Ground Loop, Noise, Getting Shocked

[travelin travis]

I think I have a ground loop some where. I don't know much about electrical stuff. I have my DAW and all it's components plugged into a power strip in one room and my mixer and guitar amp in another room. Sometimes I get a little buzz (shock) from touching my mixer or mic. This isn't static, it's a steady flow. A friend was over last night playing guitar and he accidentally touched a metal lamp with one of my guitars stray string ends. It melted the end of the string! I know that I have been getting way too much hum and buzz in my guitar amp and sometimes in my mixer. Does anyone know what I can do to fix this? Maybe a isolation transformer? Like I said, I don't know much about all things electrical. I have a multi meter if anyone could suggest how to test for problems. Any help is appreciated.

[Track Rat]

Put everything on the same circuit by running an extention cord from where the DAW and associated gear is plugged in to your remote location.

[Adam P]

I don't know about the string melting or whatever, but an Ebtech Hum Eliminator does a great job of killing those ground loops.

[Phyl]

If you're getting shocked and it's a steady flow of current, you've got more than a ground loop, you've got a lifted ground somewhere.

1 - Make sure everything is plugged into a 3 prong wall outlet
2 - Make sure the power strip has three prong outlets
3 - Make sure none of the equipment has a ground lift switch engaged
4- Make sure none of the equipment has a grounding problem, i.e., the chassis is floating.

5 - And most importantly, make sure the ground in your house wiring actually goes to ground.

Get a friend with a voltmeter to help you out if this doesn't make sense.

[Cave Dweller]

might you be using a vintage guitar amp that is not properly grounded?

[travelin travis]

Thanks for all the quick responses. All of the equipment is 3 prong, except the mixer, no ground lifts engaged. Something that concerns me is the mixer having a two prong plug. I guess it has no ground? I will get an extension chord and run the other stuff to the same outlet and see what that does. I live in a really old apartment so there may be a problem with the wiring here. Come to think of it, I have had two alarm clocks die for no obvious reason.

When I say "getting shocked", it feels like low amperage, it's pretty light but I know it should'nt be happening. How do I check for a "floating chassis"? I wish the amp was an old tube amp but it's digital. I had some problems out of the amp a while back and am experiencing some new ones now. One of the problems is when I turn the power off to the amp, it makes a loud pop. If I remove the guitar chord from the input jack before turning it off, it does'nt pop. How can I check to see if the amp is properly grounded or shorting to ground?

[MOFO Pro]

Originally Posted by TravisinFlorida

How can I check to see if the amp is properly grounded or shorting to ground?

Very carefully... I repeat... very carefully... touch one lead of the VOM to the audio shield of the amplifier while inserting the other onto the ground lug of the amp power cord (just tip the plug away from the wall a bit) The volt meter should be set to read at least 120 VAC. Any voltage you read is leaking to your ground...

Though it sounds like your problem is miswired outlets, or missing neutrals and/or grounds, on your house wiring. If it's an old house, some of those outlet grounds are just jumped to the wiring box which aren't attached to any ground...purely cometic

The actual outlet should read 110 volts between the narrow slot(hot) and ground, 110 volts between the narrow(hot)and wide(neutral) slot, and zip... nada... nothing... between neutral and ground. Neutral in 110 residential wiring is actually just a backup for a failed ground.

[travelin travis]

I got home tonight and went to grab my vom meter.......it's all messed up from being in a junk tool box, the battery is pretty much formed to the case by rust. So, I proceeded to plug everything into the same outlet. No shocking going on now. Thanks for the help.

My amp still pops when powering down and my M179 mic makes a hum in my headphones when I touch the body around where the rolloff, pad, and pattern switches are, as it did before. Any ideas on the mic? I hope it's not damaged. I might as well play the hell out of the amp until it dies again cause I know once I send it off for repair, it will be gone awhile. This really pisses me off about the amp because it sounds pretty damn good. Too bad it's so unreliable.

I don't really understand this ground loop thing. What would I have to do to be able to plug my amp and mixer into the outlet in the other room, without getting shocked?

I'm gonna get a new vom meter and start checking outlets from now on. Is there anyway to test outlets to see if there will be a ground loop between them?

[Cave Dweller]

Originally Posted by MOFO Pro

Neutral in 110 residential wiring is actually just a backup for a failed ground.

I believe it is the other way around.... ground is back-up for a failed neutral.

[Track Rat]

What can happen is this. If you have gear that plugged into two or more electrical outlets that are on different circuits (breakers or fuses from your house mains), you can have a DIFFERENCE OF POTENTIAL of AC return between the stuff on the two circuits. Connecting these two differences of potentials with something like an audio connection can result in an audible 60 cycle hum. Completing the connection between a person holding an electric guitar touching his lips to a microphone that's on the other side results in Ready Kilowatt slapping you in the mouth.

[MOFO Pro]

Originally Posted by Cave Dweller

I believe it is the other way around.... ground is back-up for a failed neutral.

I stand corrected... factually you're correct... circuit wise, the two connections are virtually identical...

