My MIM Jazz Bass buzzed a little when I first got it. It also proved to be pretty susceptible to banks of lights, etc.

To cure this and beef up the tone, I had a set of DiMarzio Ultra Jazz pups installed. They are humbuckers, potted in what looks like epoxy. Now it buzzes worse than before. Here are the facts as I know them:

The tone pot is grounded to the bridge.
The buzz stops when I touch the strings or control knob plate.
Running an additional wire from the control plate to the bridge has no effect.
Reducing the volume of a pup doesn't increase the buzz, it gets softer as the overall volume decreases.
Using a ground lift does no good.
I figure the buzz is worse because these pups are hotter than the originals.

My local guitar tech says he can reverse the polarity of one or both pups. Anybody else have some bright ideas? I'm fresh out.

Is the electronics cavity sheilded? I had this same problem with my Ibanez. I bought a new bass.;) Seriously though, check to be sure the electronics are sheilded against RF especially if lighting sets it off.

No, it's not shielded. I'll line the electronics cavity with foil, but somehow I think there's more to the problem.

Check all the wiring in your bass. Make sure that all the ground wires in the bass are attached to a single place. This usually is the case of one of the pots. Make sure that all of your pot casings are grounded. Check your output jack. If your output jack makes a poor connection to the ground, then that can be your source of hum. If your bridge isn't grounded, then you can try grounding your bridge.

I found a wiring diagram for the Standard Jazz and everything seems to match up. Drat.

The bridge is grounded, BTW.

shield thy cavity.

Where can I order some non-conductive paint? Or can I get it at Lowe's?

Stewart McDonald has copper shielding tape that works excellent. I have come across a couple how-to descriptions on a guitar web site that I forget the address of but its an easy search.

Remember that the bottom side of any pickguard or cavity cover should be shielded also. There should be conductivity or a contact point between the cavity and pickguard also. This is usually accomplished by allowing a portion of the shielding tape to lay on the surface of the body, which will be covered from sight by the pickguard so that when the pickguard is placed on the body, the shielding on the underside of the pickguard contacts the tape on the body.

Yes sheilding!

Stewertmacdonalds along with copper foil has a good conductive paint (not non conductive) that should fix it. Use two coats. This will also add a modest ground to all swtiches and pots not properly grounded.

Try different power outlets or different locations. My P-Bass buzzes very badly at my house, but nowhere else. Everything is as you describe - when I touch anything metal on the basss, it stops. It is a grounding issue, not a shielding one...

After talking to a friend of mine who knows guitars and after further experimentation, I don't think it's the lack of shielding. The buzz goes away when I turn off the tone knob. I have re-soldered the bridge ground to the tone pot to no avail. Maybe there's a short in the ground wire? Or could the pot be bad?

It sounds like the outlet you are pluggging into has a grounding problem.

You can check it with something like:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=22-141

Passive pickups can be very noisy if the amp is not grounded properly.

According to my GB Circuit Tester, my practice room outlet is grounded.

Are the pickups single coil?

If both are turned up completely, do you still get the noise?

Have you tried different cables?

Have you tried different amps?

Since the noise goes away when you turn down the Tone knob, is there anything attached to the tone pot (such as a capacitor)? And is the noise only a high frequency sound?

Originally posted by Matthew T.
The buzz goes away when I turn off the tone knob.

Does it definitely go away or does it just lessen? As the tone conctrol is a variable high frequency rolloff, it could be that it's simply removing most of the buzz from the sound rather than actually eliminating the buzz.

Try checking out this webpage, it has alot of good info about wiring,shielding and schematics.

http://guitarnuts.com/wiring/menu.html

Redneck2wild:
DiMarzio Ultra Jazz pups are hunmbuckers.
The buzz lessens slightly when I roll off one or the other.
With both pups on full, they just buzz louder.
There is a capacitor attached to the tone knob where the bridge ground wire is soldered on.
I have tried different cables and amps and they made no difference.
The buzz is the typical "you've got ground-issue" frequency.

DavidMWilson:
The buzz completely vanishes with the tone knob turned completely down.

Now I'm off to check out that wiring site.

I put the first coat of conductive paint on tonight. I'll apply the second coat tomorrow and post the results. This stuff had better work, 'cause it sure is expensive.

Hi Matthew, so you got a buzz eh? Well, as you said there's probably more to it than just grounding or shielding. Hum and noise can be a real bear of a problem, it's kept many a crusty old audio engineer employed, sometimes for years beyond retirement! KeithPas's suggestion is good, the guitarnuts site has a pretty good description of some of the "internal" grounding issues (internal to the instrument), especially the part about "star grounding" is very good.

