# Ground Loop



## FrunkSlammer

Any tips or tricks for tracking down the source of what I think is ground loop noise?

Working on a high end home theatre, and the speakers have a subtle but noticeable annoying buzz in them. A professional A/V guy is doing the project, but has asked for help tracking down the source.

Bootlegged ground(s)? Bonding screw not off in a sub panel? 

I really have few ideas of how to track it down. Won't be back there until next weekend, but want to spend some time this weekend learning about the problem.


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## Semi-Ret Electrician

FrunkSlammer said:


> Any tips or tricks for tracking down the source of what I think is ground loop noise?
> 
> Working on a high end home theatre, and the speakers have a subtle but noticeable annoying buzz in them. A professional A/V guy is doing the project, but has asked for help tracking down the source.
> 
> Bootlegged ground(s)? Bonding screw not off in a sub panel?
> 
> I really have few ideas of how to track it down. Won't be back there until next weekend, but want to spend some time this weekend learning about the problem.


The Ideal Sure Test Circuit Analyzer 61-165 will detect "bootleg grounds" greater than 15 ft to the panel or device.


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## LARMGUY

Hear... nudge, nudge, are some.

http://www.ehx.com/products/hum-debugger



http://www.musiciansfriend.com/pro-...noise-reduction?src=3WBZ4DS&CA_6C15C=65312375


http://www.enjoythemusic.com/superioraudio/equipment/0107/audiophile_tweaks.htm

*I just love the last line of this!*
*Cease and Resist — A "Courting" Order*
So you're introducing that shiny new sexy amplifier to your preamplifier yet something is unhappy. They seem to fight each other day after day and you're not sure what to do. Well, you may wanna see if they're just resisting each others "love vibe." This little ditty below discusses how to enhance your system's love vibe through less resistance.
So here what you need for this ditty:​ 
A multimeter that can measure DC resistance








A few "cheater plugs." Cheater plugs are usually gray and they attach to the male part of an electrical cord. They convert a three prong AC plug into a two prong AC plug and usually have a tab for the ground. They are available at most Home Depots, electrical supply huts, and even Radio Shack (known as Tandy to my European friends). ​ 
What you need to do is file down the larger male prong on the cheater plug so that _both_ prongs are the same height. This way you can reverse the electrical phasing of the electrical plug of your component(s) by using this re-engineered cheater plug.​ 
Next, unhook all your components from each other so that we are _only_ measuring the DC resistance of one component at a time which _is not_ connected to anything else. Please electrically plug in the component you want to test and do the following:​ 
Turn on the product we are testing and give it a few moments to get warm and happy. Set your multimeter to DC resistance and insert one of the test probe to the GROUND of your electrical outlet (the rounder lookin' thing usually on the bottom for us American folks) . Then place the other probe so that it touches one of the OUTSIDE PART of the analogue audio RCAs. Write down the DC resistance your meter says. ​ 
Turn off the component and use the cheater plug to reverse the electrical phase of the component. Turn the component back on and again test the DC resistance. Whichever measurement is _lower_ is usually the best. Now simply repeat this for every component in your music reproduction system.
There are _no_ "hard and fast" rules here so one component may subjectively reproduce music better with higher DC resistance. Like some love affairs, a little more resistance may actually be a good thing! In the end, let your ears decide which electrical phase makes the "love vibe" work. As always, if you have any questions please feel free to e-mail them to me or hire an electrician to do the above tweak. ​ 
*Important*: When in doubt while experimenting with electricity, hire a professional. :laughing:
-------------------------------------------------------------
You can use a signal generator to do this.​ 
Fist, we have all those nasty things that go buzz in the night. A great tool i used in the past was the THX "WOW!" Laserdisc. On one of its tracks is a very slow frequency sweep track. This track is basically a very slow sweep upward from about 10Hz to 100Hz or so. What we are listening for is the resonant frequency of various items in your listening room. This way as each frequency is achieved, one can track down and eliminate the extraneous things that buzz and sympathetically vibrate.​ 
Light fixtures, various furniture, and high-end audiophile components have their own resonant frequency(s) and by lowering their audibility we then may enjoy more music and less buzz and hum! There are times when only a frequency sweep such as the "WOW!" laserdisc contains may allow you to really hear, let alone track down resonating devices.
-----------------------------------------------------------
http://www.enjoythemusic.com/tweaks/​ 


Then there is always the ol ground loop isolator at RS

http://www.radioshack.com/product/index.jsp?productId=2062214


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## FrunkSlammer

Awesomeness!

I'm digging in.


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## five.five-six

Tell him that I said: "You're welcome"

http://www.newegg.com/Product/Produ...eMKP-_-pla-_-Home+Automation-_-9SIA0PG0PC1775


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## Wired4Life10

Usually ground loops in my area are easily resolved by ensuring all components are on the same leg in the panel. If two components are on different circuits on different legs, a loop is guaranteed.


