PDA

View Full Version : Parallel tracking air bearing arm



Magna Audio
11-04-2009, 20:18
Well dudes. Long weekend, some bits and pieces I had in the garage and an air pump and my protoype / test version is working.
Won't bore you with the details and at the moment it sounds like a Rega with a cheap Ortofon MM through a Nad 3020 and Mission 700 speakers - that's cos' that's what it is! - My garage system, all-be-it a carpeted and nice cosy garage).

Cut and smooth the air bearing with 600 grade wet and dry. Might try 1200 and see if there is any difference.

http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00007.jpg

Bits and pieces coming together - checking arm length and VTA.
Arm tube is made of an archery alloy arrow - Has tapered inner tube (might be good for resonance but who knows). Carbon tube is also a possibility.
Headshell and all all other brackets made of 3.5mm alloy sheet or ali angle.
vertical bearing is Stanley blade in ali channel.

http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00009-1.jpg

The air pump - I am using a 1 gallon fuel can as the smoothing reservoir.

http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00023.jpg

In operation

http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00024.jpg
http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00019.jpg
http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00020.jpg
http://i727.photobucket.com/albums/ww272/speedysteve7/SL-1210/DSC00021.jpg

I have tested it on 4 lp sides so far without hitch.
Next step is make an arm lowering mech and install Litz wire when it arrives. Litz wire is supposed to be nice and flexi and of good enough quality.

More DIY tomorrow:)

Could fairly easily knock up a Terminator style one with an under-slung short tone arm and see how that compares.

Ali Tait
12-04-2009, 11:37
Nice one looks great Steve! I've heard a couple of decks with Vic's arm and they were both superb.It's a great arm.

Sgt.Pepper
12-04-2009, 15:35
Thats a great result to get it fully working Steve :smoking:
With using angled ali for the horizontal bearing ,I assume its running at a low pressure,do you get any forward and backward movement of the arm,due to the low pressure ?

Mike
12-04-2009, 16:30
made of an archery alloy arrow - Has tapered inner tube (might be good for resonance but who knows).

S'good enough for Naim's Aro... so why not! :)

Magna Audio
12-04-2009, 17:08
Can't see any forward and backward motion.
Both sides of the carriage get continuous supply of air of equal pressure. I suppose a resonance could be set up but there would be quite a damping factor in the air pressure and the total moving mass.
I've read it's much less of a problem then a record that is not round. The duff one I am testing in is a bit out and the whole assembly moves laterally side to side esp on the first track of the disc.
The air goes through a 5L smoothing tank which stays at arm lift pressure for longer than the record takes to slow down should there be a power cut - so no stylus jump even in that situation.

I still need to check I am running the right air gap - 50 micron's or so is the recommendation. That's 0.05mm so out with the feeler gauges...
It's a pretty stable flow and can take an arm load of up to 500grams on the Rena 600 pump I have - could probably get away with a small pump...

Anyway a total load of around 300 grams is good for damping but this needs to be dialled in with the lugs (ears) once I have it on the main system.

It's all so adjustable - Lateral and vertical mass.

I'm working on an arm lift now. Don't fancy hand cueing the lovely new Audio Technica 33PTG I just got:)
Once that is done I will run it on the Technic's SL-1210 first on duff disc with Ortofon cart and then move up to the AT.

Then I'll let you all know how it sound compared to a O.L modded Rega RB250.

muffinman
12-04-2009, 17:47
Then I'll let you all know how it sound compared to a O.L modded Rega RB250.

I've got a quid on it being better (in it's own way) :)

how are finding the 'air noise' btw ?

Magna Audio
12-04-2009, 23:26
Just been making the arm lift. Will have to extend the arm due to the Techy having that sloped platter and also need to change the VTA a fair bit as the platter is lower. Techy will be in the workshop for fitting tomorrow - love this long weekend and fairly carp weather:)


I've got a quid on it being better (in it's own way) :)

how are finding the 'air noise' btw ?

There is virtually no air noise from the air bearing. The pump is another matter - it's not bad if on a carpeted floor but it's not silent. I think a wooden sound damping box will be in order. Can hear it when she's playing and I might be less noticeable tucked under a Tannoy and sitting away from it. It is sited right by me in the workshop.

Oh well more fun later today - goodness is that the time...

jkeny
13-04-2009, 16:47
Steve, you are speedy! I've followed you here from the Zerogain thread. I hope you do the terminator version - by all accounts it's superior - & give us a comparison against this arm.

The air pump noise seems to be the Achilles heel of the whole affair. You're using a Rena which are supposedly quiet! I've seen reference to this as one of the quietest around because it's a piston system rather than diaphragm! http://www.medousa.com/en/product/default.asp?prd_ln=lpac I wonder has anybody here tried one?

