Ground Loops

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bpmorton
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Post 20 Mar 2015

Yep, I got ground loops all over the place here in my little home studio. I use a Whirlwind director direct box with the ground lift switch engaged when recording a mono signal. The DI takes care of the ground loop but...I just got a pair of Mackie MR6m3's and both showcase my nasty ground loop. I can plug one into a ground lift plug and that takes care of the loop for one speaker but should I use one on both? I plan on getting balanced cables for these speakers but right now they are on cheap unbalanced cable. Is there something else I could use to eliminate the loop from the rest of the gear? I have my computer plugged into an APC power conditioner and the rest of my gear is plugged into another outlet with no power conditioning.

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selig
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Post 20 Mar 2015

The first thing to do is put everything on the same circuit (a 20 amp circuit is best, but 15 amps will do for most home setups). 

Ground loops are caused by different length paths to ground, so you want all power to come from the same place so that all paths are the same. 

Funny thing is, some wiring setups make eliminating ground loops a black art, while in other buildings I've never had a single issue! Usually a ground "lift" is a bad idea from a safety standpoint (typical disclaimer), so it's best to avoid this if at all possible. 

If your setup is already simple there's not much more you can do except to make sure all your cables are working. Having a balanced cable will ONLY address noise added at the cable. If a ground lift solved your problems, it's unlikely a balanced cable will make much difference (expect maybe that they tend to be better built for the long run).

That's all I got off the top of my head - maybe someone like Normen (who probably has more hands on electrical experience) can answer better or in more detail.

:)
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normen
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Post 20 Mar 2015

The last thing you mention is probably not a good idea. Generally you should have *all* your gear on the same ground. Then you don't have to worry about ground hum so much because all the devices have the same ground. That includes your computer and its USB connection. Most hum comes from two different grounds where the difference of the ground potentials is audible in the signal.

Edit: Darn, Giles ninja'd me ;)

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selig
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Post 20 Mar 2015

normen wrote:The last thing you mention is probably not a good idea. Generally you should have *all* your gear on the same ground. Then you don't have to worry about ground hum so much because all the devices have the same ground. That includes your computer and its USB connection. Most hum comes from two different grounds where the difference of the ground potentials is audible in the signal.

Edit: Darn, Giles ninja'd me ;)
I must have been sensing your presence while I was writing…
;)
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bpmorton
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Post 20 Mar 2015

I took a look. The APC and the other gear are plugged into the same outlet (one in each plug.) I guess you are saying everything needs to be plugged into the APC LE600 voltage regulator. I don't know if it can handle everything all at once. Also, l think the power from the wall is probably 15 amps.

http://www.apc.com/resource/include/tec ... _sku=LE600

max output power capacity 600W or 600 VA
Nominal Input Current 5A


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selig
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Post 20 Mar 2015

bpmorton wrote:I took a look. The APC and the other gear are plugged into the same outlet (one in each plug.) I guess you are saying everything needs to be plugged into the APC LE600 voltage regulator. I don't know if it can handle everything all at once. Also, l think the power from the wall is probably 15 amps.

http://www.apc.com/resource/include/tec ... _sku=LE600

max output power capacity 600W or 600 VA
Nominal Input Current 5A
I'm not an expert here, but such a device should easily support a 15 amp service, and a small studio is quite unlikely to ever draw that much power (unless you've got large power amps and you crank them up to high volumes). Maybe Normen can confirm/deny this line of thinking?
:)
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normen
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Post 21 Mar 2015

600W should be enough, depends on what you actually have connected there though. Generally I'd first try to just have everything on the same mains outlet, even without the APC.

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bpmorton
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Post 21 Mar 2015

after much mucking about on the floor I plugged the computer, monitor, and both MR6's into the APC and that directly into the wall. Still get nasty loop. I suspect the USB powered M-Audio MobilePre as the source of my loop. Both speakers are getting their audio feed from the MobilePre and it's getting it's power from the CPU ....gotta be the loop.

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submonsterz
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Post 21 Mar 2015

hmmm some usb devices just have a lot to answer for in generating humms :frown: .

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normen
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Post 22 Mar 2015

bpmorton wrote:after much mucking about on the floor I plugged the computer, monitor, and both MR6's into the APC and that directly into the wall. Still get nasty loop. I suspect the USB powered M-Audio MobilePre as the source of my loop. Both speakers are getting their audio feed from the MobilePre and it's getting it's power from the CPU ....gotta be the loop.
Can you record the noise you get? Might make it easier to pin down where it could come from.

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bpmorton
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Post 22 Mar 2015

It sounds more like internal computer noise but it behaves like a ground loop.