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## FrunkSlammer

five.five-six said:


> Tell him that I said: "You're welcome"
> 
> http://www.newegg.com/Product/Produ...eMKP-_-pla-_-Home+Automation-_-9SIA0PG0PC1775


At that price, it's worth a shot!


Wired4Life10 said:


> Usually ground loops in my area are easily resolved by ensuring all components are on the same leg in the panel. If two components are on different circuits on different legs, a loop is guaranteed.


That doesn't sound good.. all the equipment is fed from a 3wire. :001_huh: And I'm pretty sure the 240V projector comes off a different sub panel.


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## RIVETER

FrunkSlammer said:


> Any tips or tricks for tracking down the source of what I think is ground loop noise?
> 
> Working on a high end home theatre, and the speakers have a subtle but noticeable annoying buzz in them. A professional A/V guy is doing the project, but has asked for help tracking down the source.
> 
> Bootlegged ground(s)? Bonding screw not off in a sub panel?
> 
> I really have few ideas of how to track it down. Won't be back there until next weekend, but want to spend some time this weekend learning about the problem.


Possibly bad caps in the audio system.


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## Wired4Life10

FrunkSlammer said:


> At that price, it's worth a shot! That doesn't sound good.. all the equipment is fed from a 3wire. :001_huh: And I'm pretty sure the 240V projector comes off a different sub panel.


Even if it's on a different subpanel, sometimes ensuring it's on the same leg at the Main will take care of it.


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## FrunkSlammer

But I can't separate a 3 wire (2hots+neutral) on to the same leg, I'll overload the neutral.


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## CyberKnight

I am not sure if this will work but did for me. I had a buzz at times also, I have all components plugged into the same surge protector. I ran a separate jumper ground wire to each components metal case. Then tied them all to the surge protector ground. It took my buzz out but I do not know why. I did not need anymore wires for the system but it worked.


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## drsparky

In a perfect world the service, cable, phone and any antenna all would feed in the same point to a single point common ground buss. Any sub ground points would feed back to that point too.


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## FrunkSlammer

CyberKnight said:


> I am not sure if this will work but did for me. I had a buzz at times also, I have all components plugged into the same surge protector. I ran a separate jumper ground wire to each components metal case. Then tied them all to the surge protector ground. It took my buzz out but I do not know why. I did not need anymore wires for the system but it worked.


Not a bad tip.. all the equipment has terminals for bonding, I'll try bonding everything together and bringing it all back to the the electrical bond. If nothing, I'll try looking for any cross connections of neutral to ground. If nothing, I'll try the cheap feed-thru co-ax ground breaker. If nothing, I'll try a power conditioner.


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## CyberKnight

Let us know if it worked. I am curious.


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## five.five-six

Wired4Life10 said:


> Even if it's on a different subpanel, sometimes ensuring it's on the same leg at the Main will take care of it.


I don't understand how a different leg is going to affect a _ground loop_. The problem is, if it's a ground loop, that there is different equipment with different ground potential. That potential is equalizing over the shield of the analog audio line. A common cause of this differing ground potentil is an improperly grounded CATV provider's distribution amplifier out in a vault somewhere.


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## FrunkSlammer

Hmmmm coax distribution amplifier? 

Another thing to add to the list of possibles! This house is massive… definitely must have an amp somewhere.


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## five.five-six

FrunkSlammer said:


> Hmmmm coax distribution amplifier?
> 
> Another thing to add to the list of possibles! This house is massive… definitely must have an amp somewhere.


I am talking outside the prim, belonging to the CATV company. There is also inductive noise, caused by long runs of speaker wire along romex. 

Home AV is a very complicated sport. Most guys look at the huge profit margins but it takes a few jobs to understand just how labor intensive getting it just right is. I freaking hate it.


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## Wired4Life10

five.five-six said:


> I don't understand how a different leg is going to affect a ground loop. The problem is, if it's a ground loop, that there is different equipment with different ground potential. That potential is equalizing over the shield of the analog audio line. A common cause of this differing ground potentil is an improperly grounded CATV provider's distribution amplifier out in a vault somewhere.


Still a major possibility. I've worked inborn installed sound and portable sound production and it causes an issue many times believe it or not. Many companies require all sound to be on the same leg.


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## five.five-six

Wired4Life10 said:


> Still a major possibility. I've worked inborn installed sound and portable sound production and it causes an issue many times believe it or not. Many companies require all sound to be on the same leg.



I am not saying that it is impossible for equipment on different legs to cause noise, what I am saying is that it can't cause a ground loop. In fact, running 2 circuits on the same leg also means different grounded conductor, which actualy has more potental for a ground loop than running 2 legs with the same grounded conductor. How's that for a mind-F?


