TVC Preamps

[atcman]

+ 1 for the alps had one a couple of years ago tried s&b bent tap, slagle and sowter tvcs and a host of various pots the only one that came close was penny and giles Ebay item 351409768631

 

[Ayya Khema]

+ 1 for the alps had one a couple of years ago tried s&b bent tap, slagle and sowter tvcs and a host of various pots the only one that came close was penny and giles Ebay item 351409768631

wow and the rk50 was the best over all those other VC???

 

[Tony L]

How far have stepped attenuators moved on in recent years?

Here is my Audio Synthesis. It is a very early one, it dates from about 1993 and was right at the start of the craze for passive preamps and stepped attenuators. It is rather a complex thing with a dual-ganged attenuator with 3db steps on the outer ring and 0.5db steps on the inner one giving about 140 odd combinations, i.e. very easy to set any level, but it comes at a price of having an extra pair of resistors in circuit (two per channel per knob ring). It predates shunting etc as far as I'm aware. It sounds very good to my ears, I had a little Tisbury around for a while recently and that uses a tiny ladder of surface-mount resistors rather than the full sized resistors and complex switching of the Audio Synthesis, and I felt the AS sounded quite noticeably better. Just more 3d and alive somehow.

For another project I built a little single input pot in a Tupperware box:

It now has a neat knob! It is a nice TKD 10k pot and fancy cloth covered solid core wire from HiFiCollective and it sounds bloody good! It gives the AS PAS-02 a very close run to be honest, but some of that will be losing the input selector.

I'm curious as to how far ahead a 100k build with say the best stepped attenuator HiFiCollective have would move things on from where I am? The thing I don't like is that would nail me down to just the high impedance Stereo 20 whereas a TVC would be compatible with the Quad 303s or anything else I might want to try at a later stage. In many ways I don't mind spending proper cash, especially if I can do it second hand, but I want to get it right and land a preamp that will be a mainstay of the system for the foreseeable future. In other words I'm still leaning towards a TVC as the impedance matching is important.

 

[k90tour]

Very timely post for me Tony. I run a Audio Research Reference 3 pre amp into A Dark (Chinese) 300b amplifier. Sometimes it's a little bright. I listen very near field and absolute clarity and tonal fidelity are crucial to my enjoyment. I was hoping a demo Music First Classic V2 was coming here for me to try. I'll have to chase them up.
I'm also distracted by a KR Audio 300b SET set up.
A passive would helpfully reduce the amount of tube warming up and cooling down. So long as I get enough gain with vinyl.

 

[clivem2]

Hi Tony, I've run a PAS-02 quite some years ago, I then replaced this with a Passion which was shunted switched attenuator - the shunt resistor made a fundamental difference to weight and drive but impacted transparency (the typical trade-off). I've been through and S&B TX102 and now use a Slagle based Bent pre. The Bent is a little better than the S&B but close. Pots on their own just don't cut it for me, shunted they are quite good though.

If you ever drive "south" towards Altrincham you're welcome to borrow my diy S&B TX102 mkII.

 

[Dozey]

I have nothing but praise for my Townshend Allegri. As mentioned the difference between steps of 2dB iirc might put spme people off. Plenty of grunt and bass slam on offer with a suitable source.

 

[Tony L]

2db I'm pretty sure I can live with, the 3db step ring on the AS is too crude, but one click on the outer ring minus two on the inner (i.e. 2db) seems pretty usable. I think I'll get away with that with either amp on the Tannoys or 149s. The high-efficiency madness that is the La Scalas would likely preclude an Allegri/Stereo 20 combo, but that is no issue as they have their own little Decware Set and I'll just think of that as a finished combo. When I come to downsize later in life that will be the system that gets cut anyway, so no issue. I just want something that will work great with the Tannoy and the 149 systems and allows flexibility in source and power amp choices.

PS What do you think of the Allegri build quality, fit and finish? The impression often given is it is somewhat less than great, though the lid-off pics look ok to me, though there are obviously two very different versions and no explanation as to why! I really like the fact it is small and narrow, i.e. won't take up a lot of shelf space.

 

[martin clark]

How about a LDR preamp?

While there's an awful lot of effort that has been thrown in certain quarters at making a pair or quad of the things track 'satisfactorily', it's inescapable and technically unavoidable that the CdS active principle adds significant odd-harmonic distortion - 'significant' in the sense that even the crappiest nastiest cheap variable pot conceivable is likely an order of magnitude more linear with an applied, line-level audio signal.

Doesn't mean that some cannot like or prefer the result, of course. Chaque'un a son gout.


[nb: transformer vol controls are not distortion-free, either, and unless really-well-considered, likley add some very -poorly-controlled ringing out-of-band into the bargain]

 

[finchy]

Have you looked at the Schiit Saga? Gives the choice of passive (stepped attenuator) or zero gain valve buffer stage with much lower output impedance - so one should match well with the Leak, the other well with the Quad I would guess. Reviews I've read suggest the differences between the two modes are hard to detect (presumably in cases where the impedance matching isn't having a big effect) so the buffer stage must be pretty transparent.

I've no personal experience of it, but I have some other Schiit - the Saga looks like similarly great value.

 

[awkwardbydesign]

Most TVCs are autoformer designs.