First thing to understand is, that even though the symptom is in your guitar, the root cause of the problem may be in your amp. You may be dealing with something called a "ground loop". Basically what this means is that "ground" on your guitar isn't the same as "ground" on your amp. In a perfect world, they'd be the same 'cause they're connected together by the shielding in your guitar cable, but in the real world that wire has resistance and capacitance and inductance, and behaves a lot like a "transmission line" in the radio world. So, if this is the problem you're experiencing, shielding the cavity isn't going to help, and in some cases may even make the problem worse (more surface area = better antenna)!

Next thing to understand is, that most guitar manufacturers ground one side of the pickup. This is absolutely the worst way in the world to wire a pickup, when you do it that way you're just begging for ground loops. Crusty old audio engineers have been advocating "balanced lines" for the better part of 50 years, and for some reason the manufacturers haven't found it cost effective to use these. Basically the idea here is that you use a "balanced" XLR-type cable between your guitar and your amp, instead of an "unbalanced" mono cable. Doing this might require a little rewiring in your amp, but you can also do this a different way by using an active preamp with a differential input in your guitar. That way, no part of your pickup is grounded (except the metal case, which "must" be grounded), which isolates the pickup from the cavity and frees up the shield to what it's supposed to do (which is to "shield" from external EMI, instead of carrying signal).

My preferred solution to this type of problem is to install an onboard differential input active preamp. I have an interesting story to tell about this. When I bought my first F bass about ten years ago, it had a horrible hum problem. After tearing my hair out for about three months, I finally build and installed a DIAP. Now I can plug that bass into my most powerful two kilowatt amp, and crank all the volume controls all the way up, and stick the pickups right next to a fluorescent light fixture (we're talking like two or three inches away from the ballast), and it's quiet as a church mouse, not even a trace of hum. Pretty amazing really. YRMV!

So if the shielding doesn't work, where does one find a DIAP and how much do they run?

Well, try the shielding first. Follow the instructions on the GuitarNuts site, they're pretty good. Chances are, the shielding won't hurt. If it does, the odds are 99.99% that the problem is actually in your amp. And who knows, you may get a dramatic improvement with a shielded cavity, at least enough so you can live with whatever hum/noise remains.

If you use the "star grounding" method suggested by GuitarNuts, you should have a central spot in your cavity where all your ground wires connect to. Even (and especially) the one from the jack, and the one from the bridge. (By the way, you're not using coated strings like Elixir's are you?)

One more thing, it's interesting that the hum goes away when you turn down the tone knob. That might be a clue. Make sure the tone pot and the cap that's connected to it are well grounded and tightly soldered.

Can you tell me a little bit more about your pickups? Are they two wire or four wire, any coil splitter switches in use? What does the actual wire coming out of the pickup look like, is it two conductor shielded or is it just a twisted pair? If it's shielded, is the shield grounded? Can you see inside the pickup to see whether the shield is attached to the pickup casing (or measure it with an ohm meter)?

Originally posted by redneck2wild
It sounds like the outlet you are pluggging into has a grounding problem.
Passive pickups can be very noisy if the amp is not grounded properly.
i get this as well
but
only in my house in a particular socket..i think it is something to do with multiple earths in the house
when i use the bass in the place where we play...a school assembly hall there is no problem

same thing...if i touch the stings or the controls the hum disappears...
i have checked all my wiring and pots and tested them for continuity..all is well
hope you find a cure...my bass is not shielded but the body paint is conductive and wired to an earth strap...its a fender precision special with the paintjob done at baja works...1996-1998 only..
cheers:)

After two coats of conductive paint, the buzz is much quieter. I can back off my bridge pick up a little and it goes away. I've re-soldered the ground connections to and from the bridge volume pot, but that did no good. I ran a wire from the bridge to the exposed volume stob, but that has no effect. The buzz still goes away when I touch the strings though, which seems to indicate some kind of grounding problem. I'm going to see my friendly neighberhood guitar workman.

Well, the part about the buzz going away when you touch the strings, has a different explanation. What you're actually seeing is the effect of body capacitance on the antenna system that's in your ground plane (as per the "transmission line" characteristics that I referred to earlier). That's why it's very important to have a good instrument cable. A crappy cable can have a very high shidld resistance per foot which will make effects like body capacitance much more noticeable. Have you tried it with a very short instrument cable (like 3 feet)? Betcha some of your symptoms will go away with the shorter cable. :)

I went to the music store where I bought the pick ups and there was no buzz at all. There had been serious buzz at the store prior to my shielding the cavities. There is still a slight buzz at my house but I tried a 1' cable and SHAZAM! dead quiet. I'm going to get a good 10-footer right now.