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I have a noisy guitar that goes dead when I touch it.

Checking resistance between all metal parts and the sleeve of the cable is 0, except 1 pot that reads 30ohms.

What exactly constitutes a clean path to ground. Is 30ohms acceptable?

It quite possibly is the wiring of the house, but I've not had the change to test it elsewhere yet.

Why does touching the guitar stop the noise? Am I becoming the ground for the guitar, or am I being grounded, to the guitar?

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    Are you saying the buzz and noise go away when you touch the guitar, or are you saying if you play the open strings and then touch the guitar, there is no sound from the guitar at all? The former is totally normal. The latter is a problem. – Todd Wilcox Feb 11 '18 at 5:21
  • Why does touching the guitar stop the noise? This might be a good question for [name of electronics SE], maybe try posting that specific question there. – Ye Dawg Feb 11 '18 at 8:41
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This is not symptomatic of a ground loop. Noise from ground loops would not stop when you touch the strings.

It sounds like you have bad ground on the guitar, which is totally different from a ground loop.

Ideally you should have 0 ohms resistance. A slight variation is ok. 30 ohms... you have to evaluate what is going on there. If you get that reading on the strings, it could be the plating on your bridge adding resistance or other factors. On the other hand, if you get 30 ohms resistance at the ground solder joint on the tremolo claw, you need fix that.

Resistance greater than 0 ohms could also indicate a weak, cold or degraded solder joint. This may be what is causing the 30 ohm reading on 1 pot. I recommend resoldering that joint.

As for why touching the guitar stops the buzz, yes it is because you have become the ground. That can be dangerous. Electricity follows the path of least resistance. If the resistance of your body is less than the resistance of your path to ground, electricity will happily seek continuity to ground through you. That is why you want resistance of 0 ohms or very close to it.

Using a multi-meter with a continuity test function you should be able to easily determine if/where you have grounding problem.

Plug a cable into your guitar jack and touch one multi meter lead to the sleeve of the jack then touch the other multimeter lead to each ground joint in the guitar, starting at the connection to the jack and working backwards through your system from there. You should have 0 ohm resistance (or really close to it) on your connections to ground.

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As you've already guessed, what you have here is a ground loop. The way I've always understood it (corrections welcome), when you touch the strings or other metal parts of the guitar that should be grounded, you eliminate the potential difference and hence the noise.

I presume that the 30 ohm resistance is between the pot casing and the cable sleeve? In that case, chances are you've got some dodgy soldering there that's causing trouble. Given that everything else reads zero, it may be worthwhile fixing it.

Another thing worth checking is how your entire signal path is grounded. Ideally, everything you're running should have common ground (running from the same grounded outlet). That way, you minimize the impact of any wiring issues in your house.

Finally, the impact of any existing ground loops can be minimized by keeping clear of any sources of magnetic interference, so changing position and keeping signal cables away from power cables (as well as keeping your signal leads uncoiled when in use) can reduce the noise.

  • Thanks. When I run the guitar through a battery powered simulator (korg pandora mini) I get no noise at all. But I wasn't sure if this is because there is still a wiring issue with the guitar, but because it's not connected to ground, the issue cannot manifest. (Same as using a ground lift switch) – Dan P Feb 11 '18 at 16:33
  • @DanP That's likely. – user321 Mar 8 '18 at 11:20
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The other answers are all good answers, I'd just like to add that all guitars electric actually find their ground through their connection to the amplifier. If the amplifier jack is slightly corroded or dirty, the ground connection can easily be less than ideal. On older amps, the input jacks achieved their ground by being tightened up to the chassis of the amp ( a loose jack nut or dirt and corrosion around the mounting hole might compromise this connection). On more recently made amps the input jack is soldered directly to the amps circuit board and the solder connection may fatigue and break. Both instances are a pretty inexpensive fix at your favorite repair shop.

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