Mixer and a ground loop issue?

[RideTheCrash]

3 years ago I posted a similiar problem and I fixed it by removing a cable from my crappy, crazy setup.

I just started recording some tunes recently and I have an electrical buzz present. I unplugged everything from the mixer and plugged in some headphones and I still get buzz, so I've ruled out my signal chain to the computer at the moment. I did some recording back in the summer and I didn't have this problem. I have re-routed some cabling and stuff for power, but I try to keep my power and audio cables away from each other as much as possible. I've tried a wall plug and a power strip on a different plug in the room and I still get this nasty buzz. I've unplugged and turned off lights and other things in the room which no change whatsoever.

I use my board to tap off the preamps and use the inserts to go to my soundcard. If I turn up master faders the buzz changes and disappears and comes back. The pots are fine, I put in new ones about 2 years ago. Either way, it doesn't alter the signal to my card, which is only controlled by the gain pot. I have no idea what is on what breaker in this house, but do you guys have any suggestions?

 

[RideTheCrash]

!@#$.

Originally to "pull out" everything, I had only pulled out the two 8 channel snakes which run in and out of the soundcard slightly, not completely...I pulled them out completely and now I get absolutely no buzz...just some expected hiss when the headphone volume pot is cranked full. Now this means I have to troubleshoot my setup. I recently moved my computer tower elsewhere in the room because it was overheating in the space made for it in my computer desk, so cabling was tided up and moved around.

My gear runs on three wall outlets.

OUTLET ONE: Just a wall wart for a phantom power unit usually.
OUTLET TWO: Powerstrip -- Mixer, amp, CD player, and maybe the other odd thing every now and then. The other plug is used for a baby monitor.
OUTLET THREE: The computer power, desk lamp, lava lamp, stuff like that.

I'm not sure if these plugs are on the same circuit, but since they are in the same small room, they probably should be? Should my computer power and mixer power be on the same strip? The past few days I've tried shutting off things and rearranging some cables, but no avail.

Yes, unfortunately my run is unbalanced from my inserts to my 1010lt, but I just have to be careful because I didn't have this issue before. It's pretty much impossible to keep my audio and power cables at a 90 degree angle, but I might be able to think out something, but any suggestions are more than welcome...I know this is a common problem.

 

[ssscientist]

Musical gear and computers don't consume as much power as it might seem.

I use an Isobar Triplite which has four outlets and I plug a powerstrip into each outlet. That means everything is running off of a single outlet which produces no buzz of any kind in my system. If you'd like to keep the computer on the other side of the room a lawn mower extension cord what I would recommend.


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[RideTheCrash]

I fixed the problem. I tore apart my room and made a clean path for the snakes to the soundcard. With the mixer plugged into a powerstrip on one side of the room, and the computer power plugged into a powerstrip on the opposite wall ONLY, I still got nasty buzz, so I ran the computer power cable to the powerstrip the mixer was on, and it went completely away. I guess it was creating a ground loop -- and I suppose it means each wall is on a different circuit. Now I know...

When I was searching I'm sure I read that by having my audio stuff connected to my computer, and having the computer power on a different circuit, that'd be creating the ground loop. In that case, I also ran my computer monitor power from the same strip. Since my computer is across the room I have the snakes and 2 power cables running parallel with them...I know, I know, I shouldn't, but I did a test and it creates no noise. If it does become a problem in the future, I'll simply move the tower to the other side of the room.

I haven't tried any recording because I still have to hook my board back up and I'm killer tired, but I'm confident it'll be fine now because it sounds normal through headphones. My desk lamp creates an extremely quiet hum...it's on the other circuit right now, but I'll just shut it off or move it later...it doesn't matter.

 

[ssscientist]

Since my computer is across the room I have the snakes and 2 power cables running parallel with them...I know, I know, I shouldn't, but I did a test and it creates no noise.

I have mine running parallel too.

I think the only thing that really makes a diff is what circuit you've got everything running on --- hence my suggestion about the 4 outlet surge protector...

.

 

[dgatwood]

I fixed the problem. I tore apart my room and made a clean path for the snakes to the soundcard. With the mixer plugged into a powerstrip on one side of the room, and the computer power plugged into a powerstrip on the opposite wall ONLY, I still got nasty buzz, so I ran the computer power cable to the powerstrip the mixer was on, and it went completely away. I guess it was creating a ground loop -- and I suppose it means each wall is on a different circuit. Now I know...

There's no such thing as a ground loop. A proper ground is a sink. Electrical current/signal goes in and doesn't come back out. Therefore, the notion of a "loop" (circuit) in a ground connection is a fallacy.

If moving a power cord fixes a ground problem, one of two things is the case:

A. Two 3-prong devices: One of your outlets is not properly grounded. No idea which one.
B. One 2-prong device, one 3-prong device: the outlet you're plugged into currently is not properly grounded. The outlet that the computer was plugged into earlier is correctly grounded. Fix the outlet you're currently plugged into.


Explanation/Analysis:

If both devices are 3-prong (and are designed correctly), then the previous wiring caused noise to flow through the shield of the cable from the device that is not properly grounded to the device that is. There's no way to know which one is which unless you add a ground lift on one device (3-prong to 2-prong adapter).

