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MrCurwen 14th May 2013 11:03 PM

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?

DF96 14th May 2013 11:07 PM

I suspect you already know the answer!

SY 14th May 2013 11:08 PM

In the purchaser's mind. I suspect that it's really just poor English and that the actual item is a DAC with an SPDIF input and an incompetent tube output. If it really is a tube handling the SPDIF signal, my current sig line is proved once again.

DF96 14th May 2013 11:12 PM

The ebay listing appears to be a subminiature tube CF for SPDIF, with a choice of capacitor or transformer output. Unusually, this one is not from China but the old Eastern bloc. There are lots of Russian submin tubes around.

Pano 14th May 2013 11:15 PM

Yeah, it does seem that way. It does kinda look like a tube driven SPDIF.
Here is the item with a photo and a diagram.
SPDIF Output Tube Stage 6S31B | eBay

Tubologic 15th May 2013 01:09 AM

... 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" ...

vinylkid58 15th May 2013 01:16 AM


Originally Posted by Tubologic (
And by the way, they also have a "low jitter tube clock" ...

Hey, can I use a nixie tube for that?;)


TheGimp 15th May 2013 01:34 AM


The warmer and softer sound comes from rounding off the leading and trailing edges of the SPDIF (digital) signal.;)

We all know that this removes some to the odd harmonic content and therefore must make it better. :D

DF96 15th May 2013 10:52 AM

Cathode flicker adds noise-shaped jitter to the signal and so enhances the dither, adding the warmth and musicality which brick-wall filters have removed.

SY 15th May 2013 11:40 AM

The dynamic contrast between ones and zeros is enhanced, with the ones standing out against a blacker background. The increased detail in the digits make this a worthwhile upgrade.

If it's cheap, it's an interesting novelty, akin to those clacking balls-on-strings made for executive desktops.

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