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TVC Preamps

Tony L

Tony L

Administrator
I'm becoming increasingly curious about transformer volume control passve preamps and have a feeling they might just be the thing I've been looking for. I seem to be a fan of high-gain vintage power amps, specifically the Leak Stereo 20 and Quad 303, both of which suit my speakers well. Both work well enough with my stepped attenuator passive, an Audio Synthesis PAS-02, though I understand a TVC should have a bit more scale, umph and impact, especially in the bass. Anyone got any views/experience?

One issue I have had is after trying several I have yet to find a phono stage that seems happy driving the 10kOhm input impedance of the Audio Synthesis, everything sounds sat-on and undynamic, and this is with good phono stages (EAR, Dynavector, Croft etc). I assume the 200k or more of a TVC will just behave like an active pre as far as the source component is concerned? I don't understand why phono stages suffer when CDs and DACs seem fine, but what is is, and it currently renders the stepped attenuator only suitable for the digital-only upstairs rig.

The next issue is these things seem rather expensive, so I'm curious as to how much real difference there is between say a Glasshouse TVC at about £790 (built) and the apparently stunning Townsend Allegri at close to £2k? The MFA stuff seems even more expensive again, though it is the Townsend I've kind of got in my sights, assuming of course the Glasshouse isn't biting it's tale for less than half price. I like the fact both these are pretty small and unassuming looking too. If I understand it correctly the Townsend is an 'autoformer pre' rather than a 'transformer pre', and that might mean something to someone! I've no plan to jump for a while unless anything really good pops up second hand, just kind of thinking out loud.
 
passive with alps black will be just as good and remove all component matching nightmares that you can encounter with tvc
 
Logically it is the other way round - a TVC impedance maches, a pot or stepped attenuator doesn't. FWIW I'm also already a good few quality levels above an Alps Black with the Audio Synthesis.
 
Tube phono stages might be unhappy into 10k. Can't explain the Dynavector. CDPs and DACs won't care.

You could just buy yourself a 50k pot add some bodgery and see whether anything changes. Before dropping a bucket load on a technically rather ugly solution.

Paul
 
Most TVCs only have about 23 volume step positions which in my opinion is not enough for good volume control, i.e. the steps of gain are too great to get exactly the right level. This can be especially noticeable when using high efficiency loudspeakers or a source with high gain, or both.

Most TVCs are autoformer designs. If you fancy building one yourself then check out the Slagle devices from the US as they come highly recommended.

I tried the S&B TVCs over 15 years ago before they became Music First Audio. I used them as a volume control in an active line stage, i.e. before the active stage, but found the steps too great and the sound compromised. They seemed to work best on their own between the source and the power amp, assuming the power amp has good gain and high input impedance. I got the best performance with a good volume control, or stepped attenuator in front of the active stage, but if you are using a Leak ST20, a TVC on its own will be fine. When connecting a TVC to a power amp check the input impedance isn't too low as they tend not to work well with low input impedances. If the power amps input impedance is >50K they should work fine.

Note: The Tron Seven and Convergence phono stages were designed to work with TVCs as well as normal amplifiers.
 
Everytime I see a preamp mentioned it comes with the pretext that this pot that pot or the other pot is saviour.

Bruno putzeys designed a preamp which effectively removes the pot from the signal path,
mine uses a car stereo pot..

Maybe we are looking at the problem back to front ?

http://www.edn.com/design/consumer/4429968/The-G-word--How-to-get-your-audio-off-the-ground

Fully balanced, costs around £100 excluding case, distortion level FA.

http://www.diyaudio.com/forums/grou...tzeys-balanced-preamp-group-buy-part-3-a.html

PS. I previously used a TVC with some expensive transformers
 
I started with an Alps pot in an RS box I had lying around...liked it enough I then added a selector. Even this cheap lash up was embarassing my very decent solid state pre amps in some desirable areas - clarity, openness and detail.
I then bought a Khozmo stepped attenuator, and there was further improvement. I took the Khozzie to a bake off, and there was a Music First pre there and of course they were tried and compared. Hmm...Music First showed considerable superiority, and the sound was more rounded with better tonality and even less strain during loud passages - in any case a passive strength.
Couldn't bring myself to drop two grand on one though, so looked out for some transformers second hand, and was lucky enough to snag a a pair of silver Stevens and Billington tx102s.
Which I knocked up into this, currently my favourite audio component.
front2_zpslatwas8u.jpg

I'm not using it into a st20, although I do have one, using it into a Luxman class A power amp.
I won't rhapsodise, but its performance through the direct input bypassing the selector is so good I find it difficult to imagine much improvement possible in this area - and I don't say that lightly!

