A preamp for montesquieu

[Radford Revival]

I am in the process of building a prototype bespoke preamp for montesquieu, I thought people might be interested in seeing it unfold.

The preamp will be a hybrid valve / solid state design, using valves and MOSFETs. The FETs will be acting as voltage followers, but at the same time performing a bootstrapping function, allowing the valve itself to operate with lower distortion than it otherwise would (not that it would be particularly high in the first place).

Tom / montesquieu wanted to have a preamp that used 6SN7s, which as well as being aesthetically nice valves, are well known to be nicely linear and tend to produce remarkably little distortion when implemented correctly.

Here are some of the bits gathered so far. The mains transformer is bespoke for the project, the pot is a simple ALPS affair. The angled brackets you see are so that the valves can be mounted horizontally, 6SN7s would otherwise be too tall for the case.

Tom wanted a tape loop, so to avoid impedance issues I may implement a buffer using the venerable NE5532 opamp, possibly a somewhat contentious issue for a purist! In all honestly the distortion introduced by an opamp (especially the NE5532 which still remains a good performer even today), especially connected as a voltage follower, is so minuscule, it's simply not worth worrying about.

This of course brings about the argument that one could just as well use an opamp for the main gain section of the preamp, and not bother with the valve at all. This is entirely true, and from an engineering perspective makes absolute sense. From my perspective, it can be just a matter of enjoying the fact that the amplification is done by a valve, and as the colouration by either technology can be so low as to be irrelevant, it really can just be down to that alone. Tom's views may differ from that of course so hopefully he'll like the way it sounds :D

http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/02/SAM_6352-e1423254725258.jpg

[montesquieu]

My prejudices say all-valve, but I trust Will's instincts as well as his technical expertise, so not going to presume to tell him how he should go about designing it (even if I had the language to, which I dont). It will be fascinating to hear how this works out. My suspicions are it will sound ... Like a Radford!

[RobsterD]

What no foo parts,such a cheapskate Tom :)

[Radford Revival]

My prejudices say all-valve, but I trust Will's instincts as well as his technical expertise, so not going to presume to tell him how he should go about designing it (even if I had the language to, which I dont). It will be fascinating to hear how this works out. My suspicions are it will sound ... Like a Radford!

Normally (without the tape loop) there will be one solid state component in the signal path, and MOSFETs behave in a way very reminiscent of high gain pentodes so you can pretend it's a plastic valve ;)

[awkwardbydesign]

Love the brackets. Every expense spared!

[Ali Tait]

Not much wrong with a NE5532 TBH. Not something I'd have wanted until recently myself, but since getting hold of a Tandberg R to R, it would be a necessity for me too now.

[Firebottle]

Liking the approach Will, I will follow with interest.

How do you tell which has the left electrons and which has the right electrons with all white phono sockets :scratch:

:) Alan

[Andrei]

The angled brackets you see are so that the valves can be mounted horizontally, 6SN7s would otherwise be too tall for the case.
But still visible?

[awkwardbydesign]

But still visible?

That's the only purpose of valves, isn't it? ;)

[CageyH]

Not in my pre-amp.
It has to be "little finger" safe. Anything that glows is a magnet.

I get the sonic properties of valves without the worry about burnt fingers.

[Radford Revival]

But still visible?

They will be partially visible through the perforated section of the case.

[Radford Revival]

Not in my pre-amp.
It has to be "little finger" safe. Anything that glows is a magnet.

I get the sonic properties of valves without the worry about burnt fingers.

It will not be possible to touch the valves as they will be within a (vented) case.

[awkwardbydesign]

It will not be possible to touch the valves as they will be within a (vented) case.

Oh, where's the fun in that? Big, hot, high voltage, dangerous to pets and children; real man's hifi!

[User211]

Yeah. Fear of electrocution. Keeps you on your toes.

[awkwardbydesign]

Yeah. Fear of electrocution. Keeps you on your toes.
Yes, I've seen your amps!

[User211]

Well then you know what I mean!
You've also seen me turn them off with my toes:D

[awkwardbydesign]

http://poesypluspolemics.files.wordpress.com/2013/08/hobbit_feet.jpg:)

[Marco]

That's just wrong!

Marco.

[Yomanze]

Not much wrong with a NE5532 TBH. Not something I'd have wanted until recently myself, but since getting hold of a Tandberg R to R, it would be a necessity for me too now.

