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Need some help with a strange grounding problem

Discussion in 'Pickups & Electronics [BG]' started by Benjamin Strange, Jun 21, 2004.


  1. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    I've just installed two Rio Grande Pitbulls in my Steinberger, and I'm getting a little bit of hum. They are 4 conductor pups, and I've wired them with nothing but a 3 way switch between them and the output jack. I believe I have everything wired correctly, but I am still getting a little hum, which appears to be a ground issue. It's not a bad hum (like a broken ground would be), but it's annoying. When I touch the ring for the switch, the noise goes away - problem is that there's no route for a ground wire to run to the bridge, where you usually make contact for the ground to run through you. What can I do to make this noise go away? Do I have to route a ground wire to the bridge, or is there a simpler way?
     
  2. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Ah, my favorite kind of problem. These grounding deals can be a trip and a half. Let me ask you a few questions that may help get to a diagnosis. What kind of pups did you have in there before? Were they "dead quiet"? Were they humbuckers or single-coils? What did you do with the extra two wires on your new 4-conductor pups? Is your cavity shielded (with copper foil or some such thing)? What kind of amp are you using? How long is your instrument cable? When you're not touching the switch ring, does the hum level change as you walk around the room? Are you testing this at home or somewhere else? Have you tested your AC outlets to make sure they're properly grounded?

    About the ground wire to the bridge, that's a good idea on general principles, however it may or may not help with this particular problem. Basically, if your cable/pickup system is already an antenna, then adding more surface area only results in a better antenna. Although, you might get lucky and hit a node in the transmission line, but the chances of that happening are exceedingly small. My guess is, you'll probably have to diagnose this in a stepwise manner. The first step is to isolate the problem. That's a lot harder than it sounds, 'cause pickups never work in isolation, they're always connected to the controls, the instrument cable, and the amp. A bass that hums wildly on one amp may be perfectly quiet on another. Strange things happen in the universe of hum. Anyway, if you tell me enough about your system I may be able to help. Also if you can post a pic of the inside of the cavity that would be very helpful.
     
  3. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    There was nothing in this particular bass before. It was empty when I got it. I have another just like it that I was running two EMG HB pickups at 18v with an Aguilar OBP1.

    Yes.

    Not sure. I believe they are a humbucking P pickup. These new pickups are humbucking P pickups - two coils stacked on top of the other.

    I soldered them together, and taped them - as per instructions. I did not wire them all in a bunch; one pair for each pickup separate from each other.

    It has what appears to be shielding paint, but it's hard to say. No foil.

    A menagerie of Boogie amps. Every one exibits the hum.


    20 feet.

    The hum leve is the same everywhere in the room.

    Home. I've never had a problem with noise before the pickup switch, so I assume the power is ok.

    I've discovered that anytime I touch a grounded metal object in my room, the bass goes dead quiet, whether I am touching any metal on the bass or not. Hmmm...? :confused:

    I will post a pic when I get the chance.
     
  4. Dude, im having the same problem, but with Jazz pups. I've wired it like fender said, then i've wired it like stew mac, and getting that hum too. but when i touch the bridge or the strings it goes away. Im using a set of Duncan antiquities II. i hope its not the pups, im gonna try some new pots since it got the pots used.
     
  5. Update! After weeks of wiring an wiring and getting different schematics and whatnot. I found out it was just a bad contol pot. So I just switched for some old ones I had laying around, and viola!!! No more bad ground buzz. Somebody slap me!
     
  6. Benjamin Strange

    Benjamin Strange Commercial User

    Dec 25, 2002
    New Orleans, LA
    Owner / Tech: Strange Guitarworks
    Looks like mine is a combination of bad shielding and no ground wire to the bridge. I took it in to have it properly wired, have shielding paint installed, the pickups shielded, and copper foil installed in every cavity. I would have done it myself, but I'm not great with a soldering iron, and the place was going to install my Moses neck on it anyway, so what the hell? This guy, Gary Brauer works on Joe Satriani's guitars, as well as Spinal Tap's, so I know it's going to be tight when it's done!
     
  7. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Wow, thanks for those detailed answers. Now sorry, but I have to ask one more question. The wire that's coming out of the pickups, is that four separate wires (like maybe two twisted pairs or something), or it is a shielded cable with a braid? This part...

    I've discovered that anytime I touch a grounded metal object in my room, the bass goes dead quiet, whether I am touching any metal on the bass or not. Hmmm...?

    ... is very revealing. It suggests that you're experiencing capacitive effects (ie body capacitance). It's very interesting that there's no change at different points in the room. This might indicate that a quick trip to Home Depot would be a good idea, you can get an outlet checker for about 5 bucks and it might be worth a quick sweep to find out if they're okay. But the final answer depends on how the pickups are wired. If there's a separate ground connection to the pickup backplate/housing, there's probably a solution (an electronic solution, involving a couple of parts and a few minutes with a soldering iron). If there's not a separate ground, then any solution is going to be a kloodge, and you just have to use trial and error to find the particular kloodge that will work the best. Chances are you can probably find one that'll make the hum tolerable, in most cases that would be the case. The bridge wire makes sense, that way as long as you're touching "something" on the bass (which would probably be most of the time), you'll be okay. So that would be the quick and dirty temporary fix.