Hi everybody,
I didn't read everything but the PCM1794 looks like the PCM1792, same characteristics than in my Cayin CDT-17A.
So it is a real symetric scheme according to the specifications of the PCM. You have one PCM per channel. You have also from PCM to RCA output, for each channel:
- 4 X monochips AD847 I/V Section Op Amps.
- 2 X monochips Differential Section Op Amps: it looks like OPA627...
- 1 X monochip single-ended RCA Op Amp: to convert from XLR to RCA. I can't read but it looks like OPA627 as well.
NB:
Firstable, OPA637 can't be used in this CDP. OPA627BP are quite better than OPA627AP. Try to change AD847 by OPA627 in I/V section.
If you use only RCA output, take off the last (single-ended) OPA AND the RIGHT OPA of each channel on differential section (when you look at PCB from PCM to RCA output). So you keep only the Four OPA in I/V Section and the LEFT one on Differential Section. So you use only one "half-PCM", but you might be astonished...
If you use only XLR output, take off only the last OPA (single-ended) for each channel. You don't need them for output XLR. IMHO, the XLR (symetric) output should be much better than RCA output (asymetric=not symetric).
About the Tubes:
First hypothesis: each tube works for RCA OR XLR output: try to listen to the music without tube by RCA. If it works, then RCA doesn't need tube, and then tube is for XLR output. If it doesn't work with RCA but without tube, then the tube works for RCA output.
Second hypothesis: each tube works for both (RCA AND XLR) output. It means actually that half tube is used for RCA AND XLR output tube at the same time.
Actually, I think that tube works for XLR OR RCA output. So one kind of Output doesn't need the tube.
And to conclude, the best tube I have ever tried in my Cayin CDT-17A is Mullard E188CC "shield" BVA gold pins. But I have to try Siemens CCa "grey plates", RTC E188CC and AEG E88CC...
Here is a link of my tweaked Cayin CDT-17A:
http://www.homecinema-fr.com/forum/viewtopic.php?t=29777877&postdays=0&postorder=asc&start=0
NB2:
I tried discret AOP, superclock from Bursonaudio. They are far better than OPA627.
I hope that my reply will help you.
Best regards,
teiki arii. |
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