It is almost silly how much Richard Bews of LFD gets out of these classic opamps - most of his phono stages use NE5332s, my LFD pre uses a pair of opamps too and it sounds far far better than the simplicity of the circuit has a right to.

[tannoy man]

Any news about this Radford Pre? interested Radford owner

[Radford Revival]

Some updates - prototype line stage board (for one channel)


http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/08/pre1_resized.jpg
http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/08/pre2_resized.jpg
http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/08/pre3_resized.jpg

[Firebottle]

Nice attention to detail Will with the mechanical support for the pcb valve base :)

[Radford Revival]

Nice attention to detail Will with the mechanical support for the pcb valve base :)

It really makes a massive difference - the leads for the valve socket didn't even wiggle when I trial fitted a valve before soldering!

[Radford Revival]

Bandwidth for the circuit above was in excess of 100Khz - completely overkill and have included provisions for taming this if necessary. Distortion I've not measured yet but theoretically very low - the valve doing the gain is bootstrapped by the MOSFET follower so sees nearly a horizontal loadline, and negative feedback is also used, which will reduce distortion and output impedance further (it is taken after the buffer). It also will keep gain stable.

Another thing worth mentioning is that big wire wound resistor only runs luke warm, so it's not cooking the adjacent components!

[Colin Wonfor]

I am not fond of the NE5532 or 34 I prefer OP027/37 or AD820, the sound on the 553X series for me it to brittle , we used them a lot at Audio Partners on Cambridge kit but it was not what I like personally.
They were designed in on most of the kit by Mr. Self he also paralleled them up on a few designs to reduce noise this was not very satisfactory and most smoked to death. The AD797 is also a good one for me. try it some time.

[Radford Revival]

Well this project has taken a while but it is finally coming together. I ended up using an old Radford HD250 case that had been completely gutted by someone.

Here are the electronics laid out on the chassis base plate, all that is needed is the mains and input/output wiring to the rest of the casework. All circuit boards DIY. More details to come.


http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/11/sneakpeak.jpg

[Reffc]

Looking forward to hearing this on Saturday Will. You haven't long to sort the casework and controls out! (don't need to reply as you haven't got time to! :lol:)

[struth]

Looks nicely designed in modules which is always a good thing. Sure Tom will be singing its praises soon

[montesquieu]

Looking forward to hearing this on Saturday Will. You haven't long to sort the casework and controls out! (don't need to reply as you haven't got time to! :lol:)


Lucky bugger you'll get to hear it before I do!

[Radford Revival]

I've had it running today - it sounds incredibly transparent, and as much as it pains me use a term like this, "punchy" ;)

[Arkless Electronics]

Nice job. I built a gain-clone into a Radford SPA50 case (later type not the "shoebox"). Useful cases!

[Reffc]

I've had it running today - it sounds incredibly transparent, and as much as it pains me use a term like this, "punchy" ;)

How very dare you sir! :spank: The use of language such as "punchy" is only one "dynamic" step away from "inky blackness" syndrome. Next, before you know it you'll be using words like "mellifluous tranquility of tone" and "that inky well of low noise" and maybe even... "an amp with PRaT and Dynamics", or perhaps "a breathless brilliance which tings away with uncongested euphonics". Now go and have a cold shower. :ner::ner::ner:

[Radford Revival]

How very dare you sir! :spank: The use of language such as "punchy" is only one "dynamic" step away from "inky blackness" syndrome. Next, before you know it you'll be using words like "mellifluous tranquility of tone" and "that inky well of low noise" and maybe even... "an amp with PRaT and Dynamics", or perhaps "a breathless brilliance which tings away with uncongested euphonics". Now go and have a cold shower. :ner::ner::ner:


:lol: It's a slippery slope, I'll be re-wiring the thing entirely with silver and rolling the finest Mullard ECC33s instead of the lowly Russian 6N8S 6SN7 copies that are currently no-doubt ruining the sound with their measured 0.001% (entirely 2nd and 3rd harmonic) THD at 4V peak-peak!

[brian2957]

How pure is the silver :)

[montesquieu]

The suspense is killing ..... :sofa:

[Reffc]

http://i1140.photobucket.com/albums/n577/24pacman/005_zpsvxbck2bg.jpg

:ner::ner::ner::ner::ner::ner::ner::ner::ner::ner: :ner::ner::ner::ner::ner::ner::ner::ner::ner::ner: :ner::ner::ner::ner:

[montesquieu]

Spill the beans Paul ... how did it sound?

