://www.saabphotos.com/gallery/albums/album1330/DSCN0753.jpg
after removing we get this, will now polish the bronze spindle.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0754.jpg
Check this out. if you point the light the other way..
http://www.saabphotos.com/gallery/albums/album1330/DSCN0755.jpg
you can see your reflection in it.
This is the bottom surface of the cover, the mountings are simple aluminium friction fit rods with rubber grommets surrounding. This gave a compliant surface for you to put your clamp. The surface has a "give" that matches the weight of the clamp, it seemed another nice touch.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0759.jpg
Just want to make some personal observations here. A lot of the components are hard, dark, shiny and reflective, so it's important IMO to balance that with some light softer matt surface. Which is why I think the most beautiful versions of the Crystal Reference have the matt wooden finish (they also offered a gloss wood finish), which also match better with the older loudspeaker veneers before everything went black. I am actually working on the top of my subwoofer in these pictures that has a matt black top surface and wooden side panels. and the Oxford TT complements this quite well.
Also the Oxford Acoustics logo nameplate is pretty tacky compared to the rest of the bronze components which is why I removed it from mine.
Snoopdog
14-08-2010, 08:31
Peter
Nice progress:)
I recommend you get the Novus 3 part cleaning sytem to work on your acrylic items, both clear and black. Stillpoints included it with the equipment rack I bought which has acrylic shelves. The course polish will remove deep scratches, and the fine polish and finishing spray will bring it back to good as new.
http://cgi.ebay.co.uk/Novus-plastic-scratch-remover-polish-kit-/370321474723?pt=UK_Video_Games_Coin_Operated_MJ
Looking at the photos of those Allen bolt heads on the underneath of the platter, they really don't look like a good idea to me! Cosidering the mass of the two part platter (15kg) I would think that adjustment of these bolt heads would be absolutely critical to balancing the platter and achieving true level.
Try removing the Allen bolts and 'pin' on the bearing housing lip for a better mate of the two components as per the Oxford I owned. This may go some way to addressing your wobble issue.
The top of the phosphur bronze platter where it meets the acrylic upper platter is lacqered and I would proceed with caution if attempting to clean that surface.
Peter
Nice progress:)
I recommend you get the Novus 3 part cleaning sytem to work on your acrylic items, both clear and black. Stillpoints included it with the equipment rack I bought which has acrylic shelves. The course polish will remove deep scratches, and the fine polish and finishing spray will bring it back to good as new.
http://cgi.ebay.co.uk/Novus-plastic-scratch-remover-polish-kit-/370321474723?pt=UK_Video_Games_Coin_Operated_MJ
Looking at the photos of those Allen bolt heads on the underneath of the platter, they really don't look like a good idea to me! Cosidering the mass of the two part platter (15kg) I would think that adjustment of these bolt heads would be absolutely critical to balancing the platter and achieving true level.
Try removing the Allen bolts and 'pin' on the bearing housing lip for a better mate of the two components as per the Oxford I owned. This may go some way to addressing your wobble issue.
The top of the phosphur bronze platter where it meets the acrylic upper platter is lacqered and I would proceed with caution if attempting to clean that surface.
Thanks for the link, Steve. The Novus system looks ideal and I have ordered a kit.
That puts a halt on the polishing for a few days. Also I can't dismantle bearing yet as I don't have suitable oil in case of accident so I will delay that too. I am going to investigate the pin and bolts.
Looking at the bearing lip I can see where repeated turning of the platter has ground the soft lip surface a little, which would alter the critical bottom setting.
In the installation docs in connection with adjusting the bearing level it says
"(Note : a very small amount of movement is perfectly acceptable, and makes no difference to the sound quality.)"
I think any *visual* amount of movement is unacceptable for aesthetic reasons. It's bad enough that it attracts muths.
Yup, the pin and bolts are coming out. The platter is too heavy and delicate to mess with, just turning it over is a risky process when you can't get a good grip on it.
Snoopdog
14-08-2010, 10:50
Peter
The various oil options for sale on the Audio Origami website are a good bet for the Oxford bearing. Email Johnny for advice on the most appropriate.
http://www.audioorigami.co.uk/F_Sale/ForSale.htm
Spectral Morn
14-08-2010, 17:24
Looking very good so far Peter.
Well done :cool:
I have to say and no offence to anyone else but this for me has to be one of the most exciting threads for quite awhile. I can't wait to see everything up and running.
Regards D S D L
Peter
I would think that adjustment of these bolt heads would be absolutely critical to balancing the platter and achieving true level.
It turns out that one of the bolts is loose and one is only finger tight. The washers are not even shakeproof.
Closer inspection of the bearing housing shows another three grubscrew threads at the opposite end of the shaft to the ones you can get at when the phosphor-bronze platter is in place. The pin won't pull out, won't unscrew is not coming out would have to be filed. I could open out one of the bolt-holes so the pin goes in the hole. and take the other bolts out.
I can make a simple jig that can go in a vice that holds the bearing. It would then be possible to adjust all 6 bearing screws to get the bearing shaft perfectly upright, and polish the bearing lip that holds the platter to make it perfectly level if necessary.
Do you know how stable the bearing is if taken apart? for example if I align it and then take it apart to inspect/replace the oil, would it be necessary to align it again? Is it safe to turn the bearing upside down or will the ball fall out or something?
peter
Snoopdog
14-08-2010, 18:11
Peter
I disassembled my bearing by keeping it in the upright position and carefully lift the housing straight up and off to expose the vertical bearing stem with the ball bearing sitting on top. The ball bearing is quite tiny and easy to dislodge and misplace if you turn it upside down. It is useful to lay the ball bearing on a piece of white paper towell on a level work surface so that it can be easily located later. You can then clean the stem, inside the housing and the thrust pad and re-oil the bearing before re-assembly. It sounds strange, but the viscosity of the bearing oil allows it to stay relatively put while you turn the housing upside down and lower carefully back over the ball bearing and stem. I hope that makes sense. Audio Origami include some nice long cotton buds for cleaning and two small bottles of oil in their kit.
Sounds like a good plan to align all six grub screws but you are in uncharted territory there as I never performed that operation with my Oxford.
Does the pin on the bearing housing lip locate into a hole on the underside of the platter or does one of those three Allen bolt heads sit over it?
With most of the weight distributed towards the outside of the phosphur bronze platter for the flywheel effect once in motion, I would concur with your option of filing down or otherwise removing that pin and remove the Allen bolts so that the platter has a greater area of contact with the bearing housing lip.
It's strange that Oxford Acoustics altered the design so soon but I certainly never experienced any of the wobble or speed stability issues you describe with your Oxford.
As a matter of interest, I still have my invoice from Subjective Audio for the purchase of my turntable on 6th November 1987.
Cost new was £1790:)
Peter
Does the pin on the bearing housing lip locate into a hole on the underside of the platter or does one of those three Allen bolt heads sit over it?
As a matter of interest, I still have my invoice from Subjective Audio for the purchase of my turntable on 6th November 1987.
Cost new was £1790:)
Jon lined up the platter mark with the bearing and turned the housing so the pin hit one of the bolts, (can't remember which way he turned it). so the pin didn't go in the head, but any of the three holes are perfectly positioned to take the pin and are probably large enough without opening further.
You got a hell of a lot for your money. It really is shameful that they went down, they could easily have charged silly numbers.
<Rummage Rummage>
On 24.12.87 Acoustic Arts charged £1850 (included a lid and optional finish) less £1250 PX on my Oracle Alexandria, Grado pickup arm and Grado MCX cartridge that were stolen, so £600. I think I ended up paying £899 for a S/H Clearaudio Pradikat + writeoff AirTangent thrown in.
I didn't take final delivery until August 1988, so all those mods were done over a 6 month period.
I had met Howard Popeck a year before but we did not get on. Jim Dovey at Acoustic Arts could talk for hours and told some really interesting/funny stories, and a lot of what he said was in line with my own experiences, so I did a lot of business with them.
Spectral Morn
14-08-2010, 20:58
The problem was that they expanded their range too quickly by adding a cheaper turntable (about £800 ish) and a range of electronics (which were not imho very good or well built), then the recession of the early 90's hit and bamb they disappeared.
I don't remember the whole story, it was along time ago and at the time the dealer I worked for did not sell lots of their kit, a few Oxfords (3 or 4), a Cyrstalette and a few of the cheaper TTs. I can't remember if we sold any of the amplifiers.
Regards D S D L
Can we have pics of the bearing all in bits please - if possible?
Snoopdog
15-08-2010, 10:13
Peter
From your descrription and the photo of the underside of the phosphur bronze platter, an easy workaround may be to just remove the Allen bolts and locate one of the empty holes over the raised pin on the bearing housing lip to achieve a flush fit.
By carefully listening (once everything is up and running) you could rotate the platter to align each of the bolt holes in turn to see whether there was any sonic difference and if so which was the preferred position and then mark it for future reference.
The bolts could then be replaced and aligned and listening tests would again indicate which was the preferred option - bolts or no bolts.
That way, you would not have irrevocably altered the design of your deck by filing down/removing the pin.
Unfortunately I didn't take any photos of the disassembled bearing when the Oxford was in my posession. The only other pics I have are these which show the bearing housing and sorbothane spacer underneath the detachable spindle visible through the clear acrylic upper platter. The ubiquitous black ash finish of the 80's does look rather dated now!
http://i3.photobucket.com/albums/y76/crystalref/374.jpg
With SMEV and Koetsu Rosewood Signature mc cartridge.
http://i3.photobucket.com/albums/y76/crystalref/372.jpg
Another nice aesthetic touch was the veneered 'skirt' which could be raised up the stand and rested on the rear lip below the DIN socketry to allow the four lock nut spikes to be levelled at the base of the stand. The skirt could then be slid back down to hide the spikes.
http://i3.photobucket.com/albums/y76/crystalref/388.jpg
http://i3.photobucket.com/albums/y76/crystalref/389.jpg
Another view of the component parts showing the exemplary engineering and finish.
http://i3.photobucket.com/albums/y76/crystalref/404.jpg
Can we have pics of the bearing all in bits please - if possible?
Coming soon on THIS thread!
http://www.saabphotos.com/gallery/albums/album1330/DSCN0792.jpg
But first, a word from my sponsor:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0782.jpg
Techno Commander
15-08-2010, 13:07
:lolsign:
Just to round off the discussion about the bolts, another picture.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0770.jpg
Today I will take this apart
http://www.saabphotos.com/gallery/albums/album1330/DSCN0774.jpg
but first I'm going to remove the armboard . Good time to apologise upfront for the quality of some of the pictures. I am more concerned with what I'm doing than photographing what I'm doing, I'll be more careful next time.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0777.jpg
So with the armboard off we are left with this. There are 8 bolts holding the sandwich together.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0775.jpg
Inspection reveals another set of holes at the bottom of the bearing housing
http://www.saabphotos.com/gallery/albums/album1330/DSCN0780.jpg
I want to seperate the bearing from the sub-chassis so I don't damage the latter. Underneath the S/C the bearing is held on by a brass ring. it won't turn by hand but there is a thread that we can get at
http://www.saabphotos.com/gallery/albums/album1330/DSCN0779.jpg
This means a trip to the batcave:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0783.jpg
This bolt happens to fit in the thread, It's came with my flatscreen wall mounting kit.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0784.jpg
People of nervous disposition please look away now.
