Transformer Volume Controls

sqlsavior

Lunatic Member
Who else is using one? Which? Results?

I got a Promitheus Audio TVC (standard) a week ago. I ordered it with four RCA inputs, and the +6dB option. It is currently in place of the line stage of my Luxman integrated, so I am now only using the Luxman's power amp section. I have only tried phono and CD sources, and no other amps. I am very favorably impressed, so far. Very.



:p
 
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Ooooh, congrats on the nice toy! I'm a pretty big fan. :)

The very best preamps I've heard, whether active or passive, had one thing in common: they were attenuated by TVCs. I've found them to be tops for resolution.

The Prometheus you have is very nice, but the S&B offerings are a level better (and ridiculously more expensive!). Dave Slagle's offerings are my favorites but connoisseurs of these things seem fair evenly split between Slagle iron and the Stevens and Billingtons. Both are excellent.

My current preamp is built around Bent Audio Slagleformer modules...

35178203673_e28eeaa5f5_h.jpg
 
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I was lurking on your thread. Looks very nice. :yes: Also saw a different TVC in Barter Town - looked very nice, too. I decided on a lower-budget experiment. I went with the Promitheus Standard rather than the Reference to save on cost and keep a single knob for both channels. I had to wait for it to get built, but it is proving worth the wait. It is Clearly Clearer (Reg) :) than the Luxman's line stage, but that is not always for the better - I am beginning to understand what the phrase "ruthlessly revealing" means with regard to recordings. The best ones are sounding glorious, however.
 
Hah! Yeah, it can be a double-edged thing... I love going deeper into the music on good recordings but there are albums I used to like that I just can't hack any more! I save those for the car, now. :)
 
Well, I've found and fixed an issue. While switching between sources with the volume up but nothing playing, I noticed a faint, deep, shuddering sound on phono. And sure enough, if I turned it up, I could feel the subwoofer cones moving more than normal. It was not a hum - it had no discernible tone to it, just a low shudder, on phono only.

My first guess at the cause turned out to be the right one. Awhile ago on another thread here, someone mentioned that if you wire up a separate AC circuit for audio, it should all be on one circuit, not several. I remembered thinking that's not what I had done - there are two dedicated circuits in the living room, and another in the office next door, where the main turntable and phono preamp reside.

So, I put in a power strip and an extension cord from one living room circuit to the office, and plugged in the TT and phono preamp so it was all on the same circuit. The shuddering sound is gone. I blame my house-wiring mistake rather than the Promitheus, but it is something to be aware of.

It is also revealing of the Fosgate's noise spectrum, I believe. The thing doesn't sound noisy in the traditional sense when turned up loud - no hiss, no hum, no whir, no buzz - but the needles on the amp rise more than with CD, for example. It leads me to speculate that much of the Fosgate's noise is subsonic.

I'm liking the Promitheus more and more. It really seems to be telling me what's what.
 
I'm getting more curious about these.

Are the sonic advantages substantial over pot and ladder-type attenuators? Are they more flexible about matching with other gear?
 
Well, I don't know, and I don't know, to answer your questions.

Some TVCs can be ordered with +6 dB gain, like I have on mine, so that could help flexibility-wise. Not sure about impedence matching.

Indirect evidence of sonic qualities might be inferred from the fact that there are 3 TVCs in Stereophile's Class A preamplifier list, a higher model Promitheus at $890, and two Music First models at $5290 and $8590. The Emotiva Control Freak potentiometer is listed in Class D for $50. I've never tried another passive preamp, so can't say from personal experience how they compare.
 
Thanks. Definitely leaning toward having the +6 option. Probably dual mono too. My right ear is kind of wonky and I am super picky about R/L levels.
 
My neighbor is using a Slagle special TVC with a Matsushita strain guage cart.