[Audio Al]

I know , but I am not telling :D

[Reffc]

Spill the beans Paul ... how did it sound?

It sounded REALLY..[Moderating....comments removed]

[struth]

Sorry but they were rude

[DSJR]

Was my post moderated away too?

[struth]

Was my post moderated away too?
Nope. Youve no recent posts here

You posted in community

[Barry]

It sounded REALLY..[Moderating....comments removed]

Now now! If you don't behave, I'll restore the "removed comments". :D


By the way, what did that poor Radford ZD amp do to deserve evisceration and have an ugly 'chicken head' knob fitted? :lol:

[Reffc]

Now now! If you don't behave, I'll restore the "removed comments". :D


By the way, what did that poor Radford ZD amp do to deserve evisceration and have an ugly 'chicken head' knob fitted? :lol:

:D:ner:

The preamp casing is actually from a HD250 Barry and the chicken head knob is very fetching in the flesh :eek::lolsign: It was gralloched to make way for a brand new preamp circuit designed from scratch by Will as a prototype for Radfords new commercial preamp venture, this one being destined for Tom. The case work is a work in progress and will be replaced when Will gets the new casework CNC'd. It allows Tom to have the new preamp in his system until time for a full transplant into a shiny new bespoke casing....with knobs on...

[Barry]

:D:ner:

The preamp casing is actually from a HD250 Barry and the chicken head knob is very fetching in the flesh :eek::lolsign:

Ah - the cases of the HD250 look very similar to those of the ZD22. At least the knob matches those on the Radford STA amp!

[petrat]

Sounds like a winner .... looks to follow, we hope :D

[Reffc]

I'll spill the beans now as Tom's been kept in pain quite long enough.

First and importantly, I will state for the record that I have no commercial ties with Radford Revival. None whatsover. Neither have they asked me to write up anything on this new preamp design, and I chose to do this because I am impressed by their considerable achievements and this preamp is, imho, long overdue! (I mean in relation to all the STA series power amps out there crying out for something like this!)

I would never dream of posting anything other than honest opinion. I stand to gain nothing from offering my thoughts and most certainly am a person who would rather say nothing than post anything derogatory where that might affect someone else's livelihood. I cannot understand why anyone would want to do that in fact, except those of a more uncharitable bent .

Onto the pre-amp:

Radfords were kind enough to travel up with the preamp and a restored STA25 to try out with the Raptors to my recent bake-off event. We had various amps available for testing, including an Inca-Tech Claymore, nice little Denon PMA355UK, an Emille Ki-40L (new valve complement and fully serviced), and an AN OTO SE.

So, we had a range of well designed amps varying from budget to true high-end designs with the Radford combo slotting in just beneath the top spot.

The Emille has become something of a benchmark for me in so far as it always seems to just get out of the way of the music and let the music do its thing. It, like the Raptors, does not draw attention to itself in any way. The combination, for want of a better description, is entertaining, revealing without ever sounding prominent up top and about as open a picture on a recording as you'd want. It is not combo which leaves you wanting for more of anything particularly. It's very easy to listen for hours on end. Therefore when something is removed it is usually very easy to spot any changes.

The AN OTO SE had it's strengths in the system (both digital and analogue front ends) but bass control was not one of them. Strings and voices were very good indeed as was the detail that came through, again without drawing too much attention to the higher frequencies.

The little Denon with this system shows bags of bass grip (I have tried it before in the system) and punch but lacks outright refinement although for a budget amp of a fair few years old, it can proudly hold its head high even amongst many newer mid-priced amplifiers. The Inca-Tech also delivers way above its price point, both at the time of its release and even today. It is one of the better SS integrateds of it's type I've listened to. If I had any criticism, it is that separation seemed a little obvious with some recordings, a little too focussed, almost leaving a gap in the middle, plus the mids lacked the apparent depth of sound stage and detail of either the Emille or the Radford combo but given its age and price point when designed, it still shines strong as a highly competent integrated amplifier and one that most would be proud to own.

Enter the Radford combination. The power amp is conservatively rated around 35W (Will will correct me if I am wrong) so in the same ballpark as the Emille and using similar output valves (although the Emille can take E34Ls, I am running it with KT66s).

