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substitution of pots for fender Jazz question

Discussion in 'Hardware, Setup & Repair [BG]' started by Mesa Man, Dec 3, 2002.

  1. I am thinking of replacing the 250K audio pots (in my fender jazz) with linear pots, will I be able to use 220Ks instead? They didnt have 250Ks at the shop. The tolerance for the 220Ks is 20%.

    Quick! Answer now! :)
  2. nivagues


    Jan 18, 2002
    Hope this is quick enough!

    From a value point of view 220K should be ok but why are you changing to linear taper???

    Cheers. AKA "Rod Trussbroken".
  3. The reason for my change is that as stated in another thread (thanks Merl) audio pots have almost all their action in the last 15 % or so. Changing them to linear will make them more precise and hence, the tone easier to dial in.

    Now, having read the thread that Merlin suggested (read it before and forgot about it actually) Maybe I'll go with 500K instead because: ...higher potentiometer resistance values produce a little more power and treble response. Whether this is a good or a bad thing is a matter of individual taste.... (FromHere )

    Perhaps a treble bleed circuit will be a good thing too, so that when I roll off a pickup some of the highs remain.
    [​IMG] (from www.guitarelectronics.com)
    Maybe I am foolish, but I can always try it all to see if it makes any difference in tone etc.. dont you think?
  4. pkr2


    Apr 28, 2000
    coastal N.C.
    Mesa Man: The change from log to linear taper is going to have the opposite effect that you are expecting.

    Always use a log taper for the volume control.

    If you want to change the tone characteristics, why not play around with the cap value. Much cheaper than changing the pot and has pretty much the same effect.

  5. nivagues


    Jan 18, 2002
    Hi MM,

    Maybe I'm getting a little confused!

    On the standard J Bass there are 3 controls consisting of 2 volume (large knobs) and 1 tone (small knob).

    I don't have a schematic diagram at hand at the moment but the 2 volumes should be audio taper (ie log taper) and the tone should be linear taper.

    You want to change the 2 volume (audio/log taper) controls and use linear taper...is that correct?

    The human ear is not linear but log. That is why a log taper potentiometer is used for a volume control. If a linear pot. is used then your ear wont perceive a smooth variation through the full rotation/travel of adjustment. The volume variation will be bunched up into a very small area of the rotation and would be hard to fine tune. (That doesn't mean to say that a linear taper can't be used...just that it would be awkward to adjust).

    That's why I asked your reason for wanting to substitute linear controls for the volumes.

    On the other hand, the human ear is not log. in relation to tone and a linear taper is used.

    But hey, you've got some ideas there and you might come across something that works.

    Good luck.


    Edit: pkr2 posted in the meantime while I was typing my post. Yep, play around with the capacitars.
    Cheers and plenty beers.
  6. Yes I am going to play around with the CAPS :D . But why change to the linears? Better control is the answer. Now it is basically.. nothing.. nothing..nothing.. everything.. when I turn the pot, since they are audio. So with linear, I will gain more control, since with logs it all happens in the end. ;)

    Well keep em coming!
  7. pkr2


    Apr 28, 2000
    coastal N.C.
    Sounds like your mind is pretty well made up. Go for it.

    Take your old pots out carefully. You'll be needing them.

  8. nivagues


    Jan 18, 2002

    Just an observation!

    If your potentiometer is giving you "nothing..nothing..nothing..everything" when you rotate it then, IMO, someone has previously fitted a linear taper pot. or you have a stuffed audio taper pot. If you have two puts behaving that way, they can only be linear taper (maybe one stuffed audio taper but highly unlikely to have two).

    What makes you say they are audio taper...any markings etc?

  9. Oh, they are audio alright! Says so on the back, and they behave like that too.. logarithmically (sp?)nothing..nothing..nothing ..nothing.. everything, the ketchup effect ;)


    Sorry if I sounded rude or anything, didnt mean to.. I really like to get input input from you guys. More thoughts on my plans?
  10. nivagues


    Jan 18, 2002

    When you said "nothing..nothing..nothing..everything" regarding your Vol pots,I was under the imprerssion you had perceived that with your ear....thus my response that your Vol pots had to be either linear tapers or faulty Log/Audio tapers.

    You have obviously measured the RESISTANCE of your Log/audio taper pots with a Multimeter connected to the outside and middle lugs...is that correct.