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## FrunkSlammer

I believe in this case, all sound is on the same leg.. all powered from a 15A circuit. The data/av rack is powered from the other 15A leg in that 3wire circuit. 



five.five-six said:


> Home AV is a very complicated sport. Most guys look at the huge profit margins but it takes a few jobs to understand just how labor intensive getting it just right is. I freaking hate it.


It's warm and dry and pretty comfy, it's not that bad! 

I'm just on lighting control.. the A/V guy is incredible. Some hollywood guy, real meticulous. This is a temporary theatre room, until the owner can reno and build a bigger one. I'm guessing there is no budget on this, but will easily cost around $150k. The projector alone is around $60k. It's nuts, I love it!


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## five.five-six

FrunkSlammer said:


> I'm just on lighting control.. the A/V guy is incredible.


Are you using Zwave? I have put a pretty modest system in my home and just bid a fairly large residential system.. integrating with a tuxedo touch, vista 20 and some cameras. I'm a little scared. but I did move the guy off of instion


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## Speedskater

While none of these papers has a page 'how to find ground loops' they do have about 145 pages of information about AC power and audio/video systems.

_The Bill Whitlock of Jensen Transformers Seminar paper
http://www.jensen-transformers.com/an/generic seminar.pdf

The Jim Brown of Audio Systems Group white paper
"Power and Grounding for Audio and Audio/Video Systems"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

"Power White Paper" from Middle Atlantic.com
http://www.middleatlantic.com/power.htm_

Note that the Whitlock paper does have a good trouble shooting section.


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## FrunkSlammer

five.five-six said:


> Are you using Zwave?


Lutron RadioRA2, with 6 button on the wall and iPad integrated control of lighting and a/v using Keydigital compass controller. It's pretty sweet. 

Not sure if I'll be back tomorrow or Tuesday.. will take some photos of the setup.


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## Speedskater

Don't know if RCA interconnect cables are used in this installation, but RCA cables are often problematic.
Some thoughts:
a] If all the components are not powered from the same AC outlet box, noise can be a problem.
b] With RCA interconnects longer than 10 feet, noise can be a problem.
c] With boutique RCA interconnects, noise can be a problem.

The only reasonable choices for long RCA interconnects, are discussed here:
http://www.bluejeanscable.com/store/subwoofer/index.htm
http://www.bluejeanscable.com/store/subwoofer/LC1-design-notes.htm

ps. Leftover RG6/QS from the cable TV run is one of the worst choices for audio interconnects.


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## FrunkSlammer

And Speedskater, appreciate the links! I'll do some reading today and tonight!

Edit: I don't think there's any RCA connections.


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## BuzzKill

All I could ass to this is putting all stereo equipment own it's on circuit, no shared neutrals, separating grounds from everything else on it's own insulated ground bar, and running a separate GEC to the service main. You still get noise after that and it's in the stereo system somewhere. I like the idea of bonding all equipment cases together too.


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## five.five-six

FrunkSlammer said:


> Lutron RadioRA2, with 6 button on the wall and iPad integrated control of lighting and a/v using Keydigital compass controller. It's pretty sweet.
> 
> Not sure if I'll be back tomorrow or Tuesday.. will take some photos of the setup.


Have you gotten into their window coverings too?


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## Wired4Life10

five.five-six said:


> Are you using Zwave? I have put a pretty modest system in my home and just bid a fairly large residential system.. integrating with a tuxedo touch, vista 20 and some cameras. I'm a little scared. but I did move the guy off of instion


Zwave is nice for basic automation but not in the theater. Always move toward Lutron when dealing with media because it's controllable from a variety of control systems such as urc, compass, and hai.


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## FrunkSlammer

five.five-six said:


> Have you gotten into their window coverings too?


Haven't installed them on a job yet, but had I gotten into this job sooner they would have had them. 

I wanted to put them in my house, but figured my kids would ruin them and make me very angry.


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## jeffmoss26

When I did live sound for events at school, connecting laptops to the house PA often caused noise/hum/ground loops. Having a ground lift on the direct boxes helped a lot.


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## fdew

jeffmoss26 said:


> When I did live sound for events at school, connecting laptops to the house PA often caused noise/hum/ground loops. Having a ground lift on the direct boxes helped a lot.


This is the beginning of how to get around them. A direct box converts unbalanced audio (RCA plugs, 1/4 in plugs, cables with a shield and one conductor) to balanced, and changes the level, using a transformer. The transformer serves as a isolation transformer and allows you to lift the ground and get rid of the loop.