I am holding the bolt in the vice, this may scratch the S/C. Hold onto the S/C and... HRRRRRRRRRG, oops
http://www.saabphotos.com/gallery/albums/album1330/DSCN0786.jpg
This is going to be more difficult than I imagined:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0788.jpg
Interlude while I check the fixing of my TV.
Ok back in the kitchen now. Put down kitchen paper in case the ball goes walkabout, thanks for the tip Steve.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0790.jpg
This is it folks I will skip the comments on the next few photos while I look up some terminology. I'm a brain-surgeon not a shipbuilder as a brain-surgeon would say.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0791.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0792.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0793.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0794.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0795.jpg
Hold your horses, more photos are coming.
It looks like there was gap at the bottom end housing on one side, judging from the oil.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0796.jpg
I think this is the journal?
http://www.saabphotos.com/gallery/albums/album1330/DSCN0797.jpg
I am going to tease out the ball before I lose it
http://www.saabphotos.com/gallery/albums/album1330/DSCN0799.jpg
I think we need an oil change
http://www.saabphotos.com/gallery/albums/album1330/DSCN0800.jpg
Here is the ball
http://www.saabphotos.com/gallery/albums/album1330/DSCN0802.jpg
Mother and child
http://www.saabphotos.com/gallery/albums/album1330/DSCN0803.jpg
Going to clean the ball seat
http://www.saabphotos.com/gallery/albums/album1330/DSCN0808.jpg
Like so
http://www.saabphotos.com/gallery/albums/album1330/DSCN0809.jpg
Put the ball back for now
http://www.saabphotos.com/gallery/albums/album1330/DSCN0810.jpg
I am interested in where the lower bearing sleeve locates, here?
http://www.saabphotos.com/gallery/albums/album1330/DSCN0811.jpg
or here?
http://www.saabphotos.com/gallery/albums/album1330/DSCN0812.jpg
Its the bottom one, it seems a good fit as the oil doesn't leak
http://www.saabphotos.com/gallery/albums/album1330/DSCN0813.jpg
Now I shall investigate the thrust plate
http://www.saabphotos.com/gallery/albums/album1330/DSCN0814.jpg
First I shall clean it to get a clear shot
http://www.saabphotos.com/gallery/albums/album1330/DSCN0815.jpg
http://www.saabphotos.com/gallery/albums/album1330/DSCN0817.jpg
Here we can see where the top grub screws engage, I am going to unscrew one so I can remove the plate
http://www.saabphotos.com/gallery/albums/album1330/DSCN0818.jpg
It won't come out so I will get at it with tweezers
http://www.saabphotos.com/gallery/albums/album1330/DSCN0819.jpg
Got it
http://www.saabphotos.com/gallery/albums/album1330/DSCN0822.jpg
It is flat on the other side
http://www.saabphotos.com/gallery/albums/album1330/DSCN0823.jpg
It would go sorta like this
http://www.saabphotos.com/gallery/albums/album1330/DSCN0821.jpg
Does it look worn? Rumble was never an issue for me.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0824.jpg
This is where it went.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0826.jpg
That the end of this slideshow, Accepting requests before I bag everything.
Hmm..interesting (very, very interesting in fact and huge thanks for the excellent pictures).
So, how novel. The bearing is supposed to be self aligning by the look of it. At the base it is centred by the brass/bronze (but looks like brass to me) collar of the outer bearing and at the top the ball bearing rests in the little hemispherical divot (the position of which can, unfortunately, be adjusted).
Something like this:
http://i62.photobucket.com/albums/h90/markemark_2006/OxfordCrystalmainbearing.jpg
Ah no, I see - the three lower grub screws look like they could be retaining a bronze inner shell that forms the actual bearing surface - that would make more sense.
More like this:
http://i62.photobucket.com/albums/h90/markemark_2006/OxfordCrystalmainbearing1.jpg
Peter
From your descrription and the photo of the underside of the phosphur bronze platter, an easy workaround may be to just remove the Allen bolts and locate one of the empty holes over the raised pin on the bearing housing lip to achieve a flush fit.
Agreed, I wonder if spikes would be better, what with the bearing gap, it seems they were trying to avoid a good contact surface. Really tiny spikes needed though.
The only other pics I have are these which show the bearing housing and sorbothane spacer underneath the detachable spindle visible through the clear acrylic upper platter.
Your bearing housing looks a different material to my brass one.
With SMEV and Koetsu Rosewood Signature mc cartridge.
Yep, Oxford/SME/Rosewood go together like Linn/Ittok/Asak used to.
Another nice aesthetic touch was the veneered 'skirt' which could be raised up the stand and rested on the rear lip below the DIN socketry to allow the four lock nut spikes to be levelled at the base of the stand. The skirt could then be slid back down to hide the spikes.
On my TT there was only one spike, the other three supports were rubber feet. You could level the whole turntable in one axis using the Air tangent as an ultra sensitive level. Basically you set zero mass so the arm floats at 30 degrees. Get initial level so it stays in place. If you tap it lighly when level it will oscilate about the centre (the wires act like a spring which is why dressing them right is essential), If the turntable is level the arm would continue to oscillate in the middle for a minute or so. If not the arm would eventually tend to move in or out. depending on level. I found this level adjustment needed to be done quite frequently.
Ah no, I see - the three lower grub screws look like they could be retaining a bronze inner shell that forms the actual bearing surface - that would make more sense.
More like this:
http://i62.photobucket.com/albums/h90/markemark_2006/OxfordCrystalmainbearing1.jpg
According to the manual:
The ball is tungsten steel,
The journal is phosphor bronze
the spindle is stainless steel
the ball runs on silver steel thrust plate.
The Oil bath is formed by the brass ring on the top of the spindle and should be completely filled covering the BB.
It says "DO NOT ALLOW ANY DIRT TO SETTLE ON THE SPINDLE OR INSIDE THE BEARING HOUSING".
Ooops.
Yes, the phosphor bronze element is the closer red hatched element in my drawing - one can see it is a slightly different colour (darker) in the photographs). The bottom lip and the ball in the cup of the thrust pad are the only points of contact (hence the option to adjust).
http://i62.photobucket.com/albums/h90/markemark_2006/OxfordCrystalmainbearing2.jpg
Yes, the phosphor bronze element is the closer red hatched element in my drawing - one can see it is a slightly different colour (darker) in the photographs). The bottom lip and the ball in the cup of the thrust pad are the only points of contact (hence the option to adjust).
Yes and the total area of contact between moving parts is minimal, even though the bearing assy looks large. I am assuming that there should only be oil in the bath at the top and between the phospor bronze journal at the bottom and absolutely nowhere else.
Methinks two different formulations of oil may be needed ?
This also explains the play in my earlier pictures. you get that when the ball is unloaded. The gap around the thrust plate and the inside of the oil bath at the top is quite large, so probably the outer housing hitting the spindle.
Yes indeed. Although the shaft is 14 mm diameter this element does not make contact at all with the journal and the actual part that forms the bearing is actually 22mm - but only over a short length. The concave depression the ball rests in in the thrust pad will be a greater diameter than the ball and hence the ball will tend to self centre (some lateral movement may well be detectable though when, as you say, the mass of the platter is unloaded.
I like it - the element of adjustment is very awkward though and difficult to get right.
Spectral Morn
15-08-2010, 16:21
Hi Guys
This is a fascinating thread.
I will at some point move it to analogue art as it has become so much more than just a series of photos of equipment.
Regards D S D L
the element of adjustment is very awkward though and difficult to get right.
The top adjustment is easy, if the bottom one is correct. The bottom one requires a jig I suspect, and its been made very hard to do by the user. To do it I would have to seperate the bearing from the Subchassis, and that is fixed on VERY tight.
So are the platter bolts there to isolate the platter or form a level, or put there just for me because I just complained over and over about it, I wonder? Seems like one too many degrees of freedom.
Ah no, I see - the three lower grub screws look like they could be retaining a bronze inner shell that forms the actual bearing surface - that would make more sense.
More like this:
http://i62.photobucket.com/albums/h90/markemark_2006/OxfordCrystalmainbearing1.jpg
There should I suppose be a gap between the phosphor-bronze journal and the outer housing in your drawing to allow space for the journal to move when the screws are adjusted.
There should I suppose be a gap between the phosphor-bronze journal and the outer housing in your drawing to allow space for the journal to move when the screws are adjusted.
In fact there is very much less contact between the bearing and the outer housing than the drawing suggests. just the bottom and top surfaces + the screw interfaces. Even the top thrust pad had an amount of oil between it and the top of the bearing housing, sugesting a gap.
In fact there is very much less contact between the bearing and the outer housing than the drawing suggests. just the bottom and top surfaces + the screw interfaces.
Err...that's what the drawing is supposed to (does) show (notice the gap between the black hatched inner shaft and the red hatched outer bearing housing).
There should I suppose be a gap between the phosphor-bronze journal and the outer housing in your drawing to allow space for the journal to move when the screws are adjusted.
Should there? I can't see any sign of such a gap in the photographs (hence I haven't drawn one). I can't see the purpose in having any adjustment of this nature at this point (are you sure there is a gap?) and suspect the grub screws are intended to retain the phosphor bronze journal (rather than to allow adjustment as such).
I wonder, you may be able to remove the journal, turn it upside down, and re-fit it for a new bearing surface.
(the gap between the thrust pad and the bearing shaft should have been drawn bigger as it looks like they almost touch in the drawing)
Err...that's what the drawing is supposed to (does) show.
No, the bearing (journal) and the outer housing, not the outer housing and the spindle
Ah yes - are you sure there is a gap there? I can't see any sign of one in the photographs.
Ah yes - are you sure there is a gap there? I can't see any sign of one in the photographs.
If there is no gap the screws can't adjust anything unless they are simply there to hold it in place I would have to undo one of the screws to be certain.
Also to clarify the thrust plate only touches the ball, it is well clear of the spindle.
I need to provide you proper measurements really.
Ah yes - are you sure there is a gap there? I can't see any sign of one in the photographs.
My mistake sorry, I though that there was a small gap but it was just a ring of oil or dirt. It doesn't come out if I remove one of the screws.
Snoopdog
15-08-2010, 18:24
Again, very surprised that there was apparently such a radical design change within the range of five units, serial numbers CR-052 to CR-059!
My bearing and housing was stainless steel as opposed to brass or phosphur bronze and I recall the inner spindle as being much narrower in diameter with the tiny ball bearing perched on top. Inside my bearing housing was a PTFE thrust pad held in position by three grub screws and it could be reversed when signs of wear became apparent.
Peter's Oxford with the tungsten thrust pad with indent and the way it mates with the inner shaft and ball bearing looks quite different.
Still, the final arbiter is how it sounds and there was a reason I kept my Oxford Acoustics Crystal Reference for 21 years while everything else in the system changed!
