Wiring problem

Discussion in 'Luthier's Corner' started by Geoff St. Germaine, Nov 21, 2005.

  1. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    Alright, so I'm having some wiring difficulties on my 8 string and I can't figure out what the heck is wrong with it. I figured I'd throw it up because I have a feeling that I'm overlooking something that is simple and just not seeing it. Anyway, the bass is wired as such:

    -Pickups are Nordstrand fat stacks with a coil tap
    -Coil tap wires are wired to a DPDT switch that can switch them to ground
    -ground wire on the pickups are wired straight to my star ground point
    -the hot wires off of the two pickups go to a 4PDT switch where they can be routed to one of two 250K blend pots
    -these blend pots then feed into a volume pot
    the output of the volume pot goes back to the 4PDT switch taking up the last two spaces on it
    -the output of this is sent to the input of my Aguilar OBP-3 preamp

    The problem is that with the bass wired in this fashion I have two problems, an extreme amount of noise and one of the volume pots doesn't work when it is switched to that channel. I checked the both pots with a DMM and they are both working correctly. I'm wondering if anyone sees a problem with this wiring layout that I am missing.



  2. Hookus


    Oct 2, 2005
    Austin, TX
    Where do you get your output when the 4PDT switch is in the other position? Does not look like you would get any sound at all when that switch is flipped.

    You may be picking up noise from somewhere else in that circuit, I don't see off hand anything that would cause it.
  3. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    The outputs on the switch are wired together right at the switch, I actually drew it incorrectly in that diagram, the bottom pole in the switch should have the blue wire coming from the other lug.

    As far as what's happening off of the picture, it is just the Aguilar OBP-3 which I wired straight off of the Aguilar website. I know that that part isn't the problem because I have the switch and the vol2/blend2 bypassed right now and it is working fine right now. I'd just like to get the other channel working.
  4. Geoff,

    I don't understand what you are trying to accomplish here?
    is the first pickup grounded like the rear (not shown on diagram).

    Switching the 4PDT switch just chances controls to the other knobs? I don't understand the purpose of this?

    nevertheless, if this is what you are trying to accomplish...I do not see a reason (provided everything is connected as shown), why it wouldn't work.

    have you checked your switch before you wired it up to make sure that the connections operate as you understand them to? Sometimes we assume this to be set up a certain way and it turns out to be different.
  5. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    It's just two separate channels of volume/blend. I use two different volumes live (one with a neck pu solo) that I can adjust more easily this way. Yeah, there's supposed to be a ground on that top pickup. In my haste I seem to have made some errors drawing this diagram. I'm not understanding it myself. I'm taking the electronics (sans pickups) to work tomorrow and I'll use one of the signal generators and a scope to see what is happening. I don't understand why it isn't working. I can check the 4PDT switch, maybe there's something wrong with it. I built the circuit in circuitmaker and it worked as I would have thought (and would like).
  6. ahhh...I see you want it so that you can quickly swap between to "presets"...that's actually quite clever...I don't like drilling a lot of holes in my basses, so this wouldn't be for me...but I can definitely appreciate its merits.

    for what it's worth...I wired a DPDT switch for a preamp bypass once, and on first connect, it would just hummmmm hummmm hummmmm in bypass mode (very little signal, LOUD hummmmm). So I wired the preamp's battery negative through the other throw of the switch so that it would turn off the preamp when I was bypassed....this worked...I don't know why I needed it, but it worked...

    your problem seems to be something silly along the same lines...

    perhaps you could try grounding the unused knobs by connected a ground to the unused throw of poles 3 and 4....

    I don't really know...I'm grasping at straws.
  7. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    I was actually thinking of doing just that.
  8. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    Well, I found my problem. It seems that I didn't double check my check for defective pots and when I hooked up the circuit to the scope this morning it was obvious that one of the volume pots wasn't functioning. It seems that one of the outside lugs is no longer connected to the resistor.
  9. pilotjones


    Nov 8, 2001

    Cool idea for the circuit with two preset blend/volumes.

    I'm thinking that you could have used gotten away with a 3PDT instead of a 4PDT, right? First two poles wired the same. Third pole wired with the OBP-3 lead to the center (switch pivot) lug (left side of the xPDT in the schematic), and the two volume pot outs to the two output lugs (right side of the xPDT in the schem). Asking because if there's a flaw in the way I'm suggesting I'd like to learn.
  10. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    No,you're right. I had a 4PDT for the project because I had something a little different planned at the start.
  11. ahhhh...good detective work, Geoff.

    I'm happy that you got it sorted.
  12. Geoff St. Germaine

    Geoff St. Germaine Commercial User

    Thanks. Now to get a new one...
  13. when buying pots...always by 1 extra for every 10 or so...

    if you end up with a few extra, that's fine, because you'll find 101 uses for the suckers...

    I really have to get my butt back to the states and pack up some stuff that I've left at my parents house...I've got at LEAST a dozen high quality pots there taken from an old analog computer.