Thank you to all who have commented, I do appreciate your input!
Do you still have the hum/buzz from the speakers when the amp has no inputs and powered on with the speakers connected? If you have shorting RCA plugs you can put those on the amp inputs. It should be disconnected from all other equipment for the check. If it still gives hum/buzz through the speakers it is the amp power supply. At that age, probably the power supply caps or others in the amp itself.
Hum/buzz coming via the speakers as OP noted is either a possible ground loop, or power supply noise. Removing the amp inputs will isolate all other grounds.
There is noise from the amps when nothing is connected to them.
There is noise from the amps when they are muted, which prevents any signal from reaching the output stage.
There is noise from the transformers when not connected to the amps.
Curious. Were any new devices installed in system that may have introduced a Hum ? I take it this is a recent thing.
charles
No, not really recent, and no new devices, and the equipment is now on a dedicated line, unbroken between the outlet and the main breaker box.
The issue was present prior to the dedicated line, it was an attempt at silencing the noise...
Here's a look inside...
Audio Alchemy OM150 by
Barry, on Flickr
Audio Alchemy PSU150 by
Barry, on Flickr