Blend pot problem

Discussion in 'Pickups & Electronics [BG]' started by MilosJanic, Sep 24, 2017.

  1. MilosJanic

    MilosJanic

    Jan 7, 2013
    Hi,
    i m using Aguilar obp3 and Aguilar dcbs, I m using 250k Bourns Balance Pot.
    The problem i have is there is almost no "blending" Going from bridge to center i can hear the neck pickup coming in just before it hits the center position, same thing on the neck side. It acts almost as a 3 way switch and not a blend pot.
    Anyone knows what can be the problem?
     
    Freaklight likes this.
  2. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    are the pickups themselves passive?

    try the "ungrounded" trick; disconnect the ground lugs from that blend pot, so you only have the two pickups going in, the one wire jumping across, and the one wire going out. the other two lugs should have nothing connected to them at all.

    this will "slow down" the shading a little, and will also give you a bit more clarity.
    jazz bass ungrounded blend.jpg
     
    somebrains likes this.
  3. MilosJanic

    MilosJanic

    Jan 7, 2013
    Yes the pickups are passive, thanks for the tip, i ll try it.
     
  4. Blending passively is always problematic. I've spent years making custom pots, or tweaking active circuits for different ways of blending two pickups.

    An MN pot, no matter what taper and/or value is never going to give a gradual sweep from the sound of one solo pickup to the other solo pickup. The reason is that in the middle the pickups are suddenly in parallel and give a very different response and impedence. But this "scooped" sound with extra brightness is part of the jazz bass "thing". On my jazz, I have an MN (unearthed) and put up with that so I can have that tone of both pickups.

    If there is such a thing, you may want to try a 100K M/N pot if you want to keep that bright sound in the middle but you want to be able to creep up more gradually on either side. You will have to run this pot unearthed for sure or it will load the pickups too much. You will also lose the true solo sound of each pickup, unless you mod the pot by cutting the track on each end.

    Really, someone should make a blend pot that has a log and anti-log tapers that start from halfway like an (otherwise linear taper) M/N pot does. There is already s and w taper pots that sort of do this in a single gang. (The tone pot for a tube screamer is one like this.) So I think it wouldn't be hard to manufacture.

    On my PJ, I use a 200K A/C pot that I made from two individual pots that had close to a real log taper (not just an "audio" taper). I doubt one like this would be easy to find off the shelf, especially if you need to install it through 1/4" of timber. This gives me as close to a perfect morphing sweep I've heard for a pair of passive pickups. The pickups are also carefully selected as good matches in impedence and output. (Rare for a P/J set.)

    A twin buffer can be bought or made very easily if you are still not happy and don't mind installing a battery and a stereo jack.

    Another option, is to use a rotary switch and pre-set your favourite blends (or solo). I did this on many custom setups back in the 90's before the internet made it easy to find m/n and a/c taper pots.
     
  5. MilosJanic

    MilosJanic

    Jan 7, 2013
    That rotary switch is a nice idea, i could live with maybe 5 positions. I don't need every increment of the blend pot, i just want it to be easier to get for example 75% bridge/25% neck blend, right now i have to spend a few seconds finding that sweet spot which is just a millimeter of the center position, and a few seconds on a live show is too much.
     
    Freaklight likes this.
  6. Well, you need a switch with two poles, and a 6-way will be just the same price as a 5-way. But I understand the thinking behind a 5-way. Personally I've never liked the sound of a solo bridge pickup (sorry jaco fans ;)) so when I had one of these in my bass back then, I never bothered with the solo bridge pickup and just had five blends and a solo neck sound.

    As you roll away from the centre, an (unearthed) M/N pot simply keeps one pickup directly wired to the output, and gradually adds resistance to the hot wire from the other. I'd recommend using say a 50K linear pot tacked in-line with each pickup for testing. Find the two blends you like, and put the closest fixed resistor for each on a rotary switch. Oh, and if possible, buy a make-before-break (MBB) switch (AKA "shorting" switch) so you get the quietest operation.

    If you have decent soldering skills and the space inside the bass for this, you can also mount a couple of trimpots directly onto the rotary switch. This makes it easier to tweak the blends if you change your mind.
     
  7. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    no good.

    i tried that very thing (resistors on a rotary), and i found that plugged into different amps the "sweet spot" changed! sometimes it would get that ephemeral "one pickup loaded by the other a little" sound and other times it would just sound like two pickups.

    my guess is it was the result of plugging into different impedance loads, and i suppose if you had the onboard preamp then there wouldn't be this problem, the pickups would "shade" the same way regardless.
     
  8. MilosJanic

    MilosJanic

    Jan 7, 2013
    Before this i had an onboard preamp with an active blend, so I didn't have this problem, it was blending smoothly.
    I will run all of this information by my friend that does all the wiring/soldering on my basses, in the end if i m not satisfied I will probably get that Bartolini AGDB, i just hope i will have the space for it.