Jazz Bass Capacitor

Discussion in 'Pickups & Electronics [BG]' started by Craken, Dec 8, 2012.

  1. Craken


    Feb 13, 2006
    Hi everyone. I have some Bartolini 9J pickups in my Fender Jazz and I almost exclusively use the bridge pickup.

    I have found that if I slightly roll off the bridge pickup volume knob I get a lovely thick, warm tone that I like a lot. I would like to get that tone with the volume knob full on so I don't sacrifice output volume of the bass (it is quiet enough already) and so that it is easier to manage.

    Do you think that this has anything to do with the capacitor and if changing the value of it would have an effect?
  2. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member Supporting Member

    The capacitor is linked to the tone control and plays no role in what you describe.
    What happens is the capacitance of the knob itself slightly cutting highs as you roll it off.
  3. Craken


    Feb 13, 2006
    Ah yes of course, silly me. To my ears it rolling off the volume slightly does more than just cut highs though, it's a fatter sound.
  4. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member Supporting Member

    That's what you get when you cuts highs.
  5. Sponsored by:

  6. Kmonk


    Oct 18, 2012
    South Shore, Massachusetts
    Endorsing Artist: Fender, Spector, Ampeg, Curt Mangan Strings
    I recently read an article where Carol Kaye recommended never turning the volume on the bass past 2/3. She didn't explain why but I have always found that I get the best sound from my Jazz bass at between 2/3 and 3/4 volume.
  7. steve_rolfeca

    steve_rolfeca Supporting Member

    Actually, that's not strictly true. The pots (volume or tone) are about as close to a strictly resistive element as you can get.

    On a passive bass, the pickups, the pots, the cap on the tone control, the wiring, even your patchcord and amp input, are all tied together in a complex network. The darkening or thickening that you hear when you roll off the volume, is due to loading. It's mostly R, not L or C (resistance, not inductance or capacitance).

    If the OP wants to mimic that "volume on 9" sound, he could switch to a lower-value pot (ie; sub a 300K or 250K pot for a 500K), or put a moderate value resistor across the existing pot.

    Of course, he might also like the sound of a really small value cap (smaller than the normal tone control values) across the pot, either alone, or in parallel with a resistor.

    These kinds of mods give you all kinds of flexibility in terms changing the loading and the taper of the volume control. However, the differences can be pretty subtle, and your ear is easily fooled. By the time you unsolder one component and add another, you've already "forgotten" the previous tone. That's why techs like to use clip leads to a/b component combinations more effectively.
  8. georgestrings

    georgestrings Banned

    Nov 5, 2005
    It does - with a typical Jazz bass, rolling off the bridge pup a little will typically add more mids, and a tiny bit of volume, due to the interaction between both pups... If you really want a fat, punchy Jazz sound, try a series wiring setup... I have series/parallel switches in both my Jazz's, but they might just as well be straight series, because that's how I always run them...

    - georgestrings
  9. khutch

    khutch Praise Harp Supporting Member

    Aug 20, 2011
    suburban Chicago
    It might. The circuitry of a passive bass is very simple -- as long as you ignore all the complex bits. A magnetic pickup is an RLC circuit that reacts to all the loads placed on it. And the effect of the tone circuit depends on both the inductance and the resistance of the pickup but the effective resistance of the pickup varies depending on where the volume control is set. So you might be able to get the tone you seek with a different tone cap value. That is more likely to be be the case if you run with the tone pot near the bass setting than if you run it near the treble setting. Depending also on that you might be better off putting a load resistor across the bridge pickup or in series with the feed from its volume pot.

    Most likely some combination of the above could get you the tone you seek at full volume but considerable experimentation could be required.

  10. M.R. Ogle

    M.R. Ogle Supporting Member Commercial User

    Nov 5, 2004
    Mount Vernon, Illinois
    Backstage Guitar Lab owner
    Yep. I put that switch in, and it pretty much LIVES in series.
  11. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    It's the resistance of the pot doing it. When you roll down the volume a little, you have part of the pot presenting a series resistance to the pickup, which increases the impedance, and a parallel resistance to ground, which is increasing the load.

    These two things lower and flatten the resonant peak of the pickup, which gives a smoother tone, and then rolls off some high end.
  12. rimbaud

    rimbaud Banned

    Nov 17, 2011
    Totally agree: same experience on my jazz bass, I always roll off a bit the bridge pickup to "emulate" à 70's jazz bass, still far from that sound I must recognize, but fatter indeed, it suits me.