left channel buzz [resolved]

[rogerfederer]

i had not used it for months but had no buzz last time i used it (back then).  now a buzz on the left channel that does not vary with input or output selected.  also, changing volume pot does not change it.  switched tubes and not follow the tube.  not rest of system, which i tested with other preamp (LDR) and dead silent.  i used deoxit on the pots but not fix.

in an attempt to reduce microphonics i have isolated top plate from plinth with mortite caulk; maybe that allows a bit of flex in top plate that could affect solder joint(s)?

troubleshooting suggestions?  am at work but can play with this over the weekend.  many thanks!

[Paul Birkeland]

I would absolutely suspect a loose solder joint or a loose connection.  It is unlikely to be related to the pots if it's still there with the volume pot turned all the way down. 

[Doc B.]

Yup, if it sat unused a situation is created where oxidation could build up at the bad solder joint. With normal use the current flow seems to keep this process from accelerating as fast. That's kind of a shaky theory, but my experience seems to indicate it is the case.

[rogerfederer]

thanks; will heat up the iron this weekend!

[rogerfederer]

d'oh!  found bare wire touching the top plate.  bent it and buzz is gone.
thanks as always for the quick advice on this forum!

UPDATE: still getting buzz under some circumstances.  will keep trying different sources.  next will try reflowing some joints.