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Blend Pot - what's with the volume decrease when both pickups are on?

Discussion in 'Pickups & Electronics [BG]' started by Philthy, May 3, 2006.


  1. Philthy

    Philthy Supporting Member

    Jun 12, 2001
    Flanders, NJ
    Hey Everyone,

    I'm trying to figure out if I have a problem here and something is wrong with my blend pot or is this a "that's just how it is" type of thing.

    I currently have a Fender Active P Bass Special bass, made in Mexico, I believe (http://www.fender.com/products/search.php?partno=0135760359) and I decided to swap out the stock P pickups and put in Duncan Quarter Pounders to add some extra punch. I kept the original stock 3 band EQ preamp and the stock noiseless dual coil J pickup. Now I wired the new pickup to the existing 250K blend pot. However, it seems as though there is a drastic increase in volume when I pan to each pickup separately (more on the P pickup, of course) and then the volume drops when I have the blend pot dead center.

    Any ideas why this happens? Is there something wrong with the blend pot? Is it the combo of the Duncan pickup and the Fender preamp? Is the blend pot shot?

    Any help and/or advice would be greatly appreciated.

    Thanks!!!!
     
  2. It sounds like the pu's are out of phase, something that happens often between Fender pu's and Seymour, DiMarzio, etc. Just swap the hot and ground wires of the SD pickup around.
     
  3. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Yeah, check that your pickups aren't out of phase.....but it's fairly common for blend pots to have a slight volume drop when centered because of the interaction of the impedance of the pickups. That's also why your blend pot probably acts almost like a pickup switch, going abruptly from neck to both to bridge without much of anything in between. The only way around that is to get an active blend circuit which uses a buffer amp for each pickup to isolate their impedances. The J-Retro/U-Retro preamp has this feature, also can be done with components from Bartolini, also the Audere pre has it. EMG does too, but theirs only works with their pickups.
     
  4. rumblinbass

    rumblinbass

    Aug 22, 2003
    Wimberley, TX
    Does the same thing happen if each pup had it's own volume pot?

    It sux that the only way around it is an active circuit.
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    Yeh sounds like out of phase if it's a massive volume drop with no bass to the tone. If so, what it amounts to is you have the "hot" and "ground" of one of the pups wired backwards (regardless of what the colors are). Swap the P pup leads to there existing connections (probably blend and pot back - or ground anyway).
     
  6. ehque

    ehque

    Jan 8, 2006
    Singapore
    id try the out of phase fix before i try anything else. it definately looks like an out of phase issue rather than anything else.

    if your pickups are out of phase, a vol vol setup instead of a blend knob WILL NOT HELP. with both are on, you'll get that vol drop again.
     
  7. dougray

    dougray Supporting Member

    Apr 16, 2002
    western maryland

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