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Author Topic: ground loop woes  (Read 882 times)

Don T. Williams

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Re: ground loop woes
« Reply #10 on: August 16, 2017, 05:07:32 pm »

I have nothing against EbTech gear, and those may solve your problems.  My only caution is to make certain the transformers/isolators will handle line level signals of at least +4.  I know Radial makes units that handle  +18.

I once had customers that bought a pro quality graphic EQ.  After the first weekend they used the graphic, they brought it back demanding a refund and complaining that it distorted horribly.  A test in the shop showed the EQ worked perfectly.  They tried it on their next gig and had the same problem.  It turns out the customers were using Radio Shack mic transformers to "convert" the XLR balanced EQ ins/outs for use with their 1/4" mixer outs and power amp inputs.  It did sound horrible!  Those transformers were only good for a bout a -30 level.
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dick rees

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Re: ground loop woes
« Reply #11 on: August 16, 2017, 05:14:08 pm »

I have nothing against EbTech gear, and those may solve your problems.  My only caution is to make certain the transformers/isolators will handle line level signals of at least +4. 

No worries.  They'll handle it.  It's what they're made for.
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Jerome Malsack

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Re: ground loop woes
« Reply #12 on: August 16, 2017, 07:04:11 pm »

Also check and see if the xlr line level pin 1 and the body of the xlr are connected.  This may also be adding to the problem. 
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Paul Graves

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Re: ground loop woes
« Reply #13 on: August 16, 2017, 08:48:52 pm »

Thanks so much for the help  people! I am a pro musician but the live sound side of it not so. I came to the right place.
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Mike Sokol

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Re: ground loop woes
« Reply #14 on: September 12, 2017, 08:14:00 am »

No worries.  They'll handle it.  It's what they're made for.

I use the Ebtech Hum Eliminators all the time for exactly this sort of situation and they work perfectly. They're 600:600 ohm isolation transformers so there's very little (fraction of a dB) insertion loss. Note that you can also use a simple clamp ammeter around the outside of any XLR signal cable to identify ground loop currents. Hum in speakers with the pin-1 problem usually starts at around 50 mA of ground loop current on the shield, and that's easily identified with a $50 clamp ammeter.

Don T. Williams

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Re: ground loop woes
« Reply #15 on: September 12, 2017, 10:55:34 am »

Note that you can also use a simple clamp ammeter around the outside of any XLR signal cable to identify ground loop currents. Hum in speakers with the pin-1 problem usually starts at around 50 mA of ground loop current on the shield, and that's easily identified with a $50 clamp ammeter.
+1 on that tip Mike.  I never thought of doing that, but I'm gonna try it!
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Kevin Graf

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Re: ground loop woes
« Reply #16 on: September 12, 2017, 12:16:03 pm »

With XLR interconnects, try shield connected at the send ends, but open at the receive ends.
Rather than hacking long cables, just make two short adapter cables.
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Mike Sokol

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Re: ground loop woes
« Reply #17 on: September 13, 2017, 12:33:41 pm »

+1 on that tip Mike.  I never thought of doing that, but I'm gonna try it!

Like so. Because the ground loop return current is through the electrical system ground, and not in the twisted pair inside the cable, you don't have to do any sort of breakout or split to separate the shield from the twisted pair. Just clamp the ammeter around the entire cable and you'll see if there's any ground loop currents.
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