Shanling PH100 - Non-volume/input dependant hiss through one channel - diyAudio
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Old 18th October 2011, 07:16 PM   #1
danza is offline danza  United Kingdom
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Join Date: Nov 2004
Location: West Sussex
Default Shanling PH100 - Non-volume/input dependant hiss through one channel

As title really.

I noticed a hiss coming through the left channel of my PH100 a couple of nights back. It fluctuates/crackles, but is never very loud, i.e. music easily drowns it out. It sounds very much like the run-in groove on a record (less HF crackle though). I'm concerned that this could ultimately ruin my HD 650s or Denon D2000s.

All I've tried/found so far:
  • Noise only present in left channel
  • The noise stays constant, i.e. does not change with volume increase/decrease
  • The noise is present on both inputs when connected to a source
  • The noise is present with no sources connected
  • Moving the amp away from my PC (where it lives) and plugging in elsewhere makes no difference
  • It is NOT the headphones (tried two pairs with the same result)
  • The noise is present from the moment the amp is switched on, and does not appear to worsen over time

If diagnosis is possible from the above info, what's the likely cause? I can solder etc, so fixing it's not a problem. Finding the problem might be a bit harder (unless I find scorched components/bursting caps etc).

Cheers!
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Old 18th October 2011, 07:35 PM   #2
danza is offline danza  United Kingdom
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Join Date: Nov 2004
Location: West Sussex
Just had the lid off, and nothing looks untoward inside.
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Old 21st October 2011, 10:42 AM   #3
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Location: Germany
That sounds like a defective/damaged component, most likely a transistor or FET. Even bad film caps, as rarely as they occur, can cause things like that, as well as bad bias diodes (another rare occurrence). It might also be a bad solder joint.

Diagnosing problems like that generally isn't easy. One can poke around in the circuit with a scope in the hope of finding something. Having a general idea of how the circuit works definitely doesn't hurt, so if there isn't a schematic to be found anywhere, one should make a list of semiconductors at least (one channel, from volume pot to output FETs).
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