Again, very surprised that there was apparently such a radical design change .
Course, not all changes are to improve sound quality, might be stability, reliabilty, ease of manufacture, cost, availability of materials, etc
I wonder what CR-001 was like!
Somewhere out there is CR-Optima
I didn't draw the bearing to scale Peter - just quickly for discussion purposes (by eye) - a bit of resolution has been lost between the CAD software I used and the JPG image.
I think you would probably have to undo all three grub screws if you wanted to remove the journal.
I think you would probably have to undo all three grub screws if you wanted to remove the journal.
Tried that :), it is tight and I can't remove it, not a problem it just means I was barking up the wrong tree earlier when I thought it could explain the wobble, or be used to null it out.
BTW
The belt runs on the outside of a black acrylic sub-platter (which can be seen in my photos that show the underneath of the bronze platter). This puts the drive belt just below the outer housing bearing "lip" and about 5 inches away.
The bronze platter does not touch the vertical part of the housing. The light acrylic platter is in contact with the bronze platter, the top surface of which is lacquered. The light platter fits smoothly over the rest of the outer bearing height without any significant play, it is not stiff, so if you were to lift it vertically away from the bronze platter a mm and turn it there is sufficient slip to prevent it turning the bearing housing. (maybe if you removed the belt and turned it very very slowly it might).
The light acrylic platter also keeps the bronze platter flat against the bearing lip, that would prevent any wobble when stationary.
Sand Dancin Donkey Walker
21-08-2010, 22:50
Hi Peter
Very nice TT in deed.
For further help I would give Simon (very nice guy) at HiFi Sound in Stockton a call.
I beleive he has 2 of these TT's both for personal use and knows a good deal about them I believe.
Hope that helps.
Andy - SDDW
Thanks for the Recommendation Andy.
Been doing some of this:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0964.jpg
And I now can see why he has two of them.
I have been very busy and I am now at this stage:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0972.jpg
To get here I had to solve the platter support problem. Some form of spacing is necessary because without it the bottom of the platter fouls with the subdeck, so simply removing the bolts doesn't help. The spacing of my platter was wrong because one of the bolts was different to the others.
Things where going well until I sheared one of my replacement bolts so the thread was stuck inside the platter. This was the low point.
I wanted to make this project a thing that could be done from parts that could be resonable found around the home. But I need either a tap set, a lathe and other machines to resolve this. In the end I borrows a Dial guage from work. In case you don't know what this is, here is a picture:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0920.jpg
This guage has a rod with at tip containing a ball bearing. When the rod moves in and out of its shaft it registers the movement on the guage. This is very useful because you can place it in contact with wobbling things and the measure the wobble and critically find the points of maximum and minumum to an accuracy of 0.01 of a mm.
For spacing I am using 3 M5 nuts that I have selected out of about 100 units to obtain 3 with identical (as far as I can measure) heights. One of these goes around the platter support pin the other two are placed to form an equilateral triangle. The bolts are removed from the platter. This is a temporary bodge until I can get something better made.
The dial guage is then used to set the position of the thrust plate so the bearing housing is as perfectly upright as possible. I managed to do this with an accuracy of about +/- 20 Micron, this leads to a platter wobble at the outer edge of about +/- 150 Micron (+/- 0.15 mm), This is just about visible at speeds of 45 rpm. But it is streets ahead of how it was, and I think with future work I can improve it.
The next major problem was the sorbothane supports. I thought of using the original deformed supports (you can see one in the pic with a 2 pound coin covering the hole). On top of this would go the support used upside down (so the flange is the base). The flange has material from a band aid stuck on it so it will contanct the non-flat coin without too much movement (see prev pic).
That arrangement does not work because it makes the subchassis too high above the plinth. Instead I just used Steves trick of adjusting the subchassis spikes so they are extended deeper and touch the coins directly. This is far superior to any previous support mechanism as it eliminates two sections of the support and it enables much greater precision in setting the level and clearences that are vital for the TT to work. The sub-chassis must not touch the plinth anywhere (It always did before and it always sounded bad before).
Thats about for the T/T.
I only have 1 pickup and this an MC3000 that has a very low output (100uV) so I need to repair my pre-amp as my other kit is simply rubbish at such sensitivity. I have a Primare 928 preamp and this was chosen for its low noise. It can handle pickups down to 50uV and is the quietest preamp of its time, except it is very quiet now only because it is quite dead.
Here is the guts of a 928 preamp
It is very, very complex and sophisiticated peice of audio electronics:
http://www.saabphotos.com/gallery/albums/album1330/DSCN0935.jpg
Very difficult to get at things to service in some places.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0934.jpg
But really nicely made.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0933.jpg
The achilles heel of this unit is thermal instability. The case is a heatsink for the PSU and if you take it apart and run it without the case it will quickly overheat. I have had this unit fail in the past. Fortunately it has a pretty standard (crude compared to some of my PS Audio gear) power supply configuration, and the bridge rectifier had in fact failed. I replaced it with a similar one except I added a heatsink to help prevent future failure.
This time the +ve regulator had blown up (taking the rectifier with it). I had already replaced the rectifier with a much bigger sucker this time fixed to the metalwork. The regulator had gone short, putting +30V on the +18V rail. Luckily this did not cause anthing else to go, and the preamp actually worked but with a lot of hum.
The regulator is a 317T dissippating about 6W bolted to the case. It is very hard to get at, you have remove most of the metal work. The next time it fails I will build and external supply.
BTW the reason for the high dissipation comes from the need to operate over a very wide range of mains voltages 200-250V with only a single 220V position on the mains selector.
Once replaced the preamp worked, but as the case was off it got Very hot very fast and I wasn't quite sure it would last long and there was not another failure somewhere else. For example with 30V across aluminium electrolytics 25 years old rated at only 25V, would they need replacing?
Decided to risk it, it is now back together and it works but it takes approximately 30 minutes to stabilise thermally. Before then channels will come and go at random. This is down to the high operating temperatures of the devices in the signal path and probably old capacitors, but mainly it is the design decision to run with very low amounts of negative feedback.
Incendentally one of the ways the preamp gets its noise figure is by doubling and redoubling of its stages in parallel. The noise tends to cancel between stages but the signal remains unaffected. To work the stages must be matched for noise.
You can see this in the picture where you see multiple instances of four similar devices, red ones and (complementary) green ones. Oh yes the preamp is balanced and has balanced outputs. Coupled with a switched attenuator and wonderful IR remote control with touch operation, it is a really nice peice of kit and looks fab next to the turntable.
Forgot to mention that after much research into various oils I decided to just go for gloopy Mobil One motor oil, which I am using at both ends of the bearing. I think this is similar to what was used at the bottom originally. I suspect something lighter was used at the top.
There is no audible bearing noise at all. Perhaps not surprising as any noise does not couple to the pickup. For example I can drum my fingernails on the top of the arm housing or armboard and I can hear the drumming as dull thudding. I can drum on the plinth, nothing. Drum on top of the record clamp, still nothing. If I did this on my Oracle it would bounce and the pickup would leave the groove. In this case I can't even hear it.
The turntable is really only susceptible to sideways vibrations that cause it to rock around an axis sort of from arm pivout to record spindle, due to the sorbothane mounts having different degress of wear/deformity, and this takes some force, it also dies away very quickly.
It is actually rather nice to get away from the bouncing subchassis design. You can cue rapidly with confidence without thinking.
Reid Malenfant
22-08-2010, 18:40
Incendentally one of the ways the preamp gets its noise figure is by doubling and redoubling of its stages in parallel. The noise tends to cancel between stages but the signal remains unaffected. To work the stages must be matched for noise.
You can see this in the picture where you see multiple instances of four similar devices, red ones and (complementary) green ones. Oh yes the preamp is balanced and has balanced outputs. Coupled with a switched attenuator and wonderful IR remote control with touch operation, it is a really nice peice of kit and looks fab next to the turntable.
Interesting, this is similar to the way some Moving Coil preamps work, parallel the transistors & the differences in noise actually cancel each other & lower the noise floor :) Looks like a load of 4 in parallel to me & they have kindly painted the transistors in different colours to differentiate :eyebrows:
With 4 in parallel the noise floor will be lowered by 6Db, if the stages happen to have the bases of both NPN & PNP connected together you are looking at 9Db noise reduction ;)
Nice system & one i intend to employ on a home designed & built MC preamp in the future :)
By the way, lovely turntable & arm etc :wow:
Superb to see the resurrection of what is clearly an awesome piece of kit - well done Peter, and thanks for sharing.
With 4 in parallel the noise floor will be lowered by 6Db, if the stages happen to have the bases of both NPN & PNP connected together you are looking at 9Db noise reduction ;)
A good analogy for this in the spatial domain has been in use for a long time in astronomy/astrophotography. You use very fast (but grainy) film and photograph your dim nebula many times over many nights. Then you sandwich all your frames one ontop of another (using some reference stars for alignment) then when you make your prints all the grains contrubute only once but the image of the nebula is there serveral times so you end up with a less grainy print.
One other low noise feature of this design was to do with the coupling of the first stage. I don't recall the exact details but the idea was to use a common base first stage. The Re of the first transistor should be as low as possible to minimise noise figure as this is effectively in series with the pickup. So they look for the device that has the lowest Re, which at that time was a medium power device. You can see these on the MC section (they are painted silver and gold :) ) The MM section uses regular red/green devices so maybe this only works with low output impedance devices like MC pickups.
I seem to recall the CB topology was used in a later battery powered preamp where the signal passed through the batteries (Cyclons ?). I forget the details but, apart from the impracticalities of charging the batteries (couldn't use the preamp all the time), the sound quality was awesome. It was that design that the Oxford guys where thinking of using as the basis for their MC stage. I also recall there was a good article about it in HFN/RR.
Reid Malenfant
22-08-2010, 20:01
Ummm, you don't happen to be an amateur astronomer do you? I have always loved it myself ;) I have an 8" reflector that i'm making far to little use of :doh:
Yes, the medium power transistors i mentioned on one of DSJR (Daves') threads about a Lentek? MC pre amp :)
Common base would be unusual on an MC pre amp, apologies if i got you wrong & you mean something else entirely :rolleyes: Battery power though i agree with entirely, i just purchased 32 x 3000mAhr AA NiMH batteries recently to power a phono stage which i'm building. Only a kit,but a decent one that's well designed.
Another project in the future will be my own MC phono pre amp :) I already have ideas how to reduce noise & increase CMRR (common mode rejection ratio) to reduce hum & noise from the pickup arm wiring etc :scratch:
Bests to you Peter, by the way, it's too hot to run the Krell - It's why you can't hear it :eyebrows:
Ummm, you don't happen to be an amateur astronomer do you? I have always loved it myself ;) I have an 8" reflector that i'm making far to little use of :doh:
Yes, the medium power transistors i mentioned on one of DSJR (Daves') threads about a Lentek? MC pre amp :)
Common base would be unusual on an MC pre amp, apologies if i got you wrong & you mean something else entirely :rolleyes: Battery power though i agree with entirely, i just purchased 32 x 3000mAhr AA NiMH batteries recently to power a phono stage which i'm building. Only a kit,but a decent one that's well designed.
