Pa system diagnosis

eclecto-acoustic

Coal-hating feral hippie
Platinum Supporting Member
Messages
10,676
Hey folks,

Our church PA is slowly getting to the point where we can stop worrying about problems...slowly.

The issue we are getting is a random, yet regular, buzz that goes through everything. Like...everything.

Equipment list:

Mackie DL1608 w/iPad2
Peavey SP mains and amp
Phonic amps for monitors and sub
Behringer passive floor wedges
Samson Q7 mics
Line 6 wireless system for lapel mic
Shure wireless system for handheld

Watching the meters on the iPad, I can see spikes in noise every so often even in muted channels. Only unplugged channels are free from it. Otherwise, it hits everything.

Now, supposedly the building was wired so that all of our audio equipment (outlets in the booth and on stage) is on the same circuit, which I assmue means the same ground.

This isn't a constant ground loop hum...just periodic buzzing, maybe a little higher than your typical 60Hz.

Ideas?
 

Rex Anderson

Member
Messages
5,087
We had the same problem in our Performing Arts Center. It was not there for years and then one day started happening. I didn't work there on a regular basis, but the guy who did said it drove him crazy.

I think they finally tracked it down to something in the building that cycled on and off, a pump or part of the HVAC system.

A good electrician needs to help find your problem.
 

buddaman71

Student of Life
Gold Supporting Member
Messages
12,900
Light dimmers are VERY often the culprit in this scenario. Failing ballast in fluorescent lights, HVAC and commercial fridge/freezers kicking on and off are common too.
 

wpawley

Member
Messages
799
Sounds like something cycling on and off. Look to the air handler system or a fridge/freezer. If is it a random thing (as in it doesn't do it on a regular schedule) that is where I would look. Sometime when the church is not in use, turn out the lights, turn on the PA and see if it still does it. Rule out one thing at a time.
 

mattball826

Senior Member
Messages
20,810
did you try a different (perhaps analog) mixer?

best method is isolate and substitution to find the culprit.
 

dporto

Member
Messages
760
If it's "line noise" analog or digital won't/shouldn't make a difference. As was suggested above you have to try to 1) isolate the source of the noise 2) once the source of the noise is determined, figure out how to isolate it from your sound system. The simplest method would be to shut off all the breakers in the main electrical panel except the one that your system is on. Is the noise still there? Make sure you listen for a period long enough to determine if it's cycling on and off. If the sound system remains quiet (which it should if the culprit isn't on the same circuit) part 1 of your test is complete. Turn on 1 circuit at a time and listen for noise/buzz. Once again you'll have to listen long enough to give the offending culprit time to cycle if it's an intermittent thing. Once you've determined that a circuit is "quiet", shut it off and move on to the next one. If you repeat this procedure throughout the entire panel, you should be able to identify the offending circuit and/or piece of equipment. Once the origin is identified an appropriate plan of attack to get rid of the noise can be formulated.
 

Crowder

Dang Twangler
Messages
19,072
I agree with the idea that something outside the system could be causing it. At the same time, you have an awful lot of consumer grade wireless mics. You might cycle those off and on individually to see if you can recreate the noise.
 

BBN

Member
Messages
15
Even if the dimmers are full bright and not on the same circuit?
Yes, even if they're on a different circuit.

If you have time to trouble shoot, turn the system on and wait until the issue occurs. If you don't recognize a freezer or something that just turned on, then have someone stand at the circuit breaker panel and have them turn off circuits until you hear the buzz go away.....you found your culprit.
 




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