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Different tone control schem

Discussion in 'Pickups & Electronics [BG]' started by higgi, Sep 28, 2009.


  1. I was replacing a pot in my Cort bass when noticed it had a different tone control than I have seen before. Most tone controls have have a blank pot tab, but the blank one on this was wired to ground. I think when the pot is set for full tone the cap has no effect on the circuit.

    Most have upper freqs going to ground through the full value of the pot, and the low freq will be blocked by the cap. So a conventional tone control set for max treble will have 500k between the low freq and ground and 250k between the treble and ground. With the last leg of the tone pot going to ground on my setup then the cap is shorted to ground and both bass and treble have 250k between the signal and ground. So my set up would have a more flat sound at max tone with less volume. The conventional set up would have a slight treble roll off and more volume at max tone.

    Anyone seen this set up before? I searched but never found a circuit like my cort bass. I think I will wire it like most basses.
     
  2. I have absolutely no idea what you are talking about with the high and low frequencies?

    A conventional tone control uses a potentiometer to vary the amount of signal to feed into the capacitor.
    The capacitor cuts the high end, it does not affect the low end.

    This is the traditional wiring of a tone control:
    3397526992_1b3424c2e3.
     
  3. Thanks for trying to understand. So yes the cap allows high freq to go to ground, and the low freq are prevented to from going to ground. Of course all freqs go to ground through the volume pot.

    Your diagram show a conventional or standard tone control, if you connected the blank terminal to ground that would be how mine is set up.

    So with my current wiring, when the pot is set for max treble, the wiper on the pot makes a zero ohm connection across the cap. All frequencies go to ground through the 500k tone pot, not just the treble. This type of tone control should have no roll off of high freqs when in the full treble position. The circuit you provided would have a treble roll off in the full treble position.
     
  4. I'm still not fully understanding you.
    So you are saying that with the tone knob all the way up, the entire signal gets grounded, leaving you with no output, correct?

    I'm guessing that what you were trying to do then was have the capacitor short out to ground when the tone was all the way up, so that it will not have any affect on the signal, correct?
    In that scenario, you would still be placing a 500K resistance from the signal to ground which would reduce the treble in an equivalent way to adding another volume pot to the circuit.

    If you are trying to remove the capacitor from the circuit so that the tone control does not affect the signal, I would suggest using a bypass switch to do so.
     
  5. Sorry I couldn't respond faster, and thanks for your time.

    My tone pot is wired just like your drawing except the third tab is grounded.

    At max treble the cap is shorted and there is 500k between full signal and ground, when you add the volume pot in parallel you have 250k between full signal and ground. Pretend it is a P bass to keep the circuit simple.

    On your drawing at max treble the cap is still blocking the path to ground for the bass portion of the signal. The treble portion of the full signal can pass through the cap and the 500K tone pot with the volume pot in parallel that makes 250k between treble and ground. Since the bass portion of the full signal is blocked by the cap it can't pass through the 500k tone pot, and therefore it's resistance to ground is 500k through the volume pot.

    Your circuit has reduced treble volume and unreduced bass volume. The circuit in my bass has reduced treble and bass for a flat signal at a reduced volume. When you roll the treble off in my circuit you hear it as a boost in bass and a reduction in treble, on your circuit you would hear only the reduction in treble. Of course that's not including the bass boost both of our circuits will receive as a result of the interaction of the cap and the pup if the treble is rolled off.

    I think I prefer your circuit, but I was wondering if any manufacturer used my circuit, or if my circuit was a creation of the last owner.
     
  6. Bootzilla

    Bootzilla

    May 4, 2009
    Could it be that the original owner just wired it the wrong way? All he does is put the bass at half volume and make the tone knob more sensitive (if you roll of treble it will always be perceived as a boost in bass).
     
  7. The Dimarzio pups in this bass overdrive everything, so the reduction in volume is a good thing. I just have a more sensitive tone control with this circuit.

    I never leave the tone on max treble anyway, so I will wire this bass like the drawing above. I may change to all 250K pots to bring the level down.
     
  8. seamonkey

    seamonkey

    Aug 6, 2004
    It's pretty common to ground that open tab like you're saying, so on full CCW the cap is out of the circuit, leaving just the pot in the circuit.

    When I get a chance, I cut the tone control out and re-purpose it. Usually another volume, or master volume.
     
  9. Thanks for your time guys. My question has been answered. Talkbass is so handy!
     
  10. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Los Angeles, CA
    I always do the "no load" mod- where you scrape off the last little portion of the conductive material on the inside ring of the pot, taking the pot and the capacitor out of the circuit when it's all the way up. I also sometimes like to put a small resistor between the capacitor and ground so you don't get that big midrange resonant sound when you turn the tone all the way down- though that's sometimes a useful sound with a smaller value capacitor...
     
  11. Is it possible that someone was trying to make it roll off the lows? If you had that cap going out to the volume pot, as you rolled it down, everything would be sent to ground except those frequencies that could get out to the hot side via the capacitor. That'd basically be like a variable version of the "strangle" switch from a Jaguar or BassVI. Maybe that was the intent of the wiring and it got changed at some point?
     
  12. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Los Angeles, CA
    Similar to the passive bass cut on the G&L L2000/L2500, but the grounding aspect isn't necessary- the G&L just has the capacitor between the middle and right lugs- one side coming from the input, the other going to the output...

    Karl
     
  13. I think bootzilla nailed the over all effect of this circuit, less volume more sensitive tone control.
     
  14. Can you tell me more about that?
     
  15. sunbeast

    sunbeast Supporting Member

    Jul 19, 2006
    Los Angeles, CA
    A couple years ago, I was rewiring an old G&L L2500 to have the same wiring scheme as a G&L L1000 (an old discontinued bass that had a slightly different electronics setup).
    The schematic for the L1000:
    http://www.glguitars.com/schematics/L-1000_schematic_blockdiagram.pdf

    Given the way the tone control worked on my old L1000, I decided to mimic on a couple of my other basses. They added a 6.8K resistor between the capacitor and ground- it just eliminates the part of the tone knob where there is a direct connection between the hot signal to the capacitor and ground, giving the sweep of the tone knob a smoother transition (although eliminating the big "mud" at the end of the sweep). On a brighter bass though, I sometimes like that "mud" tone, so I won't do this mod.

    Karl
     

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