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Author Topic: Audio cables to amps don't have grounds  (Read 2085 times)

A.J. McGlynn

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Audio cables to amps don't have grounds
« on: November 23, 2008, 10:16:44 am »

Ok, so I had my system installed a year ago. And this week I had  problem with one of my amps that is not related to my question (known issue with Crown XTI) I was troubleshooting the problem and I pulled the connector off the audio cable to one of my amps and noticed that the ground was missing. I then looked at other cables and they too had the grounds missing.

Some background on the system. The signal comes from my M7 then to UX8800 then to my amps. The cables are custom made install cables that my installer made.

Is this normal practice for installers? I have never made a cable that way and never tried it with the ground and I have to admit that I don't know enough about grounds to know if this is a problem. The system sounds fine, no hum no buzz or anything. Should I have my installer come back in and solder the grounds or should I take the attitude "if its not broke don't fix it"?

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A.J. McGlynn, Technical Director
Grace Church
Erie, PA

Mac Kerr

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Re: Audio cables to amps don't have grounds
« Reply #1 on: November 23, 2008, 11:24:59 am »

Since it's working fine, I don't think you need to change it, but you should look at the other end of those cables to see if they have pin 1 connected on that end. Line level drive lines will probably be OK without a shield, which is what you have if neither end has pin 1 connected, but if it is shielded cable, why not gain the RFI benefit of the shield? You only need 1 end connected to pin 1 to create a ground path for the shield.

Mac
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A.J. McGlynn

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Re: Audio cables to amps don't have grounds
« Reply #2 on: November 23, 2008, 11:32:44 am »

Thank you, I will check the other ends and check pin 1. I appreciate the help. I wanted to get some info here before I went to my installer.

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A.J. McGlynn, Technical Director
Grace Church
Erie, PA

Brad Weber

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Re: Audio cables to amps don't have grounds
« Reply #3 on: November 23, 2008, 12:44:27 pm »

As a way to address many devices that do not ideally address the signal ground themselves, it is fairly common practice to drop the shield at the input end of the cable.  As Mac noted, it should be connected on the other end.  As more devices are manufactured to be AES 48 or "pin 1" compliant in how they address the ground path and to take it direct to the chassis rather than through the electronics, then this less than ideal approach will no longer be needed.
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Brad Weber
muse Audio Video
www.museav.com

Ivan Beaver

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Re: Audio cables to amps don't have grounds
« Reply #4 on: November 23, 2008, 02:22:59 pm »

Our standard install pracitice is to hook the shield up at the output device and lift it at the input.  This is to help avoid ground loops.  About 1 in 200 installs (or less)does this present a problem.  I would rather trace down that number than going ahead and hooking the shield up and have to trace a much larger number of hums.

I would not worry.

You still have a ground as long as your power cable ground is in place.
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Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
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