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General Audio All things about sound are discussed here.

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Old Sunday, January 15th, 2012, 02:12 PM
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Ground loop

I have a ground loop buzz in my video cameras.

Connections at the camera
1. xlr audio input from the mixer
2. video output rca to video mixer
3. firewire video output to computer

The buzz comes in when the xlr in and either 1 of the outputs is connected.

1 camera is on the same circuit as all the foh equipment, which is a dedicated circuit for foh
The 2nd camera is on a separate circuit, and is by itself on that circuit. The buzz is also worse in that camera.

I've taken some basic steps like placing a humx on the mixer and video recording computer. No help. A Rapco isolation transformer on that line from the mixer helps a little. I've also just started, this week, getting a buzz on 1 of the 3 stage monitor auxes.

The cd recorder also had a buzz for a while, but a few weeks ago suddenly stopped. It has it's own aux line separate from the video cameras.

I'm not sure what the best next step is. Should I place the foh circuit on an isolated ground? Is there a better/easier solution?
thanks
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Old Sunday, January 15th, 2012, 07:00 PM
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Sound circuit should be isolated from everything else. Any other fix is chasing your tail.
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Old Sunday, January 15th, 2012, 09:17 PM
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Leaving the cameras on a different circuit from the foh booth or on the same?
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Old Sunday, January 15th, 2012, 11:15 PM
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First step would be to transformer isolate the XLR feed from the console.
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Old Sunday, January 15th, 2012, 11:52 PM
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Do you also have sound from the sound mixer to the video recording pc?
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Old Monday, January 16th, 2012, 07:43 AM
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Tim: Sorry I wasn't clear. I put a Rapco isolation transformer on the xlr feed from the mixer to the cameras.

Borg: There is no direct connection from the mixer to the PC. The computer gets video and audio from the firewire connection.
Thanks
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Old Friday, February 24th, 2012, 10:19 PM
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Quote:
Originally Posted by bbrunskill View Post
Sound circuit should be isolated from everything else. Any other fix is chasing your tail.
Nonsense. We do not know enough from what he has said to prescribe a certain fix.
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Old Friday, February 24th, 2012, 10:31 PM
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Quote:
Originally Posted by unc417 View Post
Tim: Sorry I wasn't clear. I put a Rapco isolation transformer on the xlr feed from the mixer to the cameras.
The Rapco transformer is a very cheap transformer without any faraday shield between the windings. Sometimes a cheap transformer will provide enough isolation to do the job, but often it will not. A Jensen Iso-Max is expensive but provides vastly better isolation.

Before you go buying stuff, follow the step by step instructions in the "Generic Seminar Notes" on the Jensen Transformer website (sorry the system will not allow me to post a URL).
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Old Saturday, February 25th, 2012, 06:52 AM
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Quote:
Originally Posted by Ray A. Rayburn View Post

Before you go buying stuff, follow the step by step instructions in the "Generic Seminar Notes" on the Jensen Transformer website (sorry the system will not allow me to post a URL).
http://www.jensen-transformers.com/a...%20seminar.pdf

Good read

Frank
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Old Sunday, March 25th, 2012, 10:52 PM
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Disconnect pin 1 on the XLR cable where it goes into the camera.

That will break the ground loop.
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Old Monday, March 26th, 2012, 09:16 AM
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Can't believe I didn't think to try that. Thanks
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