This is important because the same transformer idea can be used where changing the level is not needed. You use a 1:1 audio isolation transformer made for audio, or for video, Coax ETC. Find out where you need one by disconnecting audio input parts of the system until you disconnect the hum or buzz. Insert a transformer or DI box there. In my opinion the best isolation transformers are made by Jensen. They will also help you with what one you need. 

A ground loop causes noise because there is current flowing in the audio ground (The shield part of the cable) somewhere in the system. This is coupled into the hot wire by transformer action and you here hum. The current is caused by AC leakage to ground somewhere in the system. This leakage can be completely normal and legal. ( A microphone at full volume is 50 mv.) It is easy to get that much hum.

You can break the ground and find the component that is causing it by temporarily putting in a three to two wire adapter at the power plug. If it stops the hum, then remove the adapter and install a isolation transformer between that component and the Amp.

BTW components that are not carrying audio can be part of the problem. for example, the sound system is OK, Connect the PC to the sound system and it is still OK, now connect the projector to the PC and you have hum. Why, The projector is pulling the PC ground up to a level where current flows between the PC and the amp. Bummer.

Isolate the ground on the video feed to the projector or isolate the ground on the audio from the PC to the amp.

BBTW There is a video hum as well, It looks like diagonal bars moving up or down the screen. 

I'm not a electrician, I am a sound guy, and I hate hum.

Frank


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## dspiffy

Did you ever get this resolved?

I've done dozens, maybe 100s, of sound installs for churches and clubs.

First thing I do is put every piece of grounded equipment on one of these:










Does that eliminate the hum? If so, I put each piece of equipment back grounded, one at a time, until the hum comes back. Realistically only ONE component needs to be grounded, the ground will transfer to every other piece through shielded cables.

If this doesnt solve the problem, you may have to lift the ground on various audio/video cables. This can be harder, sometimes you have to open up a cable. I start by disconnecting every piece of equipment that isnt necessary to the signal chain to see if the hum goes away. 

Buzz or 60 cycle hum can also come from bad filter caps, insufficient shielding, etc etc.


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## fdew

dspiffy said:


> Did you ever get this resolved?
> 
> I've done dozens, maybe 100s, of sound installs for churches and clubs.
> 
> First thing I do is put every piece of grounded equipment on one of these:
> 
> If this doesn't solve the problem, you may have to lift the ground on various audio/video cables. This can be harder, sometimes you have to open up a cable. I start by disconnecting every piece of equipment that isn't necessary to the signal chain to see if the hum goes away.
> 
> Buzz or 60 cycle hum can also come from bad filter caps, insufficient shielding, etc etc.


Shielded cables are not designed to serve as a safety ground. The adapters you show are not designed to be used without a ground screw so that the power cord it self is grounded. 

See page 6 and 7 of the paper referenced earlier.
http://www.jensen-transformers.com/an/generic seminar.pdf 

Disconnecting the shield at one end on a balanced audio cable is acceptable. It is usually done at the receive end, and it should be labeled.


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## pete87

fdew said:


> You can break the ground and find the component that is causing it by temporarily putting in a three to two wire adapter at the power plug. If it stops the hum, then remove the adapter and install a isolation transformer between that component and the Amp.
> 
> BBTW There is a video hum as well, It looks like diagonal bars moving up or down the screen.
> 
> I'm not a electrician, I am a sound guy, and I hate hum.
> 
> Frank




Nice Tips Frank 


Pete


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## FrunkSlammer

Ground loop hum was resolved, but I'm certain I don't really know how or why.

I tried everything… things like moving the projector and the audio rack onto the same electrical leg, opening every sub panel and the main gear… tightening everything, making sure no neutrals and grounds crossed paths, bonding screws removed, tried pulling the cable and tele's ground/bond off, tried removing the coax connection to the rack, tried bonding all the rack equipment, tried bonding direct from the rack to the projector (which actually did make a noticeable difference, but didn't eliminate it), tried running the projector 240V vs 120V, tried (and kept) a power conditioner UPS, tried cheater plugs (pulling ground out of power)… and on and on, I can't even remember all the things we tried. 

Now I'm fairly certain that the hum was eliminated by cutting the ground connections on certain audio/video cables. It's beyond me as an electrician. I thought I understand ground loop, but this was an exercise in futility.. I know nothing. There is definitely a career to be made in actually becoming an expert in this area. People will pay a lot of money in desperation when they just cannot figure it out and it must be figured out.


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## fdew

FrunkSlammer said:


> Ground loop hum was resolved, but I'm certain I don't really know how or why.
> 
> Now I'm fairly certain that the hum was eliminated by cutting the ground connections on certain audio/video cables. It's beyond me as an electrician. I thought I understand ground loop, but this was an exercise in futility.. I know nothing. There is definitely a career to be made in actually becoming an expert in this area. People will pay a lot of money in desperation when they just cannot figure it out and it must be figured out.