The first thing is that the Radford matches the Emille for a remarkably low noise floor. You can put your ear to the speaker cones with either amp connected with the power on and just hear a feint hum and nothing more, but your ear really does have to be pressed right up close. Both amps are pretty remarkable in this respect compared with many valve amplifiers. When the music starts, it soon becomes apparent that Will has succeeded in producing a polished and well considered pre-amp. The proponents of the straight wire phillosiphy a passive preamp are missing a fair few points if they think that is the best way to go, because it is littered with pitfalls amongst which include the need to keep interconnects as short as possible and issues with buffering impedance and matching gain. In this day and age, it's all very well to discuss high gain digital sources but the fact remains that a competently designed and executed active preamp does so little to measurably and audibly detract from the signal, the question should be "why would you choose to do otherwise?" because of the advantages of buffering the impedance for a genuinely low output impedance whilst delivering sufficient gain and low noise. Distortion I think on this preamp measured less than 0.001%.

Queue the music, and the class of the new Radford preamp shines. The drum intro of an Earl Hines track jumps into space in front with realism and authority and the breathy notes of a sax off to the left somewhere in the mix, with every key stroke audible and delivers a performance that can only be delivered like this when you have no clouding of the lower noise floor, good S/N and channel separation, allowing focus and clarity to shine through. With some modern multi-tracked digital sourced music from Andreas Vollenweider's Book of Roses album, the dynamics from barely audible far off details in the introductory track growing with the intro to the sudden explosion of the La Strega theme hits home with real punch and vitality. Turn the wick up and there's a total lack of background noise or hiss, then dive for the volume to turn it down before the speaker cones are blown across the room as the brief interlude ends. Whatever we threw at it, it delivered without colouring the music in any way that was discernible. It was, to coin a hackneyed phrase, "transparent" or appeared so.

Whilst this can be a difficult thing to assess without the benefit of auditioning the live mic feed for any recording, it is described as such with the afore qualified knowledge of my own system and performance rated against the Emille. What really shone through was a healthy amount of rhythm and punch, some real bass grip, so uncharacteristic of so many lowish powered valve amplifiers. Discussing things like damping factors, the Radfords have one of the lowest output impedances of any production valve amplifier, something that many others try, and fail to achieve without going down the hybrid route. Whilst a lot of this is to do with the output transformers and feedback design of of the STA series of power amps, you don't really truly appreciate what it means until you use them with a quality active matching preamp for best effect. I have heard the STA using a passive pre (in that case it was using a Lumley PP40 preamp or control box as I thought of it) and whilst good, it didn't have that final injection of life and vitality that only a decent active preamp can deliver.

So how did Will's prototype fair amongst the competition? Honestly, and truly, it was superb. One of the quietest in operation that I have ever heard, no hum issues (it has, thankfully, an earth lift circuit unlike many). It was easily the equal of the Emille when partnered with the STA 25 and in some respects, that combo was a tad tighter in the bass, if to my ears, the Emille seemed to dig slightly lower. The Radford was equally as sublime through the all important mid range and had the clarity and neutrality that the AN lacked (but the AN is less about accuracy and more about emotion) yet, the Radford combo lacked nothing in terms of emotional connection with the music. I could happily have listened to it not just for hours, but for good. If ever I decide to move the Emille on (and like Jerry, I am an inveterate amp swapper! I like to try different amps every year or so) then I might finally hang up my box-swapping coat and settle on a new production STA25 partnered with this new preamp. Tom I think will be delighted that his patience has paid off. This, knowing Tom as I do, will in my humble opinion tick every box that I know Tom has set. Emotion? Tick; Vitality and life? Tick, Lack of obvious colouration? Tick; incredibly low noise floor? Tick.

[montesquieu]

Gosh ... thanks Paul. Can't wait to hear this ... sounds just what I was hoping for. Much appreciated for taking the effort.

[Wakefield Turntables]

I want one!

[Radford Revival]

Wow, many thanks for the very kind comments Paul, I gather you quite liked it then ;)

Tom might too :lol:

[Radford Revival]

Some closer pics

Please note that the HD250 was already "gutted" previously (not by me) and was already missing the vast majority of its parts, so no working or near-working amp went to waste when using this chassis.



http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/11/SAM_8361.jpg


http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/11/SAM_8363.jpg

Note the custom rear panels where the heatsinks would have been mounted.
http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/11/SAM_8364.jpg


http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2015/11/SAM_8365.jpg

[The Black Adder]

what's going to happen with the facia? Will it have it's switches and sliders in the end?