I've heard that the Slagles, which are an autoformer rather than a transformer design, are also capable of top level performance. They're used in the Townsend Alegri.
This is interesting, if you haven't seen it.
https://musicfirstaudio.files.wordpress.com/2016/02/musgrave-on-line-controls.pdf
There's also a thread started by me here
http://hifiwigwam.com/forum/topic/121623-s-b-music-first-tx102-wiring-diagram/
 
Tony L said:
Logically it is the other way round - a TVC impedance maches, a pot or stepped attenuator doesn't. FWIW I'm also already a good few quality levels above an Alps Black with the Audio Synthesis.
Click to expand...

isnt it much harder to implement a TVC pre amp? if you must go TV, get copper TVC from S&B.

what I wanted to recommend is not alps black, sorry about that. its the ALPS RK50 which is the best pot ever made.


I talked to a guy who have had many TVC and eventually preferred a simple RK50

"i have no longer TVC ( not as transparent as i many thinks i have tried Silk TVC, tribute auto former, bent audio/slage auto former. ) LDR was a deception with channel mismatch at low level. and some kind of coloration too.
so i end with a simple Carbon volume pot . a ALPS RK50 ,expensive as hell but a really gorgeous sound and very precise tracking even at low volume. "

id also recommend those stepped attenuator. probably the best you can get with elma switch and top resistors. : https://www.hificollective.co.uk/catalog/glasshouse-stereo-stepped-attenuator-elma-p-9977.html
 
eastone said:
Have you tried a Pass B1 Tony?
Click to expand...

This /\ .

I have played with , passives and TVC's ( and active ) pre's and Nelson Pass's B1 would be my choice .

A nice trick with "pot in a box" passives is to shunt the pot with a resistor , takes the pot out of the signal path for an even purer purist approach .
 
The Stereo 20 has a 1mOhm input impedance, so I guess I could easily get away with a 100k pot or stepped attenuator if I were to think of this as just a preamp for the Leak rather than something that would work with the 303s too (23k IIRC). I assume a 100k pot would feel much like an active preamp to a source component?

I'm still interested in knowing what the sonic traits of a good TVC are. Hi-Fi Critic and other seem to rate the Townsend as true state of the art regardless of technology, they seem to think it is about as good as preamps get at any cost. If it has the absolute clarity, speed and lack of grain of say my Audio Synthesis coupled with a bit more weight, punch and heft and a wider source matching context I'd be very interested. Yes, it is bloody expensive, but there is no expensve vintage tube rolling, nothing to recap etc so not so bad as a 'final preamp' solution. Same argument for MFA or Glasshouse.
 
G T Audio said:
Most TVCs only have about 23 volume step positions which in my opinion is not enough for good volume control, i.e. the steps of gain are too great to get exactly the right level. This can be especially noticeable when using high efficiency loudspeakers or a source with high gain, or both.
Click to expand...

This is my experience also.
 
Tony L said:
The Stereo 20 has a 1mOhm input impedance, so I guess I could easily get away with a 100k pot or stepped attenuator if I were to think of this as just a preamp for the Leak rather than something that would work with the 303s too (23k IIRC). I assume a 100k pot would feel much like an active preamp to a source component?

