Hum in left channel - Parasound Z


I'm using a parasound Z amp and a z tuner at work. I do not have a preamplifier, so I have been using the gains on the back of the z amp. It works fine, but it's a pain to have to reach to the back side of the amp to turn volume up or down. Plus, matching levels by channel is difficult.

I obtained a 10k stepped attenuator that I wanted to use as a temporary volume control. It's stereo as I didn't want to adjust each channel independently.

I tried the attenuator at home last night with a different system. It worked perfectly. I brought it to work this morning, connected everything, and it worked great. However, about 30 seconds in, I developed a hum in the left channel. Now, I can't seem to make it go away. It's a 60 Hz hum. I've swapped speakers, and determined it is the amplifier. I've also ruled out the source.

My ultimate question is, is it likely that I damaged the left channel of the amplifier with the 10k attenuator? If so, is there something obvious that can be replaced in the amplifier to make the hum go away? The left channel operates correctly, just has a hum - which is annoying.

Thanks for any input you can provide.
s7horton
He feels it was unlikely that the attenuator did any damage, since it is strictly passive. When I told him I would likely take it to get fixed locally, he offered to send the schematic to the person doing the repair work.
That attenuator seems to have done something, or exposed some issue. It's worth phoning Parasound directly, their service is amazing. Call 415-397-7100. They may even give you the owner, Richard Schram, to talk to. Many have reported what a knowledgeable person he is.
I have a same problem with my amp which is in service center now and it is AB amp(ML no532).
According to the service center it is most likely bad capacitor and it is easy fix for them.
I had a hum in my system caused by the cable coming into the house from Comcast. When I disconnected the cable the hum went away.