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2 volume pot issue, only sound with both on

Discussion in 'Pickups & Electronics [BG]' started by gbarcus, Oct 13, 2013.


  1. gbarcus

    gbarcus Commercial User

    Jul 20, 2008
    Minneapolis & St.Paul, MN
    Owner of Barcus Basses barcusbasses.com
    I'm putting together a new bass and am trying to wire it up with 2 humbuckers, 2 volume and 2 tone knobs.
    Issue I'm having is that when only one volume knob is turned up, I get nothing. I have to turn the other volume up just a bit to get any sound.
    Volume pots: 250K Bourns
    Tone pots: 250K Bournes
    I'm using a .49uF 50WVDC Cap on the tone pots.

    I've wired it up the same as this diagram except I don't have the pickup selector switch in there. I've soldered both the positive leads to the tip ring on the output jack.
    [​IMG]
     
  2. It seems that with out the switch, there is nothing isolating the two output signals and either volume will provide a path to ground, killing the output of both pick ups. May be some one can suggest a fix such as rearranging the placement of the vol pots in the circuit so they don't act as one, or put in the switch.
     
  3. The problem is that you wired the volume pots as if there would be a pickup selector switch, and then didn't use the switch.

    When there is a pickup selector switch, it is most common to use the wiper terminals of the volume pots as outputs, because the volume pots behave better that way. The tradeoff is not being able to solo a pickup, because each pot controls the output impedance, but that is what the pickup selector switch is there for. What you need to do is use the wiper terminals as inputs, like in a standard Jazz bass.
     
  4. Projectile

    Projectile

    Feb 5, 2009
    This is normal for the wiring scheme you selected. It's how the volume knobs work on a Les Paul type guitar. A Les Paul doesn't allow you to adjust the blend level between the two pickups. When the switch is in the center position, both volume knobs affect both pickups.

    In order to fix this so that you have independent volume control, simply swap the lugs of the pickup wires with the selector switch wires on the volume pots. Basically, you want your pickups connected to the pot center lugs, and the selector switch wires (output jack in your case) connected to the left lugs. The ground connections stay the same.
     
  5. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    the overall point is valid, but this detail is incorrect:
    you can totally adjust the blend between the two pickups, you just can't turn one completely off and still get sound.

    it's the tones that end up affecting everything, rather than just their own pickup.
     
  6. gbarcus

    gbarcus Commercial User

    Jul 20, 2008
    Minneapolis & St.Paul, MN
    Owner of Barcus Basses barcusbasses.com
    Thanks for the input! Lets me know it's doing what is expected for how it's wired.
    I'll try swapping the wires on the volume and see how that goes.
     
  7. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    This is the classic problem of having to connect the volume pots "backwards" (pickup to middle lug) to enable mixing down one of them to zero.

    If you do that then you don't need the switch, but the problem is that there is more load on the pickups (when pots it not full open or close and the resonance peak is quickly killed. That is why guitarists connect them forward. For many basses this is actually a desired effect (Jazz bass players seem to like it) but other pickups can sound bland.
     
  8. robertebooker

    robertebooker Supporting Member

    Feb 15, 2013
    upstate NY
    Hoping someone here can help me...

    I have a cheapo affinity j bass I purchased for 25 bucks.. not bad at all.. I figure for the price I payed modding with pups and act/pass pre and bridge wouldn't break the bank.. I like the neck ect...
    MY isssue..
    I'm getting little to no volume from the pups until the volume for both is all the way up..
    ?- by replacing the pots will this issue be fixed???
     

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