Brian
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selig
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Post 22 Mar 2015

It COULD be a cheap USB cable causing the hum (I believe I've heard about this happening to others in the past) - any one else ever heard of this?
:)
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submonsterz
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Post 22 Mar 2015

selig wrote:It COULD be a cheap USB cable causing the hum (I believe I've heard about this happening to others in the past) - any one else ever heard of this?
:)
I've never found a cable to be the problem before myself unless it had been damaged in some way.(But I'd never dismiss it could be just a bad cable and try another just incase cover all aspects allways and rule out nothing)
But I mainly have found USB wifi dongles and such to cause things like this more the common case.
Also I think the mother board used sometimes is another key culprit having bad shielding and picking up internal things like disk activity etc. Best thing to do is start by using just the computer alone use its on board audio first connected directly to the out put source . And also try what you are using as out put source ie amp monitors using a total different input source to make shure there's nothing amiss there first. When satisfied do computer using only that unplugged everything including all USB items attached. If you hear disk activity etc then ya problems lay in the internals. Usually as I say bad shielding, bad capacitor or other bad earthing somewhere in the component build. It's a matter of finding source by stripping bare and working up to the full set up.
It's a pain but if ya gotta ya gotta .
also just to add if you rule out everything another thing to look at is where cables run and what they run next to or what other things are close or sitting by you're set up ie ya speakers monitors or tvs etc etc all throw out magnetic fields that can cause no end of trouble to other things.so check where cables run and what they run next to or touch along the way. It's amazed me in the past in just moving a cable away from x component has cleard up a generated noise or hmmm .

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selig
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Post 22 Mar 2015

selig wrote:It COULD be a cheap USB cable causing the hum (I believe I've heard about this happening to others in the past) - any one else ever heard of this?
:)
submonsterz wrote: I've never found a cable to be the problem before myself unless it had been damaged in some way.(But I'd never dismiss it could be just a bad cable and try another just incase cover all aspects allways and rule out nothing) But I mainly have found USB wifi dongles and such to cause things like this more the common case. Also I think the mother board used sometimes is another key culprit having bad shielding and picking up internal things like disk activity etc. Best thing to do is start by using just the computer alone use its on board audio first connected directly to the out put source . And also try what you are using as out put source ie amp monitors using a total different input source to make shure there's nothing amiss there first. When satisfied do computer using only that unplugged everything including all USB items attached. If you hear disk activity etc then ya problems lay in the internals. Usually as I say bad shielding, bad capacitor or other bad earthing somewhere in the component build. It's a matter of finding source by stripping bare and working up to the full set up. It's a pain but if ya gotta ya gotta . also just to add if you rule out everything another thing to look at is where cables run and what they run next to or what other things are close or sitting by you're set up ie ya speakers monitors or tvs etc etc all throw out magnetic fields that can cause no end of trouble to other things.so check where cables run and what they run next to or touch along the way. It's amazed me in the past in just moving a cable away from x component has cleard up a generated noise or hmmm .
Just like motherboards, cables too can have bad shielding. In most cases it's also a case of it being damaged - being "cheap" often means it can be damaged easier rather than meaning it won't work well out of the gate. Either way, I agree it's the shielding that's causing the issue (IF it's the cable or motherboard for the audio I/O). 

The best way to test for this is to use a different sound card (not always the easiest thing to do - maybe try to borrow something for your test?) and see if the problem persists. :)
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bpmorton
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Post 22 Mar 2015

I have second audio interface (Behringer UCA222). I got a little less noise using this one and was able to crank up the speakers louder. I'm wondering if ferrite beads placed on some of the cabling would help?


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normen
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Post 25 Mar 2015

Sorry, lots to do during the last days but I definitely wanted to come back to this.

@Giles: I had loads of USB cable issues. The thing is that they don't seem to be 100% clear about what it shield and what is ground, it seems to vary from cable to cable or from broken cables which seemingly work but don't (or do) cause a ground connection between the devices. Then you also never know exactly where the audio interface gets it ground from, proper ones normally detach the USB ground from the audio ground.

As for your (@bpmorton) tests of putting everything to one ground of course its important to DISENGAGE all ground lifts if you have all devices on a common ground, else you might cause a part of the chain to "float in the air", again having a different ground potential.

That said, this noise doesn't sound like a ground issue AT ALL. It (as Giles said) sounds like terrestrial interferences, so signals that get into the signal in the cable via air. If you have balanced connections its probably not the cable but a device directly (e.g. a soundcard inside your computer), solution would be to put the device further apart from the computer, if its a PCI card try putting it into a slot further away from the graphics card etc. If you do have balanced connections then its probably missing one leg in the cable, if you don't have balanced connections but could in theory have them, buy them balanced cables :)

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selig
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Post 25 Mar 2015

bpmorton wrote:I have second audio interface (Behringer UCA222). I got a little less noise using this one and was able to crank up the speakers louder. I'm wondering if ferrite beads placed on some of the cabling would help?

These have actually help in one situation I was getting bad RF interference on a long mic cable run (but not one on the other side of the same large room). Could help here too, but you'd have to spend money to find out one way or the other (probably not an option?). 

:)
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bpmorton
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Post 09 Apr 2015

update

bought some ferrite beads. did not fix the problem. Got the balanced cables that I was going to get anyway....now the speakers are very quiet. The Mobile Pre's main outs are balanced only, I guess. I kind of figured this would fix the problem and I'm glad it did.

Brian

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