A/C hum on main speakers

[plumber63]

We are having a real problem with our main speakers and to a lesser degree with our monitors. Our problem rears it's ugly head when we turn on lights via our low voltage light control board. I have narrowed it down to the cables that run from our mixer board to our rack mounted equalizer. I think they are just crappy cables. they say "belden instrument cable x1". I need to know if I am on the right track or barking up the wrong tree. I am no audio expert.

Thanks,
Glenn

[[Director] drew ryan]

The first place that I would look is your power. Are you running your lighting on the same circuit as your audio, or is the lighting circiut on the same leg of your power? You may have to consult with an electrician to find out the latter part of the question. Lighting should never be put on the same leg or circuit.

Belden is considered pretty much industry standard. You may have unbalanced cables running from your mixer to your EQ. Could you provide a model number for your mixer and your EQ?

[doctordale]

We need to know a little bit more about your setup to really troubleshoot this. What mixer brand/model? what EQ/amps? How far in between the different components? Is the lighting on a different circuit?

If I had to guess with the info given so far, it sounds like you're running an unbalanced signal from the mixer location to the EQ in the amp rack (near the stage?), implied by your mention of instrument cable. With the added info, the fix may be as easy as changing to a balanced cable type, if the mixer has balanced outs and the EQ has balanced ins.

Or not...

Drew, so what your saying is, if we have our entire sound cabinet and several room outlets and then finally the room light switch all on one wall panel switch....that is a major problem. Most definitly where we are receiving our large amount of hum...Also all of our video; i.e. computer, DVD, VCR, CD, Kramer Switcher/Scaler, and small mixer are all plugged into the same series on the same wall
Sounds like we have some major expenses to consider. Any suggestions??

[plumber63]

I am not sure of the model numbers and/or brands of our equipment, but I can answer a few of the questions. Our lighting is controlled by 10 volt dc control from the sound booth located at the back of the church and the control packs are located near the stage. They are almost certainly on a different circuit than our amps as they are located under our sound booth at the back. As for the amps and EQs they are located under the sound booth, approx. 10' from the mixer and are connected via 1/4" mono cables(instrument cables). That is the only ins and outs that we have. There are no XLR jacks.

[Nathan J]

Originally Posted by plumber63

As for the amps and EQs they are located under the sound booth, approx. 10' from the mixer and are connected via 1/4" mono cables(instrument cables). That is the only ins and outs that we have. There are no XLR jacks.

That's the first place I would look for hum issues. Your mixer and amps likely have TRS jacks on them (balanced, but work with unbalanced 1/4" TS instrument-type mono plugs). Your EQ may be a different story -- some cheaper EQs have only TS (mono/unbalanced) jacks, and will force you to be unbalanced between the mixer and amps. The only way to tell is by posting the exact models of the mixer, amps, and EQ here so we can check them out.

[plumber63]

Thanks NG for the great Bal/Unbal info, I had not thought about the 1/4"TRS cables. I was thinking XLR as balanced. I had our sound tech check the manuals and all of our equipment has TRS jacks, so I guess that is the first thing to try is the Balanced cables. Just for info and if you want to check for me our mixer is a Mackie CR1604-VLZ, our EQs are Gemini EQX-30 and our amps are QSC USA series 400 for monitors and 900 for mains.

Thanks Again,
Glenn

[Nathan J]

FYI, even if the hum problem doesn't turn out to be because of unbalanced signals, you will definately be better off balancing it. After I heard the difference in my system between balanced and unbalanced, I would never go with unbalanced again -- even if the amps are very close to the mixer!

[plumber63]

Did you get to check out our equipment to see if our sound tech was right? Also, I just ordered a 10' 8 channel TRS snake to run from the mixer to the EQs.

Thanks

[Nathan J]

I'm trying, but I can't find much info about your EQ. One site seemed to say it has RCA ins/outs, but I'm having trouble verifying it.

Both of your amps and your mixer do have balanced ins/outs.

[plumber63]

NG, Our EQs do have RCA ins and outs, but they also have a 1/4" ins and outs. Thanks for the help. I ordered a 8 conductor TRS snake last night. We only need 4, but i could not find 4 for as reasonable as this 8. Anyway, Thanks for the help, Glenn

[jorad]

Since the problem only appears when you operate the lights, I'd check and see if the lighting dimmers are using the same ground as your audio equipment. If this is the case then it should be a simple matter of sinking a new ground (simple for an electrician that is).