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J-Bass wiring - What did I do wrong?

Discussion in 'Pickups & Electronics [BG]' started by Philbiker, Jan 8, 2006.


  1. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    I've wired and assembled my old project bass. Here's the situation:

    * Pickups are P-J configuration.
    * Tone seems to be working.
    * Grounding OK - no buzz.
    * Either pickup individually is fine with volume maxed.
    * The volume controls seem to be working very poorly - about 90% of the volume gain is in the last 10% of travel for both pickups (don't know about tone)
    * With both pickups all the way up the volume drops gigantically and the sound is thin and weak.

    I used the J-Bass wiring kit from Stewart-McDonald, the pots are 250K. The pickups are a Reverend pickup for the P bass and a Fender single coil from a 1995 MIM Jazz Bass.

    What did I do wrong?
     
  2. the wrong type of pots are used for volume, you need audio-taper, you're most-likely using linear-taper.

    this isn't really a problem, you can live with it and learn to use the pots this way, or change the pots. My cheapo Yamaha RBX170 (my main playing bass at the moment), is this way and it doesn't bother me much, because I usually play set-and-forget, and rely mostly on my fingers for the dynamics.

    sounds like your pickups are out of phase...pick one (doesn't matter) and swap the black and white wires around on it.
     
  3. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    This makes sense, but why would Stu-Mac include the wrong pots in their Wiring Kit for Jazz Bass I wonder?
    That's what I thought, too, but I was meticulous about going white to white and black to black just like my model Jazz bass with both pickups. I guess one of the pickups is phased backwards - perhaps the J pickup if it was designed for a Jazz bass?
     
  4. MIA J pickups are wound in opposite directions, so they are hum cancelling when both are used. One is wound North going, the other is South going.

    You described the classic symptom of a polarity issue, so swapping the leads will be an easy and quick determination for the problem.
     
  5. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    Righto. And even though I read many times that the older MIMs were not wired this way, mine always worked perfectly, not humming at all when both were full up un humbucking mode. So I've installed the reverse phase pickup in my bass. Thanks very much for the explanation. That makes perfect sense.
     

  6. I don't know why Stewmac does this (linear taper pots for vol controls). My guess is they buy the kits and the supplier does this.

    I have a P/J bass set up V/V/T and when I went to put in a push-pull pot for a series/parallel mod, the only pot I could get in push-pull was a linear taper, and I put it in the second volume position (this is the position that makes sense to me). Same thing, only controls volume on the last 10-15% of the pot. But since the original pots were this way too, it doesn't matter. I'm not 100% thrilled about it, but it works.

    remember there are no standards in the pickup industry for wiring colours and often the only way to get polarity correct (especially when mix-matching pups) is by trial and error.
     
  7. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    I reversed the leads on the J pickup and the bass sounds great. Much better than I expected frankly.
     
  8. You can spot MIM pickups wound the same way by those which use the non-standard sizing in the neck pickup.

    Old MIM had the neck and bridge pickups the same size (same pickup), so both were wound the same direction. Pre-2000 MIM would hum even when both pickups were dimed, indicating a common winding pattern.

    Opposite wound pickups are fully hum cancelling when both are dimed, and perhaps both are equal loudness, but have not tried that one.
     
  9. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    I have read that many times, but I will tell you with 100% certainty, my 1995 Jazz bass was humbucking with zero hum with both pickups all the way up. Also, the pickups sounded fantastic (this one still does). No hum with both volumes all the way up or down on my '95 MIM. I replaced the pickups with Seymour Duncan Quarter Pounders which dropped in perfectly and the change was for the worse (though I thought it was what I wanted at the time).