dumbears
100+ Head-Fier
- Joined
- Sep 12, 2006
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Mind if I chime it re: AK4497 mod?
1. AD8620 is an improvement compared to OP275, especially OP275 that finds its way into DSD. Not the best sounding opamp for LPF IMO, but a very good one nevertheless. I sourced some from taobao - B-brade, which is a better grade and I have doubts about them, it's likely they are not genuine. Are those used in the mod genuine is anyone's guess, but cheapest genuine part I could find retails for $13 per opamp.
2. AD797 rocks, and it is either NOS or second hand, based on the colour scheme (recent iterations look differently, I have genuine A and B grades). I note that it is soldered in, so no opamp rolling in this version. Also, AD797 is the only opamp that was picking up EMI/RFI in my DSD (out of 20+ opamps I tried), not sure if that would be the case with modded DSD though.
3. Tantalum capacitors are generally considered inferior to electrolytics for audio (DC-decoupling in this case), higher THD etc. They are sometimes used in space-restricted designs (F.Audio FA1), but I'm not entirely sure how it is an upgrade.
4. Zishan DSD benefits immensely from improved power supplies (3.3, 5 and 9V) and changed/improved bypass capacitors (All opamps have 12uF bypass caps, but do not have 0.1uF that every datasheet recommends). Missed opportunity IMO.
5. 22Ohm output resistors is such a last century. Forget about BAs, hybrids and dynamic driver earphones don't seem to be affected too much though. No easy solution here I'm afraid, but a missed opportunity IMO. The good news is that AD8620 has higher output current compared to OP275 and is capable of handling high capacitive loads (cable and headphones form a capacitive load), so one can bridge 4 output resistors on the balanced out, this should improve things with BA's.
6. 12V improves driveability of Hi-Z earphones, but of no benefit for Lo-Z (i.e. 16-32 Ohm) ones. Opamps are claimed to sound better on higher voltage rails, so may improve things a bit.
Since my statements above appear inconclusive even to me, I believe this modded version would be an improvement, but not a drastic one and would still not realise full potential this player has.
I'm trying to mod this monster on my very own, and I'm no electronic guy. I'm just stealing ideas everywhere and do the trial. Here are some of my thoughts:
- AD8620 is good, but it's expensive, esp. the BRZ version. Why not follow AK's "recommendation", OPA1612? I do see OPA1612 is a better option in some ways.
- AD797 is a monster - it can be both a good servant and a bad master. It all depends upon how you can tame it. Are there something else easier?
- Tan caps are debatable, I believe, given the original caps were audio-grade. To my ears, the tan caps are cleaner. However, I sometimes have the thought of these caps being too clean, and I should say, less musical.
- Higher voltage magnifies everything. This is a 2-edge sword. Still, I guess it'll do more good than bad, but I'd still choose to skip. Instead, why not conduct more stability mod to the circult?
- Oh, I didn't know those aren't 0.1 caps. I always struggle with output resistors and coupling caps. I don't know when I can just let go of them. I really don't want to fry anything because of this. On the other hand, I always have this question in my head, "will my stuff really fry if I short these resistors and caps?"
Sorry for my murmuring.