passive hi-cut on pickup?

Discussion in 'Pickups & Electronics [BG]' started by isher1992, Jul 20, 2013.

  1. I'm looking at changing one of my active EQ basses to passive, because most of the time when I play, I leave it flat and I just change the pickup switch. I was looking at installing a varitone kind of circuit (bandpass filter), but something that is stumping me is the hi-cut filter on the pickup.

    It's an Ibanez ATK300/3EX1, and I've been using the ATK 100 wiring diagram as a reference point for the switch. This one, to be exact:


    I see the capacitor there as a hi-cut filter, but when I look at the switch in my own ATK, it looks as if there is a resistor wired in what I believe to be parallel. If that's so, can I wire a potentiometer like a voltage divider, with a wire on the first lug, and a capacitor wired to the second lug, and have both of them meet on the switch, like a hi-cut filter that's adjustable? Or would I wire it like a conventional tone pot, where the common goes to the 2nd lug and then the capacitor is wired to the 3rd lug and soldered to the back of the pot and grounded?
  2. What you are describing is a conventional tone control.
  3. Thanks, so in order to wire it on the switch, I would wire the common to lug 2, and then run a wire from lug 2 to the part of the switch, and put a capacitor on lug 3 to the back of the pot, correct?
  4. Signal to the center terminal of the pot, third terminal to the common. Then wire capacitors from ground to the switch terminals, the way you want to do it.
  5. I'm not sure I understand completely. Both the White and Blue/Green wires are positive leads for two different coils, and this isn't a typical series/parallel switch. All the grounds come from the black wire, so this is a little confusing.

    Would it be easier and simpler to wire a potentiometer as a variable resistor with a capacitor in parallel across the two terminals and accomplish the same goal?
  6. I'm not sure what you're talking about now. The capacitor on the series/parallel switch is a high-pass filter, which is the opposite of a low-pass filter/high-cut.
  7. Cadfael


    Jan 4, 2013
    Germany, EU
    Hi isher1992,

    the ATK100 wiring can also be found in my wiring compilation ...
    I have an additional schematic (like for every of the 300+ wirings) ...
    The you can see how the 1nF 102 works ...

    In series mode the cap is "parallel to the green-white connection" and therefore out of work ...
    In the parallel mode, one end of the cap is connected with hot (via green), the other is connected to gnd (via white). Therefore, it works like a cap in a normal tone pot - a hi-cut ...

    In my wiring diagram 1.7.711 you find a Johnson MM copy which has a hi-cut pot and a low-cut pot.

    My wiring compilation (469 pages, 7.31 MB, in German) can be found here:
  8. Oh wow, thanks. I'm gonna have to hold onto this .pdf, very helpful. Now if only I could read German! :D But your pictures are very detailed and helpful, thank you.

    So I'm guessing I should wire from the Blue (South coil positive) to the 2nd lug (I want the sweep to add bass, not cut it, so a tone control in reverse) and wire the dummy coil positive to the 1st lug, with a capacitor bridged bridged across the two lugs, similar to that Johnson control.
  9. wait, no, that cuts lows. Whoops.
  10. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    you're overthinking it; like line6man said, it's a plain ol' tone knob. wire it just like the diagram above, jumper from clockwise volume pot lug (with the pickup) to counterclockwise lug of tone pot. cap from middle lug of tone pot to ground. that's it.

    also, 104 is really big for a passive cap (.1μF); try a more normal size, .047μF ("473").
  11. I'm not talking about the tone knob, I'm talking about the .001 uF capacitor across the positive leads from the South coil and dummy coil. I know how to wire a conventional tone knob from a volume knob, I just wasn't sure how to wire a pot to adjust the hi-cut filter across the pickup leads.
  12. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    ah; yeah, that's a lot trickier.
  13. The only way to get a high-cut is to use a regular tone control. Unless you want to do it with an inductor in series with the signal path, but that changes the LCR in the circuit, and is generally impractical.

    If you want an adjustable low-cut, you put a capacitor in series with the signal, and then put a pot parallel to the capacitor.
  14. From the way Cadfael described it, it seems like I could wire the South coil positive to the middle lug, and run the capacitor on the 1st or 3rd lug to the dummy coil lead on the switch, and it would accomplish a high cut.

    Or, according to some of his other high cut filter schematics, I could wire both the dummy coil and the South coil leads to the middle lug and then wire the capacitor to the 1st or 3rd lug to the ground and it would accomplish a high-cut filter.

    I suppose I will just try and see.