As far as difference of potential between two outlets... Electrons will follow the path of least resitance to ground... If you have two outlets, one with a good ground, and one with a corroded or bad connection to ground... if you were to touch the ground of each of these outlet simultaniously... you could well become a better path to ground from the defective outlet to the good one... scarier yet, if the Hot and Neutral are swapped on one of the outlets (both would work fine individually) you would now become ground for the full potential of the outlet...wham!!! (This would weld guitar strings to lamps)

You can purchase outlet testers that will confirm wiring polarity and grounding fairly cheaply (under $10.00) from any hardware store. It won't verify a good ground, just that the outlet is wired correctly.

[Phyl]

Originally Posted by TravisinFlorida

I got home tonight and went to grab my vom meter.......it's all messed up from being in a junk tool box, the battery is pretty much formed to the case by rust. So, I proceeded to plug everything into the same outlet. No shocking going on now. Thanks for the help.

My amp still pops when powering down and my M179 mic makes a hum in my headphones when I touch the body around where the rolloff, pad, and pattern switches are, as it did before. Any ideas on the mic? I hope it's not damaged. I might as well play the hell out of the amp until it dies again cause I know once I send it off for repair, it will be gone awhile. This really pisses me off about the amp because it sounds pretty damn good. Too bad it's so unreliable.

I don't really understand this ground loop thing. What would I have to do to be able to plug my amp and mixer into the outlet in the other room, without getting shocked?

I'm gonna get a new vom meter and start checking outlets from now on. Is there anyway to test outlets to see if there will be a ground loop between them?

It seems odd that your mixer doesn't have a 3 prong plug, especially since (I think) it serves as the central ground point for all the mic and instrument cables coming into it.

This could have something to do with your mic being sensitive to handling. I'm tempted to suggest that you run an external ground wire between your mixer chassis and some ground point just to see if it helps matters any. You could do this with a piece of wire that has alligator clips on each end. You might also use a voltmeter to check the voltage between your mixer chassis and an external ground point.

[MOFO Pro]

Originally Posted by Phyl

It seems odd that your mixer doesn't have a 3 prong plug, especially since (I think) it serves as the central ground point for all the mic and instrument cables coming into it.

Could be that it's powered by a wall wart that feeds a DC voltage to the mixer... the transfomer would isolate the ground unless the ground was fed around the transformer... I've got a couple of Tascam TM-D1000 boards where this is the case... but I've always powered all my equipment from the same circuit

Like the chassis ground idea... once he's confident that the outlets are wired correctly...

[travelin travis]

So I could ground my mixer by simply running a wire from the chassis to the ground of an outlet? Assuming the outlet ground is good? I will probably pick up a new meter, or one of those outlet testers this weekend and check out my outlets. Thanks to everyone for the info and help. I wonder why a ground was'nt used on this mixer. Btw, it's a Yamaha MG 12/4. It seems like a lousy way to cut costs, if that was the idea.

[Track Rat]

If you have properly grounded three prong plugs, yes you could run a ground wire from the chassis of the mixer to the outlet. Use the screw that holds the plate on the outlet to connect.

[earworm]

sorry to interfear but i'm a real dummy concerning electronics,
i don't have a ground in my room (yes, i know, but its not me who built the house...)

my joemeek vc8 has a ground lift switch

now should i press it or not?
sometimes i do here a little tiny difference in hum,
is it only for hum, or more for protection that i should press or depress that button?

[Phyl]

Originally Posted by earworm

sorry to interfear but i'm a real dummy concerning electronics,
i don't have a ground in my room (yes, i know, but its not me who built the house...)

my joemeek vc8 has a ground lift switch

now should i press it or not?
sometimes i do here a little tiny difference in hum,
is it only for hum, or more for protection that i should press or depress that button?

In theory it's a really bad idea, because although it could reduce the hum you experience in some situations, it also decouples the chassis from earth ground, and if in the event of some internal problem with your unit, could allow the chassis to float to a dangerous level above ground. If this worst case was to happen, and you touched the chassis with one hand while touching some earth ground with the other hand, you would experience the wonders of Ohms law.

In practice it's probabaly okay to lift the ground for limited periods while you figure out a better way to deal with the problem.

[xstatic]

Phyl, wouldn't that only be true if the ground lift switch lifted the AC ground? I believe that the ground lift on something like the Joe Meek VC8 would actually be a signal lift.

[Track Rat]

Originally Posted by xstatic

Phyl, wouldn't that only be true if the ground lift switch lifted the AC ground? I believe that the ground lift on something like the Joe Meek VC8 would actually be a signal lift.

True. It floats the ground on the signal path, not the mains I believe.

[Phyl]

Originally Posted by xstatic

Phyl, wouldn't that only be true if the ground lift switch lifted the AC ground? I believe that the ground lift on something like the Joe Meek VC8 would actually be a signal lift.

Your right - how the switch is implemented makes a big difference. My experience is limited to older equipment that actually disconnected the ground.