[Radford Revival]

what's going to happen with the facia? Will it have it's switches and sliders in the end?

It just has the original volume slider and a rotary input selector, the original buttons were damaged so I couldn't use those). There is no tone control circuit either so the sliders wouldn't be functional if present. I have carefully saved everything that was left in the HD250 box as spares, and even the build into this box is reversible apart form the holes in the main chassis.

[montesquieu]

OK .. time for me to comment. Been flat out with various things going on ...

Initial impressions were very much as Paul outlined .. wonderful detail, fantastic imaging, really getting out of the way. But there was slight unease that I couldn't put my finger on initially ... quite puzzled for a bit ... just not quite 100%.

However, I got it eventually - the 6SN7s (or rather 6H8Cs) had gone bad, I guess most likely probably in transit .... they were really quite microphonic, as evidenced any time the unit was touched. It was ringing and the top octaves were over-emphasised relative to the rest of the sound.

Tube rings helped but it wasn't till some new Tung Sol 6SN7GTBs arrived (a tube I know well from previous encounters) showed up that the amp really showed what it can do.

And what it can do is fantastic. Obviously the detail and 3D-ness were reinforced but what the new tubes gave it was an additional solidity, robustness, even a confidence, that it hadn't quite shown, as well as a better way with the very lowest register. It really restored the balance. Not that it was hugely out to start with, but they really made things click into place. And I've been listening non-stop ever since they arrived, or as non-stop as working from home will allow.

I have several test records and a test CD that I always roll out when checking out new gear (don't we all).

George Bensons White Rabbit is an amazing early Jazz Fusion recording that uses a very oddball orchestra (trumpets, harp, flute) along with Billy Cobham on drums, Airto Moiera on percussion, Ron Carter on Bass, Herbie Hancock on piano, some other dude on vibes, Earl Klugh on spanish guitar and of course Benson himself. The track 'California Dreaming' I first heard back in the very early 80s and I thought it was a mish-mash, a crap recording oddly put together. As my kit got better and better I realised it wasn't - on there is an amazing layered and carefully panned, complex soundstage that needs bringing out. Well I've never heard it presented like this. Stunning. My reason for getting a new pre was initially to bring out the best in the Aurorasound Vida, which didn't get along with the MFA MkII TVC I had been running ... and now I've solved exactly that problem.

On CD I have a couple of things, some organ music from the Bach 155CD complete edition (Hans Fagius) which it passed with flying colours - the organs used in this set of recordings have been recorded very sensitively and there's a wonderful balanced effect, no too pronounced, of solo and combination pipe ensembles in space, not unlike you get from the organist's seat (as I know well). Passed with flying colours - as did bass depth. A lot of organ music is a bit flat, or recorded out in the body of the kirk ... not this set.

My Kiyujen/Leonhard Bach Gambas set went wonderfully - some preamps do terrible things to harpsichords, while the woody tone of the gamba is really easy to muck up and make sound like a cello ... also the gamba in this recording is beatifully placed about a metre in front of the keyboard. Anyway, with the new pre the harpsichord sounded as real as the one I used to have in my old place, and its spacial abilities saw Kiyujen solidly planted mid-left out in my living room :)

Fischer Dieskau and Brendel together recorded in the early 90s one of DFD's last recordings, made in his 60s, containing some of the darker Schubert songs, mostly of wandering, loneliness, old age, and death as opposed to the usual love/lust and pretty maidens. Brendel is magnificent - by turns restrained (such a full spectrum pianissimo), powerful, and poetic. DFD stands right in front of him and the preamp really brought out the room ambience as well as the sheer control (with just a tiny hint of vulnerabilities to come) in DFD's voice. Magisterial.

Finally back to vinyl and Szell/Schwarzkopf's Strauss Four Last Songs, her final 1967 version on EMI. The third song, Beim Schlafengehen, begins on solo basses, spreading across the orchestra .. it's one of the most emotive performances of any piece of music ever recorded, her soaring voice, solo violin, and full orchestra as it builds .. just heavenly. Goosebumps. Lots of them. Probably won't show up on Will's scope, but it's the most essential measurement of all.

