noise/buzz induced by stage prop on dimmer

[Chris15]

I think the lighting guys regularly plug incandescent bulbs (floor lamps, etc) into dimmer channels, but it's these non-trivial electronic devices that seem to have the problems.

It's not that these devices draw much power that's the issue. A simple light bulb copes presents a reasonably linear load. These other things present inductive and/ or capacitive loads. These DO NOT cope with the chopped power waveform that dimmers present.

Get some long power cables and run your powered speakers from the same power points as the mixer, I'm willing to bet that will remove the noise, if it does, try lifting the signal earth at the input to the speaker or feed it through a transformer.You will get earth loop hums on the same circuits, as the earth wire
loops around the building, by plugging in at the sound desk you are star wiring the supply and can't get an earth loop.

Having a thought here. I'm hoping that the speakers are fed with a balanced line, is this the case? And yeah, at least try plugging the speakers to the same power supply as the mixer. If it fixes it, you now know what you need to resolve more permanently...

 

[jkowtko]

I thought about it, but due to lack of time (again) didn't try plugging the speaker into the sound board circuit ... I can try this this weekend.

Another tidbit of info ... even though the building has a pretty beefy power supply (400 amp 3-phase into the building, split into three 100amp main circuits) we do have a "dirty" neutral from PG&E and do not have a proper ground -- the ground and neutral are simply connected together. Time and $$ permitting, the lighting guy wants to install a proper ground for the building some day.

Again, since these issues are few and far between, it would be great if we had a solution (i.e. small power filter) to attached these problem devices to. In this case, for the TV we should hook it up to an AC relay and then plug the TV into a conditioned power supply.

 

[David Ashton]

The quality of the earth is not the crucial factor in interference suppression, the crucial factor is that there is one earth point, that is your sound earth and every part of the sound system is connected back to it.As soon as any other connection is made to earth via patch panels or DI's or any other means you have the potential for trouble.A common recent phenomena has been ready made leads which connect the shell of the xlr to the shield, so that a patch panel which is earthed separately to the sound can now earth back via the xlr, so I cut off these links.

 

[SHARYNF]

IF connecting the Mackies and the mixer to the same electric outlet fixes the probem then you definitely have a ground problem on your electric most probably from using conduit for the ground and the connection getting old, Your if Foster City, so you are near the bay and the salt flats, so corrosion can be a factor.

Sharyn