Another one I found in researching is this one - again a piston type, out of production but from the UK so might be easy to find for you. If it turned out to be as quiet as it appears in the video then it would also be good to leave it on display: http://www.youtube.com/watch?v=NdhncxI9rUA

Magna Audio
13-04-2009, 19:36
I put the arm on the SL-1210 today. Not had time to swap carts etc so just ran it up with the Ortofon through the Denon surround sound amp in 2 channel mode in to the Tannoy's - sound's better than the Rega/Ortofon/NAD/Mission but miles off what the AT-33PTG/P75/TVC/Valve amp/Tannoy's regardless of arms sounds.

Will wait with the 33 PTG on the arm until I get the Litz tone arm wire as the solution I am using now if a bit stiff and gives some problems lateral loading probs. I played about 4 discs without problems today.

I put the pump under the Tannoy's (they are on low stands - er bricks actually). Even putting it on Foculpods did not help much. Do folk really put up with air pumps in their living space for the quiet hobby of fish?
I will need to make a sound deadening box or use the now defunct Sat dish cable hole in the wall for the air feed and mains cable and put the damn thing outside in a waterproof box (large ice cream container with some fine wire mesh for breathing on the bottom should do it) That would shut the damn thing out/up!
That's probably faster and more effective than all the sensible sized sound proofing boxes I can come up with.
I am lucky in that the exit for the sat cable is down the side of the house we just use for junk storage...

Those pro air-pump jobbies look expensive- quite normal for our hobby I guess:-)
Like the lack of sound with those piston ones - Not so quiet on the other Utube clips though - hard to tell / more investigation yes.

jkeny
13-04-2009, 19:53
I too find it amazing that aquarium owners would put up with anything other than a silent pump in their living room. Maybe audiophiles are more discriminating about the intrusiveness of background noise. My wifes' Dell laptop fan drives me to distraction when she has it turned on in the living room. It's quiet but the noise fluctuates & draws attention as a result.

I have a friend also putting one of these together & he has exactly the same issue with the pump noise - tried every sound deadening trick known & ended up locating it outside the listening room.

It's a pity as a lot of people can't do this & as a result are put off by this factor. I'm one of these and as a result am researching pumps to try find a solution.

One suggestion was a refrigerator compressor (which are quiet < 30dB) mounted in a sound box but I wonder if there's enough air flow from one & how long one would last without the lubrication that normally circulates in the fridge coolant liquid.

Spectral Morn
13-04-2009, 19:59
Steve

You are a man of hidden talents...record cleaners and now air bearing arms....what can't you build. GO STEVE GO STEVE GO STEVE GO! :youtheman::respect:



Regards D S D L

Magna Audio
14-04-2009, 17:42
Litz tonearm wire arrived - out with the soldering iron again :)

Hope to get the AT 33 PTG on it tonight and really hear what this air parallel stuff is all about...

Magna Audio
15-04-2009, 21:18
Got the Litz wire on and checked the tracking / skating - totally 0 pull either way from the tonearm wires now. On with the 33 PTG.

1 more thing that improve the sound - decent interconnects - I need to make up some more long ones... Using cheapies at the moment.

Had a listen after the valves had warmed.

First impressions of the air arm are

1. Amazing detail, clarity and highs I've not experienced before.
2. Not enough bass for my taste (could it be the cheap interconnects?)

so need to change interconnects and investigate is I need to load the arm / carriage up for the medium compliant cartridge...

Time to read up on that.

Magna Audio
30-04-2009, 10:40
Thought for a while I probably could not make a really good arm.

Looked at the Terminator and came up with this copy.

http://inlinethumb28.webshots.com/44123/2675417940071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2675417940071997495olpgVm)

http://inlinethumb59.webshots.com/43834/2545367890071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2545367890071997495Oaaulw)

http://inlinethumb19.webshots.com/44882/2249617260071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2249617260071997495rmOMTn)

http://inlinethumb06.webshots.com/41733/2171887850071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2171887850071997495xowQKp)

http://thumb15.webshots.net/t/73/173/7/53/77/2561753770071997495GwYxMN_th.jpg (http://entertainment.webshots.com/photo/2561753770071997495GwYxMN)

This sounded pretty good. Much better bass weight and control.

I then went onto a carbon tube arm and better knife edge bearing & brass arm carrier / counterweight - Stylus pressure is very easy to adjust with a grub screwed threaded weight.
Sounds even better.

http://inlinethumb25.webshots.com/44120/2546299320071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2546299320071997495dxhnqp)

Next step is improve the arm cradle. I made this one by cutting to allow bending to angle. Better cut the pieces out of a ready made 1 1/2" box extrusion - better precision.
Headshell needs to be improved aesthetically- no doubt it does the job sonically.

