My new passive preamp: S&B TX-102 transformer volume control

Discussion in 'General Audio Discussion' started by Redboy, Feb 21, 2009.

  1. Redboy

    Redboy a few good watts Subscriber

    doucanoe asked for pictures, so I thought a thread might be in order. This is new to me, but not new. It's a passive preamplifier, a transformer volume control built around a pair of Stevens and Billington TX-102 transformers. Single input, single output with a mute switch.

    The previous owner bought it new, purchased from K&K Audio. They built it, and they certainly did a nice job!

    That's a Seiden switch. High end Vampire RCAs. Check out the nice knob, too!

    How does it sound? Pretty phenomenal, I think.








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  2. JoeESP9

    JoeESP9 ESL's & tubes since 83

    Very nice work!
    Where did you get the case?
  3. rsfmotoman

    rsfmotoman New Member


    I assume you are giving it a test drive. In your pic you have two sources.

    Where or how do you think you will use it?

    Someday in my hifi journey I expect to give a passive preamp a try.
  4. golana

    golana analog Subscriber

    Sweet, what does the double toggle on the back panel switch?
    If it is only1 ea. In and Out? Thanks, they did a nice build, I like 'm clean
  5. wajobu

    wajobu Boing Boom Tschak Subscriber

    I'd say that it's beautiful!
  6. Strangeband

    Strangeband AK Member and Ale Monger Subscriber

    Very cool and great photos. And I have no real understanding of a passive preamplifier or what it does.
  7. doucanoe

    doucanoe Registered Audio Abuser

    I'm going to have to get over and hear it sometime soon. It will be interesting to compare with the Promitheus.

  8. RichPA

    RichPA Neurotypical, most days. Super Mod Subscriber

    Very nice. I've been curious about transformer-based volume controls - I'd be interested if you could elaborate on "phenomenal" as a description of the sound :)
  9. specialidiot

    specialidiot Break Glass, Smoke Lucky Subscriber

    I'm a pretty big fan of simple. I'll have to give one of those TVC's a try one of these days.
  10. Old1625

    Old1625 New Member

    I admire this apparatus, and certainly the quality of workmanship. But I seriously question the nomenclature.

    Could it perhaps be called a volume control?

    Passive Preamplifier seems a trifle oxymoronic....dontcha think....? :scratch2: Amplification is usually an active step. Transformers can indeed improve transmission, but amplify seems kinda extreme in describing what this inline variable attenuator does.... Mebbe I'm missing something here....

    The English "language" is always intriguing to me....

    Oh don't mind me; I know I'm a certified left-handed nut! :eek:

    At any rate it must sound great. :thmbsp:
  11. Tmac83

    Tmac83 New Member

    Very nice Nate! Very simple. Is it going to be a problem that it only has one set of inputs?

  12. Holst

    Holst New Member

    Very cool!
  13. tom1356

    tom1356 New Member

    It may help to think of "pre" as "before" amplifier.
    Besides, the transformers have a 6 db boost option making them amplifiers.
  14. zenith2134

    zenith2134 New Member

    Simple is where it's at. That looks like a high quality pre. I can't imagine it sounding bad! :music:
  15. Redboy

    Redboy a few good watts Subscriber

    One of the first things I will do is rewire this thing to have two sets of inputs. I'll do away with the mute switch, I think, and make that a selector switch.

    The back panel switch selects between "connected" and "isolated" ground. So far I'm not hearing a difference between the two.

    Rich, I've been a fan of simple potentiometer-based volume attenuators in my system. This one has similar characteristics, but the sound is somehow "fuller." There seems to be more detail at lower volumes especially, and resolution overall is excellent. I'm not very good at describing sound in general, but this is the best I've heard here.

    I like the idea of as little as possible between me and the source. I know these things are quite system sensitive, having to do with input impedances and other things I don't understand. I hoped for a good fit based on my experience with other passives, and it has played out well so far.
  16. Urizen

    Urizen AK Subscriber Subscriber

    Super nice, Nate. Enjoy!:music:
  17. RichPA

    RichPA Neurotypical, most days. Super Mod Subscriber

    Thanks, Nate, that makes sense to me. I've found pot-based passives to sound a bit thin, so if it has their good features plus a fuller sound, that seems pretty much perfect.
  18. golana

    golana analog Subscriber

    I believe you would be isolated ground. Isolated would be to panel, via outside ground rod.
    connected should be component to component ground.
    Should be right, although...
  19. Redboy

    Redboy a few good watts Subscriber

    I finally got around to adding another set of inputs to this thing. I sacrificed the Mute switch on the front panel and converted it to a Source selector.

    Before (from the first post of this thread):


    ...and after:


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    Last edited: Mar 18, 2009
  20. Redboy

    Redboy a few good watts Subscriber

    The seller also included a second beautiful wooden knob, which I think looks mighty nice against ejfud's casework on my 2A3 amp... :yes:



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