Grounding Probs

[GREGMW]

Hey guys,

Today I pluged the guitar in and it sounded like crap.

I have 2 humbuckers and I am getting heaps of noise out of them.

The drawing I have shows the pot cases all grounded in a "daisy chain" with wire on the back of them.

Because they are touching the copper foil in the cavity, they are already grounded .

Should I remove the ground from the back of the pots and just use the foil as the ground for them or go the other way and insulate the body where it sits on the foil and run a wire from the back of the pot to a single ground point.

By doing both could I be getting a ground loop which is causing this noise.It gets worse when I touch the strings

I am using a 500K volume pot is this correct ?

Oh, and can I damage the pickups using a multi meter etc on them?

Thanks again,and again!

Greg

[Dugz Ink]

First, a ground loop is caused by having two components (which share an audio input/output) grounded to two different grounding points or grounded through two different circuits. (Ground loops commonly occur when you plug your amp into one circuit breaker and your effects box into a different circuit breaker.) In this case, it sounds like you would be grounding to the same foil or the same wire, and that would not create a ground loop.

RFI in a humbucker is usually a sign of one of three things: 1) your humbuckers are not wired properly, so they do not have any noise cancellation properties, 2) you're sitting next to a huge source of RFI, like a big fat CRT video monitor for a computer or a bad dimmer switch for the overhead lights, or 3) you have cracked/loose ground connections between the foil and the other components, in which case the foil is picking up RFI that cannot bleed off properly.

In the first case, your pickup could be wired with the North Finish wire attached to the South Start wire, which is like wiring two single coils in series. It won't do anything but double the output, including the output of any noise they pick up.

In the second case, well, you need at least 1/8" of aluminum to sheild against that much RFI, and the joints in the shielding have to be perfect... but an easy alternative is to walk away from the source of RFI, or just turn off the source of RFI.

In the third case, cleaning contact points (between pots and foil) could make a big difference. Soldering a ground wire to the foil, which goes to the daisy chain that you mentioned, would eliminate that problem.

However, there's something else to consider... on top of those three things.

If the RFI increases when you touch the strings, then I would suspect that your bridge is not properly grounded. Most people think that the human body is a ground, but that would only be true if you were playing while standing barefoot in a puddle of water. Since you are probably wearing shoes and/or standing on a wooden/carpetted floor, YOU are not grounded, so your body picks up RFI and then transmits it to the guitar when you touch the strings, thus providing a conduit that transmits RFI the entire length of your guitar - your strings.

Check the ground on your bridge, as well as the three things that I listed.

D~s

Edited November 13, 2004 by Dugz Ink

[GREGMW]

Thanks Dugz,

I am sure I have the pickups wired the right way around.

They are Seymour Duncan and I have used the colours that they say.

I put the pickups in the way they show in the details that came with them.

I feel that the problem is in the grounding - some where

When I grounded the (fixed) bridge,I put a wire under the bridge then screwed the bridge down clamping the wire between the body and the bridge.Inever soldered the wire to the bridge.

Can I damage the pickups in any way?

Thanks

Greg

[lovekraft]

...can I  damage the pickups using a multi  meter etc on them?

No, about the only way you could damage your pickups with a multimeter wolud be to puncture the windings with the probe.

Should I remove the ground from the back of the pots  and just  use the foil as the ground for them  or  go the other way and insulate the body where it sits on the foil and run a wire from the back of the pot to  a single  ground point.

It's a good idea to use either one or the other - having two different paths to ground is a classic ground loop setup. I'd isolate the pots from the shield personally, but that's just me.

I am using a 500K volume pot is this correct ?

Absolutely!

BTW, what kind of noise are you getting - is it hiss, hum/buzz, or Mexican radio stations?

[GREGMW]

Thanks Lovecraft,

BTW, what kind of noise are you getting - is it hiss, hum/buzz, or Mexican radio stations?

Mexican radio stations would sound better!! but its a hum/buzz -worse when I touch the strings

[GREGMW]

I have re done all of the earths and have reduced the noise by about 80%.

What I find now is if I touch the metal jack plug at the guitar,the hum goes.

Should I use shielded cable for the output?

Every now and then I get a "cracking" noise like a capacitor discharging

Any help appreciated<

Greg

[Dugz Ink]

I have re done all of the earths and have reduced the noise by about 80%.