Cutting the ground connection on a cable could have removed the loop and the hum and is an acceptable way of solving the problem.

Here is why it works. Assume you have a bunch of equipment in a rack all plugged into a strip and each of equipment has a bit of current leaking to ground. This current is all working together to draw current on the ground wire running from the panel to that outlet. Perhaps there is more equipment beyond that outlet that also leaks to ground It might not even be audio equipment. So, with all of that stuff the outlet the audio rack is connected to is one volt above the ground at the panel (You have current through the ground wire so you have a voltage drop from one end to the other)

Now you plug in another component somewhere else. By chance this outlet has a different path back to the panel and less stuff on it. It has a 1/4 volt drop. Now you connect a audio cable between those two pieces of equipment. One of the cable is connected to a ground at 1/4 volt The other end is connected to a ground at 1 volt. That audio cable has current flowing through it. You can actually measure it with a sensitive clamp on amp meter. 

Lets say the shield has .5 ohm, then the audio cable has 1.5 amps flowing through the shield. (These numbers are high, 1 volt is abnormally high but it does happen) 

So 1.5 amps is flowing along next to a audio wire, You have hum.

BTW There are a lot of poorly designed products where this kind of current will cause hum INSIDE the product because the audio ground runs along a lot of the ckt board. It is called "the pin one problem"

By cutting the shield at one end you stopped the current flow, and the hum. but you still have a grounded shield.

I tend to use transformers because it is easer (less labor) and they show so trouble shooting is easer.

If you cut the shield please label it for the tech down the road.

If someone wants to be an expert get in touch with Jensen transformers and ask when Bill Whitlock is giving his next seminar.

Here is some reading
http://www.jensen-transformers.com/an/generic seminar.pdf

http://www.jensen-transformers.com/an/an004.pdf

Disclaimer, I don't work for Jensen, but I do build and sell DI boxes.

Frank DeWitt LBPinc.com/DI


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## Speedskater

A new easier to read PowerPoint version of the above Jensen paper:

An Overview of Audio System Grounding and Interfacing
by
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers

http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf


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## fdew

FrunkSlammer said:


> Ground loop hum was resolved, but I'm certain I don't really know how or why.
> 
> I know nothing. There is definitely a career to be made in actually becoming an expert in this area.


Here is a great resource for audio system training.
http://www.synaudcon.com/site/

I have taken this course and it is excellent.
http://www.synaudcon.com/site/shopping-cart/in-person-training/sound-reinforcement-for-technicians/

Note the first two items taught
Why is it noisy?
How do I remove that hum or buzz?

Frank


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## dspiffy

fdew said:


> Shielded cables are not designed to serve as a safety ground. The adapters you show are not designed to be used without a ground screw so that the power cord it self is grounded.


This is how most pro audio guys do it in the field. I've never seen a permanent install LEFT this way, but it is a quick, cheap, and easy way to determine the source of the issue.


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## fdew

dspiffy said:


> This is how most pro audio guys do it in the field. I've never seen a permanent install LEFT this way, but it is a quick, cheap, and easy way to determine the source of the issue.


Agreed, Just fine for trouble shooting. Not safe or good practice to leave any behind. Every 3 prong plug gets a safety ground before we leave.


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## RIVETER

FrunkSlammer said:


> Any tips or tricks for tracking down the source of what I think is ground loop noise?
> 
> Working on a high end home theatre, and the speakers have a subtle but noticeable annoying buzz in them. A professional A/V guy is doing the project, but has asked for help tracking down the source.
> 
> Bootlegged ground(s)? Bonding screw not off in a sub panel?
> 
> I really have few ideas of how to track it down. Won't be back there until next weekend, but want to spend some time this weekend learning about the problem.


You do understand that GROUND has not a thing to do with the normal operation of ANY electrical system, right?


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## FrunkSlammer

RIVETER said:


> You do understand that GROUND has not a thing to do with the normal operation of ANY electrical system, right?


Are you serious, you read this whole thread and that's what you have to offer?

You've obviously never had to deal with this problem.. because it's a real gremlin and bonding/grounding has absolutely everything to do with it.

Troll on trollah!


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## RIVETER

FrunkSlammer said:


> Are you serious, you read this whole thread and that's what you have to offer?
> 
> You've obviously never had this problem.. because it's a real gremlin and bonding/grounding has absolutely everything to do with it.
> 
> Troll on trollah!


I have not and normally do not read other posts before I attempt to weigh in on a post. Unless you have audio/ video equipment problems you rarely will solve it by worrying about grounding which has only to do with lightning...or surges.


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## fdew

RIVETER said:


> I have not and normally do not read other posts before I attempt to weigh in on a post. Unless you have audio/ video equipment problems you rarely will solve it by worrying about grounding which has only to do with lightning...or surges.