I have always been interested in astronomy but got frustrated with wobbly observation a long time before the 8' Celestrons appeared. I was that close to getting a Meade cassy with the computer tracking thingy? But I decided that you can't beat the pictures in the books, and spent the cash on some aerobatic flying lessons instead :stalks:. Today with my eyesight it would be a waste. A clear night sky is still very cool just to look at with the unaided eye. Probably the most excellent thing I recall seeing was a lunar eclipse a few years ago. They way the moon just turned red was uncanny. Ho-hum.
The MC pre-amp I am thinking of is the LFD (circa 1988). The topology used very left field thinking at the time. Its designers (Drs Bews/Hawksford ?) worked at the University of Essex, I think. I can't find the article but given time can probably reproduce the schematic. Wether it is worth studying today I don't really know. I don't know what modern technologies are capable of, been out of the loop for twenty odd years.
If your Krells can't take the heat, you should pop around and see what you think of the restored Oxford setup. You can confirm/refute my subjective findings. :eek:
Interesting article that has info about the LFD preamp design. Probably not new to AoS, but worth a look for electronics types.
Part 2 (http://www.linearaudio.nl/JDpubs/Interviews/Didden-Hawksford_Part2.pdf)
Also Part 1 which deals FF/NFB, DACs, acoustics, jitter, something for everyone to ponder.
Part 1 (http://www.linearaudio.nl/JDpubs/Interviews/Didden-Hawksford_Part1.pdf)
I still can't get over the fact that many SS preamp designs use overkill of components. I know that Primare have always made good gear, but the complexity of the circuit and the sheer quantity of components is frightening for such a device. I'm sure there are better and more capable transistors available today, let alone IC op-amps?
I once had awful problems setting up a Roksan TT as there are three set screws underneath the bearing, which you can adjust to level the bearing. It took me hours to get this just right. At one point I nearly launched the TT out the open door of the shop I worked in at the time. You thought you had it right but looking at the side profile of the platter you could see it rising and falling. This rise was on the side where the bearing housing was off :doh: I got it done eventually but at that point I swore I would not do a Roksan again. Even my mana spirit level was of little help to me.
Ah yes, I remember similar frustration trying to level mine. Not helped by the sagging wooden top plate with the big cut through it. And the difficulty in adjusting its level with the adjusment screws so that it did not touch the sides. Not to mention the strange motor bearing-against-a-spring idea. I did eventually sell mine in disgust and unfortunately my lovely SME IV went with it.
I still can't get over the fact that many SS preamp designs use overkill of components. I know that Primare have always made good gear, but the complexity of the circuit and the sheer quantity of components is frightening for such a device. I'm sure there are better and more capable transistors available today, let alone IC op-amps?
I am not really up to date and have been looking, but is it not true that the NE5532 and its derivatives are still the OPAMP of choice? That was a 1970s design.
Electronics nowadays is geared to mobile phones, unfortunately.
By way of a stutus update of sorts Here is the PCB from my Conrad Johnson Premier 4. This is not short on parts for a tube amp either.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1007.jpg
Power supply for input tubes is regulated in these amps, checkout all these diodes that are wired in series. This keeps the semiconducters that do the regulating close to the HT rail and with only modest voltages across them.
The opamp at the top is one of several comparators used for turning on an LED to help bias the output tubes.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1013.jpg
After some work I managed to get this going using half of the output tubes while I wait for parts to arrive.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1020.jpg
Getting 6CA7s for this is troublesome/pricey, and I have seen a lot of negative things written about this amplifier on the internet. The UK mag review(s) when this came out were IMHO not very fair to it. Hope to redress this a little.
But even with half the valves this amp sounds fabulous.
Reid Malenfant
09-09-2010, 17:57
I am not really up to date and have been looking, but is it not true that the NE5532 and its derivatives are still the OPAMP of choice? That was a 1970s design.
Electronics nowadays is geared to mobile phones, unfortunately.
It depends on the impedance of the circuit feeding the op amp in reality ;)
With a fairly low impedance circuit then yes the NE5532 (or single version NE5534) are still two of the top op amps out there, definately for the price :eyebrows:
With much lower & conversely higher circuit impedances then others will edge out the above mentioned op amps. However, the cost of some of them takes the mickey :rolleyes:
I still can't get over the fact that many SS preamp designs use overkill of components. I know that Primare have always made good gear, but the complexity of the circuit and the sheer quantity of components is frightening for such a device. I'm sure there are better and more capable transistors available today, let alone IC op-amps?
I think you'll find that in reality a discrete pre amp uses vastly less components than one containing even primitive ICs if you take into account the component count of the IC itself. Yes ICs can be good as has been mentioned, however they'll only work in class A up to a few hundred microamps & thermal effects make themselves known over the whole IC where as a discrete stage can be a lot more thermally stable. This may not sound that important but do you really want the output stage altering the input differentials bias & thus noise due to it warming it up with regards to an IC :scratch:
I think you'll find that this is why some manufacturers stick to discrete components as there is a lot more control over everything going on.
Reid Malenfant
09-09-2010, 18:04
Power supply for input tubes is regulated in these amps, checkout all these diodes that are wired in series.
:eek: That looks like a hell of a lot of zener diodes in series to me, i may be wrong though. Zeners are noisy things & a load in series doesn't bare thinking about :(
But even with half the valves this amp sounds fabulous.
It looks very pretty to :)
:eek: That looks like a hell of a lot of zener diodes in series to me, i may be wrong though. Zeners are noisy things & a load in series doesn't bare thinking about :(
The spec for this amp is -96dB hum and noise at full output (100W RMS min to 4 Ohms).
Am I allowed to post schematics on here?
Reid Malenfant
09-09-2010, 18:24
The spec for this amp is -96dB hum and noise at full output (100W RMS min to 4 Ohms).
Am I allowed to post schematics on here?
So that would be -76Db @ 1W RMS ;) Frankly i don't know how that measures up against other valve amps.
I'm sure you are allowed to post schematics, only as long as you aren't infringing copyright :doh: Try hunting on the net for the schematic & then link us to it Peter, that way causes no problems at all. I had to do similar with my phono pre amp, i could only find the MC section though :rolleyes:
So that would be -76Db @ 1W RMS ;) Frankly i don't know how that measures up against other valve amps.
:)
Ok, well in the meanwhile, the string of 13 avalanche ;) diodes (32V) has a current source at the top, (by my calculation about 2mA). The top (and top-1) of the string is connected to the input of a discrete darlington voltage follower stage that has 1.0 + 1.0 + 0.15 uF in parallel across the output (one of these for the each voltage used, 410V and 380V ).
Perhaps "regulated" is not entirely accurate description.
The -50V bias supply uses a similar arrangement, except just a resistor not a source.
The 500V plate supplies share a smoothed supply but have their own filter arrangements. The input tube "regulators" are fed from the filtered plate supply.
The output tube heaters are connected to a tap on the mains Transformer. The input tube heaters are fed from a smoothed 12V output.
Reid Malenfant
09-09-2010, 19:16
:)
Ok, well in the meanwhile, the string of 13 avalanche ;) diodes (32V) has a current source at the top, (by my calculation about 2mA). The top (and top-1) of the string is connected to the input of a discrete darlington voltage follower stage that has 1.0 + 1.0 + 0.15 uF in parallel across the output (one of these for the each voltage used, 410V and 380V ).
Perhaps "regulated" is not entirely accurate description.
:lol: Well it's more 'regulated' than some even if it's not perfect ;) Tbh i don't know a lot about valve amplification, though i do know that what you are describing can be improved on if you so wish. The zeners could be replaced by a TL431 & a high voltage power mosfet & a few resistors & should result in a less noisy regulator.
First up though get the whole amp working as it should, from there on you can modify it if you want to :)
Well, having the electron emitter so close to a 50Hz powered thermal noise source seems a bad plan to me, but I am no expert in tube amp design either.
This power configuration does appeal me though, as effectively it is just a load of impedance in between the PSU and the amplifier. I dimly recall such trickery is what gives the long tail pair good PSRR.
When I get around to it I will measure the noise though, and I thank you for pointing it out as I hadn't really considered it before because, honestly, it is seriously quiet, (The Primare is a howling gale by comparison and that is supposed to be low noise), and lets not even think about the vinyl.
As a point of general interest, I don't know if its commonly known that the noisiest of zeners happen to be the ones with best temperature stability (ie 5.6V) and the more you move up in voltage the less noisy (and faster) they become.
So what is the consensus on noise quality? IOW if you have to have noise, what is the most euphonic kind? (ie thermal vs shot vs 1/f etc). :scratch:
I am checking out the TL431 as we speak.
I think you'll find that this is why some manufacturers stick to discrete components as there is a lot more control over everything going on.
In the case of the Primare, it is as "complemetary" as possible, so both positive and negative swings are dealt with in the same fasion. This isn't the case in most OPamp designs (something to do with "good" PNPs being harder to fabricate or some such not helping).
Whether complementary purity is still a fasionable idea, I don't know.
Here are some more pictures of the Prem-4 having removed the covers.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0993.jpg
Power supply transformer, btw all the blue caps are for power supply smoothing and filtering, each is 1300uF 350V. They are wired in series pairs with 100K/2W resisters in parallel with each one. The plate voltage is 500V.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0996.jpg
Output transformer, these are supposed to be special, don't know the details.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0997.jpg
Labels are peeling off due to age.
http://www.saabphotos.com/gallery/albums/album1330/DSCN0999.jpg
Right, I have 30 years experience in electronics related fields, have a circuit diagram and I am still crapping myself at taking the covers of this thing. What I am about to do could kill.
Underneath now.
The PCB is double sided but not plated. No solder resist so hand soldered. No silkscreen. Not impressed, especially as I notice what might be a wiring error (white/red wires go to a green wire and not what appears to be the pin intended for connection).
Most of the wiring on the right is from the output transformers. The amplifiers is ultralinear so 5 wires per transformer.
the potentiomters are for setting the bias for each output tube. I think Kudos for using decent size pots for this and not presets.
First thing check the power supplies.
The iron items on the right are 320mH, 600mA DC chokes, these are wired between the 500V smoothing caps (2) and a seperate pair of filter caps for each channel. The "regulated" or rather "isolated" supplies come from the latter with each input tube having its own "isolated" output.
The isolated voltages are 20V higher than they should be. will need to look into this.
