johnelstad wrote:
He shoots, he scores! My amp has a three-prong plug, so I added a
two-prong adapter and the hum disappeared completely. I'm so relieved.
Thanks so much, James, for your quick and helpful response!

John

James Lehman wrote:
Does you power amp have a two prong plug? If so try adding a wire from the
chassis to a real Earth ground. If your power amp has a three prong plug,
try it with one of those two prog adapters with no ground at all.

James. )


You apparently had multiple ground points at differing potentials
causing current AC leakage current to flow through your input cable
shield, inducing hum. By breaking the power amps chassis-to-house
ground you eliminated the problem. Your power amp chassis is still
most-likely grounded, though now through the interconnect shield
instead of the power cord. If you disconnect all interconnects from
the power amp, then you have a power amp chassis that is not grounded.
So I would keep it grounded via the interconnect that connects to the
preamp to be safe, or even run a ground wire between the preamp ans
power amp chassis if they have external ground posts for that purpose.