I'm still interested in knowing what the sonic traits of a good TVC are. Hi-Fi Critic and other seem to rate the Townsend as true state of the art regardless of technology, they seem to think it is about as good as preamps get at any cost. If it has the absolute clarity, speed and lack of grain of say my Audio Synthesis coupled with a bit more weight, punch and heft and a wider source matching context I'd be very interested. Yes, it is bloody expensive, but there is no expensive vintage tube rolling, nothing to recap etc so not so bad as a 'final preamp' solution. Same argument for MFA or Glasshouse.
Click to expand...
i had a glasshouse tvc for a while. First the regular version then the souped up (C core?) one which weighed a ton. I marginally preferred the latter but got rid of it when I went on to using a dac with XLRs straight into active speakers. The larger glasshouse design did cause a bit of humming when put too close to my power amps though.

btw Is it possible to get a phono preamp with a vc which outputs 2v?
 
I had a Music First Classic Copper for a while. In some ways one of the best pre amps I've had and heard; very transparent, fast and silent. Very clear and detailed without sounding analytical.

On the down side it never went loud, even with the dial past 12o/c, not necessarily a problem but ultimately I thought it lacked drive and gusto.
 
The volume position is of no issue to me, plus my amps are high gain (the Leak 0.125v, the Quad 0.5v for full out). The lack of guts is however an issue. The Leak is so high-gain using an active preamp is all but impossible as it just finds hiss and hum upstream. Into the inefficient JR149s I can just about get away with using my Verdier tube pre on its lowest output setting (it has five switchable gain settings), and it sounds very good in this context with more heft than the Audio Synthesis, but it still highlights tube-whistles, hiss etc. It would be absolutely unusable into more efficient speakers like my Tannoys or Klipsch.
 
I think you would find the issue is not whether it goes loud enough but whether it goes quiet enough. I have an MFA Copper with a Quad 405-2 and Harbeths. The Quad I had lowered (to 1v I think, Rob did it so whatever he recommended) as at the time I was using an LDR passive and would sometimes want it just a couple of steps quieter.
I'd wanted to get hold of an MFA for around ten years having heard one and really liked it, but I started with a Prometheus TVC then a couple of LDR based units then switched back to active with a Croft then a Quad then back to LDR then Tisbury restive then finally the MFA and yes, for me, it is the best of that bunch.
I think it is the lack of any artificial edge to the sound that does it for me, I just find it a natural sound to listen to.
Having said that, and ref: Graham's comments above, one of his Convergence units arrived recently and I'm not fully comfortable with how it is all settling just yet. Cart is an AT33PTG/II and the this Convergence has higher gain to match it; there's no shortage of volume (or drive or gusto) or clarity or detail, but it's just possible you can have too much of a good thing!
 
early said:
This /\ .

I have played with , passives and TVC's ( and active ) pre's and Nelson Pass's B1 would be my choice .

A nice trick with "pot in a box" passives is to shunt the pot with a resistor , takes the pot out of the signal path for an even purer purist approach .
Click to expand...
i lived with a pass b1 for years

a good tvc is better
 
Tony L said:
The Stereo 20 has a 1mOhm input impedance, so I guess I could easily get away with a 100k pot or stepped attenuator if I were to think of this as just a preamp for the Leak rather than something that would work with the 303s too (23k IIRC). I assume a 100k pot would feel much like an active preamp to a source component?

I'm still interested in knowing what the sonic traits of a good TVC are. Hi-Fi Critic and other seem to rate the Townsend as true state of the art regardless of technology, they seem to think it is about as good as preamps get at any cost. If it has the absolute clarity, speed and lack of grain of say my Audio Synthesis coupled with a bit more weight, punch and heft and a wider source matching context I'd be very interested. Yes, it is bloody expensive, but there is no expensve vintage tube rolling, nothing to recap etc so not so bad as a 'final preamp' solution. Same argument for MFA or Glasshouse.
Click to expand...
a good tvc copper s&b is prob the best VC available
go for it!!!!
however
the difference between a tvc and the best steppedattenuator is prob negligeble and almost trade off.

best value for money would be the glasshouse: elma switch which are the best available period
plus you can choose the resistors of choice
https://www.hificollective.co.uk/catalog/glasshouse-stereo-stepped-attenuator-elma-p-9977.html

last alternative is the 1000$ best pot ever designed the alps rk50. personally for ease of use id go with the rk50. amazing VC
 
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