Sound guy needs "positive ground"

[luke warmwater]

Re: Sound guy needs "positive ground"

I have a sound company also. And my best friend has a sound company and he also wires churches for sound systens.

I agree with Wayne's post.

We just did a live sound job where they supplied us with power. One cord had substantial noise on the ground. We ended up taking half of our power from the tour bus PTO generator, and problem was solved.

 

[james wuebker]

Re: Sound guy needs "positive ground"

Things what I've seen are mostly ground loops in the system. A fast way to check this is run a power cord from mixer equipment area. Use this cord for the power you need for the sound board and all other process equipment. Now get power from were your feeding your power amps so everything is on the same grounding path & circuit. If problem goes away you now know there's a ground loop in the system. If it does help, take away all lighting circuits from the picture.(All power off to them). Dimmers could be causing the buzz. Very fast to do. If this doesn't solve the problem unhook all inputs that are to each channel of the board. If buzzing goes away then you will know that's it's in your snake cable. Insert input cables one at a time back to each channel until you get your buzz back then you know what cable is bad. These are some fast ideas to check that wouldn't take to much time.
Bye now,
Jim

 

[milwaukeesteve]

Re: Sound guy needs "positive ground"

Question for the sound experts(and thank you for your valuable insight):
Rattus mentioned dimmers, but what about TVSS's? Some the newer TVSS's limit overvoltages(not just surges), and are set very tight to normal operating voltages, to help reduce electric consumption. Do these TVSS's if mounted to the audio supply panel, or to the main panel (or switchgear) cause interference? Or has anyone had that problem?

 

[rick hart]

Re: Sound guy needs "positive ground"

TVSS will not do a thing for this problem.
A dimmer works by taking a bite out of the AC waveform, well below the clamping threshold of a TVSS.

 

[Tim Backer]

Re: Sound guy needs "positive ground"

While you as an EC shouldn't have to deal with this, there are two easy tests the 'sound guys' can do to narrow the scope of these issues...

1. Disconnect their mix position gear from the snakes / amps that are at the other end. Use a small amp or headphones at the mix position and turn up the gains on things. No buzz there, then no dirty power (at the mix position).

2. Do the same thing at the amps at the other end of the house - pull the inputs off and turn up the gain. No buzz in the system speakers, no dirty power.

3. It's considered standard practice in sound installations where a balanced, shielded line between two pieces of active (powered) gear only has the shiled connected to the end of the cable feeding an input. In this case, the ends of the cables feeding the amp inputs should have +, -, and shield connected. The other end of the same cables at the mix position should have the shield wire snipped / disconnected and only the + and - wires connected.

If these things are done, the only thing remaining is hum induced into microphone cables that are either too close / parallel to AC wiring, poorly shielded cables (cheap ones have thin shielding), or both.

Two cents from a broadcast engineer soon to be EC helper (God help us all )

 

[robcircuits]

Re: Sound guy needs "positive ground"

More quick tests...

1 - disconnect ALL inputs to console
2 - plug in a CD player at the console and test for normal system operation
3 - play CD at a loud level
4 - without moving any gain knobs/ faders,
stop (not pause) the CD player
5 - at that operating gain, is there any (unacceptable) noise?
6 - if not, then the problem is restricted to your mic lines - probally induced noise from stray EM noise
7 - if objectionable noise still exists, temporially disconnect (float) pin #1 at the input to the first processor at the "far" end (amp rack - this could be a crossover, eq, limiter, or power amplifiers, depending on system layout)
8 - if this solves the problem secure the floated grounds so they remain floated

Assumptions: all mic input lines are balanced, all console outouts to the far end are balanced, all (primary) console input and output cables are shielded, and pin #1 is tied to shield/ drain wire at both ends, and the mic input box/ panel is in no way connected to electrical power ground, and the initial test was performed without anything plugged into the mic box, and probally not last or least... you are NOT located next to a radio station transmitter or power transformer farm or industrial complex.

 

[charlie tuna]

Re: Sound guy needs "positive ground"

we had a similar problem in a movie theater and the sound contractor blamed it on our installation. we isolated power until the only thing energized was his equipment and the buz was still there!!!! we found the problem was caused by one of his amps that was mis-wired from the factory--hot and neutral reversed in the molded plug!!!

it would only cost about nine bucks -- but i would buy this sound guy a ten foot groung rod --- paint it fire engine red and put a "+" on the end with a black magic marker and present it to him in front of the gc!!! and tell what he could do with it!!!

my two john deere's don't even have batteries! they are hand crank!!! 1937 A and a 1937 B!!!