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Tone Control Issues

Discussion in 'Pickups & Electronics [BG]' started by NJL, Nov 26, 2002.


  1. NJL

    NJL

    Apr 12, 2002
    San Antonio
    I have a Fender Jazz.

    I noticed the tone control, when you turn the control, either is bright or not bright. I have tried different capacitors and there doesn't seem to be an "in-between". I have also noticed that the control is 98% bright and 2% non-bright. I primarily use non-bright.

    Any advice? I am looking for a more adjustable tone control. Do you think it's a bad pot? It is a new bass.

    I have standard pups and run it through a sadowsky pre (floor model).
     
  2. notduane

    notduane

    Nov 24, 2000
    Location
    According to the parts list for an MIA (?) Jazz Bass at Mr. Gearhead,
    they use 3 250KΩ Audio taper pots. That's fine for the two volumes,
    but like you said about the tone control - not a lotta' variation.

    You could try replacin' your tone control with a 250KΩ Linear taper pot.
    I did that on my yammer rbx260f "frankenbass". It's wired like a P.
    I used a .05µf cap. Now I can dial in a buncha' different tones.

    Discount Guitar Parts (in Texas - quick shipping ;) ) has CTS 250KΩ linear taper pots.
     
  3. notduane

    notduane

    Nov 24, 2000
    Location
    E.E. fellers -- he'p! :eek::p

    I really can't explain it too well :(. Audio taper pots are made
    to act in a way similar to human hearing, i.e., logarithmically.
    That's why they're good for volume controls.

    With a 250KΩ audio taper pot, say "1" to "10', turning the control
    to "5" does not mean ½ the resistance. Whereas it does for a
    linear taper pot. This is why they're good for tone controls (IMO).

    A passive type tone control is usually just an R/C network.
    Using an audio taper pot for this means having the major change
    in resistance occur between say, "7" and "9". But using a linear
    taper pot, the change is...well, linear :). "5" means half the
    resistance, "2" means 2/10 or 1/5, etc. IOW, a small change
    in a tone control's position using a linear taper pot yields a more
    noticeable change in...tone (vs audio taper).

    :confused:
     
  4. I am a regular at a electronics forum found here!

    Here is a write up on the differences between Audio pots and Linear Pots. It is handy. ;)

    An audio taper pot & a log taper pot are one in the same.
    What it means is that the resistance will vary with shaft rotation in a logrithmic way.

    This is done to match the responce of the human ear. Which is also logrithmic.

    If you were to use a linear taper pot for the volume control on your radio you would find that the control would seem very sensitive near the low volume end, and have almost no effect near the high volume end.


    the whole article is found here

    With the capacitor in the circuit you are making a frequency dependant filter. It'll pass frequencies in a certain range. Because a potentiometer is a variable resistor, you vary the frequencies being passed.....

    Enjoy.

    :D:D

    Merls
     
  5. notduane

    notduane

    Nov 24, 2000
    Location
    Unky Merls! :D I knew you'd sniff this one out [​IMG]



    Let's muck it up some more with a pic :) (courtesy Stew Mac data sheet)...

    [​IMG]
     
  6. NJL

    NJL

    Apr 12, 2002
    San Antonio
    what is the diff in a 250k and a 500k pot?

    Thanks for your help!
     
  7. notduane

    notduane

    Nov 24, 2000
    Location
    250,000 ohms? [​IMG]


    Sorry :). Here's a note from the DiMarzio FAQ...
     
  8. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    It sounds like you have a 500K pot on your bass instead of a 250K.

    A potentiometer (or pot) works by varying the level of resistance in the circuit.

    In theory, a 250K pot fully open would offer 0K (zero K) resistance and 250K when fully closed.

    So, in order to get the most control, you use the lowest pot value that will still create the needed full resistance.

    If your circuit calls for a 250K and you are using a 500, (especially a linear pot) you may be creating full resistance on the circuit and sending all the brights to ground with only about a 1/4 turn of the knob.

    You should use 250K audios in all three positions.

    Chas
     
  9. NJL

    NJL

    Apr 12, 2002
    San Antonio
    ditto, ditto, ditto

    this is exactly what i am talking about:mad:
     
  10. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    What is the value of the pot and cap now in your bass? Are you talking about the bass with the SDs? Did it come with pots pre-wired?

    Active or passive SDs?


    Chas
     
  11. notduane

    notduane

    Nov 24, 2000
    Location
    maybe it's visions of tryptophan dancin' in my head, but you can color me confuzzled [​IMG]

    do y'all want the tone control on your J's to do little or nothin',
    OR have a wider, effective range?

    if it's the former, you could maybe replace the tone pot with
    a SPDT switch with two different (fixed)R-C networks.
     
  12. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    Yes. You just need to experiment with a few different caps until you find the tone you want and then hard wire it into the circuit and bypass the tone pot.

    An option that might be cool for you is use a DPDT ON-ON to create kind of an "all or nothing" switch. One flip goes from your 95 percent tone to wide open.

    You'd only have two sounds, but you wouldn't have any problems finding them :)


    Chas
     
  13. notduane

    notduane

    Nov 24, 2000
    Location
    orrr...from the peanut gallery :p

    pop the knob off of the tone pot

    plug in and play like ya' normally would and dial in the tone
    control to the exact setting you like

    (the weird part - don't shoot me :) ) once you've got the tone
    pot set to where you like it, light a small candle and drip some
    wax around the shaft to seal it :eek: the pot's goin' away anyways,
    right?

    now remove the control plate and clip the wires to the tone pot
    as close to the lugs as you can

    measure the pot with a DMM set to ohms. place the leads
    on the center terminal of the pot and the terminal that was
    connected to the cap. write this value down

    get a fixed resistor (preferably 1% tol.) as close to this value
    as possible. Radio Shack, etc.

    this fixed resistor and the cap will be in "series" to ground. You could
    place it across the terminals of the output jack or the bridge volume
    control (using the pot case as ground)

    looks sumpin' like this...

    [​IMG]

    what to do with the extra hole in the control plate?...happy face sticker? :D
     
  14. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA

    I like this plan. It would work. But since it isn't my bass, I think I would possibly consider labeling the above config. my "secret weapon" tone. Get me a 250K push-pull and a different value cap.

    You could wire the push-pull as a regular tone with a different value cap (different tone) then wire the DPDT switch on the push-pull to bypass the tone pot and go to the "secret weapon."

    I like it.

    Chas
     
  15. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    I butchered ND's schematic in Photoshop.

    It'd look something like this:

    [​IMG]
     
  16. So... with the two guys who asked the question.. are you with us so far? Or would u like a drinks break? :p

    :D:D

    Merls
     
  17. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    New year's model comes standard with air conditioning. :)
     
  18. FalsehoodBass

    FalsehoodBass

    Jul 22, 2001
    Denver, CO
    hey i was searching for something similiar to this thread. here's my problem.. scratchy tone pot in a passive jazz bass.

    All i want to do is to replace it... what type of pot do i use and what capacitance? It's a fretless if that makes a difference, and i'm going for a thumpy poor-mans-URB sound.

    Thanks
    Brian.
     
  19. notduane

    notduane

    Nov 24, 2000
    Location
    A 250K audio taper would probably be easier to find -
    Stew-Mac, GuitarElctronics.com . You could also try sprayin'
    the scratchy pot with some contact cleaner or compressed air -
    Radio Shack.

    Try a .100µf for the cap to get more "bass".

    This note from Stew-Mac:
     
  20. Hey notduane.... take your jesus mask off in your avatar i see.. :p

    :D:D

    Merls