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Author Topic: Ground Loops and Tester  (Read 9034 times)

Kevin Graf

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Ground Loops and Tester
« on: December 26, 2013, 02:14:54 pm »

Ground Loops and Tester

A recent Belden Blog article:
'Ground Loops'
Posted by: Steve Lampen on November 12, 2013

****************************
From above blog a link to a rather expensive Ground Loop tester:
http://www.loopslooth.com/index.html

The 'Tutorial on Interference'  and 'Scientific Article' are interesting:
http://www.loopslooth.com/Tutorial-intro.html
http://www.loopslooth.com/Article.html
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Mike Sokol

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Re: Ground Loops and Tester
« Reply #1 on: December 26, 2013, 02:23:23 pm »

Ground Loops and Tester

A recent Belden Blog article:
'Ground Loops'
Posted by: Steve Lampen on November 12, 2013

****************************
From above blog a link to a rather expensive Ground Loop tester:
http://www.loopslooth.com/index.html

The 'Tutorial on Interference'  and 'Scientific Article' are interesting:
http://www.loopslooth.com/Tutorial-intro.html
http://www.loopslooth.com/Article.html

Wow, doesn't look too simple. I have a way to accomplish the same thing with a $50 clamp ammeter and a hair drier or space heater load. Of course, my method doesn't look quite so fancy with an o-scope and everything else.

I'll see if I can write up my ground loop test procedure in a few weeks and publish a link here. Then you guys can try it for yourself and offer any suggestions on how to make it better. 
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Greg_Cameron

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Re: Ground Loops and Tester
« Reply #2 on: December 26, 2013, 02:25:43 pm »

The thing is, ground loops exist everywhere and are inherent due to the nature of AC wiring. The problem in our world is when those loop currents induce noise into the audio interface due to improper circuit design. I don't see how these devices are going to help since you cannot eliminate ground loops in AC wiring. They only tell you what we already know to be true. You can "induce" ground loop current into any AC system when applying an AC inductive field around any ground conductor. The issues is preventing it from being rectified into audible noise in the audio circuit. These devices won't help with that.
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Cameron Pro Audio

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Re: Ground Loops and Tester
« Reply #3 on: December 26, 2013, 02:34:13 pm »

The thing is, ground loops exist everywhere and are inherent due to the nature of AC wiring. The problem in our world is when those loop currents induce noise into the audio interface due to improper circuit design. I don't see how these devices are going to help since you cannot eliminate ground loops in AC wiring. They only tell you what we already know to be true. You can "induce" ground loop current into any AC system when applying an AC inductive field around any ground conductor. The issues is preventing it from being rectified into audible noise in the audio circuit. These devices won't help with that.

Greg, in fact you can eliminate ground loops due to double-bonded G-N connections in sub-panels, which are a violation of the NEC. The fix can be as simple as taking out the green "bonding" screw which didn't belong there to begin with, and sometime installed by electricians and inspectors who don't know any better. Also, adding audio isolation transformers between gear will eliminate all ground loop currents and hum.

Also, ground loop hum is not "rectified" in the electrical sense of the word, but it is "coupled" magnetically or sometimes resistively inside gear with the pin-1 problem (which is sadly a lot). I speak from a lot of experience since I have a ground-loop maker which consists of a Glo-Melt resistance soldering transformer good for 3 volts and 40 amps output. I can create ground loop currents and measure the hum at will. So in the last few years of playing with this I've found a lot of new ways to measure and eliminate ground loop.

But more on this later. I'll detail my experiment then and provide data for all of you to review.
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John Roberts {JR}

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Re: Ground Loops and Tester
« Reply #4 on: December 26, 2013, 02:54:39 pm »

Greg, in fact you can eliminate ground loops due to double-bonded G-N connections in sub-panels, which are a violation of the NEC. The fix can be as simple as taking out the green "bonding" screw which didn't belong there to begin with, and sometime installed by electricians and inspectors who don't know any better. Also, adding audio isolation transformers between gear will eliminate all ground loop currents and hum.
This is not an audio signal integrity issue. Outlet grounds are purely for human safety in case of faults. Single ground neutral bond at panel is again a safety consideration wrt to open neutral "and" open ground faults.
Quote
Also, ground loop hum is not "rectified" in the electrical sense of the word, but it is "coupled" magnetically or sometimes resistively inside gear with the pin-1 problem (which is sadly a lot). I speak from a lot of experience since I have a ground-loop maker which consists of a Glo-Melt resistance soldering transformer good for 3 volts and 40 amps output. I can create ground loop currents and measure the hum at will. So in the last few years of playing with this I've found a lot of new ways to measure and eliminate ground loop.

But more on this later. I'll detail my experiment then and provide data for all of you to review.
Giving this some thought I speculated about testing for this with a HF signal to hopefully differentiate between a local G-N bond and distant G-N bond due to inductance.

Hopefully pin 1 issues are slowly going away as older legacy gear gets replaced.

