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want to verify blend pot wiring (and theory behind it)

Discussion in 'Pickups & Electronics [BG]' started by eastcoasteddie, Apr 4, 2009.


  1. eastcoasteddie

    eastcoasteddie

    Mar 24, 2006
    NoVA
    "hypothetically speaking" Using an active on-board preamp, a stacked blend pot has a wire leading from the preamp to the pot, just as in this pic:

    [​IMG]

    the red + wire leads from the preamp to the pot. As the pot is swept back & forth singling out one pickup, this would in essence send 100% of that pickup signal to this red + wire? is this correct?
    Using an ohm meter, I verified that if I singled out pickup #1, I would get continuity between that center connection for pickup #1 to the red + connection. Center pickup connection for #2 would yield continuity to ground, sending P/U #2's signal to ground. Sweeping the pot in the other direction did the same for pickup #2.

    If I were to use a preamp that originally had a blend pot in it for use with 2 pickups, in a bass that has only one pickup (ie. a Stingray) would I wire the hot + wire from the pickup to this preamp wire that originally went to that lower right hand corner of the blend pot as in the pic (basically eliminate the blend pot)?
    EDIT: I powered the preamp with the 9v battery and verified that this wire in question coming from the preamp to the blend pot does not have power.
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Most preamps have the blend pot before the preamp, not after. The only exceptions I know of are preamps that contain an active blend, i.e. the blend function is part of the buffered preamp circuit rather than just a passive knob that the signals pass through. I guess active pickups which run through a passive blend are another (somewhat uncommon) exception.

    If you're eliminating the functionality of a blend pot, for use with a one-pup bass, don't wire anything at all to the pot. It just needlessly degrades the signal. Just run the pups to the preamp and the preamp to the output.
     
  3. eastcoasteddie

    eastcoasteddie

    Mar 24, 2006
    NoVA
    Let me show you the blend pot:

    DSC_6049.

    the pink wire comes from the preamp module. The only other wire connected to it is the case ground. Obviously, pickup wires connect to the center poles. In order to eliminate this pot for use in a single pup...would I wire the HOT from the pickup to this pink wire? I WANT to remove the blend pot altogether, there would be no need for it.
     
  4. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Yes, at least based on what you're describing, I would connect the hot from the pup to the pink wire.
     
  5. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    you're thinking of it backwards. the pink wire doesn't "come from" the preamp, it goes to it.
    pickup hot-->preamp input (pink wire). simple.
     
  6. eastcoasteddie

    eastcoasteddie

    Mar 24, 2006
    NoVA
    thanks!
     
  7. JTE

    JTE Supporting Member

    Mar 12, 2008
    Central Illinois, USA
    I think this is vitally important. In order to effictively trouble-shoot, you have to understand signal flow. That's why I'm a curmedgeon about things like whether the jack on the bass is an input or an output. Follow the way the signal flows, and you'll be able to answer a lot of these questions yourself.

    Signal out of the PUPs to the blend pot, then to the pre-amp. So, if you're eliminating the second PUP, and therefore the blen pot, then the signal has to go from PUP to pre. So, solder the PUP wire to where the pot's output goes in.

    Know how youir signal goes from an output to an input, not the other way 'round.

    jte
     
  8. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You have to watch which lugs the ground goes to. To me that diagram is backwards as far as the pots I've used.

    If the pot is audio taper, then you have to wire it the right way. The reason is when you are at the center detent, if you take a meter and read from the center lug to either outside lug, you will see one is higher resistance than the other.

    So if it's a 250K pot, from the center to the outside will be 240K on one side and 10K on the other (or something similar). The other deck will be in reverse.

    So you must solder the ground to the higher resistance side or you will dull the tone of the pickups.

    Here's another diagram (Stew-Mac):

    3764_1.

    And one at Duncan which is the same as the Stew-Mac.

    They are both opposite that first diagram.

    Linear (B taper) pots don't matter. Most blends are something like "M/N" taper, or "A/C" taper.
     

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