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Wiring help/insight appreciated jazz bass

Discussion in 'Pickups & Electronics [BG]' started by JW-Thrax, Aug 23, 2018.

  1. JW-Thrax


    Aug 16, 2018
    Hello everyone,

    This is my first post on Talkbass so if this is the wrong place to ask this my apologies.

    I have a Jazz bass with MEC Dynamic correction (passive) pickups. I've rewired this bass as followed:

    My goal is to have a master volume (usable in both series and parallel), master tone, series/parallel switch and an ungrounded blend (which gets taken out of the circuit in series mode). My understanding is that this can be achieved using an ungrounded M/N taper blend pot.

    The problem I've encountered is that the blend pot currently seems to function like a 3 way switch. At either extreme only one pickup is on and in the middle both work but with a slight dip in volume. There is no blending taking place between either extreme and the middle.

    I hope I have provided enough information and I'd greatly appreciate it if someone could take a look at my wiring and see if it is correct. I also might be mistaken entirely on how this circuit is supposed to work, in that case I would love it if anyone had a solution.


    Edit: I've updated the schematic because I made a mistake in the one I originally posted
    Last edited: Aug 24, 2018
  2. There should be no noticeable dip in volume when middle is engaged, and 250k is great value for blend.
    Where did you take your schematic? Or you made it yourself? Also I don't see much of ground connection. It is implied they go through metal plate?

    Edit: looked over your schematic. I removed master volume for sake of simplicity for now.
    Suppose switch is in UP position, aka series mode
    1 from master volume pin to terminal bridge-
    2 and through the bridge pickup to terminal bridge+
    3 and via switch to terminal neck-
    4 and through neck pickup to terminal neck+
    5 and to switch terminal
    Now, switch connects it so that both middle lugs of blend are neck+
    supposedly blend is in middle, it has zero resistance between middle and corresponding out lug on both tapers. And there is a wire between out lugs.
    This makes yellow "blob" a common electrical spot. And that is connected to two sides of tone pot, one of which may be grounded... There I give up on actual analysis and just flag it as "highly suspicious".

    Niiiiext, switches in DOWN position, aka parallel mode.
    1 from master volume to both PU-
    2 and through pickups
    3 and to two pins of switch, both PU+ separately
    4 and to middle lugs of blend pots separately.

    Now suppose blend is middle, and we have same as above. Signal is connected to tone pot in whatever way it is. Suspicious again.
    Blend itself looks fine though.

    So, I would start with removing tone and master out of circuit, just bypass them to jack, and see how it goes.
    Last edited: Aug 24, 2018
    JW-Thrax likes this.
  3. JW-Thrax


    Aug 16, 2018
    I drew the schematic myself based on what i've read online. The circuit doesn't go through a metal plate but the control cavity has been shielded with shielding paint. It's wired up exactly as the schematic the volume pot is grounded to the bridge and the tone knob is grounded to the input jack.
  4. Edited my 1st post with "analysis"
    With master volume I assumed bridge PU- goes to right lug of master volume, you have a break there.

    Edit: I suspect one wire blend->tone is not needed. I cannot tell which is because I doubt how tone is grounded but it should be one. That is my "gut feeling" for what it worth.
    JW-Thrax likes this.
  5. JW-Thrax


    Aug 16, 2018
    Thank you, I will look this over more throroughly tonight. If I understand you correct I have to remove one of the wires going from blend to tone and see if that resolves the issue?
  6. wiring.jpg
    Parts got damaged in the process, but it should be understandable. Check it again, but IMO this should look better.

    Changes from your schematic: jack ground connected to other spot; tone re-implemented, volume lug connected to pot center.
    And check ground resistance with multimeter, be sure that it actually connects. There should be connection with close to zero Ohms between jack ground, tone pot body, volume tone body, and bridge. And be sure that blend is not accidentally grounding one of tapers in any place through case.
    Last edited: Aug 24, 2018
  7. The "ultimate" fix
    With electricity good ideas always come after some background thinking.
    Just move one of "blend" wires to master volume lug. Other connections make sense then actually.
    JW-Thrax likes this.
  8. JW-Thrax


    Aug 16, 2018
    I was just looking at my schematic and cross referencing it with the schematic I based it on. Apparently I made a mistake while drawing my own schematic.

    This is the schematic I based it on:
    I wired it up like above but with the tone pot chassis grounded to the output jack and a mini toggle instead of a push pull pot.
    I already have the master volume lug attached to the blend. My sincere apologies for this oversight and for the time you spend looking for a solution in my own drawn schematic.

    Everything works like it's supposed to except for the blend which seemingly acts as a 3 way switch at the moment.

    Again sorry for my own mistake. I really appreciate the time you took in trying to help me

    Edit: I've edited the original post to have the right schematic.

    this is how it's currently wired:

    Last edited: Aug 24, 2018
    ELynx likes this.
  9. Not a problem at all, It didn't took me that much time. Plus I am considering a series/parallel switch to my VBT, but never actually bothered to look into schematics to see interplay of blend in series.
    JW-Thrax likes this.
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