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Installing a cap selector switch in a Precision Bass

Discussion in 'Pickups & Electronics [BG]' started by petrus61, Sep 27, 2013.

  1. petrus61

    petrus61 Supporting Member

    Anyone have or know of a diagram somewhere for this mod? I was thinking of installing either a push/pull or mini-toggle to select between two or three cap values...much like a vari-tone or tone styler pot. A mini-switch would be fine for now while a decided which cap values I'd ultimately settle on. I was thinking a .1, .047 and/or a .0047 in place of the .1, with the intention of being able to select a value and still retain the tone knob function. I might swing by radio shack to see what switches are available. Is there a push/pull or mini switch that would be optimal for this sort of thing?
  2. Grissle


    May 17, 2009
    Try this
    This is what I was given when doing the same thing, just different values. I haven't tried it yet but do have a two cap version running with .047 & .022.
  3. petrus61

    petrus61 Supporting Member

    Great thanks! The tone knob functions as it should still after the mod?
  4. petrus61

    petrus61 Supporting Member

    How would a two cap selector be wired?
  5. petrus61

    petrus61 Supporting Member

    Well, it was a success:
  6. petrus61

    petrus61 Supporting Member

    I picked up a mini toggle switch from radio shack (an old made for Tandy corp.!) to use as a testing switch until I ordered a push/pull pot. I used a paper in oil Sprague VitaminQ .1 and an orange drop .047. The results are as predicted! Basically the the .047 acts as a mid boost of sorts and will be my "always on" cap, while the .1 will be used when I need sub lows or clangy highs. I just made my own vari-tone

    I think I'll call it....mini-tone.

    I know there's a lot of debate on cap composition, but I'll just say I like spending the extra money on things that serve little purpose but to confound my tone whore guitarists. No, there is no difference when the tone is full on (despite what some claim) to my ears when switching between caps, but a very obvious mid hump when the tone is rolled off and the switch is set to the .047....duh.

    I'm planning on making a few mini-tone harnesses with varying cap values. Some of the "woody" descriptions I've read about using .0047 caps intrigue the heck out of me and I meant to grab one at radio shack when I was there, but I had to pee. The next step is figuring out whether I want to modify my pick guard and possibly body to incorporate the switch (it would look cool...kind of like the Ox's "slab" precision) or just install a push/pull.

    Who knows...maybe I'll take it a big step further and install a rotary or three way selector to incorporate more cap values. This was a cheap, fun and easy mod and I'm glad I did it.
  7. EmptyCup


    Feb 25, 2013
    Nashville Area
    Very cool, I've often thought of doing this myself.
    Thanks for the update and honest review.
  8. Saxn


    Oct 23, 2010
    Nashville, GA
    I did this with a five-position selector switch. With four capacitors and a bypass, I have options all the way from "mega-growly" to "DOOOOOOOOOM!"

    Have fun with the mod!
  9. Charley Umbria

    Charley Umbria I'm Really a Drummer Supporting Member

    Jan 28, 2011
    Rock City, TN
    When I bought my 1980's ESP 400 Series P/J, all of the electronics (from pickups to jack) were trashed. Since I was replacing the pups (Fralins with 5% overwound "split" J) and controls, I decided try using push-pull knobs on the J-pickup volume and the tone.

    Pulling up on the J volume knob completely removes the pickup from the circuit, leaving only the P-pickup, volume pot, and tone pot in-line. There's a very small difference in tone between removing the J-pup and just turning it down all the way, but it is there. In truth, however, you'd never notice it, unless the instrument was soloed and you A/B'ed the two sounds. I really just did the mod for fun, and to satisfy my own curiosity.

    To get back on-topic, though...the push-pull on the tone knob switches between .047uF and .1uF capacitors for modern and "vintage" P-Bass tones. Standard (down) position is the .047 cap, which I prefer most of the time. However, the bass is strung with GHS Pressurewounds, so using the .1uF cap really gives it a nice, dark "old school" sound.

