Al,
Thanks for the response.
Second, I would discount as irrelevant all of the findings in which hum occurred when an unterminated XLR cable was connected, and when an XLR cable was connected to the AVR while the AVR was unplugged from AC power (which probably also represents an essentially unterminated condition).
Please explain your reasoning for when connected to a preamp that is powered off being the same as the cable not connected to anything, open ended.
I have had instances when a power amp was left powered up and the preamp was turned off. There was not any hum/buzz coming from the speakers. Of course I have never owned a 300 watt per channel amp either.
I still can’t wrap my head around that the Adcom amp is quiet when nothing is connected to any of it’s inputs, but when an XLR balanced cable is connected to the amp it hums/buzzes. I have been assuming the hum/buzz is only from the speaker connected to that channel of the amp.
Jim