• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube SPDIF output

I found a strange thing on eBay; search for "SPDIF output tube stage,6S31B".

If I understand correctly what this is for, it's one of the most curious way I've ever seen tubes to be sold to audio people. =)

This forum is full of knowledgeable people, can somebody explain to me where the tube sound comes in?
... and the sound is "warmer and softer" of course ! This is pure audiophile B.S What's next ? A tube CD player spindle motor driver for a more analog sound ? A tube powered remote-control with photomultiplier receiver ? A thyratron controlled power switch ?
And by the way, they also have a "low jitter tube clock" ...
A tube powered remote-control with photomultiplier receiver ?
Somehow, I find that strangely appealing. Much like the ilea of recasing a cellphone into something like shown below, with authentic ringtone.

Is anachrotechnophilia even a word, or is it just me?


  • old phone.jpg
    old phone.jpg
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If the original SPDIF source is competent then the best the buffer can do is avoid damaging the signal too much. If the source is really bad then the buffer might just improve it, but then you could probably assume that the rest of the source device is poorly engineered too. A 75ohm driver is not rocket science so a designer getting that wrong is unlikely to get everything else right.
I'm not sure that a tube C.F with 10V (they recommend 9 to 15 volts) anode supply is the best interface for driving a 75 ohms load. The circuit uses a toroid pulse transformer for coupling which is standard practice. Such transformers can be best driven with high speed gates in parallel or discrete transistor circuits. Performance will be better but not so "warm and soft" as with the tube circuit.