Re: Help! PA system AC hum
Peter go to any professional PA system supply house or guitar store that Carry's PA equipment and ask for a 1/4" 1 to 1 isolating transformer. This will loose the ground loop in a safe way. You might have to get a 1/4" to XLR matching transformer then a XLR to 1/4" to do the same thing, Switch Craft makes many different configurations that can adapt to any audio hook up. but it will work. How are the amps fed with audio, are both the monitors and main amps fed through the mixing board? you will have to disconnect each audio cable that runs between each piece of equipment until you find the offending cable(S) then put the above isolating transformers in-line with it. I would start with the audio cables feeding the amps first.
What causes the hum is the grounding between two pieces of equipment has neutral current on it and since the audio cables also share this same path this current is imposed upon the signal to the amps which are design to amplify 60hz very well.
You would have to track down this current, find it and eliminate it. Not an easy chore I might add. This will also happen when equipment is fed from two differant sub panels that at least one of them only has a three wire feed to the main service.
Wayne A. From: N.W.Indiana
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