Not in my experience. And that would make it an AVC NOT a TVC!

 

[Dozey]

Build quality seems to be variable. It is a plastic box with metal looking panels glued onto it. The knobs work with a reassuring clunk when changing position. I have had no problems with mine, but build quality is where costs have been cut - no "milled from a solid block of metal".

I got mine on a sale or return basis from the manufacturer, so you can probably return it if not satisfied.

 

[Tony L]

Wow, I had no idea it was made out of plastic!

 

[Dozey]

There may be an argument that a plastic box should interfere less with the electromagnetic fields - like your Tupperware container!

 

[Tony L]

Just to widen this thread a little to all passives rather than just TVCs can someone please explain to me in very simple no electronics knowledge required language how a shunt resistor in a stepped attenuator works and what the advantages or lack thereof may be? Is it a good thing, and if so why?

I'm still undecided as to direction of travel and if something like a real high-end build of a Glasshouse stepped attenuator pre with a 100k load and nice carbon resistors would get me a nice clean and full sound and enable me to use any phono stage with the Leak then it is certainly a contender. I do like the simplicity of a stepped attenuator and I suspect my Audio Synthesis could be improved (especially from a source load perspective).

PS I do like the look of this 46-step Seiden...

 

[Paul R]

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.

Stuff that happens before the attenuator remains in ratio regardless of the attenuation. So if your phono has a whistle it will be as audible with the Tannoys as with the JR149.

I think 'shunt' in passive pre terminology is audiophile nonsense. Unless a shunt resistor is being used to persuade a linear pot to be a bit log like. This would seem unnecessary with a stepped attenuator.

YMMV of course.

What you could do is put a motorised pot right on the input of the Leak and remote control it. Best of all worlds.

Paul

 

[clivem2]

I believe with a shunt passive there is usually one very high quality (expensive) resistor in the main signal path, the pot then varies the resistance to ground. This is supposed sound better but with two downsides:

1) the resistance/impedance seen by the load will vary

2) the output will be a few db less than the input at max volume.

I hope I have the above correct.

 

[hifinutt]

Very timely post for me Tony. I run a Audio Research Reference 3 pre amp into A Dark (Chinese) 300b amplifier. Sometimes it's a little bright. I listen very near field and absolute clarity and tonal fidelity are crucial to my enjoyment. I was hoping a demo Music First Classic V2 was coming here for me to try. I'll have to chase them up.
I'm also distracted by a KR Audio 300b SET set up.
A passive would helpfully reduce the amount of tube warming up and cooling down. So long as I get enough gain with vinyl.

make sure you try the v2 before you get rid of the arc 3 . i am surprised you find it a bit bright . i had the 5se and mfa baby ref at the same time to compare and they were neither bright . used into belles class AB monoblocks [ss] . both were very dynamic , and considering the mfa was half the cost of the ref5se it was pretty near it in terms of presence etc.

having had both copper and slver mk2 i really like the copper mfa . i love townshend stuff but just been slightly put off by some of the quality possibly

"the Allegri works very well, but the feel of the selector and volume control is not nearly as nice as with the Django, or most other amps in this price range for that matter. There's some play in both knobs and a lack of solid, positive stops, making it feel a bit loose and soft, to be honest. No problem, of course, but ever so slightly disappointing for a £2000 product. On the other hand, the whole idea of the unit is to offer audiophile top quality for the lowest possible price, so we shouldn't complain, really. Another minor niggle is that the case is very small and a bit light, resulting in a tendency to slide when used with heavy cables. Again, this has been done on purpose, to keep postage cost low when sending the Allegri to customers worldwide."

http://www.tnt-audio.com/ampli/townshend_allegri_e.html




good article here on copper vs silver mfa

http://www.tnt-audio.com/ampli/musicfirst_pre_silver_e.html

 

[Tony L]

Stuff that happens before the attenuator remains in ratio regardless of the attenuation. So if your phono has a whistle it will be as audible with the Tannoys as with the JR149.

I think you misunderstand me, hiss, tube whistles etc are in the context of using an active tube preamp, the JC Verdier, with the Leak. It is just too high-gain a power amp to partner with an active pre IMO. The AS is obviously entirely silent.

 

[k90tour]

Thanks for that. I wouldn't rush into selling Ref 3. Do you still have the 5SE?
I had heard of the Allegri until I saw this thread. It's about £800 cheaper than the MFA Classic V2, but doesn't have XLR inputs. If you asked me 6 months ago, I'd have said that the Ref 3 was staying for ever. But I find I'm sensitive to volume now (normally 60-70dB according to my phone app) and I didn't use the system for a few weeks because it is hard on my ears. My Yamaha piano is playing normally at 70-82 dB and I can play it all day.

Basically, if I can get the result of a Ref 3 from a tiny box that is 'ON' all the time, then a TVC may be a good thing for me.

 

[clivem2]

I think you misunderstand me, hiss, tube whistles etc are in the context of using an active tube preamp, the JC Verdier, with the Leak. It is just too high-gain a power amp to partner with an active pre IMO. The AS is obviously entirely silent.

This why sometimes it's better that a preamp has the attenuator on the output as it could be the preamp is adding its own noise in this case.