I suggest http://www.jensen-transformers.com/an/generic seminar.pdf

And / or http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Sound and video systems are often plagued with hum or buzz caused by Ground loops. It is a very well known and well understood problem. It is easily reproduced in the lab and courses are taught on how to deal with it. It is the reason that Direct Boxes have ground lift switches. It is the reason that papers have been written and companies have been urged to deal with "The pin 1 problem." 

Frank


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## dspiffy

RIVETER said:


> I have not and normally do not read other posts before I attempt to weigh in on a post.


I guess that's one way to get up to 8,000 posts.


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## Speedskater

RIVETER said:


> You do understand that GROUND has not a thing to do with the normal operation of ANY electrical system, right?


While the EGC is installed for safety reasons, unfortunately leakage, noise and interference currents never read the rule book.


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## fdew

For more incite into why ground loops are a problem in audio check out page 31 to 34
http://centralindianaaes.files.wordp...notes-v1-0.pdf This is relatively new research that shows that wires puled in conduit will produce a higher potential on the ground conductor, then using Romex Therefor commercial buildings will have more ground loop problems then home theater. Also, the larger the building, the bigger the problem.

The solution is to twist the hot and common, and pull this pair along with a non twisted safety ground. If the electrician and owner went to all this work then they would probably install a isolated star ground system as well. That is a lot of extra fooling around and it is not how it is normally done, so it is hard to get it done right. 

I imagine a electrician doing this would spend a lot of time explaining what he was doing and why. 

It works, but in practice it is easer to fix the problem with audio isolation transformers.

Frank


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## 8V71

fdew said:


> The solution is to twist the hot and common....


What does this do?


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## Speedskater

I was going to say -read the above link, but it got scrambled!
Try:
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf


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## Speedskater

Or if you want to read the 9 page long technical paper:

"Ground Loops: The Rest of the Story"
Bill Whitlock, AES Fellow and Jamie Fox, P.E. 

This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA

ABSTRACT
The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system
noise problems are well known. But what causes power-line related currents to flow in signal cables in the first
place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage
differences normally found among system ground connections, even if “isolated” or “technical” grounding is
used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little
has been written about this “elephant in the room” topic in engineering literature and apparently none in the
context of audio or video systems. It is shown

http://xa.yimg.com/kq/groups/20963848/268252969/name/Whitlock-Fox+-+Ground+Loops+.pdf


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## fdew

8V71 said:


> What does this do?


The short version is that it assures that the hot and the common will average out as the same distance from the ground. That means that voltage coupled to the ground wire by one is canceled out by the other. The result is zero.

With a random fill from a normal pull either the hot or the common (return) will be closer, and carrying current, so a voltage will be coupled to the ground.


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## dspiffy

Speedskater said:


> While the EGC is installed for safety reasons, unfortunately leakage, noise and interference currents never read the rule book.


A lot can be done with isolation transformers, both for audio and power supply. 

A lot of times when you have several pieces of equipment rack mounted, you can create ground loops that way as well.


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## Speedskater

dspiffy said:


> A lot can be done with isolation transformers, both for audio and power supply.


Doing the AC power and signal interconnect wiring correctly can reduce the need for expensive isolation transformers.
We should note that a lot of audio equipment is poorly designed from a noise and interference point of view.



> A lot of times when you have several pieces of equipment rack mounted, you can create ground loops that way as well.


Mounting everything to the rack and powering from the same outlet strip will reduce the ground loop problems.

If you don't have a rack, this is how Audio Precision (expensive test equipment) does it.


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## dspiffy

Speedskater said:


> Doing the AC power and signal interconnect wiring correctly can reduce the need for expensive isolation transformers.
> We should note that a lot of audio equipment is poorly designed from a noise and interference point of view.
> 
> Mounting everything to the rack and powering from the same outlet strip will reduce the ground loop problems.
> 
> If you don't have a rack, this is how Audio Precision (expensive test equipment) does it.


Problem is, it is very common for interconnected pro audio equipment to be mounted in several different rooms, often served from different different panels. Or the current draw is high enough that it requires several circuits to the same areas.

This can create a nightmare if you're using an old building with all the electrical in place already. If electrical is being installed for the sound equipment, or if it's new construction, it is very helpful when the electricians and audio installers are on the same page.

The biggest problems are usually between the control area (mixing board, eqs, processors, etc) and the racks of amps (often in a separate room). The stage area can also pose some problems, but those are usually easier to solve with direct boxes/ground lifts. Also depends how many circuits are needed for the racks of amps. Amps are pretty much the only components with high current draw. Sometimes there are amps/powered monitors on stage . . .


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## Speedskater

My post was about equipment in just one rack.