JR
 
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Greg_Cameron

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Re: Ground Loops and Tester
« Reply #5 on: December 26, 2013, 03:19:01 pm »

Greg, in fact you can eliminate ground loops due to double-bonded G-N connections in sub-panels, which are a violation of the NEC. The fix can be as simple as taking out the green "bonding" screw which didn't belong there to begin with, and sometime installed by electricians and inspectors who don't know any better. Also, adding audio isolation transformers between gear will eliminate all ground loop currents and hum.

Agreed you reduce ground loop currents by eliminating double bonding, but the devices linked to here don't appear to be checking for that issue.


Greg, in fact you can eliminate ground loops due to double-bonded G-N connections in sub-panels, which are a violation of the NEC. The fix can be as simple as taking out the green "bonding" screw which didn't belong there to begin with, and sometime installed by electricians and inspectors who don't know any better. Also, adding audio isolation transformers between gear will eliminate all ground loop currents and hum.

Also, ground loop hum is not "rectified" in the electrical sense of the word, but it is "coupled" magnetically or sometimes resistively inside gear with the pin-1 problem (which is sadly a lot).

Yes, wrong terminology. Rectification to the audio band can occur with RF signal infiltration. Not ground loops. My mistake.

Greg
« Last Edit: December 26, 2013, 03:21:51 pm by Greg Cameron »
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Mike Sokol

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Re: Ground Loops and Tester
« Reply #6 on: December 26, 2013, 04:04:25 pm »

Giving this some thought I speculated about testing for this with a HF signal to hopefully differentiate between a local G-N bond and distant G-N bond due to inductance.

I have a B&K 309 Ground Resistance Tester which does a Fall of Potential test using a higher than line frequency signal (600 Hz, I think) so it can be used on an live ground rod without having to power down. I suspect these guys are doing something similar. Also, I used to do resistance tolerance testing using a Kelvin bridge and a DC supply. But there's nothing to stop you from using any AC signal you like instead of a DC current source. You could use ultrasonic or even into the low RF range if you like, I think. But I'm not sure of the advantage of a higher frequency except to be able to gather data without shutting down a system. Got to think about this some more though.

Quote
Hopefully pin 1 issues are slowly going away as older legacy gear gets replaced.

My tests with current Mackie and Behringer active floor wedges suggests that the pin-1 problem is still alive and thriving in modern equipment. That's a shame since it causes so much grief in typical installations, and it's not terribly difficult to eliminate with proper design.

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Mike Sokol

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Re: Ground Loops and Tester
« Reply #7 on: December 26, 2013, 04:19:23 pm »

This is not an audio signal integrity issue. Outlet grounds are purely for human safety in case of faults.

I agree, but my real problem with ground loops is that it makes musicians and engineers do crazy things to stop the hum, such as cutting off the safety ground pins on power cords and ground-lifting rack gear using those $1 ground eliminators from the big box stores. One of the churches I was in last year had the ground pins cut off of EVERY extension cord and quad box in the place. They warned me not to touch any microphone while leaning on the brass rail around the edge of the stage or I would get a "good shock". I measured around 100 volts from the PA system "safety ground" to actual earth potential. Yikes!!!

They claimed that was the only way to stop the PA system hum, but they created a death trap in the process and thought nothing of it.

On a slightly different tact I had a Tel-Com student at Ball State University tell me her parents had a refrigerator in the basement with a "messed up ground". She said you would get a shock if you touched the refrigerator door while standing on the concrete floor. Their fix was the "jump in the air" while opening the door so as not to get shocked (no kidding). When I told her she needed to fix it before an unsuspecting repair guy or visitor was electrocuted, she told me it had been like that for years and "everybody" knew not the touch the refrigerator. I see and hear crazy stuff like this all the time.

IMHO Ground Lift Adapters are EVIL...

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John Roberts {JR}

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Re: Ground Loops and Tester
« Reply #8 on: December 26, 2013, 04:29:01 pm »



My tests with current Mackie and Behringer active floor wedges suggests that the pin-1 problem is still alive and thriving in modern equipment. That's a shame since it causes so much grief in typical installations, and it's not terribly difficult to eliminate with proper design.
That is disappointing.. I used to manage an engineering group and new engineers are not born (or graduated) with full knowledge, but engineering management should know this stuff and inform them.

JR
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Mike Sokol

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Re: Ground Loops and Tester
« Reply #9 on: December 26, 2013, 04:29:56 pm »

Yes, wrong terminology. Rectification to the audio band can occur with RF signal infiltration. Not ground loops. My mistake.

But I think you might be right about rectification for switch-mode ballasts in some new lighting technologies. I did a gig in a church a few years ago with some sort of modern arc lights in ceiling pots. They generated so much broad-band RF that my wireless mic receiver would do a full level noise burst whenever the  belt pak RF was turned off or experienced a drop-out when I walked too far from the antenna. We proved the lights were doing it by shutting them all off with the RF problem going away. Now, I didn't experience any other RF ground loop issues that I know of, but now I'm going to be on the lookout for them. Also, as I'm sure you know, any corrosion on a ground/shield connector can act like a radio detector (rectifier) and demodulate AM radio stations near your sound system. Been there, and got the t-shirt (from the radio station).   

Gosh, now I've got to worry about RF ground loop rectification. When does it all end?
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Re: Ground Loops and Tester
« Reply #9 on: December 26, 2013, 04:29:56 pm »


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