Got a "new used" Cambridge Audio P500 Power amp and it is exhibiting marked hum. Sounds like a quieter version of the hum a PA system gives off. Volume has no effect on it.
The device is pretty simple: Left Right Input Output and speaker terminals.
I think I ruled out screwing up the Input / Output side of things since I only need input from this thing and I also tried it with the Pre-Amp off and it had the same hum.
I WAS a little confused since CA had the posts labelled in a way I'd never seen before: it was readable from both top and bottom, which makes good sense, since half the time you're hanging over your components -- but again, it's easy once you know how.
And it actually sounds pretty good otherwise. That is to say, when I pump music through that segment of my system, it's quite nice setting aside the hum.
Are these units susceptible of noise from the mains? There is rather a lot of junk on that one circuit.
Any thoughts would be most welcomed. The seller, whom I trust, says there was no audible hum whatsoever.