The heater supply is top left near the orange cap, This was not working correctly, half the rectifier has blown up (seems a common problem for me), replaced it on this side of the PCB. Now the input tubs glow nicely.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1000.jpg
here is the dead rectifier
http://www.saabphotos.com/gallery/albums/album1330/DSCN1009.jpg
One of the channels had blown its plate fuse, most likely culprit is a cathode resistor which is 20R wirewound. By measuring the cathode to ground resistance with the tubes removed should find it, and sure enough we do. But to replace it means getting at the other side of the board and that means de-soldering some wires. I desoldered the left hand side ones after making lots of photos. This is quite scary. Before messing with this always check the big caps are discharged before approaching. Fortunately the resistors across the caps discharge them fast and the resistors are in good condition.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1004.jpg
Crikey, theres a lot of expensive caps in here.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1006.jpg
I am using an I-pod for source, it works well. It works fabulously well with my friends I-phone, but I don't want to blow that up.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1007.jpg
Hopefully you can see the blown cathode resistor. near to it you can see why it went bang. Things have a habit of falling through the holes onto circuit boards in my house. This is one bad thing about circuit boards without a solder resist. Going to examine the rest of the board for FOD.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1008.jpg
These presets are to match the gain in the phase splitter. No need to touch them yet.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1010.jpg
Near the bottom is the circuit that allows for the bias setting. There is 1M between the cathode and the LF353 input and a 6V2 Zener to ground. I confess I don't really understand how this is supposed to work. Presumably the zener is there to prevent a big excursion taking out the op-amp.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1012.jpg
Power supply isolator previously discussed. The high value brown resistors tend to drift, and these 560K resistors actually measure close to 700K. I will remove them and place them on the other side of the board for easy replacement later, maybe when this warms up the will be correct. The other resisters measure OK. This might explain the elevated voltages I read on the isolated supplies.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1013.jpg
I think the 50uF caps are there to keep the input tube heaters alive when the power goes off long enough for the HT supply to discharge.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1014.jpg
20R W/W resistors are also used to connect the screen grids to the ultralinear tappings.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1015.jpg
Input valves go here
http://www.saabphotos.com/gallery/albums/album1330/DSCN1016.jpg
I have removed the Shakeproof washer and the blown resistor at this stage
http://www.saabphotos.com/gallery/albums/album1330/DSCN1017.jpg
Ok after re-assembly, I am using only 4 of the 8 output tubes. Each transformer tapping is driven by two tubes in parallel. We should be ok with just one tube so we have 50W instead of 100W, at least to check the amplifier is working.
At this stage I have not replaced the plate fuse (they are Very Expensive, only have 3 spare). The amp will actually work with a very small current (there is an LED across the fuse that tells you it is blown, the current through the LED is sufficient for the amplifier to give a very low output when it works. Of course the bias is then wrong so the LEDs are lit.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1019.jpg
Plate fuse is in now, amp is running.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1022.jpg
Lights out
http://www.saabphotos.com/gallery/albums/album1330/DSCN1023.jpg
Start to put some covers back on and audition, while thinking about getting new parts. Those W/W resisitors are outside spec and maybe should be replaced. The high value Allen Bradleys are easy enough to find.
http://www.saabphotos.com/gallery/albums/album1330/DSCN1025.jpg
It sounds very good, not sure replacing the Vishay W/W for KOA Film type is worth the risk, open to suggestions.
Here are the Conrad-Johnson Premier four (http://www.analogstereo.com/pdf/sm/ConradJohnson_PremierFour.zip) Schematics
So what is the consensus on noise quality? IOW if you have to have noise, what is the most euphonic kind? (ie thermal vs shot vs 1/f etc). :scratch:
Noise such as white noise can act like dither and be quite benign. In fact, I don't mind a little of this type of noise at all. What I cannot stand is hum, thankfully eliminated from my system since I swapped out my PS Audio GCPH phono preamp for a Whest.
In most cases, the S/N ratio is such that you shouldn't hear much noise when playing music. Very old CDs and some LPs are the exception.
...So the subject of the Marantz CD-94 arose and I tried to photograph it, as I personally think it is rather nice looking. But none of my pics really brings out the stealthiness of it except maybe the third one. The wooden finish is very dark in the flesh.
http://www.saabphotos.com/gallery/albums/album1377/DSCN1595.jpg
It is deceptively simple having the toys under the flap. Unfortunately the phones socket and FF/REW is also there.
http://www.saabphotos.com/gallery/albums/album1377/DSCN1596.jpg
Here I am testing it in the AV rig. It has a nice tendancy to disappear.
http://www.saabphotos.com/gallery/albums/album1377/DSCN1594.jpg
The belts have turned to licorice, of course.
http://www.saabphotos.com/gallery/albums/album1377/DSCN1585.jpg
I have stolen some from dead VCRs so it just works for now, but, any idea if a belt kit (4 belts are needed) is available for reasonable money? I am pretty sure it is a Mk1 and FWIW has a vanilla TDA 1541 (no A).
peter.
Rare Bird
31-10-2010, 11:47
I have stolen some from dead VCRs so it just works for now, but, any idea if a belt kit (4 belts are needed) is available for reasonable money? I am pretty sure it is a Mk1 and FWIW has a vanilla TDA 1541 (no A).
PM
The mk1 indeed - like my Micro Seiki is based on. Drawer belts the correct size are available from Cricklewood Electronics. While the belts are disconnected, make sure the drawer glides in and out very freely, as if the drawer assembly is bent slightly, as mine was, the friction becomes too high and defeats the loading belts I found.
Cheers for the belt info chaps.
There is considerable leeway in size it seems, so I expect these from cricklewood should be fine:
2x RD038 (1.2x38mm) 1x RT040 (2x41mm) and 1x RT051 (2x51)
total about 2.10 per set + p&p.
I found the drawer was a little stiff due to dust. Cleaned and wiped on some WD40 and we're back in business.
The player is a very early version, after looking at various Philips and Meridian players and not liking them at all I bought the Marantz within an hour of seeing it. Now it just blows me away how solid it is, how fast it it is before it starts playing, and how it sounds.
In stock form it does not do badly against the 840C (that just went out the door), although I think the soundstage on the 840C is better, I prefer the warm tone of the Marantz. I am shocked actually as to how good it is.
First via the D/A in the Denon, It took 2-3 hours warm-up before it would image or soundstage or reveal any real detail though. Now warmed up and using its own D/A it sounds a hell of a lot more musical.
This warm-up time is baffling. Need to get the scope out and investigate it.
I have the Service Manual in case anyone needs it.
peter.
Reid Malenfant
02-11-2010, 18:45
First via the D/A in the Denon, It took 2-3 hours warm-up before it would image or soundstage or reveal any real detail though. Now warmed up and using its own D/A it sounds a hell of a lot more musical.
This warm-up time is baffling. Need to get the scope out and investigate it.
Interesting you say that Peter ;)
My previous transport (Theta Data Basic) actually had the digital electronics powered up all the time, even when the unit was shut off :scratch: Proof of this was that the "lock" LEDs on both DIP24/96 interface processor & DAC were always lit. Both the DIP & DAC can only be switched off at the rear so effectively they are on all the time also :)
My Krell DT10 appears to shut everything down as lock LEDS go off :scratch:
Now i'm just wondering if it's worth modifying the Krell to keep those digital circuits running & at a set temperature? I have been thinking about this for a while ;)
Nice looking player by the way :)
Spectral Morn
02-11-2010, 18:46
Cheers for the belt info chaps.
There is considerable leeway in size it seems, so I expect these from cricklewood should be fine:
2x RD038 (1.2x38mm) 1x RT040 (2x41mm) and 1x RT051 (2x51)
total about 2.10 per set + p&p.
I found the drawer was a little stiff due to dust. Cleaned and wiped on some WD40 and we're back in business.
The player is a very early version, after looking at various Philips and Meridian players and not liking them at all I bought the Marantz within an hour of seeing it. Now it just blows me away how solid it is, how fast it it is before it starts playing, and how it sounds.
In stock form it does not do badly against the 840C (that just went out the door), although I think the soundstage on the 840C is better, I prefer the warm tone of the Marantz. I am shocked actually as to how good it is.
First via the D/A in the Denon, It took 2-3 hours warm-up before it would image or soundstage or reveal any real detail though. Now warmed up and using its own D/A it sounds a hell of a lot more musical.
This warm-up time is baffling. Need to get the scope out and investigate it.
I have the Service Manual in case anyone needs it.
peter.
Its the TDA 1541 DACs they improve when fully warmed up. I have a CD94 mk2 it takes a week to reach optimum performance. Once up to full performance it sounds excellent in the bass and mid and its only in the treble where things are not quite so good. It can sound a bit gritty on cymbals etc.
So far mine keeps working drawer opening etc with no problem.....go figure.
Regards D S D L
Ali Tait
02-11-2010, 19:36
Cheers for the belt info chaps.
There is considerable leeway in size it seems, so I expect these from cricklewood should be fine:
2x RD038 (1.2x38mm) 1x RT040 (2x41mm) and 1x RT051 (2x51)
total about 2.10 per set + p&p.
I found the drawer was a little stiff due to dust. Cleaned and wiped on some WD40 and we're back in business.
The player is a very early version, after looking at various Philips and Meridian players and not liking them at all I bought the Marantz within an hour of seeing it. Now it just blows me away how solid it is, how fast it it is before it starts playing, and how it sounds.
In stock form it does not do badly against the 840C (that just went out the door), although I think the soundstage on the 840C is better, I prefer the warm tone of the Marantz. I am shocked actually as to how good it is.
First via the D/A in the Denon, It took 2-3 hours warm-up before it would image or soundstage or reveal any real detail though. Now warmed up and using its own D/A it sounds a hell of a lot more musical.
This warm-up time is baffling. Need to get the scope out and investigate it.
I have the Service Manual in case anyone needs it.
peter.
I wouldn't use WD40 for this,it dries out over time and the drawer will stick.
Interesting you say that Peter ;)
Now i'm just wondering if it's worth modifying the Krell to keep those digital circuits running & at a set temperature? I have been thinking about this for a while ;)
If you can't tell any difference hot or cold then it's probably not worth the hassle. You need to conduct some listening tests. I perceive it as bad imaging and fuzzy soundstage.
I am only just beginning to get into this but looking at the data sheets it seems that on the 94, the SAA7210 does interpolate up to 1 uncorrectable error, and the SAA7220 up to 8 sequential errors (based on EFAB (pin 4) which can be nailed). Grounding that pin should (I imagine) cause an audible "tick". If not a LED, scope or counter can be connected and the errors observed during warm up (or other tweaks), all with the intent of reducing uncorrectable errors (unreliable samples).
On other Phillips ICs I have seen, the error information is a data stream similar to to serial data, with a number of bits positions in the error word indicating more detailed information, but on the SAA7210 it simply shows that the current sample is "reliable" or not.
It could be that if one has bad tempco parts on say your Demod PLL filter it is less effective when cold at maintaining lock or similar. Also that the various adjustments were made when the transport was at operating temperature, and the transport is sub-optimal at other times (or the supplies are not stable etc).
I think the CIRC does not intruduce any artefacts but the interpolation (error concealment) does, and this is the only way the sound can be effected (as from there I go via coax to an offboard DAC, permenantly powered). After all, the concealment/filtering is there to hide itself. This just makes it more difficult to detect by ear.
Perhaps unreliable samples are much more common than we think, that it takes time for the brain to form the soundstage perception, and that process is spoiled by "bad information".
peter
Its the TDA 1541 DACs they improve when fully warmed up.
Well, I wasn't using the onboard DAC at first, but what you say sounds promising, and I'm looking to improve that later with some tweaks that Dave mentioned, The clock mods look most promising for improving the HF and low level details.
