Amplifier Hum

Might be your preamp. I had amp hum once. I changed preamps and it went away. The hum was only noticable when the preamp was turned off.

I had amp humm and initially thought it was the amp. Turns out, Toroidal (sp??) transformers are prone to this as a result of electrical interference. In my case, it was a halogen lamp on the same circuit as the amp. Turned off the lamp, away went the humm.

My current amps do humm slightly due to design, not a big deal though.

Regards,

Even number of grounds? Dimmer switch on the same circuit?

Try using a "cheater plug" on the amp (converts from
three-prong to two-prong). Often a hum is due to
a ground loop and floating the ground will eliminate
the hum.

I too had a hum problem. T began by turning off my source components, still a hum, then my preamp still a hum. Tried a diffeent amp, still a hum. Changed out the cables from the amp to preamp hum was gone.
Though sometimes the hum might be just because it doesn't know the lyrics. :)