My amp shuts down to a "standby" mode, so, just to be sure, I killed the main power switch. This completely disconnects the amp (both legs of the AC power) from the power line.
Still humming away. When I short the speaker wires, the hum stops.
The speaker wires for this speaker are not near any AC cords. The wire feeding this speaker is a Goertz "ribbon" cable, about 3 meters long.
Only remaining test is to see if the hum persists over a long period, in case it takes a while for the power supply caps in the amp to fully discharge.
I live near TV transmitter towers, about 2 km away.
Any ideas as to cause or cure from you tech types?
TIA.