The NOS hacks I've seen are also interesting, but mild oversampling seems less evil than aliasing artefacts that I know are very bad when they occur in visual images, especially when we are trying to improve the high frequencies.
This is all very interesting to me, there are just so many things that need work...
peter.
Spectral Morn
03-11-2010, 00:46
Well, I wasn't using the onboard DAC at first, but what you say sounds promising, and I'm looking to improve that later with some tweaks that Dave mentioned, The clock mods look most promising for improving the HF and low level details.
The NOS hacks I've seen are also interesting, but mild oversampling seems less evil than aliasing artefacts that I know are very bad when they occur in visual images, especially when we are trying to improve the high frequencies.
This is all very interesting to me, there are just so many things that need work...
peter.
One area of weakness is the thin bottom plate. If you have access to quarter inch aluminium plate then replace it with an exact copy just much thicker. I did this well over twenty years ago and it improved the sound a lot. I had access to a workshop back then.
Regards D S D L
Something else intriguing:
SAA7220 p7 Filtering
"to simplify the design of the digital-to-analogue convertor a d.c. offset of +5% is added to the accumulator".
What? How? Where? When?
What?
"Audio samples are available for DAO after interpolation, attenuation and muting, but before filtering"
Oh ok. that means that the DAO is not oversampled. Is that always the case? Thinking about it, it seems like it must be as the transport does not know what kind of anti-alias filter is used in whatever D/A it is connected to.
If you have access to quarter inch aluminium plate then replace it with an exact copy just much thicker. I did this well over twenty years ago and it improved the sound a lot. I had access to a workshop back then.
This is for rigidity not weight, correct?
Or can I just rest/fix it on something really really heavy. Does it have to be bolted on, and is the material important.
I ask because I ditched the horrid plastic feet and replaced them with thick black sorbothane isolation disks/feet that were all the rage in 1988. These isolation feet are now well glued onto the case and the wooden equipment table shelf, and I fear would not survive a seperation.
The isolation is very good though :)
Spectral Morn
03-11-2010, 08:21
This is for rigidity not weight, correct?
Or can I just rest/fix it on something really really heavy. Does it have to be bolted on, and is the material important.
I ask because I ditched the horrid plastic feet and replaced them with thick black sorbothane isolation disks/feet that were all the rage in 1988. These isolation feet are now well glued onto the case and the wooden equipment table shelf, and I fear would not survive a seperation.
The isolation is very good though :)
Hi Peter
The thin plate is a source of vibration. To my mind at the time it seemed daft to build the innards of the player into a nice heavy die cast box only to compromise that with a thin plate, which would rattle.
The one I made is bolted on using the original screws, its also brushed and painted with a varnish.
I used the original feet but filled them with Miliput which is an epoxy mix that dries solid and like clay. This was better but cones are more suitable imho.
However it sounded best with cones (point pointing down)...one directly under the transport, in the middle, one under the mains transformer and a cone to balance. Three is better than four and even with the new bottom plate you could still hear an improvement in sound quality as you move them around. Once you know where is best fix them with double sided tape. The effect with the thin plate base was more pronounced.
Regards D S D L
The TDA1541 based machines I tried at the time (Meridian, Marantz/Philips, Quad 66, Arcam) were very sensitive to rf muck coming in on the mains and I'm told the machines themselves could also spray loads of muck out via the screens of the signal leads, the AVI S2000 DAC being a notable exception. use of cable ferrites and a high current mains filter really works, together with getting the 2 pin mains plug round the right way. I'm stunned how good my CD player still is and the transformer coupling to the output helps too.
the SAA7210 does interpolate up to 1 uncorrectable error, and the SAA7220 up to 8 sequential errors (based on EFAB (pin 4) which can be nailed). Grounding that pin should (I imagine) cause an audible "tick". If not a LED, scope or counter can be connected and the errors observed during warm up (or other tweaks), all with the intent of reducing uncorrectable errors (unreliable samples).
OK folks, some results
On a warm player, playing an average disk, I get no movement of the EFAB pin except when starting/stopping switching tracks, FF/REW etc. I can get errors by interfering with the disk rotation physically, but no reasonable amount of shock causes the slightest problem.
With a deep scratch applied to the disk using a screwdriver (to a CD-R copy I hasten to add), I typically get two error samples per rotation. If I ground the pin (so the error indication does not get through), there is no clear audible artefact (the sample will just be a repeat of the last one), so no easy way to hear the errors.
Other signals indicate that the transport is basically giving two fingers to any attempt to disturb it , the PLL filter and motor speed waveforms are rock solid and show the transport is in control. I can apply various patterns of scratches to the disks and I can see these as dropouts on the scope but the CIRC is doing its job perfectly.
Judging from reported variations in transports (and own recent experience) I was expecting the error concealment signal to be chattering like a geiger counter, but this is not the case.
I will repeat the tests tomorrow when the machine is cold.
On the analog side I can see how the various mods being discussed would improve the D/A section. While the D/A chip has a good spec, I doubt it acheives its potential in the environment it is placed, on that single sided PCB which is a joke in todays multi-layer, ground planed, EMC aware world.
It beats me they did not put the entire section in a metal can.
peter.
The thin plate is a source of vibration.
Normally I would be suspicious of this kind of thing except I came across my own box issue with the Primare (which has stalled further work on turntables and the like).
Martin has pointed out that the worst kind of noise is HUM, and I have to admit that this was a problem (its audible between tracks) so I tried to reduce the level of hum by improving the filtering in the PSU, which has about 800mV of ripple on the +/- 30V supplies. Changing to a pi filter arrangement before the regulator reduced the ripple voltage to 100mV but actually increased the hum because the ripple current had gone up as a result of the extra capacitors. In fact everything I did increased the audible hum. After regulation there is no measurable hum, so it's probably induced anyway. In the end I decided I would build a proper hefty external supply later and would live with the hum for now as it didn't seem as bad as I first thought.
As I slid the steel cover back on I was still listening to the preamp and noticed that the more the cover was in place, the louder the hum was getting. It also changed the sound of the hum. Download from here (hum.wav 3Mb)
Primare MC input,Hum and Noise, with cover (http://www.mediafire.com/?bnlgml96lldvld3)
Now, mega-gain has been applied here. plus the preamp is working at maximum sensitivity so this isn't quite as bad as it sounds.
It's as if the hum leaks out of the box without the lid but is trapped inside with the lid on.
I thought I could filter it out with a simple 50 and/or 100 Hz notch filter but if you try this you will find the hum is still there. This is probably because it's ripple, which is a sawtooth waveform, not hum, and stretches all the way up the frequency band.
peter
Spectral Morn
04-11-2010, 11:19
There was a noticable improvement in sound quality.
Regards D S D L
There was a noticable improvement in sound quality.
I do accept that.
I have evidence to suggest that electromagnetic coupling may be a strong contributing factor.
If true, then your aluminium base, or a wooden base, plastic base, concrete base, granite base, even no base, is better than the steel (ferrous) base that they put there. This would apply not just to the CD94.
I have nothing yet that explains how weight or rigidity would effect the sound, but I am looking.
peter.
But first, I needed to resolve the hum with the Primare. This is largely caused by coupling of EM radiation from the transformer on the right of the box via the lid to the left of the box (where the MC board is).
You can't operate the Preamp without the lid as this also serves as the heatsink for the regulators - rock/hardplace.
Inspired by what I saw over in the DIY section, I made a new DC supply and stuffed it in a PC PSU box, which also now provides some mains filtering power switch and a fan. Here it is.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1637.jpg
The fan is wired across one of the the resistors in the Pi filter, so it goes around very slowly and is not audible.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1639.jpg
The preamp now has much reduced levels hum, so now we can do some listening.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1645.jpg
Andre - :lol:
The Quad 306 make an excellent mat. Other uses include
Bookends for when you can't afford Naim kit:
http://www.saabphotos.com/gallery/albums/album1400/DSCN1649.jpg
Record holder
http://www.saabphotos.com/gallery/albums/album1400/DSCN1651.jpg
Chicken warmer
http://www.saabphotos.com/gallery/albums/album1400/DSCN1647.jpg
Quality Peter, Quality! LMAO! :lol:
Rare Bird
20-11-2010, 21:33
:eek: I only need one :(
That Primare pre amp is just plain drop dead gorgeous. I remember it being reviewed in in HiFi News with the matching mono blocs..... must be over a decade ago. It still looks so charming today.
The Grand Wazoo
22-11-2010, 21:59
........must be over a decade ago. It still looks so charming today.
......and the rest.
I've just been & checked - It was March 1988! But I do agree about the look - I fell in love with that stuff back then (the Gryphon stuff too).
Spectral Morn
22-11-2010, 22:05
......and the rest.
I've just been & checked - It was March 1988! But I do agree about the look - I fell in love with that stuff back then (the Gryphon stuff too).
+1
I have only ever seen them (Peters pre etc) in bits on a repair bench and the vintage Gryphon kit in a shop window once many years ago (i was in the UK on a Yamaha training course).....
Those were the days....when HiFi mags were good :(
I have all the HiFi News issues from that period....they survived a cull of magazines just after I got married.
Regards D S D L
The Grand Wazoo
22-11-2010, 23:40
Those Gryphon units - a single fascia with two boxes mounted behind were just exquisitely built - beautiful to handle.
I still hanker after the preamp...........
http://www.hificlub.co.kr/upn/0901/market/GRYPHON%20LINE%20STAGE.JPG
Rare Bird
22-11-2010, 23:53
Those Gryphon units - a single fascia with two boxes mounted behind were just exquisitely built - beautiful to handle.
I still hanker after the preamp...........
O yes i used to lust after Gryphon,i had the brochures, those alone were well nice
Maybe I skimped a little on the photos of the Primare, forgetting about the optional remote control with touch sensitive pads. The shape/size of the remote is such that it would fit where the switches on the front panel are (if you took out the switches). The silkscreen has worn off on the pad next to STANDBY which should say MUTE.
http://www.saabphotos.com/gallery/albums/album1404/DSCN0945.jpg
The little box is the sensor which is on a long lead that plugs into the back of the preamp allowing you to place it wherever
http://www.saabphotos.com/gallery/albums/album1404/DSCN0940.jpg
The box honed from a solid hunk of aluminium and is the heaviest remote I have. The tech is bleeding edge for the time.
http://www.saabphotos.com/gallery/albums/album1404/DSCN0941.jpg
Fitted new battery, sensor box again here, you can see the logo in the front (there is a transparent section under the bottom of the omega that the sensor sees through)
http://www.saabphotos.com/gallery/albums/album1404/DSCN0942.jpg
and the bottom panel also machined from aluminium.
http://www.saabphotos.com/gallery/albums/album1404/DSCN0943.jpg
It controls the volume control (a stepped attenuator) using a stepper motor
http://www.saabphotos.com/gallery/albums/album1404/DSCN0932.jpg
One other photo showing a blown tantalum (serious kaboom stuff) just follow the blue wire...
http://www.saabphotos.com/gallery/albums/album1404/DSCN1563.jpg
Back panel. The fuseholder is now gone and the hole is used for the new DC power cable arrangement.
http://www.saabphotos.com/gallery/albums/album1404/DSCN0939.jpg
I sit my preamp on a speaker stand so it is right next to the T/T and the MC wires are therefore very short. IMO this matches the turntable and looks better than just putting it on a table. I had Acoustat 2+2 originally so everything was tall or on stalks!