    I used good-quality caps, but more for their manufacturing tolerances, than tone. At least this way, if I like the sound of the .047uF cap, I can be pretty sure it's actually a .047uF cap, and use one again in the future. The idea of keeping an older bass original-looking (even though it's not very original any more...), but still having a couple of extra tone options really appeals to me. I should mention, though, I used linear taper pots in the volume positions and an audio pot for the tone knob, so the controls on my bass may behave a little differently from those on other instruments.


  10. petrus61

    petrus61 Supporting Member

    That's pretty much exactly what I had in mind...late 50's bottom and 60's low-mids at the flip of a switch. I used the orange drop as a test bed and it will be replaced by either another VitaminQ or blue molded Ajax .047 I have. This was a trial run to see if I liked it. I've got another switch, better pots and some good tinned cloth wire I'm going to use for the final version. This mod probably won't be of any use to someone who plays with the tone knob cranked, but I use my tone knob very sparingly so I've almost always got a cap bleeding off treble. The differences between the two values are night and day and I'm going to experiment with some non-standard for bass caps as well. I'm interested in a .0047.

    I'm like you in that I selected my caps based more on tolerance than type. I might get nerdy and do a cap type comparison of matched values of same or very close tolerance, for example comparing a ceramic disc .1 to a paper in oil, etc, but I'm guessing my findings will be that they are the same as long as the tolerances match. When researching for this project, I stumbled on a post at the Eden forum where someone absolutely, 100% swore that two caps of the same exact reading but different make sounded vastly different. They were comparing a PIO to a metal film orange drop. I had to chuckle at the comparison, knowing that the function of a cap is to take away rather then add frequencies. There is a very obvious difference between two cap values because more or less treble is being shunted to ground depending on the value. This leads to perceived bump in the low mids in the case of the .047 with the .1 caps. But between two types? I know it has been debated to death, but it would be interesting to see the results. I'm predicting the results to be negligible and probably not worth taking the time to experiment with.
  11. Charley Umbria

    Charley Umbria I'm Really a Drummer Supporting Member

    Jan 28, 2011
    Rock City, TN
    Yup, I ended up using some brand of "magic" orange tone cap for the .047uF and a green Radio Shack cap for the .1uF. Actually, I think the specs were a little better on the green one! :D

    And, you're right; there really is a usable difference in tone between the two. Considering how iconic the "P-Bass with its tone rolled off" sound is, I'm not sure why more aren't built with this as an option...

    For anyone who wants to try, though, here's how I wired up the tone pot:


    (Not my image, BTW. I'm sorry I can't give proper credit, `cause its a good drawing!)
  12. petrus61

    petrus61 Supporting Member

  13. petrus61

    petrus61 Supporting Member

    So I wound up completing my 1.0 version incorporating the push back cloth, matched CTS pots and better switch with a VitaminQ .1 and Sprague orange turd .047 (the leads for my tone snob VQ and blue molded being too short) and I'm a happy camper. I have to admit, this was an exercise in gratuitous over analyzing and cork sniffing, but what the hell. She's a sound vessel and I've completed my "mini-tone" project.
  14. petrus61

    petrus61 Supporting Member

    tedsalt likes this.
  15. T-34


    Aug 11, 2005
    France, Paris region
    I've done the mods ranging from 2-capacitor mini-switch selector all the way to 11-caps rotary (from 470 pF to 0.2 mF :) They're all usable and useful!
  16. Grissle


    May 17, 2009
    I'm still trying to find a better diagram for an .047, .022 & .01 setup?
  17. petrus61

    petrus61 Supporting Member

    I'm digging mine. So fun and inexpensive too. I'd recommend it to any one with a passive bass that doesn't always necessarily feel the need to dime the tone knob. It's pretty much what made this mod so inviting to me...I've never been one to roll the tone pot wide open so this just gives me another option to work with. It's almost like having two Precision basses in one, really...at least with the values I chose.
  18. petrus61

    petrus61 Supporting Member

  19. Precision345


    Feb 19, 2013
    Great job OP! Very interesting to see this!
  20. T-34


    Aug 11, 2005
    France, Paris region

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