Musician Forum - Band Discussion Board - BandMix

Posted: **Fri Nov 25, 2011 4:32 pm**

I just put a main cab and sub into our PA. I'm getting a lot of hum thru both mains and subs. Even without the mixer plugged in. Any ideas what might be going on and how to overcome? These are two each: swa1801z active sub-woofer and sa1532z active loudspeaker and srm450 active speakers as monitors. The quality of the power at the building might be suspect and there are a lot of other pieces of equipment pulling from the same power outlets.

Posted: **Fri Nov 25, 2011 5:30 pm**

Yes.

1 You are using unshielded cable from your mixer. You can not use standard unshielded cable to run powered devices.

or

2 You have the shield and the signal wires reversed.

Posted: **Mon Nov 28, 2011 5:56 pm**

Right.
Also -
Sometimes old buildings have the wiring wrong.
Some amps have a polarity switch to make up for this.
If yours does not - then try this:
Unplug the amp, turn the plug 180 degrees, and plug it back in, see if it makes a difference.