Gosh, no wonder that Primare cost a lot of dosh, it must have cost them a packet to build each one. What happened to the company?
Gosh, no wonder that Primare cost a lot of dosh, it must have cost them a packet to build each one. What happened to the company?
"The man" behind he original stuff is Bo Christensen, I do hate cult of personality articles but the information is in these. If Primare is still going it is perhaps going a different way now.
Bo Christensen - Stereophile (http://stereophile.com/interviews/bo_christensen/)
and here (http://www.inner-magazines.com/news/105/67/Bo-Christensen-Bow-Technologies/)
The Grand Wazoo
24-11-2010, 07:46
They're still going:
http://www.primare.net/
.........but don't appear to have a UK presence
Spectral Morn
24-11-2010, 19:09
I too lusted after one of these at the time and having seen yours I still do :) The 920 series was and is still very tasty looking and no doubt sounding.... though I have never heard them.
Bo went on to form Bow Technologies which also make/made some stunning looking kit. http://www.inner-magazines.com/news/105/67/Bo-Christensen-Bow-Technologies/
Not sure if Bow Technologies are still trading ?
Regards D S D L
Reid Malenfant
24-11-2010, 19:40
http://www.saabphotos.com/gallery/albums/album1404/DSCN1563.jpg
Well blow me down if i don't see an LF353 in a top quality bit of kit from yesteryear :eyebrows:
Stanley B eat your heart out :lol:
If it's good enough for Primare then i'm sure they were good enough for a homemade active crossover on veroboard back in the early 90s made by myself ;)
Thanks for the post & picture Peter :) Much appreciated...
The Grand Wazoo
25-11-2010, 00:38
Bo went on to form Bow Technologies which also make/made some stunning looking kit.
Ah yes, how could I forget the Bow Wazoo?!!
A recent interview with Bo Christensen here (Feb 2010)
http://www.inner-magazines.com/news/105/67/Bo-Christensen-Bow-Technologies/
Well blow me down if i don't see an LF353 in a top quality bit of kit from yesteryear :eyebrows:
Stanley B eat your heart out :lol:
If it's good enough for Primare then i'm sure they were good enough for a homemade active crossover on veroboard back in the early 90s made by myself ;)
Thanks for the post & picture Peter :) Much appreciated...
Well at least it is a Motorola one :eyebrows:
But you weren't paying attention earlier, here are some LF353s in the CJ Premier 4, a green-spot matched pair in fact ;)
http://www.saabphotos.com/gallery/albums/album1330/DSCN1012b_001.jpg
It Cost How Much!?!
07-01-2011, 15:30
But first, I needed to resolve the hum with the Primare. This is largely caused by coupling of EM radiation from the transformer on the right of the box via the lid to the left of the box (where the MC board is).
You can't operate the Preamp without the lid as this also serves as the heatsink for the regulators - rock/hardplace.
Inspired by what I saw over in the DIY section, I made a new DC supply and stuffed it in a PC PSU box, which also now provides some mains filtering power switch and a fan. Here it is.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1637.jpg
The fan is wired across one of the the resistors in the Pi filter, so it goes around very slowly and is not audible.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1639.jpg
The preamp now has much reduced levels hum, so now we can do some listening.
http://www.saabphotos.com/gallery/albums/album1399/DSCN1645.jpg
.
enjoy.
peter
Very interesting thread, especially to me as I have a Oxford Acoustics Crystal Reference / SME V / Lyra Helikon and some Primare 928 power amps (in white). Quality items indeed and built to last. I am seeking a 928 pre and also a Gryphon Pre also.
I purchased my Oxford from Snoopdog on this forum and its he who pointed me to this thread
hifi_dave
07-01-2011, 16:33
After the failure of Bow Technology, Bo started up on his own again for a short while but ( to my knowledge) no products appeared in this country.
The original Bow products were beautifully put together, superbly finished and (obviously) stunning styling. Unfortunately, the sound quality didn't live up to the promise and there were various quirky features which made them a difficult sell.
Doing a clearout and found some more pictures of the Oxford that my be of interest to turntable fans.
Sorry about the timewarp, but this is where we were last time with the bearing section removed. Just noticed that the thing is still plugged into the mains and on!
http://www.saabphotos.com/gallery/albums/album1440/DSCN0827.jpg
Underneath the plinth - it is fixed with four bolts (damped by cobwebs)
http://www.saabphotos.com/gallery/albums/album1440/DSCN0828.jpg
Near armboard. We will remove the little screws near the edge in a bit.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0829.jpg
The plinth is connected via some ribbon and DIN plugs. IMO this is bad but it is at least cheap and would have helped keep the price of the table reasonable. We enter the realm of questionable engineering here - (IMO) emulate with caution.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0830.jpg
The plinth has been unbolted.
This is the sorbothane isolation for the table. It is critical to the design. It is not thermally stable though and it sags under the enourmous weight of the platter and the heat from the PSU beneath.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0831.jpg
It should look something like this but the turrets (next picture) would actually fall through if any weight were placed upon them. The spikes of the bearing assembly rest somewhere in the bolt heads.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0832.jpg
http://www.saabphotos.com/gallery/albums/album1440/DSCN0833.jpg
Maybe we will fare better with the plinth. Need to inspect it just in case there are organisms inside.
Lets take the screws out
http://www.saabphotos.com/gallery/albums/album1440/DSCN0835.jpg
0 bio-entities detected, but hmm.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0836.jpg
Switch PCB, V1.1 already.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0837.jpg
Motor, the optocoupler is looking for a short length of black tape.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0839.jpg
Note to DIYers Don't ever let a wire bend at a solder joint (ie use sleeves) this is for mechanical integrity as well as to to keep things from shorting out. Please also say no to IDC for this.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0840.jpg
See that tape on the motor more clearly here. Not sure what happens if it falls off. seems to be well stuck, good.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0841.jpg
The other side is prepared to accept the motorised Air-Tangent arm lift wiring.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0842.jpg
The brass mountings are where the plinth is bolted to the base below
http://www.saabphotos.com/gallery/albums/album1440/DSCN0843.jpg
The white screw mount is cheap simple and effective as far as I can tell. Going to look under the PCB for amusement..
http://www.saabphotos.com/gallery/albums/album1440/DSCN0844.jpg
No connector for the ribbon, sigh. The FR4 should be cleaned up also, can get nasty splinters with this stuff.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0845.jpg
Corner cabinet fixing is discrete. I know nothing about woodworkery mindyou.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0846.jpg
This is a little disappointing, probably why I "lost" these photos.
Due the fragility of the ribbons/DIN fix them securely with gaffer tape before attempt at cleaning.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0847.jpg
Gonna use this. It works well on my flatscreen.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0856.jpg
Filled the holes with kitchen paper.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0857.jpg
Better.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0859.jpg
Not cobwebs but clingfilm for temporary storage.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0864.jpg
Continued...
Before leaving the plinth just check out the rubber debris shed around the spindle
http://www.saabphotos.com/gallery/albums/album1440/DSCN0850.jpg
Guess this is what the Formula One chaps call "the marbles"?
Remember that the platter wobbles up and down so the belt is always wandering up and down the outside of the platter.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0851.jpg
Here is the base, the bottom cover is lifted and placed in this position to adjust the screws that set the level at the bottom plate. This is fantasticly heavy. I can't lift it although it can be "walked" from room to room.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0867.jpg
On this incarnation there are three feet and one spike
http://www.saabphotos.com/gallery/albums/album1440/DSCN0868.jpg
Again the weight is so great that the foot has penetred the sorbothane damping (fuzz from carpet)
http://www.saabphotos.com/gallery/albums/album1440/DSCN0869.jpg
Going back to the bearing now. In this series of pictures I am adjusting the three top screws to set the level as perfect as possible at the centre
http://www.saabphotos.com/gallery/albums/album1440/DSCN0876.jpg
http://www.saabphotos.com/gallery/albums/album1440/DSCN0877.jpg
round and round until the the circumpherence is concentric with the shaft.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0878.jpg
Now with the platter on we can check its level. Not a chance.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0889.jpg
This is the reason - remember there are three bolts that support the platter:
http://www.saabphotos.com/gallery/albums/album1440/DSCN0760.jpg
Taken them out. they are not the same length but hey
http://www.saabphotos.com/gallery/albums/album1440/DSCN0893.jpg
This measurement is the important one.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0906.jpg
and this
http://www.saabphotos.com/gallery/albums/album1440/DSCN0910.jpg
and this, WTF.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0905.jpg
Ok the plan is to replace them with these three that can be filed if needed. They are used in PCs for cable mounts and I have picked 3 similar ones from a large collection.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0913.jpg
they are slightly thicker. Should be ok.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0915.jpg
The photo series ends here because when I screwed one into the platter I was so furious I over tightned it and it sheared off - no way it is coming out.
Game over.
Just a few more pictures left...
It is not possible to simply put the platter on the bearing housing because of the pin. I am not filing off the pin and can't remove it. In the end I just place three nuts on the housing, one surrounding the pin Carefully replace platter to rest on them. Takes a few attempts to prevent them falling off (the platter is so heavy and the surface is laquered and cannot be touched so it can only be lifted at the rim, eventually it goes on. That happens later on but is how it is done.
Meanwhile I still have to solve the problem with the deformed white sorbothane supports. Originally the sorbothane had a surrounding ring and there were three more holes through which three spikes where screwed through to the base plate. This was later changed to the type I have now.
My intention is to change the supports by placing coins over the holes and rework the turret like this:
http://www.saabphotos.com/gallery/albums/album1440/DSCN0920.jpg
then when placed on the base it would look like this (although just looking at it will make something fall over):
http://www.saabphotos.com/gallery/albums/album1440/DSCN0921.jpg
Now this is very fiddly and it is has always been rather difficult to place the plinth over the top without something falling off or touching something else. I discover that the best way to do this is to unscrew the bottom of the plinth as we did earlier and attach this to the base first. Then fit the suspension and the the rest of the plinth folds easily and accurately over the top. I would suggest this for a normal Oxford setup.
http://www.saabphotos.com/gallery/albums/album1440/DSCN0923.jpg
The turrets thankfully turn out to be superfluous and when the spikes in the subchassis are screwed all the way down they rest directly on the coin surface. Snoopdog has suggested using Stillpoint cones instead of the spikes/coins and I think that is perhaps the better option. Either way, ditching the turrets makes it a lot simpler to set up without things moving as weight is applied, or when the unit is polished.
It is a simple matter then to assemble the rest of the turntable:
http://www.saabphotos.com/gallery/albums/album1440/DSCN0924.jpg
There you have it, warts and all this time.
Peter.
satanfriendly
16-01-2011, 13:25
Absolutely beautiful Peter and I am immensly jealous being as it on my list of 'must have' turntables. I recall when these first entered on to the market and thinking 'yes, yes, yes!'.