Costing wise
To make 1 arm is about £30. The pump and hose ~£30.
From the materials bought I can make a further 1 to 2 arms...

Tools
I do have a lathe (1940's Southbend) and a cheap pillar drill. A cheap taps and dies set and drills / files /saws etc.

jkeny
30-04-2009, 14:31
Well done Steve,
Looks even more industrial then the first arm - I consider this is an advantage, BTW.

So better bass, better control than the MKI & with carbon arm & better pivot & counterweight another upgrade in sound. On a scale how much better is this now to MKI?

Magna Audio
30-04-2009, 14:38
It is miles better than the Mk1.
I think it is down to the shorter tone arm and better bearing arrangement
The blade is thicker which cuts out resonance - the fizzy sound. One of Ladegaard's tricks was to dampen the thin (0.61mm Stanley) blade with Blutak, but the whole arm to bearing arrangement had too much flexi'ish material flexi'ish there and not enough engineering.

It now surpasses the O.L Rega RB250 with consummate ease and probably many other 9" pivot arms too.

jkeny
30-04-2009, 14:55
Do you think there is much more to be squeezed from the design by the use of even shorter tone arm (how much shorter can it be made), better knife edge bearing (what did you use for this?), counterweight & headshell improvements?

Magna Audio
30-04-2009, 22:02
1. Shorter tone arm. This would mean the arm carrier would sit more over the record making it harder to put a disc on + you need some arm length to handle any disc warping. It's possible a bit shorter could be optimal though.

2. Knife edge bearing - Used a thicker blade for a hand planer. Stanley RB106.

3. Counterweight - probably no sonic improvement but it looks nicer than the Meccano brass worm gear:)

4. Headshell - perhaps could make a difference. I intend to craft something out of billet ali.

Setting up is not difficult but it is crucial to extract the best sound.
Arm length, parallelity (is that a word?) of the carrier and trueness of both platter, air arm and cartridge to the disc. VTA set by ear.

twelvebears
01-05-2009, 10:08
Re air pump noise, try and find a cheap flight-case (I have one which came with a set of hair clippers). These are foam lined and can easily have holes drilled for the power lead and airline.

Magna Audio
01-05-2009, 14:19
Nice one Twelveb. I was thinking of making one of MDF and foam but that will cost a bit... Currently the pump is in the under the stairs cupboard where you can't hear it unless you put your ear the stair carpet.
How they can put 'Silent' on all these pump / box descriptions is a matter of amazement to me...

jkeny
01-05-2009, 17:24
Hi Steve,
I listened to one of these Terminator style DIY air bearing arms at a DIY audio meeting on Saturday & it sounded excellent. It's replacing a Rega RB250 arm & some present, who own an Artemis arm, rated the Terminator higher. This arm still needed some final work on it in the form of wiring as the existing wires were still too stiff - I supplied some litz wire which will be used.

The two pumps were in a flight-case situated in another part of the room (actually in another room but open to the listening room) & I said that on examining the case & opening it, that it didn't sound that loud. But I was told that in late night listening it's intrusive if in the same room.

Magna Audio
02-05-2009, 20:52
Litz wire seems excellent for the job. I have found having a stiff (Cat5e) wire from the phono sockets shooting straight out to the rear and the Litz wire hanging down in a natural unstressed loop to be the best.
Testing done on the glass Rega platter (on the Tecni deck) I have showed no appreciable pull in any direction on any playable part.

I finished the arm lift mech today and an happy with it.
Also a front plate to hide the adjusting mech and gubbins.

The sound is developing - perhaps the Litz wire is burning in or my constant tweaks are paying off... I ditched the arm hook and fitted a new headshell (still made out of a brass door bolt housing) attached to the arm with grub screws instead of epoxy.
M3 hex grub screws have replace all the temp M3 threads with a saw cut in them to hold the arm to the arm carrier etc.
Even a nice knurlled brass VTA securing knob on the side instead of the M6 nut. Haven't had the knurller on on my lathe for at least 10 years...

I asked my wife who happened to pop in if the sound was CD or TT -"oh obviously TT", she said. "so much detail and aliveness, this is sounding really good now" - Alway nice to get the WAF.

What shall I call this arm? I thought of Steve's Air Force II - bit corny.

Air rate II, perhaps? What can you come up with???

Here's how it now looks

http://inlinethumb21.webshots.com/43284/2306635520071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2306635520071997495oOXIfh)

http://inlinethumb23.webshots.com/22550/2747647530071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2747647530071997495TVBGHv)

Only the headshell improvement remains.

