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Jazz Bass bridge pickup "thins out" at top end.

Discussion in 'Pickups & Electronics [BG]' started by MorganDaniel, Nov 15, 2018.

  1. MorganDaniel


    Nov 15, 2018
    I'm working on a Jazz bass with traditional wiring and pickups: Vol. knobs for bridge and neck pups and a single tone knob.

    The problem: Each volume knob seems to work individually, but when I turn both up I get a sudden "thinning-out" at the top end of the bridge volume.

    I've tried changing the phase on the pickups and that doesn't fix or change it. Any other thoughts?
  2. 96tbird

    96tbird PLEASE STAND BY

    If I understand what you’re describing, it’s normal. Dial one or the other back a notch and it will fatten back up? Normal.

    Your pots wide open resist the signal being sent to ground and most of it goes to the amp. PLUS The full resistance of the pickups push against each other and that effects some frequencies output. Close one pot a bit, resistance to ground of that pup lowers and some of that pickups signal is going to ground and it’s resistance on the wide open pup lessens, so more of the resisted frequency from that pup get through to the amp.

    Ps. That is a thumbnail “for dummies” sketch of what is going on. There’s more to it but I’m not that guy. More investigation by you, should you chose to accept this mission, will yield true enlightenment.
    Last edited: Nov 16, 2018
  3. lz4005


    Oct 22, 2013
    If you heard no change from putting the pickups out of phase then you're doing something wrong. It should sound either dramatically better or dramatically worse when you do that.
    InhumanResource and MorganDaniel like this.
  4. sikamikanico


    Mar 17, 2004
    Yeah, running both at 100% thins out the mids, due to phase cancellation. Also, the resonant peak shifts up (in frequency) with both pickups in parallel, though I’m not sure how much of that happens in that last part of the pot turn. You can get some beef back wiring them in series, or with a loading cap (which shifts the resonant peak back down).
    MorganDaniel likes this.
  5. MorganDaniel


    Nov 15, 2018
    Hmmm. Okay, I'll listen again. What didn't change was the described thinning out, and that's what I was really listening for. Thanks.
  6. MorganDaniel


    Nov 15, 2018
    Thanks all for the info! So much to learn!! I'm glad to hear it's normal...I was tearing my hair out testing each component individually and quadruple-checking the diagram.
  7. MorganDaniel


    Nov 15, 2018
    I suppose there is the great possibility that I'm not using the right terminology. When I got the bass, the black and white leads on the bridge pup seemed reversed (white to back of the vol. pot, black to the lug). I switched them because I was worried that was the cause of the "problem." That's what I was calling "changing the phase." Is that correct, or is that something different?
  8. smeet

    smeet Gold Supporting Member

    Nov 27, 2006
    Woodland Hills, CA
    Yes, reversing the leads on one pickup will reverse the relative phase. A jazz bass will normally get a cut in the midrange when both volumes are all the way up, but the low frequencies should still be nice and strong. If the pickups are out of phase, the lows will drop out also.
    jamro217, Aqualung60 and MorganDaniel like this.
  9. lz4005


    Oct 22, 2013
    Reversing the leads on one pickup reverses the phase relationship between the two. Out of phase sounds like all the low end drops out when both are at 100%, while each pickup will sound unchanged when soloed.

    In a correctly wired J, you get a mid bump when one pickup is full on and the other is less than 100%. When both are full on you get a darker, mid scooped tone and slightly less apparent volume.
    jamro217 likes this.
  10. micguy


    May 17, 2011
    The neck pickup on a standard wired jazz bass soloed has a good amount of low end. The bridge pickup soloed has considerably less. When both are on, the amount of low end is literally averaged - somewhere in the middle- less than the neck alone, more than the bridge alone. This is, for that circuit, normal.

    There are ways to keep the low end with both on - a capacitor that blends the bridge pickup in at high frequencies avoids the “averaging” problem. I did this on my J, and it works really well. Rickenbacker does (or at least did) this on some of their models.
  11. InhumanResource


    Dec 28, 2012
    It should be very obvious when your pickups are out of phase. You'll know. :)
  12. Hounddog409


    Oct 27, 2015
    Is this a MIM Jazz? my pots were about useless on the 2016 MIM I have. After about a month use, neither volumn seemed to do anything and the tone pot did absolutely nothing. Not to mention the Jack got loose after about 2 months.

    I replaced the pots, cap, and jack with quality components. All good now.
  13. Here's my 2 cents:
    Just listen to the hum of the pickups and when you have them wired phased correctly (assuming you have a proper pair of jazz pups) the single coil hum should be reduced with both pickups at 100%.

    OK ... once you are sure they are wired to act like a humbucker when both pups are at 100%, the next step is to play and listen then raise/lower one pickup or the other closer/further away from the strings to get the tonality you prefer when using both pups on full. I generally end up with the bridge pickup much closer to the strings than the neck pickup - but this is purely a matter of taste and what you are after.
  14. How would this differ if one went to vbt from vvt? Or does it depend how the blend is wired?
  15. lz4005


    Oct 22, 2013
    It wouldn't. Out of phase is out of phase.

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