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The +6dB option on some of the S&B trafos is of questionable value, from what I've read, and there's even some discussion of some sonic degradation with that. It may just be audionervosa, but I wouldn't make that a defining factor in my search for a pair of TVCs. That, and I've never felt like I needed any gain from my passives...
 
Went back to the Luxman for comparison - boy are they close! On CD, maybe a little less glare and a little more air with the TVC - maybe. The difference on CD is not nearly as great as the difference that the Fosgate phono preamp made for records.

Here's a pic with the top off:

 
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...revealing of the Fosgate's noise spectrum, I believe. The thing doesn't sound noisy in the traditional sense when turned up loud - no hiss, no hum, no whir, no buzz - but the needles on the amp rise more than with CD, for example. It leads me to speculate that much of the Fosgate's noise is subsonic...

I found a real difference between the Promitheus and the Luxman line stage - the above is not true for the Luxman when amplifying the Fosgate's noise - it sounds more like a typical phono preamp through the Luxman, with a lot more noise at high volume with nothing playing, and some character - a hiss + a buzz.

I figure this is simply because the Luxman is amplifying the noise before attenuating it, while the Promitheus is not. The Fosgate Signature through the Promitheus really is exceptionally quiet for phono. So there's that.

I went listening for some stuff that I thought the Prometheus was missing or attenuating (some bass on Yes' "Close to the Edge", and some effects on Frank Zappa's "The Best Band You Never Heard"), and determined that it was basically my imagination/memory - they sound really similar, and nothing's missing that I can tell, either with or without the subwoofers. It's nice to have the Luxman L-505u as my reference, a solid known quantity.

Maybe I'll substitute in the C-1000's line stage, and my Music Angel tube line stage just for "shoot-out" grins, but I'm really itching to try the Luxman MB-3045 tube monoblocks with the Promitheus...

:yes:
 
Out of curiosity,what were the determining factors in deciding to choose the +6db gain unit? I am considering the passive preamp move,(a Promitheus)and I am trying to figure out if I need the +6db option.
 
Out of curiosity,what were the determining factors in deciding to choose the +6db gain unit? I am considering the passive preamp move,(a Promitheus)and I am trying to figure out if I need the +6db option.

For me, the deciding factor was "just in case" - I haven't used it so far.

It's a little different to be running a volume knob higher than 2 o'clock, but I'm getting used to it, because my satellite receiver's output is way lower than phono or CD.

Basically, if your source output level is lower than your amp's input sensitivity, it's possible that you may not be able to get full power out of your amp, but I think that would be pretty rare. A typical preamp might have a gain of 10 db, so 6 db gives you 4x the source's max voltage output by itself, compared to the typical preamp's 10x. If one of your sources is a lot weaker than the rest, or if your power amp's sensitivity is unusually low (i.e. input voltage required for full power is unusually high), I'd consider it, otherwise it's probably unneeded.
 
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Well, I've added it to my signature... :D

I've been listening through the TVC exclusively for awhile now, and I'm convinced that the only thing I'm missing is a bit of noise. Tonal balance seems the same as the Luxman, with no shortage of drive or impact, or of dynamics, either. I'd love to have a $5K+ line stage to compare it to, but have none lying around...

One of these days I'll throw my First Watt B1 clone in, and perhaps the Music Angel, for some comparison. My friend is due to visit in a few weeks, and we'll probably compare different amps using the Promitheus for the pre, as well.

Someone on another thread said something about it seeming complicated, but really it's just transformers, wires, and switches. The two smaller transformers handle the 6dB boost when it is switched in. The two bigger transformers each have 23 taps (plus off), going to the 24 position switched volume knob as a wire bundle. The bundles stay put as the knob is turned. Since there is no gain, for weaker sources, like my satellite, you really do have to crank it, to "11" it seems, but I'm used to that now.

Simple and transparent. :yes:
 
I just purchased a used Promitheus TVC with the 6db option. I should have it by the middle of next week. I am very excited to get this in my system.:D
 
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