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Transcendent Sound 'Slider' Pre-Amp

Discussion in 'd.i.y.' started by davidjt, Apr 25, 2023.

  1. davidjt

    davidjt pfm Member

    On the off-chance that it might be of interest to someone else out there I thought the following might just be worth posting.

    As mentioned elsewhere, I stumbled across this kit by accident, checked the detail above and decided that it was worth a shot. The obvious stumbling blocks for those in the UK will be p&p from the 'States, VAT and the cost of the 6386. Mine was already on the right side of the pond and came with all the valves.

    The build was pretty straightforward, albeit with a couple of amendments to the instructions handwritten, by whom I don't know. There was scope to upgrade some of the components, for which I had help; believe it or not the 'front panel' is made of linoleum, and I've put a cover over the toroid to lessen the half-finished look. So, maybe 5/10 for appearance.

    The reasons for posting are first of all the sound, which imo is wonderful. My ESLs have never sounded this alive before. Second, and the main one, is that after reading the TS forum I began to experiment with different settings of the independent volume and gain controls. Having established that (for me anyway) it's essential to evaluate amplifiers and speakers together, the consequence was an awful lot of trial and error when attempting an upgrade. As suggested on the forum the characteristics of the 6386 are such that by juggling with the gain one can fine tune the sound. So, for example I can run electrostatics here and conventional speakers elsewhere (admittedly, running adjustable subs helps) and get the best of both.
    The two listening rooms also have very different acoustics and to some extent I can adjust for those, also.
    If absolute fidelity and zero distortion float your boat then this sort of adjustment will probably be anathema, but if you like warmth and detail, and you can either find one to audition or afford to take a punt, I'd say definitely worth the effort.
    Last edited: Apr 26, 2023
  2. garyi

    garyi leave blank

    Is that like the transformer just plonked on the top? I don't know a lot about valve amps, perhaps its a thing, but why not put it indoors, its not the most attractive thing is it?
  3. James Evans

    James Evans Bedroom Bodger

    Definitely "a thing" ;)
  4. davidjt

    davidjt pfm Member

    Yep, the mains transformer, which is why I used one of the covers that Audiophonics (and AliExpress) sell to hide it. The chassis would have to be much bigger to accomodate the tranny, and Bruce's declared aim is to keep prices low, as in "High End Audio for the Rest of Us".
    But once the valves and caps had settled down it just sounded so good I could have tolerated the looks. (I have Frugalhorns and Lx-Minis after all.:D )
    Before trying the Slider with the ESL57s I had been happy with the set-up, while feeling that the G57 amp might be just a bit stodgy with both a Roksan pre- and a diy WHAMMY. It may simply be that the Quads need valves to really shine - for me they've been a revelation.

    As an afterthought, once I've traced and fixed a gremlin in a KT88 amp build it'll be interesting to see whether I prefer that on it's own or valves + solid state, and whether that choice is confined to 'statics.
  5. bugbear

    bugbear pfm Member

    Could you explain the difference between "volume" and "gain" [in this context] please? :confused:

    EDIT; ah the website sort of explains. I think "gain" is "(positive) input gain" and "volume" is "(negative) output gain" AKA attenuation.

    Last edited: Apr 27, 2023
    Dan K likes this.
  6. PigletsDad

    PigletsDad My intelligence test came back negative.

    It is a very unusual tube, I think originally intended for AGC circuits in radios. It has a very non-linear characteristic, so you can vary the gain by changing the bias point; I think there are some old studio compressor circuits that use this part.

    Not something I would have thought of in a million years! Whatever makes you happy is good.
  7. bugbear

    bugbear pfm Member

    Googling shows it listed as a spare for some compressors so - yes.

    Looks like vintage guitar prices are just as whacky as audio-phool prices

    The listings also say "Twin triode with exponential transfer characteristics"

    Given the normal search for linearity in amplifier circuits, this is ... unusual. Even if you're selecting a point on the curve via bias, it must distort at any (non zero length) subsection of the transfer curve?
  8. PigletsDad

    PigletsDad My intelligence test came back negative.

    Yes, but if the audio signal is small (a volt or so) and the scale of the curve is big (200V or more) the distortion is not too bad, mostly low order harmonics, and washes everything with a warm sepia tint; everything sounds like a 1960s soul record - not a bad thing!
    bugbear and martin clark like this.
  9. davidjt

    davidjt pfm Member

    I would describe the audible effect (in this set-up) as far more subtle than that - and I don't think Bruce would sell any pre-amps if it were that pronounced. The effect is of more detail and substance, not less. Granted it's hardly conventional, and as such is bound to offend some pre-conceptions, but it's novelty and my enjoyment were the reasons behind the original post. As you say, whatever makes you happy.....
  10. bugbear

    bugbear pfm Member

    I was quite startled by this, at the end of the page:

    "Distortion: See above, from 0.2 to 1% depending on setting and input."
  11. toprepairman

    toprepairman pfm Member

    Plonking the rectifier valve in the middle of the audio circuit is plain bonkers, no wonder there's some 180Hz present in the noise (third harmonic of US 60Hz mains).
  12. davidjt

    davidjt pfm Member

    Fwiw, the pre-amp is completely silent with no signal applied, precisely as stated on the website. And it still produces the most enjoyable sound of the half dozen or so I've tried.
    Dan K and Darren like this.

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