Ground Loop ?? Please help !

Thanks to every one for all the great info on this forum. I am having some hum issues while tracking guitars in my studio The amps are humming pretty bad . My guitars that have humbuckers are very sensitive to where they are located while tracking like if Im using single coils . I did a test with a long guitar cord walking all through the control room and the noise would get really bad in some spots The amplifier heads are in the control room with me . The cabinets are in a iso room in another part of the studio. I have two 20 amp dedicated circuits for the studio that are wired with 12/4 BX cable . My rack gear and computer on one only using 3 amps on the circuit. Guitar amps on another. Im wondering if I created a ground loop. The receptacles are wired as follows Red - Isolated ground that goes to a ground bar in its own small panel then to its own earth ground . That ground is tied to the main ground of the building. Green - goes to the outlet boxes then to the ground in my panel where all of my other grounds are . White- neutral Black - Hot My studios panel is sub panel . The main panel is in the basement of a two story building . There is also a tenant below me that also has a sub panel from the main. Im wondering whats gong on its driving me nuts ! Do I need my own panel main panel for the studio ? Is my wiring off ? How do I test for ground loops ? Please let me know Thanks !

Red - Isolated ground that goes to a ground bar in its own small panel then to its own earth ground . That ground is tied to the main ground of the building. Green - goes to the outlet boxes then to the ground in my panel where all of my other grounds are . White- neutral Black - Hot My studios panel is sub panel . The main panel is in the basement of a two story building . There is also a tenant below me that also has a sub panel from the main. Im wondering whats gong on its driving me nuts ! Do I need my own panel main panel for the studio ? Is my wiring off ?

For starters, put some green tape on both ends of that red wire since you're using it as a ground. Secondly, my first instinct, is yes, you have a ground loop with multiple points to ground. Question: Is your outlet box metal, and is it connected to conduit, metal studs, etc. Is the outlet an ISG type or a standard outlet?

Thanks for posting I already labled the red wires as ground with green tape. Yes my outlet boxes are metal and they are connected to conduit ( the armour jacket of the BX I used ) My outlets are ISG type. What is the best way to track down this problem ? I notice some amps( Marshalls ) are worse then others. Any help would be great . I really need to take care of this problem Thanks

Does the problem still exist when the head is in w/ the cabinet and using a shorter cable? What else is on the same circuit as the amps? What happens if you tie the "separate" ground wire from the ISG that is currently going to it's own rod and moving it to the main ground on the house? Have taken a multimeter and checked to see if you're getting voltage on the ground?

Hi, I have tried different amps is different places in he studio. I tried my my main Marshall with short cables . The circuit that I use for the amps in the studio is separate from everything else nothing but the guitar amp are on that circuit. I even took my Marshall to other spots in the building and got the same results . I also turned off every circuit in the building except for the one I use for guitars and still got the same noise . The separate ground from the ISG goes to the ground rod and from there it is connected to the house ground . Should I try separating it from the house ground ? I have not tried using a multimeter to see if I have voltage on the ground. Im not sure how to do that ? There are a few things I have noticed and found out while doing my testing. The noise I have is the same noise I had before I put in the individual circuits for the studio . So it leeds me to believe it is an existing issue with the power coming into where I have the studio. Im wondering if I have enough amps for the studio. Right now I have 100 amps . Is that enough ? I am laso wondering if there is an issue with how my service is split at the main. At the main were it is separated the neutral and ground are tied together The electrician I had said thats the way it should be ? Another thing I noticed is something similar to something mentioned in the Rod Gervias book on page 103 concerning a studio that had a similar problem as mine. He talks about the water service being shared by two buildings. I have a similar situation here. The water main comes in and then is shared buy the building next to me. The main ground in tied to that water main . I am thinking to try what he did and add a non metallic connector on the water service between the two buildings. I am going to try the things you suggested I really want to thank you for your help !

Short on time at the moment, but can you pull the ground off the Water Pipe and run that ground to your new rod? As far as the Neutral & Ground tied at the panel, yes that is correct and is code.

I was thinking to do that. I will do that tonight or tomorrow

One other thing... are you recording to computer? If so, are you using CRT (tube) monitors or LCD's? If you are using CRT's, try turning them off and see if the noise goes away. Dave.

Ok heres what I tried . I took the ground off of the water main and connected it to the new ground rod . It did not help at all . Yes I am recording to a computer . I turned everything off in the studio and still had the issue. I also tested to see if I have voltage on the ground and I do not. The electrician who wired everything was here and he is stumped .He says everything is the way it should be and up to code. He thinks I am getting outside interference . I now have to try connecting the separate ground wire to the house. I was thinking of trying an isolation transformer . Where do I hook that up ? Also do you think a balanced power unit will help me out. Some thing like an Equitech or Furman IT-20 ?

Computers and other newer electronics don't like balanced power very much. If you have turned *everything* off, except for the guitar and amp (no connection from the amp to anything else in the studio) then you have either a guitar problem, an amp problem, or a rediculously noisy environment... :( Dave.

What kind of lighting do you have? Do your lights have dimmers or ballast's (fluorescent or CFL)? Have you tried turning the lights off? Ellery

I dont have dimmers or ballasts. The Guitar I use most is a 59 Reissue Les Paul . The Amp is a 1970 50 Watt Marshall. The Guitar and Amp are fine. I just used them in another studio and I did not have the same issues. I think there is something going on in my building with the power or some kind of interference that my guitars are picking up. I will have some time this weekend to go threw some more things. I will be trying my friends isolation transformer . I really dont know what else to do. Everything else in my place works fine.

A 1970 amplifier just might have a capacitor connected from the primary AC wiring to the chassis.

When the amp is turned up with out a guitar pluged in it makes no noise.When a guitar is pluged in it does. Like I said in one of my earlier post a humbucker acts like a single coil. The noise gets louder then quiter when you turn the guitar in a circle . This should not happen with humbuckers

On re-reading all of this, it looks like you may be picking up radiated EMI at the guitar. If the hum changes when you rotate the guitar (without changing your position) it's a good indication that your getting a strong Electro-Magnetic field. Fields are not always easy to find. Roam around the room with your guitar, look for the loudest hum. At my old day-time job, the CAD room had a field that messed up the CRT monitors. The smartest people I know, never solved the problem. Check near the floor, walls and ceiling. Check all the pipes and conduit and anything else thats metal.

Thanks speedskater. Ive been thinking I have that kind of problem here . A very good tech I know in NYC said my issue may be a strong hum field coming into my place and it may have nothing to do with the way my place is wired. Im at my wits end with it . I have found the position that picks it up the least I really would like to figure this out

If i am picking up radiated EMI what do I do ? How do I get rid of it or make it better ?

I just saw an ad for a $30 US, EMI / RFI meter.

Where did you see that ? Id like to get one

A web store called: Cyberguys Cellular Phone/emf Detection Meter Item # 250 1304 $29.95 I have made 3 purchases from them in the past 3 years. They seem to be OK.

Thanks Im going to check it out