Very loud background hum

[andrewrx7]

Hi there,

Just returned from a gig last night - bit of a nightmare. Just wanted to see if there were any electricians out there who could offer some thoughts?

Scenario: We have played at one particular club several times now, and each time the place causes serious background hum/buzzing on the guitarist's amps and the PA. It is the only place this happens. We were told that other bands used to suffer this to, but the place has been re-wired which had apparently got rid of the problem - until we turned up! The buzzing was so bad, that we were told it was almost unbearable at times.

The gear: I know it is a bass forum, but the bass gear was not affected. I also run the bass through a Unibass pedal and use a guitar amp in conjunction with my bass gear -neither had any issues. What was being affected was the guitarists' amps - he was using 2 AC30's, one a '63 and one a '06 model. Also the PA, which is a Mackie mixer unit with 2x dbTechnologies powered speakers.

As I said, any other place we play, the equipment is quiet. It is only this place!

Any ideas what is producing this interference? The lights around the stage area were all turned off (although not throughout the entire club - it was pretty large).

Any thoughts would be very much appreciated!

Thanks,
Andrew

[2x18]

We had a similar bad hum problem recently, the problem in our case was using different 13amp power sockets for linked gear! and was solved by using one 13amp power source for each linked set of equipment.

Will.

[BOD2]

+1 to what 2x18 said

Sometimes you'll find that 13A sockets in the same room are actually on different eletrical circuits - just teh way the room was wired or wiring changed at a later date. If this is the case then connecting one piece of equipment to one 13A socket and another piece to a different 13A socket - and then link the equipment together via a mic cable or something can cause serious earth loops or humming.

Try connecting all the audio gear to the same single 13A socket if possible.

Alternatively, identify which cables connect equipment that is plugged into different 13A sockets and look into ground lift options for these cables (but NEVER be tempted to remove the earth wire from a 13A plug).

[andrewrx7]

Interesting comments, thanks. Will certainly bare this in mind the next time we play there.

[Charla]

Check the lights at the venue; I had a similar problem which was caused by a rather curious decorative light and the problem was solved as soon as it was switched off. First thing I ask them to do when I play there!

Cheers

Charla

[Vasquez Rich]

I had an amp once that developed a loud hum that came on about 5mins after switch on. I took it to rehearsal and it didn't do it. Took it back home and it did it again. Took it to the shop for repair and couldn't get it to do it at all. Got it back home and guess what, did it again. I phoned the shop and let them listen down the phone. They took the amp and couldn't find anything wrong with it.

Never bottomed it but always thought it must have something to do with the mains as it was suspiciously 50Hz ish.

Richard

[stingrayfan]

[quote name='Charla' post='291496' date='Sep 25 2008, 09:31 AM']Check the lights at the venue; I had a similar problem which was caused by a rather curious decorative light and the problem was solved as soon as it was switched off.[/quote]
Dimmer switches and halogen lights are a nightmare.

But +1 to the single socket solution above. That's the most likely I would have thought.

[Hamster]

Another possibility is the way the leads are wired. I had this problem and found a couple of XLR to XLR leads were wired wrong. With a 3 pin XLR you have screen, centre hot and centre cold, each to their own pin. Someone had wired the centre cold to the screen pin, which made an earth loop. You also get XLR - jack leads where the screen and centre cold are wired together, result - earth loop.