Grounding issue hum

Relayer59 · #1 06-21-2007, 04:18 PM

I have a G&L SB 1 that sounds and plays great except that it has a buzz/hum that I can stop by touching the jack. It's not a RF issue, it seems to be a ground at the jack issue. I took the pickgaurd off and inspected all the wiring including the black wire (ground) from the jack to the bridge and all looks fine. Any ideas on how to fix? Thanks.

202dy · #2 06-21-2007, 04:31 PM

Does it hum when you touch the strings?

Relayer59 · #3 06-21-2007, 04:36 PM

Yes, sorry I left out that detail...touching the strings doesn't do anything, it still hums. Only touching the jack edge or the male jack on a cord (if it's metal and not insulated). I've tried different cords, etc. My other basses don't do it. Does that give you more to work with? Thanks.

Turnaround · #4 06-21-2007, 06:03 PM

Quote:

Originally Posted by 202dy

Does it hum when you touch the strings?

While I think of it -

When you ask if the hum stops when you touch the strings, it's worth asking what strings are being used. Thouching tapewounds and some coated strings (like DR Black Beauties) will have no effect since you don't actually complete an electrical circuit. The tape or coating insulates you from the string.

FWIW.

Relayer59 · #5 06-21-2007, 07:26 PM

Stainless steel rounds. I'm thinking maybe there is a short in the wire between the jack and the bridge. Ideas?

Relayer59 · #6 06-21-2007, 09:38 PM

Great questions...anybody have any answers?

Relayer59 · #7 06-22-2007, 08:40 AM

Hmmm...nobody has any ideas? I'm hoping to play it tonight at a gig and was thinking I might find an easy fix.

T-Bird · #8 06-22-2007, 09:24 AM

Hi.

The bridge ground wire is just broken (open), no biggie. You can bypass it quickly by tying a wire somewhere on Your bridge and running it under the jack nut. This is, if the wire is broken in the bridge end. If it's the pot end, just solder it back.

I personally never ground bridges/strings because i sing also and a phase or isolating issue between bass/guitar rig and whatever rig the mike is connected to tends to be quite shocking

.

Just my 0.02E
Sam

pkr2 · #9 06-22-2007, 09:32 AM

The symptoms point to an ungrounded bridge.

The ground wire is usually just "pinched" between the bridge and the wood of the body. Since the metal in the bridge and the copper wire are dissimilar metals there is a possibility that corrosion could develop through electrolysis at the connection, causing a less than perfect connection.

You can do a quick and dirty test by simply attaching a temporary ground wire between the bridge and the attaching nut on the output jack. If the problem goes away, or improves, remove the bridge and scrape the ground wire clean and shiny, sand the bottom of the bridge plate where it contacts the ground wire to clean the surface and reassemble everything.

If your bass isn't shielded, it may be a good time to do so. It can never hurt to do a good shielding job.

If your bass is not "star" grounded, it's an easy mod that definitely makes for less noisy electronics. Star grounding is basically just bringing all of the grounds to one common point, usually, the ground tab on the output jack or the back of one of the pots. There's lots of info on the web with a more thorough description, if you decide to go that route.

Star grounding helps to eliminate "ground loops", which are very hard to diagnose because the ground connections can be electrically sound but still cause AC hum.

Good luck with the problem.

Relayer59 · #10 06-22-2007, 11:24 AM

Thanks T-bird and pkr2! I did just a few minutes ago "jump" a wire from the jack ground to a screw on the bridge and 90% of the noise went away. I had already checked the solder joints and they all looked good, so there must be a short inside the ground wire's insulation?

I need to look into star grounding! Do you guys know where I can see a schematic of a split coil passive P setup...that's basically the same wiring as the G&L. ?? Thanks again.

202dy · #11 06-22-2007, 01:08 PM

Quote:

Originally Posted by pkr2

The symptoms point to an ungrounded bridge.

The ground wire is usually just "pinched" between the bridge and the wood of the body. Since the metal in the bridge and the copper wire are dissimilar metals there is a possibility that corrosion could develop through electrolysis at the connection, causing a less than perfect connection.

You can do a quick and dirty test by simply attaching a temporary ground wire between the bridge and the attaching nut on the output jack. If the problem goes away, or improves, remove the bridge and scrape the ground wire clean and shiny, sand the bottom of the bridge plate where it contacts the ground wire to clean the surface and reassemble everything.

If your bass isn't shielded, it may be a good time to do so. It can never hurt to do a good shielding job.

If your bass is not "star" grounded, it's an easy mod that definitely makes for less noisy electronics. Star grounding is basically just bringing all of the grounds to one common point, usually, the ground tab on the output jack or the back of one of the pots. There's lots of info on the web with a more thorough description, if you decide to go that route.

Star grounding helps to eliminate "ground loops", which are very hard to diagnose because the ground connections can be electrically sound but still cause AC hum.

Good luck with the problem.

Another quick test can be performed with a multimeter. Set the meter to continuity and touch the leads to the bridge and the ground lug on the jack. If continuity registers all is well. If not it is time to start hunting.