The 'Tight' control - simple passive bass cut

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Thread: The 'Tight' control - simple passive bass cut

  1. #1


    Join Date: Sep 2008
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    The 'Tight' control - simple passive bass cut

    *This is a huge edit of the original post*

    The typical guitar tone control doesn't get used a lot. A lot of players disconnect it in search of that extra touch of clarity. However, it is very simple to rewire the existing pot to give you something that most metal guitarists will benefit from - an extra touch of tightness

    There are a couple of approaches to this one, one is slightly easier than the other, but the effect is less pronounced. BTW this is for passive pickups only at this stage.

    First up we'll look look at a fairly typical humbucker pickup frequency response with a 500k volume pot at maximum. You'll see it's a flat response until the resonant peak, then it drops off.



    Next is the same theoretical pickup with a 1 Meg volume pot. You'll notice the peak is taller, which is why a 1 Meg pot sounds brighter and clearer than a 500k pot.



    Next up is the effect of using a 500k pot and cap as a bass cut, combined with a 500k volume pot. This is the easy mod. All you need is a different value of capacitor, and maybe some extra hookup wire. And a soldering iron, solder, and the appropriate skills.
    The capacitor value that worked best for me was 0.0033uF (marked 332 on the cap itself). Smaller values will move the cutoff frequency up. The 0.0033uF works to kill the very low bass frequencies and make the low strings sound a little clearer. This is most noticable on the 8 string low F# and B strings. You might want to try 0.0022uF (222) and 0.001uF (102) as well, it depends what works best for you, but the cutoff point gets higher and starts effecting the mids. For reference, most humbucker equipped guitars use a 0.022uF (223) cap on their standard treble cut tone pots. This is the response with the 0.0033uF cap...



    Changing the bass pot from 500k to 1 Meg gives slightly more cut....



    So, how's it wired? I'll assume the guitar in question has a master volume control that runs straight to the output socket. The cap goes between lugs 1 and 3 on the pot. The wire that normally runs from the volume control to the socket now runs from the volume pot to lug 2 ('in') of the 'tight' pot. Another wire runs from the 'out' lug, as specified in the drawing, to the socket tip. You can wire it to cut bass when turned clockwise or anticlockwise, depending on your preference. Remember to bridge lug 2 to the outside lug that is not the output. And ensure the body of the pot is earthed. Here's a wiring diagram...



    OK, that's easy enough, but what if you want more bass cut? It can be done, but to retain the typical 500k volume resonant peak characteristics we actually need to change to a 1 Meg volume and add a 1 Meg resistor to the 1 Meg bass cut control. The choice of caps changes slightly too. The point of this is to cut more bass without screwing with the mids too much.

    This is the response using the 0.0033uF cap, could be interesting on a pickup/guitar combo with excessive bass and low mids...



    Changing to a 0.0047uF (472) value gives us what I'm currently running in my own guitars...



    And a 0.0068uF cap takes us to a similar response to the first circuit...



    Here's the modifed wiring diagram...



    And here are the diagrams to wire it in permanently, or switched with a SPDT toggle...



    Adding a standard tone control

    It's possible to add a standard tone control in the usual spot, again using a 1 Meg pot instead of 500k. Swapping the 1 Meg resistor to ground for a 4.7 Meg should give the same resonant peak characteristic as the graphs above.

    As always, the only way to know if this kind of mod works for you is to try it
    Last edited by dpm; 10-13-2008 at 02:28 PM.

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  3. #2


    Join Date: Sep 2008
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    That's awesome! Now I wonder if there's a way to do a passive midrange control also?

  4. #3


    Join Date: Sep 2008
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    ooh very cool dpm!!

  5. #4


    Join Date: Sep 2008
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    That's a great idea Dan.

  6. #5


    Join Date: Sep 2008
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    BTW, where does the bass "tight" knob start rolling off bass frequencies at? What frequency do most standard treble tone knobs start cutting treble at?

  7. #6


    Join Date: Oct 2008
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    Very cool idea

  8. #7


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    I'd love to try this but I'm at a loss as to how anyone is able to live without a tone control.

  9. #8


    Join Date: Sep 2008
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    Quote Originally Posted by drache713 View Post
    That's awesome! Now I wonder if there's a way to do a passive midrange control also?
    Yes, there is, but if it's an apparent boost you're after it has to be done as a treble and bass cut, which might give the effect of less gain. Then again, mids are what drive the amp input hardest, so the drop in gain might not be too drastic.

    Quote Originally Posted by drache713 View Post
    BTW, where does the bass "tight" knob start rolling off bass frequencies at? What frequency do most standard treble tone knobs start cutting treble at?
    The bass cutoff frequency depends on the input impedance of the amp, I believe. I have to check calculations about 60 times before posting them so I'll look into that over the next day or so. For now let's say the 0.0033 is very subtle, it deals with 'thud' and 'woofy' bass. I'm not sure how much the pickup impedance effects this one. Same goes for treble cutoff. I can never remember the theoretical stuff

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