Anyway I hope that this gives a flavour. Will is really onto a winner here.

http://i1181.photobucket.com/albums/x440/montesquieu61/will-pre-jpg_zps5wvnvau3.jpg

[struth]

forgot to put the top on tom :eyebrows:

sounds like a fabulous amp mate, and looks the part too along with that big power fella on top ...lucky man

[User211]

Russian valves gone wrong? Highly unusual.

I always find they can be bettered sonically without exception, really - no matter what the type. Reliable as hell usually, though.

Glad it appears to be a good pre.

I wouldn't stop there lots more 6SN7s to try. To be sure you are reaping the best from the unit you just have to try more...:)

[petrat]

.. just heavenly. Goosebumps. Lots of them. Probably won't show up on Will's scope, but it's the most essential measurement of all.

Anyway I hope that this gives a flavour. Will is really onto a winner here.



No! Don't say that! You've probably just added a zero to the price tag :(


Nice write up, as always Tom, and very pleased it's a success. Be interesting to see what the final 'look' of it will be ... modern, retro, bling?
I do like your approach of using 'artisan' craftsmen to create your kit ... power amp and speakers ... turntable, too?

Anyway, I guess as long as it does lieder well, then your world is a fine place :D

[Marco]

Hi Justin,


I always find they can be bettered sonically without exception, really - no matter what the type. Reliable as hell usually, though.


I agree, if you're talking about the cheapo ones [the 1980s-2000 vintage ones] you can get for around a tenner a pop (such as those that were in the amp to start with), but NOT the proper 1950s NOS ones from the old Melz factory (with 'holes' in the anodes), which sound STUNNING, and are without question my favourite 6SN7/6SL7 types (6H8C and 6H9C respectively).

They're not cheap though, at around £80-100 a piece...

Beautiful looking system (and new preamp), Tom. Love it's retro-looks sexiness! :drool: How do you find the volume slide controls? Are they noisy compared to modern pots or stepped attenuators? :)

Marco.

[User211]

You know when I posted that I was thinking you would possibly contradict that - specifically with regards to the awesome looking Melz you posted about. I can't comment but assume yer lugholes are good on that one.

Fair enough I haven't tried all types but with EL84, KT88, various small signal valves and 6X5 rectifiers all have been bettered, sometimes quite markedly, by European or US types. I'm also finding some PSVANE Chinese efforts to be really quite good indeed e.g. 2A3T and 101D replica.


Hi Justin,



I agree, if you're talking about the cheapo ones [the 1980s-2000 vintage ones] you can get for around a tenner a pop (such as those that were in the amp to start with), but NOT the proper 1950s NOS ones from the old Melz factory (with 'holes' in the anodes), which sound STUNNING, and are without question my favourite 6SN7/6SL7 types (6H8C and 6H9C respectively).

They're not cheap though, at around £80-100 a piece...

Beautiful looking system (and new preamp), Tom. Love it's retro-looks sexiness! :drool: How do you find the volume slide controls? Are they noisy compared to modern pots or stepped attenuators? :)

Marco.

[Reffc]

Nice write up Tom, really pleased it's worked out well for you. I thought that it might ;)

Also, to echo Peter's comments and to add to them, well done, and a big thank you from me for putting so much faith into small operators such as Will and myself. It is always a worthwhile venture to see so much pleasure derived from this sort of collaborative working between clients such as yourself and smaller like minded businesses dedicated to providing you and others with the sort of musical sound quality enjoyment and pride of ownership you seek. It is a risk to many, but not to those in the know and I am as grateful to you for your vociferous and public support as you are to myself (and no doubt to Will who made this final link in the amplification stage possible...he's a talented guy). I hope that you get many years of enjoyment now and can finally feel that the major tinkering days are over!

[Radford Revival]

Went down well then I see :lol:

Glad you like it Tom :)

Regarding the 6H8Cs, I believe they weren't flat out broken but just fairly microphonic, to the point where it was an annoyance in Toms system. I'm quite fond of the 6H8C but it can be a bit finnicky at times, they can be quite microphonic and the heater-cathode isolation isn't great. The susceptibility to these issues can depend on the circuit itself - certain designs can exaggerate a microphonic or heater coupling issue, depending on how the valve is used.

