DC resistance on blend setting... help

Discussion in 'Pickups & Electronics [BG]' started by tubestuff, Oct 21, 2017.

  1. tubestuff


    Aug 14, 2013
    San Pedro, CA
    Hi TB,
    Can't find an answer anywhere for this yet.
    Just picked up a passive PJ style bass on TB, love it. (Kawai KRB105)
    When I measure the ohms from my guitar cable, one pup is around10k and the other around 7k. No problem.
    In the blend position it shoots up to over 100k... ?
    What's going on?
    Everything works as it's supposed to... I guess. It has two series/parallel p/p pots that don't seem to affect the dc readings that much (!?) but do affect the tone.
    Miswired somewhere? That's my first guess. Everything looks original, no obvious mods.
    On my jazz bass the blend goes down to around 4-5k like normal.
    Don't want to operate... but...
    Any thoughts?
    Thanks all!
  2. lz4005


    Oct 22, 2013
    Put your meter down and use your ears.

    Does it sound good?
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  3. You probably have an A/C taper blend, which is two regular volume pots running inverse parallel. At the center detent, both pickups are being attenuated, so the resistance that you are measuring is that of the pickups in series with the resistance from the pot. That's perfectly normal. Don't let technical specs concern you. DC resistance is effectively meaningless.

    Edit: As for your other bass, it probably has an M/N taper blend, which works differently. At any given point in the rotation, one pickup is wired directly to the output of the blend, while the other one gets attenuated. There are no positions where both pickups are attenuated at the same time.
    Aaarn and tubestuff like this.
  4. tubestuff


    Aug 14, 2013
    San Pedro, CA
    To my ears, only in the neck or bridge full on settings. That's why I pulled out the meter.
    The series/parallel switches make the tone thin out which also had me scratching my head.
    There may be nothing wrong but the numbers don't crunch.
    Love the bass overall, it's a keeper.
  5. Sounds like you may have a phase issue. Try swapping the leads on one pickup.
    Jay2U and tubestuff like this.
  6. tubestuff


    Aug 14, 2013
    San Pedro, CA
    Sweet! Thanks Line6man.
    That makes sense.
    I saw one other post somewhere on TB that suggested nominal readings for a similar setup were in the same ballpark as mine but never owning or wiring anything with this wiring config had me stumped.
    Looks like I need to make me a schematic so I can see what's what.
    Thanks a bunch.
  7. tubestuff


    Aug 14, 2013
    San Pedro, CA
    Definitely going to try this! Just for fun. Thanks.
  8. tubestuff


    Aug 14, 2013
    San Pedro, CA
    A/C taper = ? M/C taper=?
    Familiar with audio & log taper.
    Thanks again.
  9. M/N is like this:

    I can't find a similar diagram for what A/C does, but this is an example of an audio taper curve.


    If you imagine the mirror image of this graph (flipping horizontally) then you have a reverse audio taper. Superimpose the two, and you can see that the intersection of the two curves does not occur at y=100. Rather, it might be somewhere much lower, and hence, that 100k resistance you are measuring.
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  10. tubestuff


    Aug 14, 2013
    San Pedro, CA
    Ahhhhh! Capiche! (Almost) Appreciate the data. You've given me some good new (to me) insight on what I'm seeing.
    Thanks Line6man!
  11. tubestuff


    Aug 14, 2013
    San Pedro, CA
    Found this:
    Potentiometer Taper Charts | Antique Electronic Supply
    Thanks again, this is new to me.
    Aaarn likes this.
  12. micguy


    May 17, 2011
    Flipping the polarity of a pickup will not change the dc resistance you see at the output. If the tone gets really thin sounding in the middle of the blend control, then you have a phase problem. If it doesn't, you're fine.

    My guess is the dc resistance thing is the result from a different kind of blend control. In a passive bass, blend controls have inherent tradeoffs. You have different basses where they chose to optimize different things.

    Play 'em both. Learn to work with their quirks.