Ground noise that dissapears when touching the strings

[pk317]

Hi guys,
It's been a mystery for me and I hope you could help me.
I did rewiring on few guitars recently (P90, SC, HB). And I have this ground noise that goes away when I touch the strings, or bridge, or output jack. The interesting thing, that I have it on two guitars only, and others are fine. I'm using the same tools, same technique, same skills, basically same everything. I run continuity tests, all seem to be connected and grounded properly, so I don't really understand the nature of the issue. For example, I have a really noisy guitar with HB (DiMarzio PAF) and really silent one with SC (Fender TexMex set). Doesn't make sense to me. I will rewire these "problematic" ones, but could really use your advices of what could possibly cause this issue.
Thanks!

[newey]

May 17, 2022 8:49:39 GMT -5 pk317 said:

I did rewiring on few guitars recently (P90, SC, HB). And I have this ground noise that goes away when I touch the strings, or bridge, or output jack.

This is an indication that the bridge/string ground is working normally. Why your HB-equipped guitar is noisier than the SC guitar I don't know, could be a wiring issue with the HB. But a reduction in noise while touching the strings is expected behavior. Since you have to touch the strings to play, the noise is usually not bothersome while playing; if it's an issue where you leave a guitar plugged in onstage as a backup, just turn down the volume.

The reason it gets quieter when you touch the strings, bridge etc is that your body is a significant source of noise; the string/bridge ground is thus grounding noise from your body. (Perhaps it is more exact to say that your body isn't producing the noise, your body is focusing the noise from the environment into your guitar electronics.)

[pk317]

Thanks, newey.
I get now the logic of why it's happening, but what's really killing me, is that I don't understand why there are guitars that much noisier than the others.

[unreg]

Continuity tests are great for quickly checking solder spots. 👍

Resistance tests are extremely grand for finding spots in your ground paths that need fixing for noise reduction. Measure resistance from your Vol pot’s lug1 (its ground lug) to the sleeve connection on your jack. If it’s extremely close to or preferably at 0, then that ground path has been soldered well.

I found solder spots & wires that needed adjusting or replacement while using resistance tests. Helped a lot.

[pk317]

Thanks, unreg. Will definitely check this out. 
If I got it right, lower resistance indicates better connection, right? Does it work for pickup wires as well?

[newey]

May 18, 2022 5:33:11 GMT -5 pk317 said:

lower resistance indicates better connection, right? Does it work for pickup wires as well?

Yes, a good connection should show close to zero Ohms resistance, single digits at most. If you put your meter across the pickup leads, you're measuring the pickup's resistance. What unreg means is checking between the two ends of a connection.

There are any number of variables involved in why one guitar is noisier than another. Shielding typically helps with single coils moreso than with HBs, since the HB is already reducing hum, at least in theory. But if your HB-equipped guitar is particularly noisy, shielding might help.

You may just have a particularly noisy electrical environment where you are playing. You can try plugging in elsewhere, in a different room on a different electrical circuit to see if that makes a difference in the noise level. You can also try to pinpoint the source by turning off fluorescent lamps, fan motors, TVs, computer monitors, etc. You may be able to find a particular culprit.

[pk317]

May 18, 2022 7:59:45 GMT -5 newey said:

May 18, 2022 5:33:11 GMT -5 pk317 said:

lower resistance indicates better connection, right? Does it work for pickup wires as well?

Yes, a good connection should show close to zero Ohms resistance, single digits at most. If you put your meter across the pickup leads, you're measuring the pickup's resistance. What unreg means is checking between the two ends of a connection.

There are any number of variables involved in why one guitar is noisier than another. Shielding typically helps with single coils moreso than with HBs, since the HB is already reducing hum, at least in theory. But if your HB-equipped guitar is particularly noisy, shielding might help.

You may just have a particularly noisy electrical environment where you are playing. You can try plugging in elsewhere, in a different room on a different electrical circuit to see if that makes a difference in the noise level. You can also try to pinpoint the source by turning off fluorescent lamps, fan motors, TVs, computer monitors, etc. You may be able to find a particular culprit.

I didn't mean to measure the pickup resistance. Let's say, I connect hot wire to switch lug, then I measure the resistance from that lug all the way till the output jack. If my soldering is good, then it shows resistance close to 0, right? 

Shielding is something to try on my list, I started it with one guitar, but then got distracted by some other stuff. Will get back to that, thanks for the tip.

[unreg]

May 18, 2022 15:10:53 GMT -5 pk317 said:

Let's say, I connect hot wire to switch lug, then I measure the resistance from that lug all the way till the output jack. If my soldering is good, then it shows resistance close to 0, right?

Hmmm… yes. Make sure to check all ground locations with the sleeve of the jack. You are trying to solve a noise issue, so ground wires and their paths need to have a low ohm reading.

[EDIT]If you find a ground path with a high (maybe multi-digit, but I wanted mine to be ultra-close to 0 ohms) resistance reading move the probes closer in on that ground path, take new resistance readings, to determine where adjustments are necessary.[/EDIT]


Note: it’s also beneficial, noise-prevention-wise, to make sure your signal grounds stay separate from your shield grounds. If you desire this, signal and shield grounds should be separate until they’ve passed through all of your guitar electronics. So, join them together near the sleeve of your jack.


Final edit: Trying to help with examples:

signal ground = Vol pot’s lug1 (ground lug)

shield ground = wires grounding the back of your pots, pot cases

[newey]

May 18, 2022 15:10:53 GMT -5 pk317 said:

Let's say, I connect hot wire to switch lug, then I measure the resistance from that lug all the way till the output jack. If my soldering is good, then it shows resistance close to 0, right? 

If the pots are in between, that can affect your measurements.

[pk317]

It turned to be problem with a pickups (HB) - sent it back to store, got a new pair, and it is dead silent now