1960s Jazz Bass - Isolated Dual Stacked Vol/Tones - How does it affect tone?

Discussion in 'Pickups & Electronics [BG]' started by Antisyzygy, Jan 1, 2016.

  1. tortburst


    Apr 1, 2007
    New Jersey

    In this diagram of the 62 re-issue, would the resistors attach to the clockwise lugs of the volume pots before joining to the output wire?


    Ok so is this right?
    the arrow is the wiper.
    anti-clockwise lug is the one connected to earth
    So then if your circuit line turns and connects into the center of your pot symbol then it's the center lug, if it's connecting with the line coming out the top it's the clockwise lug.
  2. tortburst


    Apr 1, 2007
    New Jersey
    Did i do this right?

    From the stack knob VVT layout

    Now with 15k resistors
  3. Insulate the resistors so that they don't touch up against the control plate and kill the output.
    Bill Whitehurst likes this.
  4. tortburst


    Apr 1, 2007
    New Jersey
    Will some black electric do the job?

    I'm assuming I placed them correctly or you'd have said something.

    Learning is fun!
  5. Electrical tape works fine.

    Yes, the resistors are wired properly.
  6. tortburst


    Apr 1, 2007
    New Jersey
    I cleaned it up a bit.

    Tried 15k resistors but doubled it up to 30k. Even at 30k I find the tone independence still benefits from dialing the volumes down from 100%.

    Also tried .047uF and .068uF caps(pictured) but settled on .1uF.

    Thanks again for the help and advice

  7. That's actually 7.5k. Wiring two 15k resistors in parallel halves their value.
  8. tortburst


    Apr 1, 2007
    New Jersey
    I had it in series then re-did in parallel to save space without realizing the diff


    Thanks again
  9. That's odd. How are you actually testing "tone independence"?
  10. tortburst


    Apr 1, 2007
    New Jersey
    testing it in various setting
    volumes at 100%, drop each tone down to 0%, see if i can hear any difference btwn the two. Repeat with volumes at 80%. Etc
    I ran through a lot of scenarios I just don't feel like drafting up my test cases bc then it'll feel like my job not my hobby.

    though i messed up the series/parallel wiring so all bets are off on previous comparisons.
    I wired the resistors in series now

    going through my various tests again and I can't hear much of a difference btwn the two tones.
    Wondering if any difference I thought I heard is emperors new clothes effect, i.e. Just fooling myself into thinking I hear a difference.

    IF there is a discernible difference it's very subtle and probably not worth fussing over
    Antisyzygy likes this.
  11. The only real way to tell is by tapping the tops of the pickups with a metal screwdriver or something similar. With both vols full up, roll one tone down and tap both pickups. You should hear one go dull but not the other. Then of course, try the other. Make sure your amp isn't up too loud.

    I'm not sure if I said it in this thread, but I've said it before when this topic comes up; isolated tone pots is all a bit academic TBH. With the combined signal from two pickups, when you roll down one tone pot, the overall signal will dull. I doubt you could hear by ear, which pickup is losing treble. Especially with a jazz bass where the two pickups are so similar, relatively close, and with identical tone caps.

    But I guess it's nice to know the controls are operating a little more intuitively and you are not losing so much volume and tone as in the original 1960 circuit.
    Antisyzygy likes this.
  12. Antisyzygy


    Dec 8, 2014
    Well, I went for it. I took RobbieK's schematic and modified it a little using G&L schematics for reference (for the tone pots). I also opted for no summing resistors because I can get a similar effect by rolling the volume down.

    A guy named SteveCS here on TB said that was possible and I checked the schematic, he was right. Kudos (and thanks!) to @RobbieK and @SteveCS for making this come together right!!

    Long story short, I wanted to keep the stock SB-2 functionality with the volumes but have isolated tones available as needed. This achieved the goal!

    Schematic (0.015uf is for the bridge) :

    Doc - 3-3-16, 10-00 AM.jpg

    The harness :

    IMG_2461.JPG IMG_2459.JPG

    The bass with the harness installed (dual concentric pots) :

    IMG_2521.JPG IMG_2520.JPG

    The tone pot on the neck pickup is exactly the same as what's on my SB-1, so now I have a fully functionality backup for my SB-1. I do use the tone pot on my SB-1 quite a bit so it's nice having a backup like this. The tone pot on the bridge is just an extra.

