Budget stage snake.... getting hum?

[Rodgre]

Hi all. I was just helping out a local church to set up a new PA system. We ran their brand new, but kind of low-budget snake above the ceiling tiles to the stage. Once plugged into the board, even without mics plugged into the snake, we were getting hum. It was cumulative on the channels....unmute them one by one and the hum got worse and worse.

Am I missing something? Are "better" snakes shielded around the entire bundle of wires as well as each balanced pair to eliminate hum, or is this unnecessary?

Has anyone else had an experience like this?

Roger

[Scodiddly]

Professional snakes generally just have the individual pairs shielded. There might be an overall shield, but almost nobody connects that to anything.

Does the snake run by anything like a transformer or area with a lot of power wiring? Maybe right by some light fixtures?

[Snarl 12/8]

Does the snake run by anything like a transformer or area with a lot of power wiring? Maybe right by some light fixtures?

Don't run parrallel and close to any electric line. If you have to cross one, do it at a 90 degree angle and then get away from it. EMRadiation doesn't respect walls and floors either, so even if you don't see the culprit above those tiles, it could be sitting on the floor above them somewhere. That said it dies off pretty quickly over distance. 1 foot away is orders of magnitude better than 1 inch, etc. For some reason flourescent lights really can hum the fuck out of your gear sometimes. They can do it from really far away somehow, as well. It seems like their ballasts throw dirty up the power on the circuit somehow, but I know that's probably not exactly it. Quick way to test rather than moving the snake all around. Turn out the lights and any circuit breakers that might be powering anything "up there." Run an extension cord to the mixer if you have to.

Is the mixer grounded? And grounded to the same ground as anything else plugged into it? The mixer doesn't do this without the snake plugged into it?

[kevin206]

Probably picking up hum from the lights. Other things could be mixer on same 'leg' of service as lights or other noisy things. Try using an extension cord to power the mixer from other outlets in the building.

Here's one that got me once. I bought some cheap mic cables and they picked up my flourescent lights and refrigerator in my studio. Name brand cables were fine. I checked the connections inside the XLRs and every one was wired wrong. I moved the wires to the correct terminals and all was well.

And try a different mixer if you can. I had a board with a bad grounding design that was sensitive to hum. A few hours re-structuring the internal grounds gave a nice clean board.

[The Scum]

even without mics plugged in

In that case, you've got an antenna leading to a high gain preamplifier.

Does it behave differently with mics connected (thus terminating the antenna)?

And previous posts about checking for proximity to AC lines likely ring true.

[cavemusic]

Balanced cables get most of their ability to reject noise from being balanced. The two conductors in each pair have to be very close in impedance in order to do a good job of rejecting noise. The pairs have to be carefully twisted during manufacture. It's pretty likely that cheap cable is not as well balanced as expensive cable. Balance at the mixer inputs is also important, and the longer the snake, the bigger the problem.

[norsehorse]

Are you using powered speakers?

Do you have PA equipment plugged into different parts of the building/room?

If so, you might have ground loop. Simply having your gear connected will cause you to hear it.

Lift the ground, and it should go away.

[rydaken]

I recently had a similar issue with a "value priced" stage snake that had a horrible hum. I opened up the box end of the snake and whoever wired it had pin 1 & pin 3 flipped on all of the female xlrs. The loose end (male xlrs) was wired correctly, though.

[rydaken]

I recently had a similar issue with a "value priced" stage snake that had a horrible hum. I opened up the box end of the snake and whoever wired it had pin 1 & pin 3 flipped on all of the female xlrs. The loose end (male xlrs) was wired correctly, though.