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I've been modding the DAC Ah for a few days now and finally getting to the output stage, (which is all stock except for panny FM caps). It runs 8 TDA1543's, Vdd 6V. Outputs trimmed to 3.3VGoing passive with cap values from 0.2uf to 2.0uf and 100K for the load.
The caps are from Hovland and SEC. Riken 100K. My Pre has input's of both 100K and 200K. Yes there is a sonic difference between the too.
Proper RC impedance matching would be from 1uf to 2uf.
I'm finding the small caps sound lean but fast and for the obvious reasons. Up around 2.0uf it sounds full but bloated and blah. In-between sounds very musical but lacks dynamics, when compared to the opamp.
By upgrading the opamp rail to Schottky's and LDO VR's, add in OPA604 or OPA627, I'm pretty sure the opamps will win hands down. From what I understand, it should be the passive, being the clear winner.
Is there some magic cap value that's out there, perhaps in increments of 0.1uf + putzing?
Any other folks go through, what appears to be a very long road the best sounding recipe?
Follow Ups:
As soon as I bypassed the output stage (as recommended in the Digital Asylum), the damn thing gave up the ghost. I don't know if it was the modification itself, or just the cheap quality(?) of the DAC to begin with. I haven't figured out exactly what's wrong with it yet, but everything sounds overly distorted and grainy. Something is clearly not working properly.I think that I could sit down and troubleshoot the thing, but is it really worth it? I have listened to one (that is modified) on several occasions and I've had time to NOT focus on the DAC itself. For all of the trouble and fuss, it just doesn't sound that good to me. Not even for the price. It has a very crude and disconnected rawness to it that seems to be inherent to the design itself. That's my take on it anyway. On the other hand, maybe the consistency with these things is very poor and I just have'nt heard a good one yet. I hope you have better luck with yours than I did with mine.
All is not lost. I keep mine for a paperweight on the workbench. It reminds me that you get what you pay for.
If you're running the chips with the stock 6V supply, then you need to change their load resistors (R35,36) to 150ohms. Then adjust the Vref to 3.3V or 3.85 MAX.The opamp must be removed as well. D/C'ing the opamp PSU ,leaving in the opamps and going passive, will sound absolutely awful.
Well, it went from awful, to bad with potential, to unacceptable. I guess that's why I kept messing with it. I did everything that you mentioned ecxept for "setting Vref to 3.3V". I don't remember that little piece of advice, I will check it out. I've kind of lost all hope for the thing . . .I apologize for my lack of enthusiasm. Next time I want to tinker I think I will by a kit. I do appreciate your help though - thanks!
That's too bad it didn't work out. I'm very pleased with mine.
Let me know if I can help.
;> )
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