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How to Bake-In Jazz Roll-off

Discussion in 'Pickups & Electronics [BG]' started by DigitalMan, Aug 24, 2019.

  1. DigitalMan

    DigitalMan Wikipedia often mistakes my opinions for fact Supporting Member

    Nov 30, 2011
    Probably an odd question. Is there a way to bake-in the slight roll-off of one or the other volumes in passive Jazz wiring that would effectively remove the mid scoop as if you had actually rolled off one of the pickups slightly?

    The obvious answer is why not just roll off one of the pickups. I get it.

    Ok, now that’s out of the way, is there a way to make it so when both volumes are dimed that there is enough differential that the mid scoop does not occur? Asking for a friend with OCD.
  2. cataract

    cataract Supporting Member

    Feb 14, 2007
    Richmond, VA
    This is a really great question. As a former owner of a Rickenbacker 4003 & current owner of a Jazz (my very first Jazz bass ever, but actually two now) it’s kind of crazy how knocking one of the two pickups back the slightest bit makes everything sound “just right.”
  3. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    Just a guess here, but as the volume control is being rolled down resistance is being added in series with the pickup, so perhaps, add a resistor in line to mimic that added resistance?
  4. RattleSnack

    RattleSnack Supporting Member

    Sep 22, 2011
    Agreed, my favorite setup finishing touch for 60's jazz spacing - I drop neck pickup, turning screws one turn. Result: high mids pop-up, and without hum.
    pbassnut, nnnnnn, Beej and 1 other person like this.
  5. Axstar


    Jul 8, 2016
    East of Eden.
    A fixed resistor would do it. Didn't the Reggie Hamilton Jazz basses have this?
  6. Domespeed


    Oct 7, 2010
    a trim pot might be even better in finding the sweet spot.

    Something like 10k should do
    john m, JaseyT and Warpeg like this.
  7. El Güero

    El Güero

    Oct 5, 2015
    ^^^ It looks like the ground wire for the output jack is missing, or is grounded through the control plate?
  8. Do you want to eliminate mid scoop with
    1. each coil dimmed but equal volume?
    2. both pots rotated equally but with baked in differential in volume?
    3. or both pots at full but baked in volume differential as if both were dimmed?

    I don't think option 1 is going to happen with only a series resistor. Option 2 or 3 can work.
  9. The resistor trick will work as long as the resistor is between (in series with) the hot lead of the pickup and the pot terminal it connects to. When the pot is maxed this fixed resistance functions as if the pot is set less than max. I can see the benefit of using a trimmer to find the “sweet spot” if OCD is an issue to deal with.

    For those who want a modicum of rudimentary theory:
    The volume pot is a voltage divider. The pickup coil acts as an AC (signal) generator connected to the outer terminals of the pot. The middle terminal of the pot is the wiper that slides along the pot’s resistance surface. When the wiper is closest to the hot lead’s terminal it’s at the full pickup voltage; when closest to the pickup’s common lead’s terminal it’s at minimum or zero voltage. At in-between positions the voltage on the wiper terminal is in proportion to its position. So, what the resistor in series with the hot pickup lead does is make it so the wiper never sees the full pickup voltage. HTH
    wraub, JaseyT, Domespeed and 2 others like this.
  10. Marcus Willett

    Marcus Willett Supporting Member

    Feb 8, 2005
    Palm Bay, FL
    Endorsing Artist: Bag End - Dean Markley - Thunderfunk
    I think the Fender Roscoe Beck sig had a switch wired to a resistor that did exactly what you are talking about.

    Always seemed like a cool idea to me, had I liked the neck on the 5 string, I would have pounced on one long ago.
    Last edited: Aug 24, 2019
  11. Exactly right, and why the resistor trick doesn't work while maintaining equal pickup volume.
    Domespeed likes this.
  12. MarkA

    MarkA In the doghouse. Supporting Member

    Sep 26, 2008
    I was going to suggest trying something like this -- you can also experiment with favoring the neck or the bridge, depending on what you want to hear more of with both pickups dimed.

    You can fine-tune the differential between the pickups with how much you turn the screws and, if it's not what you want, it's easily reversible.
  13. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

    Please be aware that the mid scoop is caused by phase cancellation between the 2 pickups. This happens whenever there is more than one pickup. The 2 pickups are slightly out of phase with each other at some common mid-range frequencies and they get cancelled out due to different positions > mid scoop. Reducing the volume of one of them with as resistor or height change will reduce the amount of cancellation and less scoop heard. If you reduce the level of both of them, you haven't really changed anything except level.

    ALSO - in general - you should put a 50K resistor in series with each pickup on a 2 -pup bass so that the the 2 pups don't interfere with each other by loading at max volume. And no - it doesn't affect your level significantly. Who knows - this may fix your "problem".
    mikewalker and Domespeed like this.
  14. DigitalMan

    DigitalMan Wikipedia often mistakes my opinions for fact Supporting Member

    Nov 30, 2011
    I'm thinking option 2-ish. Both pots dimed with baked in volume differential specifically to get out of the mid-scoop zone. I suspect that I'd have to pick one volume to be dominant over the other at the time of wiring.
  15. DigitalMan

    DigitalMan Wikipedia often mistakes my opinions for fact Supporting Member

    Nov 30, 2011
    PS - for the record this line of inquiry is more academic than practical.
  16. JaseyT

    JaseyT Guest

    Jun 18, 2009
    I think it's pretty cool to see this pop up, as it is something I've wondered for my Jazz as well. And, judging by your name, you're a fan of Geddy like myself?
  17. Option 2 can be done with single a fixed resistor, provided one always wants the same result. If it were me, I would think about adding another pot with the wiper connected to the output jack, to enable options of which pickup to dim and how much. Set it then forget it.
  18. In my experience, using Jazz Bass pickups at, let's say, 70% - 70%, sounds less scooped than 100 % - 100 %.
    I actually use this set up a lot and I only realized that after 30 yrs of playing Jazz Basses.. It still has the punch but it is a bit darker sounding.
    walterw likes this.
  19. Dean N

    Dean N

    Jul 4, 2006
    Pittsburgh, PA
    Maybe add a 3-way toggle to pad either pup output: Neck - Off - Bridge.

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