Does Shielding Create Ground Loops?

[ArieBombarie]

Hi there,

I posted this question at the end of another thread, but somehow you all missed that one So here is my question regarding shielding and groundloops:

I've read in a post that it is important to avoid ground-loops with your wiring. So you should always use one single point to which all your ground wires will connect and not have multiple paths to ground. In another post, the importance of shielding the cavities is discussed to reduce interference from electromagnetic fields (cell phones etc......)

But if you use shielding in your cavities, your pots, pick-ups and switches will touch the shielding and in doing so you will create an alternative path to ground. You will end up with ground loops between these parts...

Is this a problem? Should I make sure these parts don't touch the shielding or am I just paranoia here ?

Please advise...

Grz Arjan

[thirdstone]

Star grounding sure works on strats , i can attest to that. See guitarnuts for that. Isolate the pots by putting electrical tape under the pots. don`t forget to cut the shielding a little wider than the holes. Use one of the full coverage strat scratch plate shields available on the net. Callaham guitars makes one, they work well OR just buy noiseless pickups. Much better as most of the noise comes from the pups.

[ArieBombarie]

Star grounding sure works on strats , i can attest to that. See guitarnuts for that. Isolate the pots by putting electrical tape under the pots. don`t forget to cut the shielding a little wider than the holes. Use one of the full coverage strat scratch plate shields available on the net. Callaham guitars makes one, they work well OR just buy noiseless pickups. Much better as most of the noise comes from the pups.

Thanks for the feedback, I'm using humbuckers so they should be pretty noiseless. But if I understand you correctly you’re saying that I should make sure that the shielding doesn't touch the parts... Funny thing is that in all the posts I read on either shielding or ground loops, this wasn’t mentioned…

Grz Arjan

[curtisa]

The idea with avoiding ground loops is to avoid creating more than one path between two earthed parts back to ground. Star grounding is the surest method to avoiding loops. The shortest, most direct path for each component is also good practice.

In the case of shielded wire it can mean only connecting the shield at one end, but it depends on the application. For example if you had a pickup with a shielded cable, the shield will already be connected at the pickup end. Earthing the shield on the cables at the pickup-selector-switch end will be fine unless the shielded components of the pickup itself come in contact with another point connected to earth (eg conductive paint, earthed pickup covers etc). In this case you've created a loop between ground lug on output jack/pickup cavity shielded paint/pickup/pickup cable shield/earth connection on switch/ground lug on output jack, and the loop needs to be broken somehow.

A little bit of exploration of your guitar will reveal what's earthed and what's not, and using that info will help you build a "map" as to the best way to run your earths in the guitar. For example, you may find that the shield on the pickup cables does not connect to anything on the pickup that will come in contact with an earth inside the pickup cavity when installed (eg plastic encapsulated single coils), in which case you can safely earth the shield of the cable to a common point inside the control cavity without creating a loop within that section of wiring. The ground lug on the volume pot can also be connected to this common point safely aswell, as can the ground lug on the output jack. A shielded cable between the volume pot and the output jack cannot however, as you will then be creating a loop between the cable shield/ground lug of output jack/ground wire of output jack/volume pot ground lug/cable shield. In this case the loop can be broken by either ditching the earth wire between the output jack and common point (my preference), or lifting the shield of the cable at one end only.

Errr, dunno if that's helped things or confused them further!

[thirdstone]

In short if you are using humbuckers you dont have much to worry about. Me, I wouldn't even bother shielding the control cavity, just do what gibson have done for years, it works . P90 `s and other single coils , on-board electronics ect are a differant kettle of fish.

[GregP]

I'm not 100% sure I'd worry about it either, with humbuckers, but humbuckers are not "dead" silent... it might still prove useful.

TBH, I'm in the middle of other stuff online, so I didn't read Curtisa's post completely. The important thing to remember is that the shielding will touch your pots, at which time I like to think of the whole thing as one continuous "shell"... the shielding material, the pots, and the braided shield of the pickups -IF- there is one. These things can all be continuous with one-another. But then only ONE lead (I use the back of one pot with a wire soldered) goes to star, where the rest of the grounds (from electronics) also go. None of this "bent back lug" stuff... everything that's supposed to go to ground goes to star.

Then from star, ONE lead goes to the output jack ground lug.

So, to answer the question-- shielding doesn't inherently create ground loops-- but you have to know what to watch for. Although I sort of know what I'm talking about, all 3 times I've done a full shielding job on a guitar, my very first test run was noisy. Twice, I had the output jack wired in reverse; can't remember what the third one was.

[metalwarrior]

When I shielded my guitar I managed to kill the sound completely.

I had an EMG 85, 1 volume, battery and a stereo output jack all wired up and working correctly, but when I touched the pickup with my finger there would be a buzz so I decided to shield the pickup cavity as well as the control cavity in the back. When I did there was no sound at all, unless I unplugged the cable most of the way, then there would be sound, but the volume control seemed to be bypassed as the volume didn't change no matter where on the dial I turned it to.

When I pulled it apart I tried it again with the volume control hanging out the back, but with everything still wired up exactly the same, and to my surprise it worked again, the only difference being the volume pot was no longer in contact with the shileding paint.

After searching here on pg for similar threads I see that it might be caused by a ground loop or wiring things to the wrong place - and that's what it turned out to be. I am using a flush mount output jack that came with no instructions so I had to guess which lug was which. When I switched two of the wires around it worked in reverse to how it had been before ie, when touching the shielding paint it would now work when the cable was plugged all the way in.

The only thing that still confuses me is the ground wire between the volume pot and the out put jack - it makes no difference if it is even connected or not. I tested the guitar before connecting it (so only two of the three output jack lugs were connected) and it worked perfectly with no buzzing or cutting out. I connected it any way and it still works with no problems.

[guitar2005]

When I pulled it apart I tried it again with the volume control hanging out the back, but with everything still wired up exactly the same, and to my surprise it worked again, the only difference being the volume pot was no longer in contact with the shileding paint.

There must have been something funky or reversed in your wiring.

Shield the whole thing. I have the control pots and all outer metal parts of the electronics touching the shielding. All of the external casings of the electronics should be connected to ground.

[Tim37]

i may not be remembering right its been a little over a year since i wired a set of emg's but i don't think you ground the bridge or shielding with them.

[djhollowman]

i may not be remembering right its been a little over a year since i wired a set of emg's but i don't think you ground the bridge or shielding with them.

That's right. It explicitly says to remove the bridge earth in the installation instructions for active EMG's.

In Melvyn Hiscock's book he's very sure of the benefits of shielding the control cavity, but he says you must earth the shielding material as well, eg. by using a small screw with a wire going to ground.

DJ