s_r

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About s_r

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  1. Well I've reflowed a bunch of joints (probably more than was needed). Since then I haven't had problems with oscillation, excessive offset, etc. The sporadic noise seems to have gone as well, but of course just as I say that it'll come back to spite me. Anyway, thanks for the help. I think I can stop fucking with it and just use it to listen to music.
  2. Shouldn't have opened my mouth apparently, the T2 is acting up. I replaced the four K216s of the right channel with ones from my old board with resistors at their gates, also trying a 5pf bypass cap right now. Neither of these changes seems to have helped though. It's been a complete gamble when I first turn it on as to whether the offset will be fine, -30V or -450V. Sometimes I'd measure around -30V offset, then as I try to use a scope to see if there's oscillation, the offset fixes itself and there's no oscillation. Other times I'd adjust the batteries, which fixes the offset, then as I'd turn the amp off to put back the top cover it'd regain its problems when turned back on. Regardless of the offset/oscillation I get an intermittent scratchy noise. Just maddening.
  3. So I've installed a 10pf bypass cap. At first the value for offset was way high (like 400V give or take) but after adjusting the batteries it fell back to within normal values. The T2 has been on for at least 5 hours now, and it hasn't misbehaved in that time. I've had to go back and check after hearing some puffs of noise which turned out to be in the recording itself. At the risk of jinxing it, that seems to have worked.
  4. I was thinking of adding resistors to the gates of the K216s in the battery next. If I recall correctly this helped solve some noise in Inu's T2. I'll also try lowering the value of the bypass cap and seeing what that does.
  5. Well I loaded up the gerbers and took some screencaps of the relevant parts. There's certainly a difference between channels. I've also noticed that R86/R87 are physically higher off the board on the right, if that makes any difference.
  6. Put in the second 2.2pf cap just now, and the oscillation looks nigh identical as before. Guess I'll try changing the bypass cap value next. Edit: This is what the oscillation looks like with the bypass cap set to 20pf.
  7. Just the right channel, and it's come and gone up until now.
  8. Your board version is probably older than mine too, right (production v1.07/silkscreen v1.03)? Either way I'll see how it responds once I've added a second 2.2pf cap. On that note, what about soldering in SIP sockets to make swapping bypass caps easier?
  9. Seems like oscillation was indeed the cause of the noise & high offset which has been sporadically happening. Happens now with either tube or solid state input. For reference both channels have 15pf bypass caps across the 100k feedback resistors. What about populating both C12 & C13 with 2.2pf caps? Apparently doing this killed the oscillation in pedefede's T2 a few years ago.
  10. So after setting up my scope to see if there was any oscillation, the distortion and high offset disappeared. Afterwards the distortion would show up after a few hours of it being on, and it's sometimes cured by just unplugging/replugging the headphones. Feels like I'm chasing after Schrodinger's distortion Whatever the case, I've put heatsinks on both the 3840s and LSK389s now.
  11. Haven't checked that yet. Where's the best place to measure that? Could try the +200V output of the battery, or the final output, like the measurements I did some months back.
  12. The batteries measured fine last I checked, the K216s beside the J79s all measure similarly to each other. Replace the LF353 maybe? No change after swapping out the LF353 either.
  13. Tried that just now, and the values between all four seem to be within the margin of error. The two on the right channel measure pretty similarly, while the left two differ moreso, strangely enough.
  14. Guess I spoke too soon. The exact same behavior is happening again (-70V offset, distortion in the right). Something else causing the J79 to have issues?
  15. With the solid state input, yes. Both tube sets I have, even the 'low noise' philips, are intolerable to me.