Ground loop observations - AVS Forum
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post #1 of 5 Old 10-02-2012, 08:41 PM - Thread Starter
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Hello all, like most of us DIY'ers I was using a Behringer EP4000 for a sub amp and I didn't notice any issues.

I say notice any issues cause I decided to "upgrade" my amplification and tried to do something I consider pretty radical and that was I decided to replace my home audio 2 prong plug-in style amps and switch everything over to EP4000's 3 prong plug amps.

I'm running four 8" woofers in huge cabinets in a WWMTMWW configuration, I have caused my previous amp (Acurus A200x3) to reach it's near clipping point on occasion so I thought the hell with it I'm going big on the amps and throttling back the juice via the amp volume.

I hooked up two EP4000's (one for each sub) then I put in three more for the 5 main channels, leaving one channel open to add some mid bass bins in the future.

Then to really mess things up, I decided to run pro audio EQ's to fine tune my speaker response before they are processed through my Anthem MRX500 using ARC.

I get everything all hooked up through what I thought was 4 dedicated breakers (including my stack of ps3, AS-EQ1 and such) I turn it all on and OMFG what a gross sound.

I have hiss like you wouldn't believe, I have 60hz ground loop hum, I pretty much fubar'd my previously great sounding home theatre.

I talk to my home audio guy who basically says...um yeah good luck with that... he's honest at least smile.gif

I talk to my pro audio guy who says...yeah you don't mess around with balanced and unbalanced, here buy more cables and a couple Ebtech HumX adapters....

I go home and for good measure I bought some inline RCA isolation boxes from radio shack-the source whatever they are called this week and I plug that all in.

Same mother *&^&^%$(* noise as before.

So then I call an electrician on KIJIJI (cause thats where the best in any field are found right?) I pay him to house call where he tells me the problem is my speaker wired walls are too close in proximity to my power wires in the wall and I need to lose those and just wire my speakers direct without all the fancy wire hiding I had.

Down to the Source I truck, get a couple hundred feet of 14 guage and go about redoing all my speaker wires.

Sit down, turned it all on and still ______ ____ sound and hiss etc

So I kick an old sub I had laying around, hurt my foot but my head feels better and I sit and pout.

This is the part that I actually learned something and made observations, but I had to give some background..........

I take a deep breath and rip every plug out of everything and start putting it all back together as I test for noise and hiss as I go.

First thing to realize is that pro audio gear is supposed to go in a metal rack for a reason and as I learned they are chassis grounded to create a common ground as you install them together, this eliminates ground loop. When you add another electronic piece to this and it doesn`t share an equal path to ground you can get a ground loop buzz. Ebtech makes this HumX piece to basically break the ground unless it senses a shock hazard where it will reactivate the ground in a split second to avoid killing you.

That being said I eliminated the ground loop, plugged them all into a single outlet on a power bar with no inputs at zero volume and there it was....dead silence. Excited I quick tried plugging in an EQ first through the isolator then to my amp..just one to try it out. Instantly I get hiss and buzz, so I`m thinking WTF and I pull out the RCA from the EQ and it still buzzes! It`s the F&*&)(?& isolator causing the buzz! The stupid thing I bought to remove noise is causing noise, so I throw that back in the return this garbage to the store bag and plug in the EQ straight to the amp...stupid buzz is there again! Remove the EQ and plus into receiver...dead silence.

Okay I`m on to something here.....I run an EQ and I run isolators and they both had to be chucked.

I plug in all my inputs back and forth as simply as possible, I have my rack mounted amps in a common ground, I run a ground jumper wire from back of outlet boxes to rack to ensure common ground, I plug everything into separate outlets and the god damn buzz comes back?!?!?!?!

Then I phone the internet electrical wizard up and said come to my house.

I said look and listen, I showed him one outlet no noise, same common ground box split up the plugs and I have buzz and we then realize something.

When I had the boxes wired the previous KIJIJI guru I hired used one three wire to supply two breakers to two outlets. To do this "ground" and the negative become one and the positive is used to split the other two wires 15 amps each. THAT move was causing the buzz.

I had him pull two wires through instead of one, I had him wire one breaker to one wire to one outlet and common ground strap each outlet to one another it all went away.

