** Updated to reflect completion (more or less...). Details on latest post below (23/5).
Jan: while checking my board, I tried to trace the connections for C1. One pin is on the +5, but the other seems to be NC? I expected it should be GND. Have I misunderstood something here?
Jan / anyone else: my 2nd AMP3 works beautifully, but the 1st board I attempted still has a problem.
- power on slight thump (normal); dc offset normal; completely quiet when no source connected
- with source connected, pretty good sound produced; no noticeable distortion or other problem, except:
There is a moderate level hiss (similar to white noise) on both channels. The hiss remains same level throughout. Sometimes there are clicks and bumps, but mostly its hiss only.
- Disconnect source from one channel; that channel goes quiet. Disconnect both cables -- both channels quiet.
- Connect shorting plug to one channel -- that channel starts to hiss(!).
- Tried other cables -- same result
I've traced and checked most of the incoming pins, and replaced input caps. No change.
Power supply is 12V SLA.
Any suggestions on where to focus my troubleshooting would be appreciated.