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60 cycle hum caused light dimmers

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Con Van Dyk:
I am one of the A/V team members in our church and for some time we have experienced a 60 Hz hum sound coming through the sound system. As it is not very loud most people donít pick it up. However, we recently upgraded our streaming/broadcasting setup from SlingStudio to a more advanced one consisting of PTZ cameras, Atem etc. With SlingStudio with did not have a 60 cycle hum problem while broadcasting but we do now with the upgraded system.
Through experimentation we found out that when we turn the lights off in the sanctuary the hum is not present. The type of lights is a mixture of incandescent and fluorescent light. Since fluorescent light can cause interference, we turned those off, but we still had the hum coming through the sound system. Once we turn ALL the lights off the hum disappears.

We have about 16 groups of lights, meaning that we can turn different groups of light on and off depending what light effect we want to create. The various lights are controlled by dimmers and through research we discovered that dimmers are notorious for creating a hum sound. This light system is about 21 years of age. An electrician tryed installing "Chokes" around the power supply to the sound desk and other realted equipement with no results.

Has anyone on this forum have had a similar experience and if so, would you mind sharing what you did to resolve the problem.  Thank you.

Mark McFarlane:
1) Make sure the console is on its own circuit, one with no dimmers of any kind on it. That means knowing everything on the console's circuit.  This may fix the problem or only help a bit.  I did something similar a few months ago and removed 60Hz from a console: just traced the circuit and removed a few string lights with noisy dimmers.  2) I believe some dimmer types are 'electrically noisier' than others.  Light dimmer tech has changed a bunch in the last decade to deal with LED lights. 

Someone more knowledgable than I will hopefully chime in.

Mike Caldwell:
Hunting the lighting dimmer noise needs to be done, check power circuits for proper grounding.
For your production lighting check and see if the load is somewhat balanced between phases on the building's power service.

For the live stream chances are even aside from the dimmer issues you are going to need transformer isolation between the sound system audio output and the audio input on the ATEM.
Keep in mind the audio inputs on the ATEM are 3.5mm stereo inputs, you can not directly take a balanced line straight through hardwired cable as in an XLR to 3.5mm TRS plug and have it work properly.

Brian Jojade:
The type of dimmer being used definitely matters.  Cheap dimmers will create massive amounts of hash on the line and can induce noise anywhere nearby.

With that type of dimmer, there's pretty much nothing that can be done to completely eliminate the mess, all you can do is try to reduce it to a tolerable level.  Make sure you're on separate circuits, and all audio lines are kept as physically far away from any circuits with dimmer loads on them as possible.

The proper solution would be to replace the dimmers with ones that don't create hash on the line, but this can get pretty expensive pretty quickly.

Working 60hz hum issues can be very challenging and elusive.  I go back to the days of dance clubs with magnetic phono cartridges.  Recent noise experience that I had to troubleshoot came through the HF amp in a 3 band or tri-amped sound system that's on my computer for the studio monitors.  In the end, the issue was the midrange amp caused a hum in the HF amp.  Solution was to replace the HF amp that didn't pick up noise from the midrange amp.  It wasn't so much the midrange amp was dirty and emitting ground loop or noise, but the HF amp was sensitive to it and the new amp isn't.  The old amp was a mid 90's Carver TFM-6CB and the new amp is a ART SLA-1.

I learned a little about processing and amplifiers being sensitive to electrical noise doing some automotive audio system installs and alternator noise.  Sometimes it's the alternator/regulator, the battery, the wiring and other times its the equipment itself.

Good luck with it.


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