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J bass still humming after Dimarzio Model J install...

Discussion in 'Pickups & Electronics [BG]' started by Scotch11, Jan 24, 2012.

  1. So I went ahead and installed some Dimarzio Model J pickups in my MIM Jazz bass. It sounds great but I'm still getting a nasty hum whenever my fingers leave the strings. It goes away as soon as i touch anything metal on the instrument (strings, bridge, tuners)

    I followed the install instructions on the Dimarzio website word for word...

    Did I install the "hum-cancelling" Model J's wrong or is this definitely a shielding issue?

    If it is a shielding problem, can someone point me in the right direction about how to shield a fender jazz?
  2. JLS


    Sep 12, 2008
    Emeryville, Ca
    I setup & repair guitars & basses
    Your bridge isn't grounded.
  3. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    No, his bridge is grounded, otherwise it woundn't stop when he touched the strings.

    This is not hum, this is buzz. The Model Js are humbuckers, and they get rid of 60Hz hum, which is magnetic field noise.

    What you are hearing it electrical field noise, which is that higher pitched buzzing. This can be cause by lack of shielding, and even bad grounds where you have the bass plugged in.

    There is a sticky on shielding a Jazz here:


    Currently the images are not showing.

    Basically what you want to do is get either some copper foil tape, or shielding paint and cover the surfaces in your control cavity and under the pickups. Then you have to ground the foil or paint by either soldering a wire to the foil, or if you use paint the usual way is yo screw a screw into the body with a ground lug on it, and solder a ground wire to that, and then paint over the lug to make a connection.

    Another thing to check for; sometimes with Jazz basses Fender skimps from having to run a ground wire from pot to pot by using the control plate as ground. That often works fine, but you will find that soldering a ground wire between the backs of the pots (cans) and to ground can often quiet things up.
  4. Ah ok, excellent explanation thank you SGD! Its a shame those pictures aren't working but I think I can figure it out. While I'm operating on this thing, could you recommend a cap to install?

    Awesome website by the way, lots of interesting things to look at.
  5. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Caps are caps. They all sound the same in a tone control.

    The only thing to worry about is what value cap to use.

    I like .047µF, but some people like .1µF for bass. I have .02µF in one bass. That just removes the top end and leaves all the mids.
  6. Yahcoob


    Jul 4, 2011
    Hi! I've got a similar problem with my Warwick Corvette. I replaced MECs with Delano JMVCs which are supposed to be hum-cancelling but I still get a lot of noise when I don't touch the strings or other metal parts. My tech examined the bass, shielded the electronics cavity, checked the ground connection to the bridge and everything seems to be alright. The noise is still there, though. I think i tried everything from plugging to different amps in different places to measuring resistance of the shielding, pole pieces and pots.

    Lately I've found there is no continuity between the shortest terminal of the output jack and it's 'outer part'. The medium length terminal responds only with the cable plugged to the jack. I don't know if that's a problem.

    The noise also disappears when I touch the 'plug of the cable connecting the 9v battery' (I'm sorry I don't know the right term). There is no battery in beacuse with the preamp on, the noise gets even worse.

    I'm starting to blame the MEC preamp. Replacing all of the electronics including pots, output jack and wires seems to be the only solution left.

    Do you think there is another way of getting rid of the noise?

    I will be grateful for any advice.

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