For large system's, Tony Waldron has several papers.
Warning they are written in British.

http://www.fragrantsword.com/twaudio/


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## FrunkSlammer

dspiffy said:


> Problem is, it is very common for interconnected pro audio equipment to be mounted in several different rooms, often served from different different panels. Or the current draw is high enough that it requires several circuits to the same areas.


That is/was the situation for us. 

We had a rack that was powered by a 3 wire 20A circuit, speakers that were powered by the other leg of the 3 wire circuit and video projector that was in an entirely different location and could either be run on it's own 120V or 240V circuit.

All I can say is there has been some very knowledgeable posts here, this turned into a valuable resource. And ground loop / dirty power / noise is difficult for the average electrician to understand and correct. I don't feel we're trained whatsoever in this area of expertise. That's a missed opportunity for training institutions. But no time like the present to learn!


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## fdew

The connections between the mixer board and the amp rack is one of the easier places to solve ground loop problems. As has been pointed out it is also a common place to have these problems because the amps are often at the other end of the building and have a different power source. In the case of the church I attend the amp rack is fed from a completely different panel then the FOH (Booth) At one time these panels were in different buildings. There is a very long AC power run between the panels.

The problem is easy to solve because
1. There are only a few connections between them. Typically main audio, and Sub woofer, Some times left, right, center, and sub.
2. The signal is usually balanced (Shielded twisted pair)
3. The signal is at Line level 

The first thing that can be done is to check gain structure. Is the Mixer putting out about 1.2 volts at normal volume settings? If not, turn the main amps down and the mixer output level up. This gets the signal input to the rack higher above the noise. It is very common for this to be wrong. Many people set the amp gain at max and then turn up the mixer until it sounds loud enough (and have hiss)

Next, Cut the shield connection to the audio input plug at the amp rack end. (and label it) You will probably need to do this for all the line inputs for this to work. We can cut the shield because in a ballenced connection it is not carrying audio, only a shield for the audio. this is diferent then the cables that use a RCA plug or a 1/4 in plug such as a guitar. Those cables use the shield as a return for the audio. If you cut the shield on one of them then the only path for the audio return is through the equipment safety ground

If that doesn't work, put the ground back and install one audio isolation transformer per line. About $125 each from Jensen. If the problem is a ground loop this will work.

BTW If there is a separate panel along the route such as a patch panel on the wall or a nice convenient interface panel in the rack where all the lines pass through make sure that the shields are NOT connected to the metal shell of the connectors. This is counter intuitive. A good electrician grounds the mounting tabs of all outlets, switches, and anything else he is mounting in a box. These jacks are not carrying a safety ground. They are carrying a signal ground or shield. We don't want these shields connected to one another or to the building ground or building steel anywhere along the route.

Frank


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## 8V71

Speedskater said:


> Mounting everything to the rack and powering from the same outlet strip will reduce the ground loop problems.
> 
> If you don't have a rack, this is how Audio Precision (expensive test equipment) does it.


Did somebody mention Audio Precision? Sorry FrunkSlammer for my shameless post that is no help to your thread. :whistling2:


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## Speedskater

_While on the topic of Audio Precision, this is about their building wiring._

Notes from the Test Bench *
By Bruce Hofer, Chairman & Co-Founder, Audio Precision*

Recently, AP celebrated the 15th anniversary of our custom designed building. Photo albums were displayed showing the construction and the move into our facility back in 1998. (My, how some people have changed in appearance!) Among my many memories of that time, I was reminded of a particularly nasty problem we experienced as we restarted operations in our new production environment.
Almost immediately after moving we began to experience failures of certain bench tests that are performed by our technicians during the course of product assembly and adjustment. After some research, we discovered our new building had some extremely large magnetic fields in the production area, almost as if it was haunted. These fields coupled high levels of hum into our products that were causing the test failures. AP products are designed to reject reasonable levels of stray magnetic fields that would typically be encountered in a lab or production environment. However the magnitude of the fields we faced were at least 20 dB worse.
We ultimately discovered that several of our AC outlets had been wired incorrectly, having their neutral and ground connections swapped. This is a big no-no from the safety viewpoint, but it also caused all of the neutral currents in a particular circuit (outside of our production area) to return through the safety ground connection and ultimately through plumbing and drainage pipes. Some of these plumbing pipes were located in the space directly above our production area while the main drainage pipe was buried directly below; thus our production area was effectively inside of a huge coil. Our electrical contractor was embarrassed but confirmed our diagnosis, and the problem was quickly fixed.
Sometimes one has to think “outside of the box” to correctly perceive or understand a given problem. In this case, our new building plans provided the necessary insight to recognize the inadvertent source of our unwanted magnetic fields (plumbing that formed a coil around our production area). Perhaps you might want to check the neutral and safety ground connections of the AC outlets in your own work space—there could be some ghosts present!

