Ultimate No-load Ungrounded Blend Pot (Pics!)

Discussion in 'Pickups & Electronics [BG]' started by walterw, Aug 13, 2014.


  1. JKos

    JKos Supporting Member

    Oct 26, 2010
    Torrance, CA
    Screefer,
    Were you measuring between the correct two terminals of the bottom?

    - John
     
  2. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Bringing this back from the dead.
    I understand the pot modifcation as per Walter and others, but what if:

    Goal is to isolate 2 pups from each other from loading and not add any holes.
    There are at least 10 other projects ahead of this one in the shop so it would be ages before I could get to modding a pot (although a VERY clever idea).

    Could one use 2 push pull pots for volumes and keep the stock tone layout?
    This would allow turning each pickup off separately and then when both on, blend with the 2 volume controls.

    Would this work and could one of you sharp guys draw up a wiring diagram?
    Would it still make sense to go to 500K pots for a standard Fender PJ when both on?

    I really like the P and J tone with the 250K volume pot load and don't need any more brightness.
    OTOH, I'm thinking that it might allow for a better blend condition?
    I'm assuming that one could roll off some high end at the amp to get very close to the stock sound?
     
  3. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    if you like the two volumes thing and aren't trying for less of a load (i.e., more brightness) then just stick with regular stock jazz wiring, there's nothing in this idea that you're actually looking for.

    at most, you could try linear volumes instead of audio for a smoother sweep.

    if you really wanted a master volume + blend thing but didn't want a tone change, just use 250k lin volume, use the ungrounded blend pot but don't bother with cutting the traces, then use a 250k audio tone. that'll get you basically "stock" tone. (all the stuff about cutting traces and higher value pots is all about avoiding high end loss from loading, if that's not the goal then you don't need to bother with any of it.)
     
  4. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Hi Walter,
    So my issue is that I can hear the difference in the P pup when the J pot is completely off, vs. no J pup.
    I suppose I could be hearing things but maybe not.
    I could go the 3-way selector route but wanted to unload the pup with the ability to blend.

    Sounds like your cutting the traces method is still the best route for 250K pots.
     
  5. For documentary purposes, if anything.
    I finally did and tested my wiring idea with splitting P pickup and blend.
    Split-P.png
    Idea here that switch allows to split P pickup and send treble side over ring of output jack, independent of bass side and J.

    In default configuration (switch A) sides of P are in series in correct phase, and together form regular P pickup that goes to one side of blend, J going to other.
    Then blend allows to either dial proportion on Tip, or send P and J separately over Tip and Ring.

    In switch B position P pickup's treble side is send over Ring, whereas bass side is sending remainder of the signal to blend. This way blend can be dialed to P only, which is bass side only, J only, which is all strings, or combination of them (but I find volume difference unpractical, for what practical is worth here). Then blend is send over Tip as usual.

    Dual volume pot per taste, and I skipped tone controls.

    If someone ever needs this, pay attention to switch wiring, this part is easiest to misinterpret, and when doing actual assembly pay attention to phases of halves of P and J in all combinations.

    I tried this combination, and I like to use 5th down synth with treble, and "clean" on tip channel. This way strings B-E-A give regular bass tone and D-G give "power chord-y" sound, like piezo with individual sounding will do. If I dial J I get bass for all strings, if I dial P I get bass only for B-E-A.
     
  6. PawleeP

    PawleeP

    Oct 8, 2012
    East Coast
    When you cut the trace does the ground lug {3rd lug} still need to be bent over and attached to pot chassis ground or does it matter?
     
  7. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    we're talking about cutting traces on the blend pot, not the volume. there's no bending of lugs there.

    the whole point of this thread is to not ground the extra lugs of the blend pot.
     
    PawleeP likes this.
  8. speyer

    speyer Supporting Member

    Do you still use the jumper if you don’t cut the traces? Just use the exact same schematic and it won’t end up fully no load Without the traces cut correct?
     
  9. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    correct.
     
    speyer likes this.
  10. bassically_eli

    bassically_eli Supporting Member

    Feb 7, 2010
    Mebane, NC
    Do basses with active pickups benefit from these mods, too? I am referring to active pickups with passive controls, such as EMGs. What would be the appropriate pot values, 25k all around? EMG seems to use all (or mostly) 25k pots. Wouldn't there be any issues due to not grounding the blend pot with active pickups?

    I recently picked up a used Brice bass that needs to be completely rewired. (It actually came wired VVBT, believe it or not, and no, that's not a typo, it actually had two volumes and a blend control.) The pickups seem to be EMG copies more-or-less, at least according to a few TB comments (I have never used EMGs). It has four knobs, so I would like to wire it VBT plus a selector switch with different capacitors for the tone control.
     
  11. bigtone23

    bigtone23

    Dec 10, 2014
    Denver, CO
    EMGs, being low impedance, don't load down quite the same. Not sure that the no-load option would improve the blend, but it seems likely that it wouldn't.
     
    Elias86 likes this.
  12. bassically_eli

    bassically_eli Supporting Member

    Feb 7, 2010
    Mebane, NC
    That was sort of my thought too, but I'm not that knowledgeable about electronics. What about cutting the traces?
     
