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Is adding a 250k pot master AFTER a V/V/T jazz config reducing treble ?

Discussion in 'Pickups & Electronics [BG]' started by Clemouze, May 9, 2018.

  1. Clemouze


    Sep 1, 2016
    Paris - France
    Salut all !
    I did this on my geddy lee bass (Crazy Modded Geddy Lee Jazz bass ( SMB-4D + OBP-1 ) ) :

    I add a master volume pot (250k) after the classic V (250) /V (250) /T (250) system
    Why ?
    1) I needed a volume pot for my new MM style pickup
    2) I needed a master volume just to reduce the volume without touching both jazz neck pickup volume pot and jazz bridge pickup volume pot

    But I think, or maybe I just imagine, that this jazz configuration lost some high end.
    Is adding a 250k pot master AFTER a V/V/T jazz config reducing treble ?

    I guess since it is adding some loading composants to the jazz circuit..

    Since this new pot is the only pot controling the volume of the MM style pickup, I don't want it to be 500k because I'm affraid of the brightness of this MM pickup.
    But what if I use a 500k pot to both the jazz neck volume and jazz bridge volume ?
    Last edited: May 9, 2018
  2. Yes, slightly. You could offset this with a no-load tone pot. Or use an un-earthed blend pot instead or two volumes. Or both. IMHO, I think a blend pot setup will work better for you. You can just leave the blend where you like and use the master. You can have master vol and passive tone on the same stack - a 250K log dual-concentric. Then you just have to switch its input (should be the clockwise lug, not the middle) between the ouput of the series/parallel MM switch and the blend pot output.

    Also there's no need to switch the earths at your jazz/MM switch. Just leave the earths all connected.
  3. Clemouze


    Sep 1, 2016
    Paris - France
    Thank you for this answer !
    With a unearthead blend pot , will the load on the pickup only be master and tone ?

    What's the difference between standard grounded pot and unearthed pot and why to do this or not ?
  4. Yes. As I mentioned, you could also use a "no-load" tone pot to reduce this load even further, but you won't find this as one half of a dual concentric (stacked) pot. But you could mod it yourself, if you are handy with a jeweler's file. You cut the pot's track right before the clockwise lug so the load of the tone cap and pot resistance is lifted. You get a nice little bump in the treble just as you roll up the tone control to 10. It's a very old trick...

    A blend control will still work just fine if the earth sides of the pots are not connected. I first heard about this around 10 years ago. There's bound to be a few threads kicking around this site on it. It will also reduce the load on your jazz pickups and give them a slightly more open tone. If you want to hear the actual effect on your bass, you should wire up a blend pot and put a temporary switch on the earth wires. Then you can hear it for yourself and decide whether it's worth doing.


    The only drawback is that the bridge pickup won't be completely off when the pot is rolled around to solo the neck pickup and vice versa. But honestly, there is only the tiniest level of signal from the "off" pickup. You'll probably have to tap the magnets to hear it. But if you like the tone of the unearthed blend, and you also really want the true solo pickup sounds, you can do Walter's mod. This is the same idea as the no-load tone pot, where you cut the track right before the clockwise lug on one wafer and the anti-clockwise lug on the other.
    bigtone23 and Killed_by_Death like this.
  5. Clemouze


    Sep 1, 2016
    Paris - France
    Wow thanks OK I got it , I read some threads about this truly ungrounded pot, seems good !

    So my pickups will only see 250k tone and 250k master volume !
    But with a standard V/V/T the pickups see 250k neck volume and 250k bridge volume + 250k tone , no ?
    I will not retrieve the exact stock tone , am I right ?

    I have trouble to find infos about the loads calculation. On a V/V/T , are all the pots on parallel ? So is total load 83,3 k ohms ?
    With the ungrounded pot + master tone, is the total load only 125k ohms ?
  6. Clemouze


    Sep 1, 2016
    Paris - France
    Well , tone pot appart :
    With two volumes from a V/V/T ( each 250k) I have 125k volume load , right ?

    With my current config of M/V/V/T, if I put a stacked 500k for volume, I will also have a total of 125k volume load, like in the original config, am I right ?
  7. Hey mate. Please don't take this the wrong way, I really don't mean to be a smart-arse, but I feel you are over thinking all this. Yes, when the three 250K pots on a jazz bass are all turned up full, their resistances are in parallel and that's the load that the two pickup (now in parallel) will see. But as soon as you adjust one of those pots, things change. Plus there are factors like the capacitance of the guitar cable and the input impedance of the amp/pedal/di you are plugged into.

    And there's no one answer to this. If you like the sound of played-in strings or you have a fairly warm sounding rig for example, you'll barely hear the difference between 250k and 500k pots or a no-load tone pot or whatever.

    You really must wire up a few little test circuits like the one I posted and hear for yourself the effect of lifting the earth and changing the load.
  8. Clemouze


    Sep 1, 2016
    Paris - France
    Yes I understand for sure !
    My concern is that I am not so good at soldering : Ok I can change and wire a standard big fender pot but here I left all the soldering to a luthier since the control plate is super busy and I choosed to use mini pots

    Testing by myself will be very hard but letting the luthier do all the tests will be very costly !
    I will try
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