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About them caps

Discussion in 'Pickups & Electronics [BG]' started by abemo, Jan 17, 2013.

  1. abemo


    Feb 27, 2012
    Arvada, co
    So I've been reading several threads recently about high-pass and low pass filters, tone caps, etc for the last few days, and it got me thinking about setting up a basic two band passive tone control circuit. I would try this on a frankenP first, and possibly later on a frankenJ, but I wanted to confirm that this would work properly to bleed off just the very high freqs on the low pass, and just the very low freqs on the high pass. Mainly I wanted to check that I have the right caps in the right places to achieve this (.1 for the high pass and .015 for the low pass), and whether or not I have to put an additional resistor in place to prevent backflow on the high pass. Sorry for the sloppy hand drawn diagram, sitting at work while I think. uploadfromtaptalk1358456681351.jpg
  2. abemo


    Feb 27, 2012
    Arvada, co
    Oh, and I should specify, the bass I would be adding this to currently has just the killswitch, so the wiring layout would be high pass-low pass-killswitch-output
  3. scottbass

    scottbass Bass lines like a big, funky giant

    Jul 13, 2004
    Southern MN
    This should tell you what you need to know:


    The original Fender tone pot in both J and P basses is 250K. You can play around and figure out what value pots and capacitors give you the rolloff at the desired frequencies. Make sure you buy audio taper pots.

    I won't ask why you want to roll off low frequencies on a bass guitar!
  4. Cadfael


    Jan 4, 2013
    Germany, EU
    Hi abemo,

    your schematic itself seems to be correct. A hi-cut / low-cut / Kill switch without volume.

    Americans seem to measure in µF? In Germany we measure in nF ...
    Your .015 cuts the hights. This is a very low value! Normal would be .022µF - .1µF (22-100nF).
    The .1µF for cutting the low frequencies is much to high - I think ...
    In my Johnson MM copy is a 1nF, so .001µF capacitor.

    I think you left the wrong contact free?
    In diagram 1.7.81 (page 204 in version 3.86) you see the original wiring of my Jophnson:

    In this wiring Hi and Low Cut are in another order. But your order is okay, too!
  5. abemo


    Feb 27, 2012
    Arvada, co
    Cool, thanks. The idea is to set caps with a big enough differential that I could roll off the high and low ends if necessary and keep the mids intact. I'd like to be able to roll off lows specifically to combat muddiness, give the kick more space sonically, and to be able to get closer to a J tone from my P if needed.
  6. abemo


    Feb 27, 2012
    Arvada, co
    Oh, and which tab am I leaving open? On the high pass I have input/output/grnd with the cap bypassing the pot, on the low pass I have input/grnd/cap to ground, which one am I leaving open? I tried to access the link but got hung up on the german.
  7. Cadfael


    Jan 4, 2013
    Germany, EU
    Here is a pdf how it should look like to my mind (without and with volume pot):

    One of the pot contacts should stay free!
    The low cut capacitor is on the other side.

    So, putting a pot to "10" always makes the sound brighter.
    (means that it works on the Low-Cut but doesn't work on the Hi-Cut).

    The caps have "no" influence when the Low-Cut is on 0 and the Hi Cut on 10 ...
  8. abemo


    Feb 27, 2012
    Arvada, co
    Ah, thanks, I see it now, basically I need to leave the third tab open instead of grounded on both the high and low pass filters.

    Thanks again.
  9. Cadfael


    Jan 4, 2013
    Germany, EU
    Ooooops - I mixed the texts for HI and LOW CUT in my pdf for you - but I think you understand anyway?!

    On the Hi Cut (Los pass), one end of the capacitor is soldered to ground, the other end to a contact of the pot. The middle contact is soldered to Hot. So, there is no more gounding needed.

    Maybe you click the link in my post again and scroll down to the end of the page. There you find the huge PDF (6MB) and there are about 10 methods to wire a low cut pot ...

    The Low Cut is a series capacitor (with restistor/pot).
    The Low Cut is normally in the "Hot line".
  10. abemo


    Feb 27, 2012
    Arvada, co
    Thanks so much, I saw the translated version in another thread, and I've been flipping through it since last night. Excellent stuff, and yes I understand it. I think I'll try it with a concentric pot, getting ready to go shopping.
  11. bassbenj


    Aug 11, 2009
    "right" just depends on what sounds best. So some experiments may be needed. This is what I call "Leo's last circuit" and that more or less is what is in G&L L2X00 and Asat basses. So to help you out, I'll try to describe his circuit which is slightly different from yours.

    First off you come from the pickup and it goes to the "bass" control which is the "high pass". It's just as you show EXCEPT that the third terminal on the bass pot floats and is NOT grounded. That pot is 1 meg in value and for your information is reverse taper but I wouldn't worry about that at this point. But let me say that when I wired "Leo's last circuit" into one of my SX basses I just bit the bullet and ordered the Bass pot from G&L. Worked out fine. The Bassi Cap that Leo used is .0022 uF. (the actual value you use may depend on the impedance of the your pickups so like I said you may have to try some things)

    The next thing is the Treble tone control. This is standard, which is to say a 250k pot to ground with a .047 uF cap to the signal line. The difference is that Leo attached the tone circuit to the INPUT side of the bass pot rather than the OUTPUT as you show it.

    And for some reason (I don't know why) There is a .001 uF cap ALSO from the input side of the bass cap and pot to ground. Just saying. I'm guessing it's to tone down some of the brightest highs so the treble (tone) circuit (which it's in parallel with) is always a bit rolled off.

    And while you don't show a volume control, That is located on the output side of the whole tone circuit. Personally I not only have this setup in my G&Ls but also in the SX I modded and I really like it a lot!
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