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Author Topic: Weird  (Read 1917 times)

Frantz Mathias

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Weird
« on: April 05, 2016, 10:29:36 am »

Hi

Neophyte here in Sound System but not system integration. We were amateurs, moonlighting in PA system and opportunities came. We have installed a few system without a hitch.
We installed recently a system for a conference Hall. IN the Hall there are 2 wired microphones and 2 line input. Equipment room is about 200 feet from the Hall. Amps are TOA and Automixer is Symetrix. We installed and tested the system and everything appeared to ne OK. We tested the line input from a battery-operated generator.. No problem.. Plug laptop with external M-Audio soundcard analog balanced output and everything went well. We were satisfied and ...

We have to close the contract and on a whim tested the system with a console plugged in an AC outlet inside the Hall... Noise, not exactly hum but a kind of creaking noise with some very slight hum in it...
Could be the console we thought, took a Denon CD player and used the line output .. same
TV? although consumer-line level.. Same
A CD player with Pro-level, XLR output ... Same

Back to the laptop on batteries on XLR balanced and Pro level .. No problem
Laptop with headphones jack ouput to the line level of system .. no problem
iPad on its headphone jack (consumer level) output to line input ... No Problem
Android  cellphone on headphone out ... No problem


Anything plugged on the AC in the Hall will results in the creaking , grizzle type of noise.

What do you think could cause this? How do we solve this issue? Wehre do we begin to look.

We have verified our connections and they're OK no crossed wire.

We thank you in advance. We have completed the installation and the system is to go live in less than a week! Help!

Rastaf
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Ray Aberle

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Re: Weird
« Reply #1 on: April 05, 2016, 10:47:38 am »

Rastaf, Welcome to the Forums! However, before we're permitted to assist you, your Display Name does need to be your Real, Full Name. Would you mind popping back into your profile to update that?

... also, a moderator might move this over to the Lab Lounge; the "Classic Live Audio Board" is primarily aimed at the regional/national providers, touring engineers, mixing Bands You've Heard Of. :)

Thanks! Again, welcome- I hope we can help you work out your problem!

-Ray
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Kelcema Audio
Regional - Serving Pacific Northwest (OR, WA, ID, BC)

Kevin Rudolph

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Re: Weird
« Reply #2 on: April 05, 2016, 07:26:12 pm »

Anything plugged on the AC in the Hall will results in the creaking , grizzle type of noise.

What do you think could cause this? How do we solve this issue? Where do we begin to look.

Sounds like a electrical grounding issue.

Verify that all equipment is properly grounded, both in equipment room and in hall. 

It's not uncommon in a banquet hall install, especially in your instance with the equipment room 200' away, that the AC may be from a different electrical service panel. This can result in a ground loop inducing noise like you are describing.

You are going to need some kind of inline 1:1 isolation transformer, maybe in the form of a direct box with a ground lift switch or something more discreet that you can wire in permanently in the install rack.

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duane massey

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Re: Weird
« Reply #3 on: April 06, 2016, 01:37:44 am »

If everything is balanced, lift the ground on one end of the cable.
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Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

Frantz Mathias

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Re: Weird
« Reply #4 on: April 06, 2016, 07:03:57 am »

If everything is balanced, lift the ground on one end of the cable.

We will do that today and report. AN electrician friend has seen such issued and his experience is that they were due to improper grounding at the AC.
We'll try any suggestion. IN the meantime please keep posts coming.
Thanks
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David Allred

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Re: Weird
« Reply #5 on: April 06, 2016, 09:12:46 am »

We will do that today and report. AN electrician friend has seen such issued and his experience is that they were due to improper grounding at the AC.
We'll try any suggestion. IN the meantime please keep posts coming.
Thanks
I don't think he is recommending that you eliminate electrical grounding, but rather the shield (ground) on a balanced audio signal cable.
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ProSoundWeb Community

Re: Weird
« Reply #5 on: April 06, 2016, 09:12:46 am »


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