So remember this if you are running 3 prong power amps:

1) Never use one wire to power two breakers and outlets in any part of your home theatre wiring...anywhere! not even for a projector or cable box.
2) always rack mount if you have two or more pro audio amps in your system to ensure a common ground or daisy chain wire to connect them chassis to chassis
3) don't use stop gap measures like HumX to try and stop a deeper problem
4) If you need an isolation adapter, there is a deeper problem don't be cheap or lazy
5) outlet box to outlet box (if you can) run a common ground strap so they can ground to each other and mother earth
6) don't let anyone tell you you can't run a dead silent pro amp system on your home theatre. Right around 10,000 watts RMS into 4ohms for $2000 is a ridiculous deal.
7) rip everything apart before you spend money and reattach until you find the problem

Enjoy my misadventures.

Jeff

Whether you think you can or think you can't...you're correct!
Henry Ford
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post #2 of 5 Old 10-02-2012, 10:49 PM
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Quote:
Originally Posted by Noxdowne View Post

First thing to realize is that pro audio gear is supposed to go in a metal rack for a reason and as I learned they are chassis grounded to create a common ground as you install them together, this eliminates ground loop. When you add another electronic piece to this and it doesn`t share an equal path to ground you can get a ground loop buzz.
Nope. Equipment is mounted in grounded metal chassis for safety. That way under fault/damage conditions the chassis will not be able to rise to a potential that can harm a person. The upstream protection device should trip and remove supply under fault conditions. Two prong devices should only be used where they are properly double insulated for this reason and here are laws that specify exactly what this entails and how a device needs to be tested for that.

There is no need whatsoever to have gear mounted to a metal rack. Pro gear in rack chassis are not inherently designed to use the rack as an earth - they should already have an earth conductor in the cable for this.
Apart from #2, I agree with your list.
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post #3 of 5 Old 10-02-2012, 11:38 PM
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Classic post , I've been in your shoes!
You need to re-post it here, the sticky thread for HUM issues http://www.avsforum.com/t/322698/hum-faq/150
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post #4 of 5 Old 10-03-2012, 06:06 AM - Thread Starter
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Originally Posted by A9X-308 View Post

Nope. Equipment is mounted in grounded metal chassis for safety. That way under fault/damage conditions the chassis will not be able to rise to a potential that can harm a person. The upstream protection device should trip and remove supply under fault conditions. Two prong devices should only be used where they are properly double insulated for this reason and here are laws that specify exactly what this entails and how a device needs to be tested for that.
There is no need whatsoever to have gear mounted to a metal rack. Pro gear in rack chassis are not inherently designed to use the rack as an earth - they should already have an earth conductor in the cable for this.
Apart from #2, I agree with your list.

It sounds like you know more than I, so I'll concede and leave it on the list for people to see common misconceptions.

jeff

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post #5 of 5 Old 10-03-2012, 07:54 AM
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Quote:
Originally Posted by A9X-308 View Post

Nope. Equipment is mounted in grounded metal chassis for safety. That way under fault/damage conditions the chassis will not be able to rise to a potential that can harm a person. The upstream protection device should trip and remove supply under fault conditions.
+1
Quote:
Originally Posted by A9X-308 View Post

Two prong devices should only be used where they are properly double insulated for this reason and here are laws that specify exactly what this entails and how a device needs to be tested for that.
If only. There are many two-prong devices that aren't double-insulated, but still pass UL. Then as time goes by they end up with leakage to the chassis, and you got a new hum issue where there was none before. This can also happen with 3 prong devices. There are also many many pro and consumer devices that use wall-wart supplies, usually no ground either. It's often necessary to add a ground wire on your own.
Quote:
Originally Posted by A9X-308 View Post

There is no need whatsoever to have gear mounted to a metal rack. Pro gear in rack chassis are not inherently designed to use the rack as an earth - they should already have an earth conductor in the cable for this.
Apart from #2, I agree with your list.

The main purpose in using a metal rack is structure, mounting and serviceability. The fact that it provides a de-facto ground is actually a problem. You really don't want more than one ground for each device, and the rack creates a second for 3-prong devices. The audio ground a third...etc.

A slight elaboration on point #5, a separate ground wire is a fine idea, but don't "daisy chain" the ground wire, or cheat on its size. It should be equal to the hot and cold and home-run to a single ground point at the panel, and this may not be true in some wiring types like non-metalic building wire (Romex). People will argue about the size issue, saying that the ground wire never has to carry any current, which hopefully is true, but you want the lowest possible resistance in the path to the common ground point. One caution, however, is that some styles of wiring create two different ground paths when you add the ground wire. Systems that use metallic conduit are a good example. The problem is that if you try to lift the default ground path through the conduit you have essentially violated code. So you have to be a little careful about this.
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