Help to diagnose/fix my electronics problem (L2500)

[Jeff Moote]

The bass is a newer L2500 (c. 2002 or so)

I've always found it a bit noisy and microphonic actually, but I just ignored it. Now it's had a ground related noise problem that hasn't been that noticeable since my hands were always on the strings, but I recently put some tapewounds on breaking the ground and...

- the bass hums, mostly in certain environments (fluorescent lights, etc.) but a little bit all the time.
- it's worse with the preamp (active) on than off (passive)
- it goes away when I touch the bridge or knobs (thus my diagnosis of a grounding issue)
- it is worse with both pickups on than with either one
- it happens independantly of series/single coil/parallel (I've currently done the single outer/parallel/single inner mod)

In addition, I find the pots are getting a bit noisy in their age, but that is an easy fix whether I decide to replace them or spray some contact cleaner in.

Before I decide what to do, I need to know if this is as simple as a ground issue somewhere in the circuit, if it's the pickups (worst case, perhaps?) or just in the nature of this circuit.

Any ideas?

[spideyjg]

Improve your bridge to ground wire contact....That may cure or at least help it.
Run a bare wire from the plug sleeve to the knobs or bridge and see if that improves it before gutting it.

[Jeff Moote]

Originally Posted by spideyjg

Improve your bridge to ground wire contact....That may cure or at least help it.
Run a bare wire from the plug sleeve to the knobs or bridge and see if that improves it before gutting it.

Thanks for the suggestion. I'll take a look under the bridge and see how it was done, but the fact that touching these locations indicates to me that they are already grounded.

[spideyjg]

They just stick the wire under there. I added the strip of shielding tape to improve the contact. Other guys have run the wire to one of the screw holes to improve it on theirs.

Jim

[Jeff Moote]

Originally Posted by spideyjg

They just stick the wire under there. I added the strip of shielding tape to improve the contact. Other guys have run the wire to one of the screw holes to improve it on theirs.

Jim

I checked under the bridge and throughout the cavity and the ground was continuous. I feel that this is a shielding issue as with further investigation I can get it to go away by moving to different locations. In my room where I found it the worst, I could stop the hum by shutting off my (fluorescent) light. The basses from that era were not shielded at all, though I don't know why. Someday I might get around to that job...

[sunbeast]

If touching the knobs makes the problem go away, you might want to check whether your amp or electrical socket is grounded properly (because that means the bridge connection is already grounded to the knobs- if all the pots work correctly, then those are correctly grounded to the jack as well...)- my G&Ls display the same problems, but only where there is a bad ground in the electrical system (wall socket or bad ground jack on my amps cord, for example)...is there a ground lift switch on the back of your amp? if so, try that- also, if touching a metal plate on the amp makes the noise go away then your bass is not the problem!

Karl

[Jeff Moote]

Thanks for the tips Karl. I didn't think it was the bass because I checked all these spots for proper wiring.

I tried the ground lift on my amp, but I'm pretty sure that switch is only for the DI signal. The thing that makes me think it's a shielding thing is that all my other basses (with shielded cavities) don't have this problem at all.