Clive
02-05-2009, 21:07
What shall I call this arm? I though of Steve's Air Force II - bit corny.

It's great that you've built this and it should sound great, even if it sounds only half as good as the real thing. As for the name - how about Terminator-copy, well almost a copy anyway. :)

The arm needs the needs to be closer to the spindle, this makes a big difference.

jkeny
02-05-2009, 22:00
The arm needs the needs to be closer to the spindle, this makes a big difference.
Do you mean the arm needs to be shorter?

Looking really great now, Steve & I bet it sounds as good as it looks?

Clive
02-05-2009, 22:03
Do you mean the arm needs to be shorter?

Looking really great now, Steve & I bet it sounds as good as it looks?

Yes I guess so, I mean the wand needs to be shorter or put another way the arm mechanism needs to be closer to the spindle. The improvement will be worthwhile but not as much as moving from the traditional Ladegaad to the Trans-Fi Terminator config in the first place.

jkeny
02-05-2009, 22:11
Yes I guess so, I mean the wand needs to be shorter or put another way the arm mechanism needs to be closer to the spindle. The improvement will be worthwhile but not as much as moving from the traditional Ladegaad to the Trans-Fi Terminator config in the first place.

But as Steve said: This would mean the arm carrier would sit more over the record making it harder to put a disc on + you need some arm length to handle any disc warping

I wonder if a swivelling mounting post could be devised that would allow this shorter arm but what about disc warps

Clive
02-05-2009, 22:19
But as Steve said: This would mean the arm carrier would sit more over the record making it harder to put a disc on + you need some arm length to handle any disc warping

I wonder if a swivelling mounting post could be devised that would allow this shorter arm but what about disc warps
You get used to slotting the LP in between arm and platter, unless you're playing LPs after a boozing session it's not problem. Warped LPs aren't an issue either, I've not have one problem with warped LPs and a short wand (that's not a personal comment!)

jkeny
02-05-2009, 22:28
What would you say is the optimum length? (for the arm, of course)

Clive
02-05-2009, 22:34
What would you say is the optimum length? (for the arm, of course)
From blade to stylus about 75mm to 80mm seems to work well but it's not hyper critical. Of course this assumes the wand has the same resonant behavior as the Terminator, which it probably doesn't simply because the wand is unlikely to be using exactly the same material. So if it sounds worse when short this could be the reason.

jkeny
02-05-2009, 22:50
Ah OK, I should have asked another way - what resonant frequency or range do we want? How is this resonance best measured? Sorry for all the Qs

Clive
02-05-2009, 22:58
Ah OK, I should have asked another way - what resonant frequency or range do we want? How is this resonance best measured? Sorry for all the Qs
It's not so easy.....res freq behavior of these arms doesn't seem to follow what pivoted arms do, actually they seem a lot less critical than pivoted arms in terms of res freq in that they cope well will seemingly mismatched cartridge / arm combinations. Suck it and see if you'll pardon the expression when discussing wand length....

jkeny
03-05-2009, 12:01
Suck it and see if you'll pardon the expression when discussing wand length....

LOL!:lolsign:

Magna Audio
04-05-2009, 10:00
Ladegaard talked of getting the res freq down to a couple of Hz. The carbon wand does sound better than the ali one - have done back to backs with it now, same vertical pivot blades etc...

Other idea a friend came up with is to dampen the blade contact point with some correctly viscous material - trying a spot of Vaseline at the moment.

Could have tiny end plates to the V part of the bearing and run an oil drop but that would be messy.

Magna Audio
06-05-2009, 21:05
The Vaseline worked very well :eyebrows:
Top end is really good now. Nicely balanced with the rest.
To answer the arm length issue - I think the photo's I took make it look like the manifold / arm carrier is a long way back.
The total length from stylus to knife edge bearing is 90mm. That's how it has to be with the Rega mount on this deck unless I make another adaptor (pretty easy to do admittedly) - Something to play with when I am bored.

Headshell project is coming along. Took a couple of hours to hue this out by hand.
Must make sure not to cock it up when drilling / tapping for the cart retaining holes/threads - yes, I know, should have done that first but tap is in the post...

http://inlinethumb34.webshots.com/44129/2624395640071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2624395640071997495bisReu)

http://inlinethumb63.webshots.com/35070/2857684580071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2857684580071997495UmPIfG)

Magna Audio
09-05-2009, 21:12
http://inlinethumb40.webshots.com/42855/2797341380071997495S600x600Q85.jpg (http://entertainment.webshots.com/photo/2797341380071997495HLHBNK)

Now for an acrylic dust cover... Just happen to have a sheet in the garage...