Not usually a problem in a phase splitter but in a line-level stage it could be a problem, Tom has neatly sidestepped altogether this by putting in tung-sols ;)

[montesquieu]

Nice write up Tom, really pleased it's worked out well for you. I thought that it might ;)

Also, to echo Peter's comments and to add to them, well done, and a big thank you from me for putting so much faith into small operators such as Will and myself. It is always a worthwhile venture to see so much pleasure derived from this sort of collaborative working between clients such as yourself and smaller like minded businesses dedicated to providing you and others with the sort of musical sound quality enjoyment and pride of ownership you seek. It is a risk to many, but not to those in the know and I am as grateful to you for your vociferous and public support as you are to myself (and no doubt to Will who made this final link in the amplification stage possible...he's a talented guy). I hope that you get many years of enjoyment now and can finally feel that the major tinkering days are over!

That indeed is the idea Paul ... my days of kit swapping (barring the odd cartridge of course) are coming to a close. I have not just appreciated but also very much enjoyed the interaction with Will over the preamp and look forward to when he can hear it in situ with the RFC Canterburys, STA100 and my (IMHO) pretty accomplished front end, next time he ventures over the flat vs fizzy cider equator somewhere around the Wiltshire border!

I have a personal connection with just just about every bit of kit I have here, all either designed, built, restored or modified by a whole raft of - well in many cases very talented people I would now call friends - your good self of course, Graeme Hirst (Valvebloke), Russ Collinson and Speedysteve uppermost, and a few others as well (for example J7 at Audio Origami, Guy Sergeant, Nick Gorham, Tony Whittle and Simon Shilton who though not personal friends as such have still been incredibly helpful over the years).

As for the valves it may well be just a design thing rather than a failure ... the Tung Sols (also Russian?) look far better constructed to me and as Will pointed out, probably less likely to go microphonic. Not even sure if they are 100% electrically identical.

[Marco]

How do you find the volume slide controls? Are they noisy compared to modern pots or stepped attenuators? :)


How about this, Tom? Just curious how accurate/quiet they are compared with modern pots or stepped attenuators....

Marco.

[montesquieu]

How about this, Tom? Just curious how accurate/quiet they are compared with modern pots or stepped attenuators....

Marco.

The slider works fine, indeed it works like new (I'm sure Will must have cleaned the contacts etc before it went out. I'm not the biggest fan of sliders (rotarys are more satisfying to use, I find) but it's temporary pending Will's final casework, so I can live with it ... as I say it works absolutely perfectly.

I have some inkling what Will is planning to do for the eventual casework but no detail yet ... I'm sure it will be in-keeping with the rest of the product line.

[spendorman]

Should look like this?

http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2011/11/SC22-Leaflet-P1.jpg

[Marco]

The slider works fine, indeed it works like new (I'm sure Will must have cleaned the contacts etc before it went out. I'm not the biggest fan of sliders (rotarys are more satisfying to use, I find) but it's temporary pending Will's final casework, so I can live with it ... as I say it works absolutely perfectly.

I have some inkling what Will is planning to do for the eventual casework but no detail yet ... I'm sure it will be in-keeping with the rest of the product line.

Ah, I see... So it's not a finished product yet? Cool. I think you'll be in for a nice sonic upgrade when a decent pot or stepper is fitted. Don't forget, it's all part of the signal path ;)

Yes indeed, I'm sure that Will will come up with something nice and in keeping with the product range, and also retro looks of the kit :cool:

Marco.

[Radford Revival]

Re: sliders, I would have put an Alps or similar in but the casework was made for the sliders and I didn't want to damage the front panel so I just used the one that came with the casework. It's a little bit lower in value than I'd normally use (22K) for a line input, as the source has to drive it directly because there's no input buffer, but frankly if a source struggles to drive a 22K load I can't help but question it!

[montesquieu]

Should look like this?

http://www.radfordrevival.co.uk/wordpress/wp-content/uploads/2011/11/SC22-Leaflet-P1.jpg

Indeed. Gorgeous. Along these lines would, indeed, be awesome.

[spendorman]

I still have a Radford SC22 and find that it's pretty good, it came with my STA25 III and FMT2 many decades ago. Interestingly, there seem too be two different layouts for the SC22, the one shown on the link, and my type that has two extra push buttons and one less rotary switch. I wonder if Will knows why.

[Radford Revival]

I still have a Radford SC22 and find that it's pretty good, it came with my STA25 III and FMT2 many decades ago. Interestingly, there seem too be two different layouts for the SC22, the one shown on the link, and my type that has two extra push buttons and one less rotary switch. I wonder if Will knows why.