Enjoy this month’s edition of our newsletter…
Bruce


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## 8V71

Speedskater said:


> _While on the topic of Audio Precision, this is about their building wiring._


What luck for that to happen to this company.:laughing: I think it's common knowledge but AP was founded by Tektronix engineers that went out on their own.


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## dspiffy

fdew said:


> The problem is easy to solve because
> 1. There are only a few connections between them. Typically main audio, and Sub woofer, Some times left, right, center, and sub.


And anywhere from one to dozens of monitor channels. And crossovers. And any other rack mounted gear that connects directly to the amps and doesnt get adjusted on the fly.

You posted a lot of really good information. This thread is becoming a great resource. I have met very few sound engineers that understand electrical contracting, and I have met very few electricians that understand sound engineering.


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## fdew

dspiffy said:


> And anywhere from one to dozens of monitor channels. And crossovers. And any other rack mounted gear that connects directly to the amps and doesnt get adjusted on the fly.


There certainly be crossovers, EQ and DSPs in the rack but usually the ground loop problems are between racks such as between the booth and the amp rack, or between the AC powered stuff on the stage and the booth.

Your right about the monitor feeds. I tend not to think of them because I have been spoiled by In Ear Monitor systems but a lot of places use monitor speakers.


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## dspiffy

EQs and DSPs are usually with the board, but crossovers and other processors that are only adjusted during installation are often with the amp racks or in a third location.

And then, any larger venue will usually have a second mixing board for the monitors just offstage . . .


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## RIVETER

dspiffy said:


> EQs and DSPs are usually with the board, but crossovers and other processors that are only adjusted during installation are often with the amp racks or in a third location.
> 
> And then, any larger venue will usually have a second mixing board for the monitors just offstage . . .


What is a mixing board?


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## dspiffy

RIVETER said:


> What is a mixing board?












Usually the monitor boards will also have their own set of EQs, processors, etc.

I dont think I've ever met a sound install guy who's thought about the power supply other than "I need X 20 amp circuits). Probably could save a lot of headache if the requested isolated ground outlets, on the same panel, etc.


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## dspiffy

Whoah. Big picture is big. How do I fix that?


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## Speedskater

If you Right Click on that photo in your hard drive you may find a re-size photo command or your 'open with' options may have a re-size button.


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## dspiffy

Speedskater said:


> If you Right Click on that photo in your hard drive you may find a re-size photo command or your 'open with' options may have a re-size button.


This wasnt from my hard drive, I found it using a Google Image Search.


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## Wired4Life10

dspiffy said:


> Usually the monitor boards will also have their own set of EQs, processors, etc. I dont think I've ever met a sound install guy who's thought about the power supply other than "I need X 20 amp circuits). Probably could save a lot of headache if the requested isolated ground outlets, on the same panel, etc.


That's what I do. When I spec out a system installation, everything has to have isolated neutrals and grounds as well as being on the same leg and lighting can be on the other leg. And yes, I also calculate loads to assure leg load balancing.


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## RIVETER

Wired4Life10 said:


> That's what I do. When I spec out a system installation, everything has to have isolated neutrals and grounds as well as being on the same leg and lighting can be on the other leg. And yes, I also calculate loads to assure leg load balancing.


How do you isolate your grounds from your neutrals?


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## Wired4Life10

What I mean is no common neutrals.


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## RIVETER

Wired4Life10 said:


> What I mean is no common neutrals.


With all respect, what does NO common neutrals mean?


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## FrunkSlammer

RIVETER said:


> With all respect, what does NO common neutrals mean?


Means no MWBC? Keep the loads separated and isolated... makes sense.


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## Wired4Life10

Mwbc?


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## RIVETER

Wired4Life10 said:


> Mwbc?


I'll give you that. But...how does that help?


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## markore

five.five-six said:


> Tell him that I said: "You're welcome"
> 
> http://www.newegg.com/Product/Produ...eMKP-_-pla-_-Home+Automation-_-9SIA0PG0PC1775


Thanks for wasting my time on a broken link!


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## FrunkSlammer

markore said:


> Thanks for wasting my time on a broken link!


lol it did work at the time.

I think it was a coax ground isolator if memory serves me right..


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## RIVETER

FrunkSlammer said:


> lol it did work at the time.
> 
> I think it was a coax ground isolator if memory serves me right..


What is a co-ax ground isolator? And what does it isolate anything from?


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## FrunkSlammer

RIVETER said:


> What is a co-ax ground isolator? And what does it isolate anything from?


Opens the ground on a coax cable, stops or helps stop loop currents that can cause noise in audio and video signals.










That's not an accurate depiction of the use of a co-ax ground loop isolator. But at least you get a quick idea of how and why a ground loop can occur, and how isolating the ground connection in a cable can stop a ground loop.


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