    If I roll off the volumes about 5-10% the associated tone pot becomes isolated. So for example, I can get unusual configs like :

    1. 100% P 90% J -> P tone is master tone, J tone is isolated
    2. 90% P 100% J -> P tone is isolated, J tone is master tone
    3. 90% P 90% J -> Both tones are isolated
    4. 100% P 100% -> Both tones are master tones, and can be combined for more treble cutting

    I tested it out and the tone isolation works. It does produce some interesting tones, but most are pretty subtle differences. I was a little disappointed by that, but honestly, the primary goal was to get a full backup for my SB-1 and that was achieved.

    For example :

    1. 100% P , 90% J , 0% J tone produces an upper-midrangy P sound, but it's pretty close to the stock P sound

    2. 90% P , 90% J , 0% P tone produces a scoop, it's boomy with a bit of pop on the top end.

    2. 90% P, 90% J with both tones at 0% produces a tone with lots of mids, upper and lower mids that is. It's got more upper-mids than the P bass pickup by itself. It might work well with fuzz.

    I also like that I can solo the J pickup now with it's tone rolled off. It's much less nasal sounding and might be useable in the mix. The J pickup on a SB-2 normally doesn't sound good all by itself. It's primary use is to color the tone produced by the P pickup.
    Last edited: Mar 5, 2016
    tortburst likes this.
  13. tortburst


    Apr 1, 2007
    New Jersey
    I've been tinkering with my stack knob harness and have been learning some interesting things.

    I removed the resistors bc I can get the same effect by lowering the volumes a bit.

    The 62 reissue harness has a .05mfd on the neck stack pot, and a .033mfd on the bridge stac pot.

    100% Neck and 100% Bridge volume and each tone can be master

    Roll off the neck and you're at .05mfd
    Roll off the bridge and you're at .033mfd

    So that's cool, kind of like a varitone with only two caps.

    I like 0.1mfds so I put a 0.1mfd on the neck and a .068mfd on the bridge

    Noticed the tone pots can cause a 60 cycle hum like the volume pots when they're not in sync.

    Also noticed which ever volume pot is up higher will produce more hum if the tone pot in the same stack is also higher than the other.

    Lots of little options to play with

    Assuming 100% means wide open and 0% means the pot rolled all the way off.

    Currently digging...
    80% Neck vol, 90% Bridge vol
    80% neck tone, 20% bridge tone


    90% Neck vol, 80% Bridge vol
    20% neck tone, 80% bridge tone
    Last edited: Mar 21, 2016
    Antisyzygy likes this.
  14. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    Um...I must insist: unless there was a parts shortage on a particular instrument, on the 1960 wiring, the tone cap on the neck pickup was, as stated, .05. But the tone cap on the bridge pickup was .03 instead of what has been listed above.
  15. tortburst


    Apr 1, 2007
    New Jersey
  16. WillieB

    WillieB Battling Bass Guitar Bulimia since 1975 Supporting Member

    Apr 26, 2010
    Columbus Ohio
    This has been a wonderful thread .... thank you very much for all the technical advice offered - Robbiek, line6man. I have wired many basses but never a
    stacked knob. I just completed it and used the 15k parallel resistors. Sounds very nice !
  17. okabass


    Mar 19, 2005
    Thanks for the very good info.
    I have a -73 Jazz modded with stack pots and Lundgren PUs. I tried different wirings (schematics on this site). I liked the original best (with carbon comp resistors). It has most mojo to me.
    I think the volume drop is no big deal. The 15 k-15k wiring is surely better electronically, but to me it sounds too neat.
  18. boomsville


    Jun 25, 2016
    Hi all. First post here.
    Was wondering if this mod also helps reduce the sonic difference heard when rolling back one Vol knob.

    Ex:Both volumes at 100% sounds full,
    Roll one back 10% and it becomes nasally.

    Is that just the nature of the beast or?
  19. tortburst


    Apr 1, 2007
    New Jersey
    Nature of the beast
  20. smeet

    smeet Supporting Member

    Nov 27, 2006
    Woodland Hills, CA
    That "nasal" sound is just you getting back some of the mids you lose when both pickups are all the way up. It's not only the nature of the beast, it's actually a good thing IMO.
    Datsgor likes this.
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