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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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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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Hear... nudge, nudge, are some.

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



http://www.musiciansfriend.com/pro-audio/isp-technologies-decimator-pro-rack-g-stereo-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:
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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.
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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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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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Discussion Starter #7
At that price, it's worth a shot!
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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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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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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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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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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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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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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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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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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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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Discussion Starter #20
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.

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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