  13. vin97

    vin97

    Mar 7, 2016
    Germany
    Cutting the traces is the no-load mod. It only affects the treble loss due to pickup loading in solo mode. Not grounding the blend pot is the important part as it will permanently keep the highs from bleeding to ground no matter how the blend pot is set.
    The blend behaviour is improved by chosing the right value blend pot. I found 100 kΩ (linear M/N) curve to be the optimum for two single-coils but this may be different for active pickups. You might have to do some experimenting. For volume and tone, I would stick to the same values you have in your bass right now. Maybe change the volume to linear, though.

    BTW, I put push/pull series/parallel and phase-reverse switches in my fretless Fender Jazz and I have to say that the phase-switch works brilliantly in conjuction with the right blend pot. Except for middle position, the whole blending range offers usable sounds with crazy mids and definition, perfect for cutting through or solos (especially chords and harmonics). I initially put it in just for the heck of it and didn't even think about the fact that the blend pot allows you to finetune the "out-of-phase sound" so that it won't just sound like the bass is broken.
    Anyway, those small contacts on the push/pull pots are a bitch to solder and I made the mistake of soldering ground wires to the bottom of the chassis, which resulted in the pots not fitting into the electronics cavity because every millimeter of height counts. Together with the orange drop cap, the cavity is now basically completely filled with the push/pull pots sitting right against the bottom shielding/grounding plate.

    Sorry for the low quality pics, my iPhone camera is dusty from working construction. I made them before noticing my mistake and resoldered the ground wires to the side of the pots instead of the bottom.
    IMG_1922.JPG
    IMG_1926.JPG
    IMG_1932.JPG
     
    Last edited: Aug 16, 2019
    Elias86 likes this.
  14. bassically_eli

    bassically_eli Supporting Member

    Feb 7, 2010
    Mebane, NC
    Thanks for clarifying that. I read no-load and thought no ground.

    That's a problem. The bass came to me with a 250k blend pot, a 100k tone pot, a 100k neck volume pot, and a 25k bridge volume pot. I can't tell what's original and what's not. I ordered some 25k pots, but maybe I should order some 100k pots too and experiment. I'm not really sure what the affect is on active basses. Is it the same as for passive basses: brighter tone and lower output?

    That sounds like a really cool mod. Unfortunately, I don't believe it's possible with active pickups.
     
  15. BlueTalon

    BlueTalon Happy Cynic Supporting Member

    Mar 20, 2011
    Eastern Washington
    Endorsing Artist: Turnstyle Switch
    So you'd be using the selector switch to choose which cap to use in your tone circuit?
     
  16. bassically_eli

    bassically_eli Supporting Member

    Feb 7, 2010
    Mebane, NC
    Yeah, exactly. Based on this thread, the idea has quite a few fans, even including some TB celebrities.

    That said, I keep entertaining other ideas for the 4th pot as well. A 6-way or 12-way selector switch seems like overkill to me, so now I'm thinking of maybe two tone pots in parallel, with just two different cap values. (Not individual tones for each pickup, more like duel master tone controls.) The idea would be to have one fairly subtle tone control, one medium control, and use the two together as stronger control. Not sure if that will work though. I'm not sure if the two filters will just be superimposed on one another, or if the result will be more than the sum of its parts. Sorry, I'm veering way of topic now
     
  17. BlueTalon

    BlueTalon Happy Cynic Supporting Member

    Mar 20, 2011
    Eastern Washington
    Endorsing Artist: Turnstyle Switch
    Well then, allow me to propose an alternative. I'm an endorser of Turnstyle Switch (the link goes to the bass he did for me that became my main player). In a nutshell, it's a 6-position rotary switch that can allow your bass to have 6 different voices. Add a Turnstyle to your VBT controls, and you give yourself more flexibility than you might have otherwise imagined. Mine is set up to give me voices for Precision, Jazz, Rickenbacker, Thunderbird, overdrive, and one channel for manual control. You can choose those voices or others, it's up to you. I think it would give you way more tonal flexibility than anything you are currently considering.
     
    Elias86 likes this.
  18. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    agreed!

    if you're gonna use up two knobs just for the tone control, make them a tonestyler (which is really just a large bank of selectable tone caps) wired into a regular tone knob in place of the regular tone cap.

    that said, tone caps don't really sound different than each other until you get the knob below like "4", above that you're just hearing the pot itself loading down the sound to make it duller. if you're just using your tone knob to "take the edge off a little" and aren't dumping it all the way to get those low-mid resonant peaks then don't bother, a regular tone control is all you need.
     
    Elias86 likes this.
  19. BlueTalon

    BlueTalon Happy Cynic Supporting Member

    Mar 20, 2011
    Eastern Washington
    Endorsing Artist: Turnstyle Switch
    Just FYI in case you missed it, I wrote Turnstyle, not Tonestyler. Two different things. The Tonestyler would be a great replacement for the tone control knob, but he was looking for something to do with the fourth hole. I think the Turnstyle will do what he wants in that fourth hole better than anything else.
     
    Elias86 likes this.
  20. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    oops!

    yeah, two different things. the tonestyler is a bank of 6 different tone caps, the turnstyle is a whole crazy new switching scheme.

    the website (which is thoroughly confusing, it shows pictures of guitars instead of pictures of what they actually sell) makes all kinds of claims for the turnstyle switching your strat to sound like a PAF or like a P-90 or whatever, claims i don't believe for a second from a passive system. still, a bunch of new tonal variations is always fun.
     
    Elias86 likes this.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Aug 5, 2021

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