Blend Pot Problem

Discussion in 'Pickups & Electronics [BG]' started by E.O.M., Mar 9, 2005.

  1. E.O.M.


    Dec 7, 2001
    Grand Rapids, MI

    I've had this issue for a long time, but I've never had enough free time to actually address it. I installed an Aguilar OBP3 in my Yamaha John Patitucci, and everything works great except the blend pot. The pot itself works (I presume, since it pans between the two pickups), but I think there's something wrong with the taper or value.

    The problem is that it's working more like a 3-way switch than a blend pot -- I can get neck solo, bridge solo, and both full. I cannot get 75% neck 25% bridge etc. Any movement away from the center detent yields solo output of the selected pickup.

    Any ideas? Wrong value? Bad hookup/ground?

    edit: I think the pot is 500k, but I'm not sure - the Aguilar diagram doesn't specify and I don't have my bass on me at the moment.
  2. dougray

    dougray Supporting Member

    Apr 16, 2002
    western maryland
    it is important that you use a "linear" taper blend control, sells a 250K blend control to use with their pre-amps. good-luck. :bassist:
  3. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    It's very likely the pot. A 500K pot is a very high value for an active system, assuming the blending is happening post-preamp gain.

    You probably need something like a 100K linear pot, but if you go too low, you won't be able to solo either of the pickups.
  4. east


    Jun 21, 2004
    §I use a linear 100k end it works great!
  5. BruceWane


    Oct 31, 2002
    Houston, TX
    The OBP-3 doesn't have active blend. All blending is done before hitting the preamp.

    Where did you get the blend pot from? I recently installed one (put an OBP-3 in my Dingwall) I got from Stewart-MacDonald.......not happy with it. Not smooth at all. I've heard that passive blend pots can be pretty hit-and-miss, so I'm on a mission to find a decent one. I've heard a few folks say the pot works well. And my Modulus has an OBP-3 in it from the factory, and the passive blend pot works perfectly.....but it also has Bartolini's in it, so I don't know if the blend pot was supplied by Modulus, Aguilar, or Bartolini.

    I'm going to try the Allparts first, since I need to order some knobs from them any way.

    From what I understand, passive blending causes an impedence interaction between the pickups, so it can be affected by whether you use a 250K or 500K pot. In a plain volume pot, the only difference between a 250K and a 500K is simply that the 500K technically loses less highs, although the difference may not even be perceptible in a bass. As long as the blend pot has an equal or higher value than your master volume, it shouldn't affect your tone, so you may want to try both a 500K and a 250K to see if the impedance interaction works out better.
  6. E.O.M.


    Dec 7, 2001
    Grand Rapids, MI
    I don't remember where I got the pot (it's entirely possible I ordered it from Allparts).

    What is the difference between audio and linear taper, and how would it affect the controls if I had one or the other as a blend?
  7. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    You can't use a "standard" pot for the blend pot. Audio or linear taper, doesn't matter. You need a "special blend pot", the kind that Bartolini makes. It's a "dual" pot, and it's wired in a special way. Ordinary pots don't work very well in the "blend pot" capacity. Here's a link:

    All the "standard" pots will give you that "extreme in either direction from center" behavior, and it doesn't matter what taper they are. Follow Bartolini's instructions, and you'll be a happy camper. :)
  8. nonsqtr is correct.
    It is esentially two pots in one.
    Each one is wired in a way that makes one "ascend" while the other "descends" and visa versa. In other words while one turns up the other turns down by exactly the same amount.
  9. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    So does that bartolini method work with any dual gang linear pot?
  10. Yes
    You crisscross the wires as shown. This makes one decrease in value while the other increases and visa versa.
  11. Funky Doctor

    Funky Doctor

    Aug 28, 2003
    Thought so. Looks/seems pretty standard.
  12. E.O.M.


    Dec 7, 2001
    Grand Rapids, MI
    What do you mean by a "special blend pot?" What I use is wired like the diagram posted, with the criss-cross wires. Did you mean that generic blend pots aren't worth my time, and that I should get a Bartolini pot?
  13. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Well, the original post sounded like you were using an "ordinary" pot. But, if you already have the dual blend pot, then maybe there's something wrong. I'd recommend a linear taper pot for blend purposes, because in an audio taper, the midrpoint is "not" the electrical midpoint. You can check this with an ohm meter, but you'll have to take the pot out of the circuit to check it. There should be some numbers stamped into the pot casing, something like "500k A" or something like that, if you read those you should be able to tell the pot value and taper. It might not even be worth messing with, it might be cheaper and easier just to replace it. Do you have the wiring diagram or schematic for the electronics in your bass?