Execellent work and I hope the reproduction is as seductive as its looks.
Hi just joined the forum after seeing some discussions regarding the Oxford Crystal Reference. Just wanted to say I m also a lucky owner of one of these, however mine differs as I have one of three, I believe, wall mounted models. I have never seen another and I believe the designers believed there to be audible benefits by developing the wall mounted model, however it was probably launched just before the company wound up.
Great post as these turntables become older parts will need to be replaced or supplanted
Spectral Morn
29-01-2011, 21:43
Hi just joined the forum after seeing some discussions regarding the Oxford Crystal Reference. Just wanted to say I m also a lucky owner of one of these, however mine differs as I have one of three, I believe, wall mounted models. I have never seen another and I believe the designers believed there to be audible benefits by developing the wall mounted model, however it was probably launched just before the company wound up.
Great post as these turntables become older parts will need to be replaced or supplanted
Hi Terry
Can you pop into the welcome section of the forum and say hello. Tell us a bit about yourself, taste in music and your system.
Regards D S D L
So, no way can I afford the PS Audio Power Plant, but for grins put this together:
It is a sinewave generator feeding a Quad 306 which then drives a backwards transformer to power an illuminator.
http://www.saabphotos.com/gallery/albums/album1400/DSCN1724.jpg
Can probably improve this arrangement with a more suitable transformer and using both channels of the 306.
http://www.saabphotos.com/gallery/albums/album1400/DSCN1725.jpg
Close up of transformer.
http://www.saabphotos.com/gallery/albums/album1400/DSCN1726.jpg
After the chicken was warmed up, I tried connecting it to a pair of Acoustat Interfaces. The older type interfaces have lots of mechanical hum (caused by the 5kV energising transformer). By adjusting the frequency the Hum can be completely removed. They are near silent at 60Hz, which is where I suppose they were designed to operate. Makes me wonder what the importers of this stuff actually do to earn those fat commi$$ions.
There should be plenty of power remaining to run the turntable and phono stage in the system which uses a passive preamp and another Quad 306 which will just have to run from real mains.
Still testing to see if there is definate audible improvement using this clean supply, but IMO just getting rid of the mechanical hum is a big plus.
Peter.
PS: I think I should mention that this might be dangerous and may harm you or your 306.
Reid Malenfant
09-02-2011, 11:12
Hi Peter, if i was you i'd connect a rather large capacitor between the amp output & transformer, or if you are bridging the amp just on one side. This will prevent any DC offset from causing too much current flow & also keep DC away from the transformer ;) The voltage rating can be low as you aren't expecting a lot of offset, just use as big a capacitance as possible :)
Nice idea btw, that is effectively how a power plant works at the end of the day :eyebrows:
Hi Mark,
Before experimenting further with this I will be adding caps per your suggestion. The waveform generator does have offset adjustment which when not set correctly give noticable loss of output and other grumblings.
Any suggestions as to what to do with the secondary earths? Seems a shame to connect them to a "public" supply.
Some new transformers are being made locally (JMS transformers) to replace the noisy US made ones in the ESL interfaces. A voyage through the factory was quite interesting, lots of thick shiny copper stuff lying about.
Having completed repairs and restoring the Premier 4 to the full complement of 8 tubes, it pulls near half a kilowatt before sound gets anywhere near it. As a result, the mains transformer also gets mechanically very noisy and the amp needs to be placed out of line of sight. If the little ESL transformers are successful I may look into getting a custom power transformer done for that too.
Reid Malenfant
12-02-2011, 12:07
Any suggestions as to what to do with the secondary earths? Seems a shame to connect them to a "public" supply.
Some new transformers are being made locally (JMS transformers) to replace the noisy US made ones in the ESL interfaces. A voyage through the factory was quite interesting, lots of thick shiny copper stuff lying about.
I'm assuming you are refering to the transformer primaries in this case which would be 240V AC out? What i'd do is earth the centre taps (or what would be the centre taps) so you effectively end up with balanced mains about earth ;)
The firm you are refering to - JMS Transformers, are they over at Ivatt Way industrial estate out of interest? I was thinking of possibly commisioning a firm over there to build me some custom power transformers as they advertise that they do custom jobs. Just depends on the price & if they can make them silent or very nearly so :hmm:
Yep, I was thinking about the equipment earths that are on the clean mains supply side. Connecting then to the centre tap makes good sense and allows for fault currents to blow fuses which is good, but should there not also be some sort of connection to mains earth to avoid possible electrostatic build up of potential between to clean earths and the mains earths?
On the one hand it seems this is needed for safety and on the other avoided for purity. Perhaps just some kind of choke would do the job?
Yes JMS are in Ivatt way, sort of between Peterborough grass machines and Radical motorsport, there is just a plain looking door with a combination entry lock and a push button. Just turned up without notice and they were pleased to help. AKAIK they don't do audio transformers or small power toroidals but make anything from the little 25VA up to sub-station stuff. The website gives some idea, but I think its always best to visit when having custom stuff made.
We are looking at about 3 working days before collection, two units only no problem.
Edit: JMS do toroids and others according to their site, just did not see anything like that during factory visit.
Reid Malenfant
12-02-2011, 16:53
Connect the earth at the centre tap of the secondaries (really primaries) to mains earth & use that as your system earth for that circuitry using you balanced power PSU. Very little current should ever be running in mains earth anyway as you know, it'll be vastly cleaner than what's going on in the proper mains Neutral wiring :eyebrows:
Nice one on JMS, that's great news :) Think i'll give them a ring & pop round to see what they could do & more importantly how much for :)
Here is a picture of my very sad looking Oxford Crystal Reference TT, in need of restoration. It's not been used since my Premier 4 (also pictured) blew up over 10 years ago.
I would now like to play vinyl again, but the TT has many design issues and I need help from anyone who has some experience with this product to help me get it working properly.
Oh yes, and hello to everyone!
Peter.
http://www4.mediafire.com/imgbnc.php/d8fdae10477aa11bcbcbe19d254c4012b976a597cf741bbd2b c6b25d261a46a06g.jpg
I just discovered that none of my picture links in this thread work any longer.
The pics are now found by clicking on the nearest index thumb below and scrolling from there. Sorry about that.
Peter.
http://www.mediafire.com/imgbnc.php/5ab80572eb1302b24ee5a7e5b848a2b94282aba07eec93213c dd26bc9aff36b82g.jpg (http://www.mediafire.com/imageview.php?quickkey=qr2pl1sjodlo4c8&thumb=5) http://www.mediafire.com/imgbnc.php/a4a62725315057525f74e69be405e5db9e3e3536ec3c5870f2 b25222f324799a2g.jpg (http://www.mediafire.com/imageview.php?quickkey=47k382rmk3owdbm&thumb=5) http://www.mediafire.com/imgbnc.php/1f651570a39bc000a49be72c423ee116c074c12c1f0a4ce272 fb7fee61db8cdb2g.jpg (http://www.mediafire.com/imageview.php?quickkey=poi04cy5o3t8y3m&thumb=5) http://www.mediafire.com/imgbnc.php/cff5de11fdf462c38afdeb09a143141fa00aa2a49f7f68eec1 2b5c148dc994142g.jpg (http://www.mediafire.com/imageview.php?quickkey=4rkrby5tcnk6qb4&thumb=5) http://www.mediafire.com/imgbnc.php/9fe0e4aee09bb28706c3add2d4eca574049cded4bfe763e0ba f3ddc5ca5f6d662g.jpg (http://www.mediafire.com/imageview.php?quickkey=bvr3n1sdt0ibykl&thumb=5)
http://www.mediafire.com/imgbnc.php/8db501f74aea1a635427c442b9a9827ed4a16580982d071bc3 9665bee10d527a2g.jpg (http://www.mediafire.com/imageview.php?quickkey=2ud8x6h5lhijllq&thumb=5) http://www.mediafire.com/imgbnc.php/7c23b040ea6e55e4d16300d287f82db54eb74c95d6304c196e 4c6fbdd6a41f3e2g.jpg (http://www.mediafire.com/imageview.php?quickkey=ecf4bfmml8uk5ss&thumb=5) http://www.mediafire.com/imgbnc.php/8a1ccf208428ebd88297df30338bdfe3878920f7c4589486a8 29bb33aa28a4e02g.jpg (http://www.mediafire.com/imageview.php?quickkey=dk6dbesskapjtql&thumb=5) http://www.mediafire.com/imgbnc.php/cc4ef1b2ab0add04d5b8f16afd90a89dec11d1cb182586a334 e30c0285cc355a2g.jpg (http://www.mediafire.com/imageview.php?quickkey=vxhbvureo2m11bu&thumb=5) http://www.mediafire.com/imgbnc.php/0706e7a080e501be85add699c842626febe7d12c2509554aa2 6f51432eeae2432g.jpg (http://www.mediafire.com/imageview.php?quickkey=k0miut7pye9ix11&thumb=5)
http://www.mediafire.com/imgbnc.php/d7b839f8598b839f84dc75f1c6311e272c24bd0eca2049d55e 336538b8a8775b2g.jpg (http://www.mediafire.com/imageview.php?quickkey=213oxebwwmz2de4&thumb=5) http://www.mediafire.com/imgbnc.php/7fc73145022906d8c0e80462a4327974ff72e387ce2c36d61a 2b6a6ba2466c0d2g.jpg (http://www.mediafire.com/imageview.php?quickkey=yzg7268ohp6edkw&thumb=5) http://www.mediafire.com/imgbnc.php/40693c9265a20e1075c5a99b2bfab1dc18f7819264dd4b88c1 4e9d9c306402662g.jpg (http://www.mediafire.com/imageview.php?quickkey=ftzbvvq9w8jivl3&thumb=5) http://www.mediafire.com/imgbnc.php/c4fd6978090295386e54a5fbec41f76efe54790bace9405510 98e67a630809fb2g.jpg (http://www.mediafire.com/imageview.php?quickkey=7ttmz4tfeqq0edt&thumb=5) http://www.mediafire.com/imgbnc.php/2cc0f0b8fca2691be07d21b42e91d218815379eca1eb5b24fd 658f09a0cc7aac2g.jpg (http://www.mediafire.com/imageview.php?quickkey=ua93wdfa89q1xve&thumb=5)
Reid Malenfant
13-10-2011, 17:16
Good to see you are still about Peter :)
You didn't happen to move any pics about on the photo hosting site did you? That would cause all the pics moved to vanish from your posts :(
Glad you got the pics up ok, Peter - looking good! :cool:
Marco.
Hi Mark,
Unfortunately the problem is that Elkparts, Ltd. who used to host the saabphotos.com server that I originally used for the photos ceased trading since June or July. Those tornado powered Red Flags have been waving for some time now and I should have heeded them.:doh:
I noticed it yesterday when I tried to upload this nice picture of my 16 year old SAAB:
http://www3.mediafire.com/imgbnc.php/ae2b5ee61cf496907161c13eaf863ffaea8f40a6ca578955c2 a2d7b88628d8545g.jpg
(Well, Hamish might like it).
Peter.
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