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Noise from LED lighting circuit getting into audio circuit?

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Douglas Cyr:

--- Quote from: Paul G. OBrien on October 14, 2022, 12:02:30 PM ---So many possible sources but that effect hilighted above I have seen before so the first thing I'd try is to simply unplug the power supply to the laptop so it runs on battery, if that eliminates the random noise then you just need a line level transformer isolator between the computer and mixer.
The hum in the speakers system could be a differernt problem though. Is all the equipment rack mounted together? If so I'd suggest lifting the mixer out of the rack, the chassis may be grounding through the rack creating a ground loop that causes hum. If the mixer isn't racked then you may have to start at the speakers and work backwords, long poorly shielded inwall wires can act as an antannae, but there may also be something generating noise on the power line that has nothng to do with the sound or EFX lighting systems like dimmers on the venues regular lighting. I have a venue I visit where the hum on the audio system is quite noticable and nothing I do to the system makes any difference, last time there I discovered that the hum almost totally disappears if the dimmers on the house lights are set to full on. A lot of good that does for me come event time, this dimmer doesn't have an on/off switch which would take the dimmer circuitry out of action when the lights are full off but that could be a solution if you find the house lighting control to be the source of the problem in your case.

--- End quote ---

Well when I was at the club the first thing I tried was unplugging the control iPad and the MyDMX go box from the wall and the noise didn't go away, I think it may have gotten a little quieter though.

The alto mixer and MyDMX go setup are all in the DJ booth, which is one floor below the amp rack/it room in a separate location.

I guess the next time I'm there for another service call I'll try to work troubleshooting this into that price, I just don't want to quote the owner for a service call and leave myself the chance of leaving without solving the issue.

Tim McCulloch:
Hi Douglas-

A few years ago we bought some "Chinesium" clones of the Clay Packy "Sharpie".  LD put the around the edges of the drum riser, and had other moving head fixtures at various places on the stage.

We had a noticeable buzz (not so much a 60 Hz hum) in most all of the drum inputs.  We tried Pin 1 lifts, tried isolation transformers, all kinds of hum busting tactics from 1980... and at one point we thought we'd knocked it down enough to get through 75 minutes of show.

Then the LD started a new focus and the noise came back.

Turned out to be inductive noise FROM THE FIXTURES.  We moved them off the riser, away from mic cables and microphones, and things improved.  We removed power from them and it all went away.  LX and audio were on separate services, separate service transformers, and there was no interconnection between them (LX coms were separate, electrically and physically, from audio coms).

This may not be your exact problem but it might give you some other ideas to check out.

And a Tim stated here's some more food for thought.  I did a high end sound system install into a 2004 Chevy Blazer about 10 years ago.  Used some old car audio stuff that had be laying around for years with some new stuff.  The shop owner nailed it before we even powered it up.  He said something to the effect of "the older stuff wasn't as noise tolerant of the vehicle electrical system".

Alternator whine right away.  Before messing with capacitor and other noise abatement in the SUV's electrical system, I pulled the old analog crossover and replaced it with a Rockford Fosgate 3sixty processor and new amps.  Noise gone.

Not suggesting the lighting system isn't the culprit.  But, it could be something in the audio chain may not be as noise tolerant as it could/should be.

Look there too.

Have definitely done a few club installs and chased noise issues.  That can be some real fun.

Douglas Cyr:
The first thing I'll try is unplugging the dj booth input from the processor and see what that does, if it does go away I'll try the pin 1 lift on the Euroblock as suggested.

I was hoping the Rane ZonePro processor might have a noise gate I could try to implement, but it doesn't appear to have that feature.

I'm sure the venue owner won't want to move lights around - if the noise is on the inputs to the processor, Would a rackmount gate unit before the input of the processor help?

Was the entire system intact and operating fine, then all of the sudden the noise manifested?  Or, can it be attributed to an event such as installation of additional lighting instruments or other disturbance to the building electrical system?


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