Mixing board AC hum

Greg Crawford · From: Tennessee, USA

I have an old Rane Matrix Mixer that I run my mikes and instruments into. I have 6 amplifiers of various kinds plugged into its six line level outputs, and I can combine any amp with any and all inputs so several folks can play or sing in my music room and output any instrument or vocal into any of the amplifiers.

I noticed an AC hum in my new to me Session 400 amp when I plugged into the board. No hum if the amp is connected only to a guitar.

If I unplug the other five amps (all of which are shut off), the hum stops. But if any one of them is plugged back in, the hum comes back, and gets louder as I plug in more of them.

Any suggestions on how to minimize this?

Thanks.

Jerry Overstreet · From: Louisville Ky

Maybe a ground loop. Try a 3/2 plug adapter on the Session's power cord and see if the hum goes away.

Jeff Highland · From: New South Wales, Australia

Is the Session 400 plugged into a different wall outlet or power board than the mixer and other amps? Sure sounds like a ground loop to me, but I would be reluctant to remove the amp's grounding by using a 3/2 adapter.
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