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Dimarzio Model J Buzz (and pot question)

Discussion in 'Pickups & Electronics [BG]' started by Addni, Mar 10, 2014.

  1. Addni


    May 16, 2009
    Akureyri, Iceland
    I've been experimenting with the wiring of my Model J PU's

    One thing I notice constantly trough the wiring, is that on the neck pickup, when my thumb hits the coil screws for the E and A string I get a nasty buzz (and it actually happens while I play, since I usually rest my thumb on the pickup and tend to slide onto the coil)

    The strange thing is that it is only on those coils, and only on the neck pickup, I can touch every other coil without problem.

    I've shielded everything really well, and the bass is otherwise dead silent, both when I touch any part of the metal and not.

    It's wired like this now:


    I tried both parallel and series wiring within the pickup itself, same results with the touch-buzz.

    I'm using a 500k dimarzio pots for both PU's.

    Other thing while I'm at it. I tried buying a 1Meg pot to use as a tone control, but it's giving me really little results, I wired it like that:

    With a 47uf cap. I was getting some change, but really small, I thought the 1Meg cap would make the difference more noticeable.

    I also tried wiring both my pickup straight to the jack output. To me it sounds exactly the same as going trough the volume pots (I made recordings before/after) but everyone keeps saying "500k pots really helped with brightness".

    Do the pots really matter when the volume is turned all the way up ? (I always play with bass volume at 100%, usually both PU's at 100%) vs going straight to the jack. A part of me really just wants to find blanks for the holes on the control plate and skip all the buttons (or maybe add a DPDT on switch)

    I know this post has gotten pretty chaotic, hope you bear with me.
  2. Sounds like one coil is not properly grounded. Is there a zero Ohm path to ground for all of the pole pieces?

    47uF if three orders of magnitude too capacitive for use in a tone control. Did you mean 0.047uF?

    It is not a good idea to use a 1M pot for a tone control, at this signal impedance. You would have to roll it almost all the way down before you would get a resistance low enough to allow any signal through.
  3. Addni


    May 16, 2009
    Akureyri, Iceland
    The ohmmeter I have at home only measures unto 1K ohm (it's a meter specially designed for electricians, with no need for accurate ohms metering) but none of the coils showed any connection to ground.

    Yes 0.047uF - I had the bass wired before with a 500k push-pull pot(phase reverse, but I never used it, and I was getting a pretty noisy electrical system, so I decided to simplify everything) and then the tone pot worked, being that the 1M is sold as a "Tone Pot" I thought I might give it a try.

    Should I go to 500k for the tone pot, or would a 250k be a better bet (with 500k volume pots).
    I don't really need the tone pot, but I'm not sure what else I should do with the spare hole on the control plate :)
  4. ImageUploadedByTalkBass1394508262.240252.
    When I installed my Model Js I removed the tone and replaced it with an acorn nut.
  5. Addni


    May 16, 2009
    Akureyri, Iceland
    Interesting idea!
  6. Addni


    May 16, 2009
    Akureyri, Iceland
    I figured out the touching problem.

    I opened the control cavity and measured connectivity from the first coil in the neck pickup to the red wire. Removed the pickup and saw that the coil had been lying on top of the wire and there was a small rupture in the isolation of the wire, making direct connectivity between the coil and the red wire.
    Put some tape around the wire, and carefully paced the pickup back in and voilah!.