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Thread: Xiang Sheng valve output modifications

  1. #1
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,920
    I'm Alan.

    Default Xiang Sheng valve output modifications

    I've had the Xiang Sheng DAC-01A for a while now and was never struck with the quality of the 'tube' output, preferring the 'normal' output.
    However even though the DAC is of commendable quality at its price point, the normal output does have that little bit of digital glare.

    On investigation of the valve output/buffer stage I found that both input and output coupling capacitors were of Polyester dielectric, a definite no-no in my book, plus the valve was run at quite a low anode (plate) voltage, so certainly not in the best linear portion of the characteristic curves.

    Also, just to provides that sods law element, the valve pin out was like nothing else, a 6N3P. So a little more complicated modification than I would have hoped for.
    First off I replaced the output capacitors with some decent polypropylene's but that didn't make much of a difference on its own.

    The valve socket is on a vertical daughter board so that had to come out and an alternative provided that could offer the different pinout.
    The heater and HT power supplies were simplified in order to provide a greater voltage. The valve chosen was a PCC88.

    The input capacitors were also changed for some polyprops, the yellow ones in the picture.



    The end result was a healthy 90V across the valve plus a much cleaner 'tube' output without the digital glare of the normal output.

    Result
    Firebottle - for the no bottleneck approach.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  2. #2
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 41,076
    I'm Grant.

    Default

    nice mod alan. i run both outputs into 4 speakers. cant say ive noticed the valve to be that bad although i prefer the ss, which goes to the main speakers. the tube goes to my little active ones on top for extention of the full range driver purposes
    Regards,
    Grant ....

    I've said it before and I'll say it again: democracy simply-doesn't-work
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  3. #3
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 4,470
    I'm Oliver.

    Default

    Well done matey
    Technics SP10 MK2 > Phonomac AT-1010 tonearm > Ortofon Kontrapunkt b > Rothwell MCX SUT > Wizard MM Valve Phonostage (Telefunken Valves) > Slagle AVC Passive Preamp > Firebottle Monoblocks (Telefunken Valves) > IXOS Speaker Cables > Pioneer CS-77A Speakers > Oliver's IC Cables Throughout

  4. #4
    Join Date: Jan 2013

    Location: Bristol

    Posts: 3,501
    I'm Justin.

    Default

    I just ordered one to play with/mod.

    Plus some bad boy valves. Believe it or not some Western Electric and Sylvania Gold pins. Will get the soldering iron out too I expect.

    Western Electric Xiang. Has to be cool. Or crap. One of the two.

  5. #5
    Join Date: Apr 2016

    Location: London

    Posts: 185
    I'm Richard.

    Default

    Hi Alan, interesting stuff. I know there are at least 3 different versions of the 01A.
    Was your Xiang Sheng the one with the Cirrus chip & upgraded TE7022 daughter board?

  6. #6
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,920
    I'm Alan.

    Default

    I believe so.

  7. #7
    Join Date: Jan 2013

    Location: Bristol

    Posts: 3,501
    I'm Justin.

    Default

    I went for what looks like an older one. More boxes to play with. And a French DAC 3 too.

    https://www.ebay.co.uk/itm/XiangShen...EAAOSw5cNYSBOc

  8. #8
    Join Date: Feb 2011

    Location: Oxfordshire, England

    Posts: 261
    I'm James.

    Default

    What was the HT before the mod?

    Jim.

  9. #9
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,920
    I'm Alan.

    Default

    Originally there is a simple shunt regulator on the board limiting the HT to +77V.
    The valve then sees 65 volts anode to cathode.

    With simplification the HT is raised to +118V, then with a change of cathode resistance the valve sees 88V anode to cathode, could be made slightly more.

    Around 90V is ideal for an ECC88 or PCC88.

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