Speaker hum

[ram11379]

So there is not a perfect place to post this topic so I figured here is a good spot. I am wiring a church and they wanted a high end a/v system($100,000 give or take) I did all the wiring for the a/v company as per there specs and they were very satisfied with the quality.

I even ran a new sub panel for only a/v usage off the existing main panel to elimintate noise. All was well untill I was working late tonight and it was quiet because I was only one there and I noticed a hum from 2 main speakers. Then when I turned on the lights I just installed(yes with a dimmer) the noise got pretty loud. Like I said new panel and the lighting circuit is not in any way related to the audio circuits.

A ground loop is I'm sure the first thought, but should I be getting this even though I ran a new 60 amp 240v 4 wire from the main panel? Or should I have ran the ground to a new rod outside? I am a little out of my area of expertise in this so I would appreciate everyones thoughts. Thaks in advance.

 

[zbang]

The separate panel has nothing to do with it, I can make a nasty ground-loop hum with battery-powered gear. IMHO it's really the sound company's problem.

 

[StephenSDH]

Dimmers are generally poor power quality devices. The noise can be induced onto the lines instead of traveling back through the mains. Perhaps you could use a different dimmer, or apply a choke to the dimmers to reduce the rate of rise of the switching transistors. If you add a choke it will remove the noise.

Lutron makes chokes.

Model Rated Capacity
LDC-10-TCP 600-1200W
LDC-16-TCP 1200-1920W

http://www.lutron.com/applicationnotes/360283.pdf


http://www.epanorama.net/documents/lights/lightdimmer.html.old

 

[ram11379]

Dimmers are generally poor power quality devices. The noise can be induced onto the lines instead of traveling back through the mains. Perhaps you could use a different dimmer, or apply a choke to the dimmers to reduce the rate of rise of the switching transistors. If you add a choke it will remove the noise.

Lutron makes chokes.

Model Rated Capacity
LDC-10-TCP 600-1200W
LDC-16-TCP 1200-1920W

http://www.lutron.com/applicationnotes/360283.pdf


http://www.epanorama.net/documents/lights/lightdimmer.html.old

I did run seperate neautrals to the dimmed fixtures. So I did not think a choke was necessary.

Does anyone think the problem could be solved with isolating the ground for the a/v sub panel and running it to its own ground rod, or is this futile as the neutral would still be running to the main panel?

I am feeling(as the other poster stated) that the a/v guys most likely will have to fix the problem as well, but if there is anything that I can do I would like to.

BTW all the lines are all seperated in pipe and only run with like wires in each pipe, so that is not an issue.

 

[mivey]

Any details on the specs? Did you maintain spacing between parallel audio and power runs, make crossings at 90 degrees, shielded cables, balanced connections, use shielded snake for long runs, isolate XLR shells from pin 1, separate speaker and mic cables, use twisted speaker cables for open runs, don't coil excess cable lengths, etc.

Is all the equipment powered from the same source (people like to "cheat" after you finish). Have you stepped through the equipment to see if one is guiltier than the rest?

You said the hum was there before the lights were on so I suspect it is not just a dimmer problem.

 

[ram11379]

So like I said it was late last night when I noticed this and I was a little burnt out so today I went in with a fresh head and I figured it out. Ready for this one... The problem was somebody decided that if we arent using the audio equipment we should just shut the breaker off when we leave! Yup you got it there was no power to the amp!! The speaker power is on a seperate breaker so they were just sitting there powered on with no amp controling them. With the amp on there is no hum at all with or without the lights on.

So thanks for everyones help on this anyway. I figured as stupid as I feel for not checking the power first I would still share it with you folks for helping me.

 

[mivey]

Glad you figured it out. Thanks for the follow-up.