Odd grounding issue I've never encountered

[JohnL]

Background info: Lakland JO-5, Fralin pups, passive factory electronics.

Just recently noticed a 'ground' buzz when I was playing a gig, which would stop as soon as I touched the strings or bridge. Finished the gig with my hand wrapped around my strings between songs.

Back home, I took the control plate off to see if the groundwire or any other solder joint had worked lose, but no dice.

I removed the strings to look under the bridge, just to check that the groundwire was still making contact; it is. Replaced the bridge, but not the strings, and plugged it in to a totally different amp, to see if the buzz was still there; it is. So I guess I eliminated the bridge/groundwire possibility, as well as a problem with the gig amp.

Now the weird part. I touch the bridge, the hum goes away, as before. But if I touch the bridge pup, and the buzz gets TWICE as loud. Touching the neck pup has no effect on the buzz whatsoever. I should also mention that I soloed each pup prior to removing the strings, and the buzz was consistent, save for touching the bridge pup.

I am fairly capable of soldering and such, and the wires all have solid connections with their pots and to the jack, and like I said before, this is something that just popped up.

I've solved grounding issues before, usually where a wire came lose or the bridge wire was yanked away, but this is a new one on me. Anyone else have this issue? Would this problem indicate a bridge pup problem, or possibly the pot to which the bridge pup is connected? Thanks in advance guys!

[SGD Lutherie]

That's not a ground buzz, that's electrostatic interference.

When you touch the strings it goes away because you are grounding your body to the strings.

The pickup is humming because the magnets are not grounded, and the hot end of the coil is on the inside, touching the magnets.

So try this, on both pickups, swap the hot and ground wires. So fir example, if white is hot and black is ground, swap them so white is ground is black is hot. You have to do both pickups.

That should fix or reduce the issue when you touch the pickups.

The other issue can be reduced with better shielding.

[JohnL]

Thank you so much for the reply! I will try that. I've seen all the threads on shielding, and I can do that, but since this was an 'all of a sudden' thing, I figured it was more than a shielding issue. Again, thanks!

[JohnL]

Originally Posted by SGD Lutherie

That's not a ground buzz, that's electrostatic interference.

When you touch the strings it goes away because you are grounding your body to the strings.

The pickup is humming because the magnets are not grounded, and the hot end of the coil is on the inside, touching the magnets.

So try this, on both pickups, swap the hot and ground wires. So fir example, if white is hot and black is ground, swap them so white is ground is black is hot. You have to do both pickups.

That should fix or reduce the issue when you touch the pickups.

The other issue can be reduced with better shielding.

David, I tried what you suggested. The only thing it accomplished was moving the very loud buzz caused by touching the pickup from the bridge pup to the neck pup. The constant buzz is still present, and with all due respect to those with more knowledge than I have, I have a hard time believing that a bass that just started buzzing after 3 years of quiet operation is just a shielding issue. Seems that would have been a problem that would have been there from the start. But...I'm out of ideas. Anyone?

One further observation, maybe an elementary one, but with the tone knob all the way off, there is no buzz whatsoever. I'm guessing the electrostatic interference is confined to a higher frequency range, and not consistent across the spectrum, but there is no noise at all with the tone off. As I turn the knob up, it gets gradually worse. I have also swapped out the cap just in case...no affect on the buzz whatsoever.

[SGD Lutherie]

Originally Posted by JohnL

David, I tried what you suggested. The only thing it accomplished was moving the very loud buzz caused by touching the pickup from the bridge pup to the neck pup.

I had a feeling that might happen. That's because the two pickups are reverse wound. You can try grounding the magnets with a piece of adhesive copper foil on the bottom so it touches the magnets, and then ground that.

You can also try wrapping some copper foil around the coils. Take the covers off and wrap the foil around. Before you wrap the foil around, solder a wire to it that can reach a ground point. You don't want to solder when it's touching the coil. The ground that wire.

The constant buzz is still present, and with all due respect to those with more knowledge than I have, I have a hard time believing that a bass that just started buzzing after 3 years of quiet operation is just a shielding issue. Seems that would have been a problem that would have been there from the start. But...I'm out of ideas. Anyone?

One further observation, maybe an elementary one, but with the tone knob all the way off, there is no buzz whatsoever. I'm guessing the electrostatic interference is confined to a higher frequency range, and not consistent across the spectrum, but there is no noise at all with the tone off. As I turn the knob up, it gets gradually worse. I have also swapped out the cap just in case...no affect on the buzz whatsoever.

The buzz goes away when the tone is turned down because it's a high frequency noise, and the tone control removes high frequencies.

Has anything else changed when the buzz started? Different amp? Different outlet it's plugged into? New light dimmers? Any new equipment close to the bass?

The buzz is external, and for some reason has appeared in your environment. Shielding will help either way.

Did the bass always have these pickups, or are they new? leo, is your patch cord new? Have you tried a different cable to plug the bass into the amp? I had a buzzing that started like this and it was my 20 year old Monster cable getting flakey.