Hi Alex,


You're indeed correct, there was the SC22 and SC22b, which came a bit later. In fact I need to update that portion of the site and include it. The SC22b moved the treble rolloff control to buttons along the bottom, and in doing so introduced a silly design flaw where two sets of parallel capacitors that are used to create the rolloff are switched off of individual poles of a ganged switch so that if the switch gets dirty you can end up with a different rolloff point for each channel. Speaking from bitter experience!

[spendorman]

Hi Will,thank you, I did not know it was called the SC22b, not ever noticed the problem that you mentioned, but I hardly ever use filters. There is of course the SC22P, which has a built in power supply so that one does not have to supply HT and LT from the power amp.

Here is a pic (not very good) of my SC22b with FMT2. I prefer the look of the SC22b to the SC22.

15863

[tiguan]

I just saw the topic. It passed little bit but about 6Sn7 s after using rca, sylvania, raytheon 6sn7 nos, sylvania vt231 and 6n8s from nevz and foton, best I got from my Sp14 pre with sylvania vt231 at voltage amp and foton 6n8s which was bought from this supplier below
http://www.ebay.com/ulk/itm/221922555416

Which I bought afterwards some more into my stock for the future.

[Radford Revival]

Hi Will,thank you, I did not know it was called the SC22b, not ever noticed the problem that you mentioned, but I hardly ever use filters. There is of course the SC22P, which has a built in power supply so that one does not have to supply HT and LT from the power amp.

Here is a pic (not very good) of my SC22b with FMT2. I prefer the look of the SC22b to the SC22.

15863

Very nice :)

I shouldn't worry about the issue I mentioned, I've only personally encountered it once, but the cause was quite silly (unless I was missing the point somewhere!)

[pgarrish]

Ah, I see... So it's not a finished product yet? Cool. I think you'll be in for a nice sonic upgrade when a decent pot or stepper is fitted. Don't forget, it's all part of the signal path ;)

Yes indeed, I'm sure that Will will come up with something nice and in keeping with the product range, and also retro looks of the kit :cool:

Marco.

If sliders are good enough for Neve mixing desks I reckon they might just about be good enough for an amp....

[Marco]

Lol - in your opinion, perhaps. Just because they're used on such equipment doesn't automatically make them the best!

I'm not saying that there's anything wrong with sliders, per se. I was merely curious if they were as accurate/sonically transparent (whichever terminology you prefer) as the best modern pots or stepped attenuators, as I've done a lot of experimenting in that area, and so know how much such things influence the sound of a preamp.

Whilst I appreciate that the brief, as it were, with this amp, was to respect the original design of the Radford, it would be a shame to do so whilst introducing an (arguably) notable sonic bottleneck.

Marco.

[Light Dependant Resistor]

Lol - in your opinion, perhaps. Just because they're used on such equipment doesn't automatically make them the best!

I'm not saying that there's anything wrong with sliders, per se. I was merely curious if they were as accurate/sonically transparent (whichever terminology you prefer) as the best modern pots or stepped attenuators, as I've done a lot of experimenting in that area, and so know how much such things influence the sound of a preamp.

Whilst I appreciate that the brief, as it were, with this amp, was to respect the original design of the Radford, it would be a shame to do so whilst introducing an (arguably) notable sonic bottleneck.

Marco.
Quite right Marco, but further choices should also include transformers, light dependant resistors LDR's, voltage controlled amplifiers/ modules and junction fets. explored here: http://www.cresttech.com.au/pdf/Silonex/levelcontrol.pdf

Cheers / Chris

[Radford Revival]

It's hard to beat a pot for simplicity and performance in a level control application. Aside from the noise penalty proportional to the value you use, their bandwidth is DC to low RF (though you don't want either going through your pot in audio applications!), and have tiny/immeasurable amounts of distortion. Stepped attenuators may be better for inter-channel tracking at the expense of complexity and cost.

[Marco]

So where do sliders sit amongst that lot, in your opinion, Will? ;)

Marco.

[Radford Revival]

So where do sliders sit amongst that lot, in your opinion? ;)

Marco.

They're potentiometers so exactly as above ;)

[Marco]

Heh-heh, yes ok ;)

Marco.

[sjs]

The very best mixing desks use Penny & Giles linear faders, and if they are anything like the P+G rotary faders they are likely to be the best volume controls you have heard :-)