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buzz/hum what is going on here?

I have a pair of monoblocks in a 2nd system (Counterpoint Sa20s) and run them off separate dedicated circuits, use PS Audio Power cords, have the grounds cheated, etc etc. If I leave the amps on over 8 hours, one channel(monoblock) begins to hum. The hum does not get louder as more volume is added. It is not audible over most music, but can be heard during quiet passages. If I shut down the amp and restart within a short time, it is still there. If I wait overnight, it is gone. Im puzzled.
justlisten
seandtaylor99
1,262 posts
 
Does it hum at the amp or at the speaker ? If it's at the amp it's possible that as the amp warms up a parts expand mechanical tolerances change and the transformer starts to hum. You might be able to fix this, but unless it's really loud and annoying I'd just leave it alone.

If it's at the speaker then that is very interesting, and might warrant a call to the manufacturer.
justlisten's avatar
justlisten OP
489 posts
 
it is at the speaker. i ran the amps for 3 hours today and the hum was lower than it was last night after being on for 8.
seandtaylor99
1,262 posts
 
These are tube amps ... unfortunately I have no experience with tubes ... but I have heard others comment that hum can be caused by tubes ... is it easy to swap the tubes between the amps ? You might isolate a bad tube.
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