[JohnL]

Nothing has changed for me, atmosphere-wise. same house, same pups, cables, amp, etc. This showed up on a gig recently, and I tried playing it in a couple other venues, once only with a di, once with my amp. Its just very frustrating that its just a recent development, when the bass has been dead quiet for 3 years. I have another MIA Fender that I've been using since to play, and its fine with all the same equipment, so I know its not the external gear.

[walterw]

it's odd that the pickup would make that loud buzz when touching the poles; proper pickup winding puts the ground end of the coil against the magnets, whether it's reverse-wound or not.

as for mysterious new hum, look for the shielding to be compromised somewhere; is there a grounded screw sunk into the wood in there that's maybe come a little loose? a contact point where say, pickguard shielding is supposed to touch an exposed section of body cavity shielding, and isn't anymore?

[praisegig]

Just for grins, plug the bass into the amp, with the control cavity open. Tap each solder connection, listening to see if the hum changes. It might simply be just a solder connection.

[bassbenj]

Originally Posted by walterw

it's odd that the pickup would make that loud buzz when touching the poles; proper pickup winding puts the ground end of the coil against the magnets, whether it's reverse-wound or not.

as for mysterious new hum, look for the shielding to be compromised somewhere; is there a grounded screw sunk into the wood in there that's maybe come a little loose? a contact point where say, pickguard shielding is supposed to touch an exposed section of body cavity shielding, and isn't anymore?

Unfortunately a great many (even expensive) pickups are not made properly. I had to get a radio shack conductive pen to ground all the pole pieces on my G&L basses for that reason.

As for the hum that came to dinner, the key is that it goes away when you touch ground. That means it's an electrostatic shielding problem. You didn't describe the shielding in your bass. Is it copper? Is it conductive paint? Is it none?

I'm guessing since the bass worked before and hums now, that it has some shielding. But be aware that hum pickup depends on the hum in the environment around the bass. So it actually may NOT be that the bass has changed but that hum sources around the bass have changed: new lights in room, new venues, new AC gear etc..

But given that something has happened to the bass. If there is no shielding, you must add it. If it has shielding and it's copper make sure all the copper pieces are connected. Solder them! Stew Mac conductive foil works but DOES dry out after a time! When it drys out it can lose connections. If it has paint shielding, remember that the shield MUST be grounded to the output jack to work! Usually there is a wire from the jack body tab to a screw with a lockwasher that bites into the paint. Resolder ALL the solder connections on this wire. AND; then loosen the screw and retighten it using an ohm meter to make sure you are making contact with the paint.

One of these should fix the problem.

[JohnL]

Thanks for all the suggestions guys. There is no shielding paint or foil. There isn't any in my MIA Fender Jazz either. So the verdict must be, after 3 years of quiet operation over a hundred gigs, the Lakland bass is now suddenly being plagued by electrostatic noise. I guess I'll get the stuff to shield it, it just doesn't make sense to me that the Fender is still fine in the exact same venues with no shielding either. I didn't realize a bass could just suddenly become vulnerable like that....

[JohnL]

ok, now armed with a soldering gun, copper foil, and unbridled enthusiasm...will let you all know how it turns out...

[walterw]

Originally Posted by JohnL

There is no shielding paint or foil. There isn't any in my MIA Fender Jazz either.

is this a fender american standard bass? (i.e., mid-'90s on?) or maybe even an '80s instrument?

if so, it very much does have shielding; there's a layer of conductive paint under the finish in the control cavity, which is grounded by a wood screw sunk into the wall of the cavity somewhere in there with a ground wire attached to it. if this screw gets loose and no longer connects the shielding paint to ground, the paint becomes "antenna paint", actually adding noise.

[Bassamatic]

My Lakland JO also has this same kind of noise pickup when the pups are not balanced. When I changed strings I did the complete copper foil shielding and it made no difference. Since I shielded and grounded the pup cavities - is this the same as wrapping the foil around the pups? I did not know about grounding the magnets, etc. and will try this next time.

Of course, I play mostly Ps, so I am very sensitive to hum. I changed my MIM jazz to the excellent Fender SCN hum bucking pups after one very noisy night near the light dimmers.

Thanks Guys.

[JohnL]

Ok, good news/bad news, but overall better. First, I now have a fully shielded bass! It cut the annoying buzz quite a bit, almost silent now. So that's good. Still a mystery to me why it would just appear like that, when I still have the same cables, equipment, same venues, etc. But moving on!

I still have the loud hum if i touch the top of my bridge pup, but not if I just lay my thumb on the side in an anchor position. So that's a minor issue, and I'm not a guitar tech, so thats as far as I'm going into that without messing with (and messing up) the pups. Thank you for all the suggestions!

(Bassamatic: I use both my pups on full volume 90% of the time anyway, thats how they cancel hum. I think the uneven volume hum is just the inherent single coil issue that all jazz basses have...I know all my Fenders have had it too)