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Author Topic: ground loop woes  (Read 1172 times)

Paul Graves

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ground loop woes
« on: August 15, 2017, 05:08:07 pm »

Our setup:

X32 and an analog mixer located in different places and different AC circuits.

Two large powered speakers with built in two channel mixer, each again different AC circuits

Impossible to get all on one or even two AC circuits.

Each mixer has its Left and Right connected to the powered speakers.
I am fairly certain it is ground loop causing hum, I ran some tests connecting and disconnecting and actually I believe there are several loops. Don't want to expose or person or  the equipment to risk of damage by doing something stupid.

Solutions I am considering .
1) Putting a isolation transformer each XLR cable feeding the powered speakers.
2.) Using a barrel ground lift on each XLR cable feeding the powered speakers/


Any thoughts or experience and also what would be best with our new Behringer X32 rack?

Thanks,
Paul
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Re: ground loop woes
« Reply #1 on: August 15, 2017, 06:13:47 pm »

It might help to use one mixer foor the feed and the other as a sub-mixer via the main mixer.  X-32 would do for the main mixer and let you use more of the processing power over the entire setup.  Scenes, user permissions, etc. as well as fewer points to isolate.
« Last Edit: August 15, 2017, 06:51:13 pm by dick rees »
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Mark Cadwallader

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Re: ground loop woes
« Reply #2 on: August 15, 2017, 06:41:46 pm »

Option #1 is my vote (of the two).
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Don T. Williams

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Re: ground loop woes
« Reply #3 on: August 15, 2017, 06:47:06 pm »

Radial Engineering and other companies (Sescom and Whirlwind I think) make combining transformers that will isolate the two mixers from each other.  In my opinion, the use of one of these transformers is probably the best and easiest solution. 

The other possible solution would be to feed the two mixers into a third mixer's line level inputs.  The third mixer would actually send the signals to the loudspeakers, but this increases the chance of a ground loop because you are adding more possible places for a ground loop to occur.  A mixer with transformer inputs and outputs would be preferable, but you will still probably have to lift grounds (a combination) to get rid of the hum.
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Keith Broughton

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Re: ground loop woes
« Reply #4 on: August 15, 2017, 07:15:53 pm »

Option #1 is my vote (of the two).
My vote is for #1 too
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Paul Graves

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Re: ground loop woes
« Reply #5 on: August 15, 2017, 07:36:23 pm »

My vote is for #1 too

The mixers are far from one another really can't connect them
Thanks!  Here  is a schematic. I am leaning towards (2) two channel Ebtech  Humbuster ISO transformers as shown in the schematic. Is an Ebtech a good choice in the reasonably priced ones?
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Re: ground loop woes
« Reply #6 on: August 15, 2017, 07:53:20 pm »

I have a few EbTech HE-2-XLR's I use for interfacing various systems as needed.  You could use them at the two mixers directly after the output and not have to have single channel units in the middle of the runs. 
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Paul Graves

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Re: ground loop woes
« Reply #7 on: August 15, 2017, 08:05:34 pm »

I have a few EbTech HE-2-XLR's I use for interfacing various systems as needed.  You could use them at the two mixers directly after the output and not have to have single channel units in the middle of the runs.

Yes, that is exactly what I was thinking putting that same EbTech unit in each equipment rack with a short cable to L/R out of mixer then on to each speaker. Do you notice much loss of signal with these EbTechs? Do you find they remove the hum effectively?
« Last Edit: August 15, 2017, 08:07:54 pm by Paul Graves »
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Re: ground loop woes
« Reply #8 on: August 15, 2017, 08:18:33 pm »

Yes, that is exactly what I was thinking putting that same EbTech unit in each equipment rack with a short cable to L/R out of mixer then on to each speaker. Do you notice much loss of signal with these EbTechs? Do you find they remove the hum effectively?

You shouldn't lose any signal through the transformers. 

I'm curious, though, as to how this layout came to be and how it's used.  Something just doesn't feel right...
« Last Edit: August 15, 2017, 08:31:31 pm by dick rees »
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Paul Graves

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Re: ground loop woes
« Reply #9 on: August 15, 2017, 08:55:29 pm »

You shouldn't lose any signal through the transformers. 

I'm curious, though, as to how this layout came to be and how it's used.  Something just doesn't feel right...

The layout is really a result of budget. The old mixer and speakers came first and are used for the existing permanent install of lectern mic, choir mics and wireless pastor mics. Then cames the new digital mixer to add a band since our church is moving towards contemporary music and a new mixer was needed, so we got a digital one. Ultimately the old analog mixer will go and we probably relocate the digital mixer in place of the old analog and add a digital snake or two.
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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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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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