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Noise from LED lighting circuit getting into audio circuit?

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Douglas Cyr:

--- Quote from: Steve-White on October 25, 2022, 12:03:18 PM ---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?

--- End quote ---

A staff member told me it was a recent development, the only change I know of was new carpentry/decour being installed behind the bar (which is next to the DJ booth). I don't think any new lighting was installed.

Scott Holtzman:

--- Quote from: Tim McCulloch on October 23, 2022, 02:57:00 PM ---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.

--- End quote ---
Tim, our SKU for those uses the Charpie description. 

doug johnson2:
Can't really help much but, a few years ago a church client called to complain about a hum in an under balcony fill system that had been in place for several years.  Turned out they had just switched out all the bulbs under the balcony to cheap leds.  They were causing the noise and the only solution I could come up with was to replace the bulbs.

Douglas Cyr:
So to follow up:

I went back to the club today to officially diagnose/fix the issue (last time I was there for another matter, and the staff brought this up to me right as I was wrapping up).

It was so simple, the installers ran 100'-200' of balanced audio line, then terminated it as RCA into the processor instead of using balanced terminal blocks.

Mystery solved, fixed in a couple minutes.


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