Now that IS interesting. If your pot is grounded to a wire AND the shield, and both connect to the same ground, you DO technically have a loop... but that won't matter unless one path has more resistance than the other.

That's what creates the noise; the flow on one path is slower than the other path.

D~s

[lovekraft]

Where is the ground on your output jack connected? It sounds like you got rid of most of the ground loop problem, but you might still benefit from running all grounds to a single point, or star-grounding. I usually connect all grounds, including the bridge grounding lead and the shielding foil lead(s), to the back of the volume pot, just to eliminate any chance of a ground loop. You might want to take a look at John Atchley's tro8bleshooting guides over at Guitar Nuts - he's done a good job of showing you how to isolate and eliminate noise problems step by step:

Guitar Nuts Troubleshooting Guides

[GREGMW]

Where is the ground on your output jack connected? It sounds like you got rid of most of the ground loop problem, but you might still benefit from running all grounds to a single point,

The ground is run back to a "single"point like all of the other earths.

The only thing that I was thinking is that I painted the whole cavity with conductive paint then lined ,over the top of the paint with copper foil .

Could doing it this way be causing some noise.I have soldered all of the earths to the copper and all the joins on the copper have been soldered.

Its still too noisy to play..

Thanks

Greg

[lovekraft]

If you're using the copper foil as your ground point, that could be the problem. Try soldering all the ground/earth wires, including a single wire from the copper foil, to the back of the volume pot. Have you had a chance to run through those troubleshooting guides yet?

[Dugz Ink]

Welcome tothe world of grounding... a world full of myths and mysteries.

I spent numerous years of my broadcasting career chasing ground-related problems... which included RFI getting into the audio chain through the ground system... and I still don't have all of the answers.

But there is one "grounding" fact that is absolute: Resistance is the enemy.

You MUST have a nearly resistance-free ground system, otherwsie you WILL have trouble. (None are truly resistance-free, because wire/solder/etc. create minute levels of resistance.) As I pointed out before, resistance is the cause of what we call "ground-loop hum"... and the point of resistance can also be the reception point of RFI. Resistance can be caused by a little oxidation (rust) between a casing and the pot that is mounted to it. It can be caused by two pieces of metal that barely touch each other. It can be caused by a mediocre solder joint.

All of the shielded equipment that I worked on was set up in one of two ways: 1) All components where grounded to the shielding, or 2) All components where insulated from the shielding, and had their own grounding location, which was then attached to the same point as the shield's grounding.

If you're in an area where there's a lot of RFI, the second option is the best because the shielding is less likely to introduce RF into the audio chain. Otherwise, one will work just as good as the other... as long as there isn't any resistance.

With all of that said, look at your problems and your wiring, and follow the paths.

Your body introduces RF indirectly to the guitar. (That's a fact, not a myth.) In your case, this RF disappears when you ground yourself by touching the output jack/plug. But it looks like you're saying that it does NOT disappear completely when you touch the strings. That leads me to believe that you don't have a resistance-free path from the strings to the output jack. This could also mean that the strings were working as an RF antenna, picking up energy and transmitting it into the "ground" system... thus introducing it into the audio chain.

I don't know how your bridge is grounded, but the best advice I have seen on this forum is to solder your ground wire to a piece of copper plate/foil that was almost as wide/long as the bridge... then place that piece of copper under the bridge.

Of course, if your bridge is powder-coated (like the one I just bought) you'll need to file off all of the coating where the bridge contacts the copper. Just make the base-surface of the bridge as level and shiny as possible... without using chemicals to polish the surface.

And if that doesn't fix the problem, then you move down the chain, in an orderly fashion, checking every connection, and everything that is connected to every connection.

And sometimes you do all of that and you don't find the problem, so you throw out the pots, jacks, wires, and switches and start over... and the problem is "mysteriously" fixed... because there was a crack somewhere in something that was too small to see, but it was creating huge problems.

Yeah... that's what I used to do for a living. It was so much fun... NOT!

D~s

[GREGMW]

Thanks Lovecraft & Dugz for your constant help.

I will do what you suggest and will probably end up starting from scratch,bit by bit.

I might start off removing the copper foil and just leaving the paint to do the job.

Its probably the easiest to try.

Anyway if nothing else,the guitar looks good!

I will post how I go,

Regards

Greg

[thedoctor]

Since the noise is better when you touch the JACK, what are the chances you have your output to jack reversed? I know, I know. It can't be that simple but I've done it more than once.