(Robert B: Wish I knew how to lift the ground
using an extension cord. You all are too smart
for me.)

Two-conductor extension cords have no ground lug. This suggestion was only
for a temporary means of lifting the ground to see if that's the problem.

(Barry: this is more than a little hum. It overpowers
the other 5 speakers, even with the gain on the subwoofer
fairly low.

Did you say something about having opened and worked on the inside of the
powered sub? I must have missed that but someone else made a comment to
that effect. If so, it's beginning to sound as though you've accidentally
shorted (or opened) something inside. This might be a good time to trundle
on down to your local electronics repair shop.

Alarm and Home Automation System FAQ
http://www.bass-home.com/faq/masterfaq/faq.htm

Regards,
Robert

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