Any of you electronics guys think you can figure out the source of the buzz?

[Matthew T.]

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.

[pbd]

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.

[Matthew T.]

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

[xyllion]

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.

[Matthew T.]

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

The bridge is grounded, BTW.

[giantjerk]

shield thy cavity.

[Matthew T.]

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

[giantjerk]

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.

[Moo]

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.

[Alexander]

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...

[Matthew T.]

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?

[redneck2wild]

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.as...ct%5Fid=22-141

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

[Matthew T.]

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

[redneck2wild]

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?

[David Wilson]

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.

[KeithPas]

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

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

[Matthew T.]

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.

[Matthew T.]

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.

[nonsqtr]

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!

[Matthew T.]

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