MM Electric Dual Channel Power Amplifier

[Matthorton]

Hi everyone!

I've got this big old amp and its really confusing me. My college gave it to me and I don't know anything about it. I cant find it on the net. But i was wondering if someone could help me out.

basically...

the amp outputs a hum (like a low frequency earth hum) with no input connected the humming increases in volume as i turn the volume up. the humming stops if i touch both the chassis and the metal jack on the speaker cable. but the output jack sockets are made of plastic (im guessing to isolate them from the chassis).

the input jack sockets have a metal nut but a plastic washer (im not sure if they are supposed to be connected to the chassis or not) if i connect a jack to jack cable into the input socket and touch the sleeve of the jack to the chassis the humming stops almost completely. BUT.. touching the metal bolt on the input jack socket and the chassis has no effect on the hum.

Also, with a jack cable plugged in, the humming is loudest at mid volume.

if i touch the tip of the input jack onto the chassis it squeals really loudly and high pitched.

i know this is a grounding issue but is it broken? can it be fixed safely?

i would really appreciate any help. i'm going to university next next month to study music production and I need this amp to monitor my mixes and this hum is really off-putting.

thanks so much in advanced for your time.
matthew horton