Plugging one device or the other through a ground lift adapter will probably make the hum go away. When it goes away, the outlet that the ground lift adapter is plugged into at that moment is the good outlet. Fix the other outlet and remove the *#$*&% ground lift immediately.

If you still get hum no matter which device is plugged in through a ground lift adapter, that's a little awkward to deal with. It means that both grounds are valid grounds, but that each has high resistance to a true (earth) ground. In that case, the problem could be a case of poor wiring and both outlets should likely be checked out by a trained electrician, though if you find any of the stuff talked about under "Remediation", you should try fixing that stuff first.

If either device is 2-prong, noise is likely to flow from the 2-prong device to the 3-prong device via the cable shield so long as the 3-prong device is grounded. If moving the cable makes this go away, it means that the 3-prong device was grounded before and no longer is. Fix the outlet into which the 3-prong device is currently plugged.


Remediation:

In the case of two 3-prong devices, you need to fix your outlet(s) ASAP. In the case of a mix of 2-prong and 3-prong devices, you still need to fix the outlet since the problem should not have disappeared. However, you should also add a ground bus to shunt the noise to the building ground. More on this here.

If the circuits are on separate grounding rods, this indicates that the grounding rods are inadequate. Drive a new rod a few feet away and hook them together with a heavy gauge copper wire.

If the circuits are grounded via a copper pipe, you should connect all of those grounds together PROPERLY with a heavy gauge solid conductor wire and run that through the wall to a real grounding rod.

 

[RideTheCrash]

Really? Everybody seemed to suggest something like it creates two paths to the ground, but I have almost no electrical knowledge. I wouldn't be surprised if the wiring is messed up in this house, they honestly did some extremely sketchy things when they built it. I guess if I really wanted to I could have my father in law, who is an electrican, look through everything, but it's not too big of a deal. The only thing we have in our house to check outlets is a little pen thing that flashes if the circuit is live.

What if I plugged my mixer and computer in the same strip on the other side of the wall and the buzz went away? I would try, but I don't want to move everything around again. But both the mixer and the CPU are 3 prong cables.

I read about a (dangerous) trick of ripping off the ground pin to eliminate buzz. My old Farfisa organ me I got a while back has had it's ground pin ripped off, and I never knew why, but maybe the previous owners had some horrible buzz problem and took the lazy route to "fix" it. I still have to get to the store and buy a new plug, because I don't like running the organ on a 2 prong cable.

 

[dgatwood]

Really? Everybody seemed to suggest something like it creates two paths to the ground....

Two paths to ground isn't inherently a problem. Two paths to ground of unequal quality can be, but only if the path of least resistance is through an audio cable. The solution is either to improve the other path to ground so that it is significantly better (which usually involves fixing a broken ground on an outlet or wiring grounding pigtails for a 2-prong device) or to split the path so that the better path is no longer connected (usually with a transformer). Improving the mains ground is the better solution for safety reasons, but a transformer will do in a pinch.

I guess if I really wanted to I could have my father in law, who is an electrican, look through everything, but it's not too big of a deal. The only thing we have in our house to check outlets is a little pen thing that flashes if the circuit is live.

Get yourself a three-prong quick tester. You plug it into the outlet and it checks to make sure that hot-neutral and hot-ground light up and neutral-ground doesn't. That said, even this will only tell you if the ground is grounded, but won't tell how solid the ground is....

You know, I just did the math, and I just realized that if the difference in length of wire for one circuit is significantly different, this could make enough difference in resistance to cause the problem you describe even if the ground is relatively solid. (I assumed cable shield resistance would be higher than it actually is. Probably depends on the quality of wire.)

A 10 foot difference in length would be 0.0187 ohms (assuming 12 AWG house wiring). A really good audio cable shield could be as low as .017 ohms for 10 feet. This means that the difference in length of the ground wires in your house wiring needs to be slightly less than the length of the audio cable between devices or you'll start to get a bit of leakage across the audio cable.

Note: this is why I always suggest 10 AWG wire for ground straps. At .0118 ohms for 10 feet, you can get away with a lot more. If only houses were consistently wired with bigger wire....

What if I plugged my mixer and computer in the same strip on the other side of the wall and the buzz went away? I would try, but I don't want to move everything around again. But both the mixer and the CPU are 3 prong cables.

It should go away. If the single outlet you pick is good, you'll have a solid ground path via the outlet for both devices, so no noise will flow across the audio cable because the best path to ground will be through the power cord. If the single outlet is bad, you'll have no viable ground path via the outlet, so no noise will flow across the audio cable since neither device is grounded and the noise wouldn't have any place to go once it reached the other end of the audio cable.

I read about a (dangerous) trick of ripping off the ground pin to eliminate buzz. My old Farfisa organ me I got a while back has had it's ground pin ripped off, and I never knew why, but maybe the previous owners had some horrible buzz problem and took the lazy route to "fix" it. I still have to get to the store and buy a new plug, because I don't like running the organ on a 2 prong cable.

Something that old more likely had the ground pin ripped off because it was used in a house that had two-prong outlets.

 

[RideTheCrash]

I figured it was because somebody didn't have a 3 plug outlet too, but honestly, around here the only house I've been in with 2 prong plugs was the house my dad grew up in which recently left my family's possession. We were packing up the place and I found a ton of them.