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Capacitor Questions

Discussion in 'Pickups & Electronics [BG]' started by Aram, Feb 19, 2004.


  1. Aram

    Aram

    Feb 2, 2003
    New York, NY
    I have seen that people are wiring caps into their preamps to 'roll off the highs'. My setup (Basslines soapbars with an OBP-3 - 9 volt) when set flat is too bright, to the extent that I roll off the treble pot (set at 6.5khz) almost all the way. I am hoping that wiring a cap into the preamp will aleviate this problem.

    My questions are this:

    (1) Is there a correlation between the size of the cap and the frequencies which are rolled off? If there is, how do I determine which cap is right for my setup? Rolling off 10-15db at 6.5khz seems to give me the sound I'm looking for -- can I find a cap that will do that?

    (2) Does the quality of capacitor matter? I just bought .022 and .045 caps from Radio Shack (I just guessed on what I size I needed based on what I have seen other people post). Will these work? Will they burn out? Should I go for better ones?

    OK that was more like 5 questions...sorry. Please let me know if you have any input. :help:

    Thanks!
    Aram
     
  2. sounds like you should visit a luthier or tech to have this work done. while it is technically feasible, it's the type of work that requires knowledge and experience to do properly. it sounds like you're fishing for "the right way to do it", when you've already found a solutiong -- just turn down your treble control on your bass.

    if you want to mod your bass like this, go to a tech or luthier to get it done right.

    robb.
     
  3. Aram

    Aram

    Feb 2, 2003
    New York, NY
    Hey Robb -- thanks for the reply. I did consult Rudy's repair shop and they said that it can be done fairly easily myself.

    I'm not worried about the mechanics of how to install so much as how to choose the right capacitor. Does anyone know? I read the stewmac blurb on caps, but it seems to be contrary to what everyone else is saying.

    Anyone else have some input on choosing the right cap?

    Thanks!
     
  4. Carey

    Carey

    Jan 18, 2002
    Redlands, CA
    I depends on how much cut you want. An .047 will give you the most and a .022 the least, and these are standard tone caps. I like to use a .033 for the middle of the road approach.

    Is the bass you're adding the cap to very bright? If so I'd add the .047. Or, you can get all three and switch them out to see what you like the best...
     
  5. Aram

    Aram

    Feb 2, 2003
    New York, NY
    Thanks for the responses guys. Carey - the active p/u's are too bright when set flat -- rolling the treble off all the way helps a lot, but I'd prefer not to have to do that, so I'll definitely start with the .047. Is it possible to tell what frequencies are cut by that size? Or is it generally just done by ear?

    Smash -- that thread is what inspired me to try this in the first place :) My pickups are active though, so the results may be quite different.

    I will keep you all updated...thanks again for your help!
     
  6. Carey

    Carey

    Jan 18, 2002
    Redlands, CA
    Aram,
    I just go by ear. If you have a .047 on your passive tone now and you want the bass to sound like that while active I'd definitely start with the .047. Just be aware that higher values will eventually affect the taper of the volume pot. .047 shouldn't be too bad though.
     
  7. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    I've done this a few times and what I do is grab a few wires with alligator clips on each end, you can get a pack of varied caps at Radio Shack for a few bucks and experiment. I'm assuming you just want to tune your pickup and are not adding a knob for this. Then I would go with a smaller value as you just want to cut off the glass on top.

    You can do each pickup individually, put one alligator clip on the hot lead right off the pickup and the other wire on ground. If you can play and have a friend connect different caps between the two wires you can rather quickly find the range you want. If you find your range but find it's cutting too much add a resitor in series.
     
  8. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    There is a formula for frequency cut, but you need to know the output impedance of your system to use it.

    Keep in mind these simple R-C filters are not shelving, they cut about 40db an octave, that is -40db per an octave above the center frequency. If you want a softer drop off put a resister in series with the cap. And as has already been said, a larger value cap will give you a lower cut frequency.