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odd preamp wiring problem--help!

Discussion in 'Pickups & Electronics [BG]' started by PB+J, Jan 24, 2006.

  1. PB+J


    Mar 9, 2000
    arlington va
    I'm trying to install a Aguilar OPB-2 and two Bartolini single coils in my MIM jazz bass. Vol., blend, bass/treble. I wired it up as on the diagram, and the blend pot is acting wierd--when I have it set to center, I get nothing--no sound at all. When it's set to either extreme, both pickups are on full.

    I called Aguilar, and they suggested reversing the wires going to ground and to the vol. pot. Did that, no change. Called Aguilar back, and they suggested a bad (250k) blend pot. Tried the 250k blend pot that came with the fender--same thing. with the blend pot centered, I get no sound at all, on either extreme, l get both pickups.

    Any ideas?
  2. the wires appear to be landed incorrectly on the blend pot.

    one ONE level of the blend pot (not both) swap the wires on either end, leaving the middle wire (the wiper) in tact.
  3. PB+J


    Mar 9, 2000
    arlington va
    That's what the guy at aguilar told me to do, and that's what I did--multiple times, with both the blend pot from aguilar and the blend pot from fender. I kept the bridging wires in place and switched the wires going to volume pot and ground. i'm really stumped
  4. can you trace the wires and put up a schematic?

    I don't think that we're talking about the same thing here...

    if you have a ground connected to either of your blend pot wipers (the center connection), then that's the problem...

    the pot top-left and the pot bottom-right should be the same connection...

    the pot top-wiper should connect to the front pickup +....
    the pot bottom-wiper should connect to the rear pickup +...

    the pot top-right and the pot bottom-left should be the same connection...

    I don't know how your preamp is wired in, (after the volume pot???), so I can't give you much more information than this...

    for a schematic on how a PASSIVE bass is wired V/B/T...go here...
  5. PB+J


    Mar 9, 2000
    arlington va
    Thanks pilbara, I really appreciate you taking a shot, but I've done exaclty what the diagram says--the middle lug on each level of the blend pot is connected to the hot lead from the bridge and necks pickups respectively. The lower left lug bridges to the upper right, the lower right bridges to the upper left. A wire from the volume pot runs to the upper right lug, and a wire to ground runs to the lower right lug. I've tried switching those two several times, and I'm just at a loss.

    At this point I've taken the preamp completely out of gthe picture and I'm just trying to figure out how to get the passive blend to work
  6. PB+J


    Mar 9, 2000
    arlington va
  7. klocwerk


    May 19, 2005
    Somerville, MA
    perhaps your pot has a weird layout.
    Get a set of alligator-clip leads (a piece of wire with an alligator clip at each end), clip one on to each of your leads, and swap them around on the pot until you figure out what the heck's going on. Easiest way to troubleshoot wiring imho.

  8. good suggestion, klocwerk...

    perhaps you could take the original pot (the one that's not connected) and run it through its paces with an ohm meter.

    let's back up to what is happening...
    the bass is making no sound when the pot is centered...and both pickups are full on when the pot is dialed to eithe extreme...

    Also, is your pot an audio taper? IT MUST be an audio taper on both levels. Otherwise, you're signal will be soo attenuated near the center, that it will seem like it is off, when in fact it is just VERY weak.

    you can verify audio taper by using the ohm meter and breaking down your turn into segments...

    for instance
    a linear taper will have EQUAL drops (or increases) in resistance per equal amounts of pot movement (halfway being half the total resistance to either side)

    an audio taper will have LOGARITHMIC drops (or increases)...halfway would be about 90% of the total resistance on one side and 10% on the other)
  9. PB+J


    Mar 9, 2000
    arlington va
    This is the pot aguilar supplied, and not only is there no signal at the center detent, there's a full signal--both pickups on--at either extreme

    I've given up on the blend pot--I'm going with a volume/volume/b/t setup. I have a gig tomorrow night and want to use this bass. In an hour or so I'll try to wire it up v/v/bt and see what happens

    It's very frustrating--I took it today to the local store, where the amp tech looked at it and said, yep, it's wired up right and should be working

    I followed the drawing extremely carefully. The pickups both work. I just don't get it
  10. PB+J


    Mar 9, 2000
    arlington va

    Tonight I gave up on the bypass switch and the blend pot and just went with a second volume pot. Now with both volumes on full, I get no sound, with either volume backed off I get--yep--both pickups on

    I want my money back
  11. look...there's something wrong, that you are jumping over...

    you're going to have to start at ground zero on this...I mean ground ZERO...first step...

    put the pickups into volume pots ONE PICKUP at a time, test it every step of the way...

    you'll get to the bottom of it, but you're actually losing time because you're trying to jump ahead, and you're missing the problem...

    start with a good ground on the pickups and then go from there, step by step...

    I'm confident you will find it.