    A RESISTANCE reading of nothing nothing everything on a Log/Audio taper Vol pot is WHAT IT SHOULD BE!!! The human ear is not linear...it is log. Therefore, a Log/Audio tapered pot has its resistance specifically designed this way (ie. nothing nothing everything) so that the ear will perceive an evenly spaced volume response across the full adjustment/rotation of your Vol pot. The human ear is Log with respect to VOLUME.

    It appears that you mistakenly believe (with due respect) that, if you use a linear taper resistance pot, then you will get an even better control of your volume than you would with a Log/Audio taper. A linear resistance measured with a multimeter does look nice and evenly spaced over the pots adjustment range and it's natural to think that it must work better than a pot that has a nothing nothing everything resistance taper range (ie an audio/Log taper).

    As said before, the human is Log with respect to volume and not Linear. If you use a Linear pot the ear will not perceive a natural volume responce across the full adjustment range of the pot. In fact, you will now HEAR with a linear pot what you READ as resistance on the Log /Audio Pot. The audio will all be buchched up in a small section of the volume range and will be awkward to adjust.

    In a nut shell, if you use a Linear pot for the volume you are going from good to bad.

    On the other hand, the ear is LINEAR with respect to tone and a Linear taper pot is used. If a Log taper pot was used you would not get an even tone adjustment across the complete travel/rotation of the pot.

  11. Well I havent measured anything really, just listened (found the diagrams in another thread).

    The MIA Jazz bass comes with 3 audio pots installed, all 250K. At least that is what mr gearheds part list say (and the back of the pots). The reason of my perception nothing...everyhing is just what I hear when I turn the knob. Well there is not just nothing or everything, but as stated before, most noticeable difference in volume is in the last 15-20% of knob travel or so. This kmakes it a bit difficult to easily dial in the balance between the two pickups (in my opinion). My Sterling (ok, active but still) has got a much smoother volume curve with more action at the start and less at the end, maybe its linear? It could be since the last part of the rotation is not very exciting. But as you said, I think that the best alternative is to go with linear for the tone if any, and play around with the caps, can anyone tell me where to find a diagram of what the cutoff will be using different caps with that 250K pot? Now if I just can get my hands on some of those "no-load" click-pots then I'm on the way..
  12. Ehh... just pop in a J-Retro, you'll be much happier. :D
  13. nivagues


    Jan 18, 2002

    Yep, all the schematics I've looked at show ALL controlls as AUDIO taper for both Vol and TONE!!!

    Stuffed if I know why Fender does that...maybe they know something more than I do...then again they're the experts/designers! Maybe, because it's a production Bass, they're buying in bulk to try and keep costs down????

    I can't explain the prob you have with the Vol pots. I've never noticed it but, then again, my Vols are normally turned full-on (including Tone).

    Re your tone control...seeing that you're into experimenting, try staying with the standard capacitor but fit a Linear taper Pot...you'd have to get a smoother tone adjustment!!!!!!!.

    Keep me posted...I'd like to know the results.

    Cheers. All best for Xmas.

    PS. Tell us more about your Bass...where made...year...model etc. :cool:

    PPS. OK...the answer...have been pondering your Vol probs while consuming some of Australia's finest Beer...XXXX (read Four Ex)...the Vol Audio/Log taper on your Bass is running in series with the Vol control on you're power Amp which is also Audio/log...altering the overall curve which your ear is perceiving. (Please don't tell me your Bass has a pre-amp and you've been using head phones in the output socket). Sheeeeez!! you must have pretty good hearing. :p
  14. :confused: huh? The preamp or?? excuse my ignorance.. :)

    Righty Niva.. Well I dont have any real problem with my tone pot.. I just dont really like the way they act.. since everything happens in the end, as normal with logs. I usually have the bridge full on, the neck pick. , say, 85-90 % to get some nice growl, the tone is usually at something like 50%(of a turn). The bass in just a Jazz, MIA, fretless made '00. I am now more into trying to fiddle with the tone control.. tried out a couple of caps yesterday (the easy way) just by holding them in place and listen to the tone change. I found the 0,1uF + the 0,05uF (original) in parallel (make 0,15uF) to defeat very much of the higher content when fully off. Rather cool. :cool:

    No I havent been altering my amps volume, static. Maybe i am dumb, Maybe I shouldnt care.. Maybe I should make it master vol, bal and master tone.. By the way the "treble Bleed" thingy was no success.. yeah it bled the terble, but also altered the sound of the other pickup when the bleeding one was full off.

    Well experimenting is fun, and easy and cheap in this case. The problem seem to be to find a good, fitting linear pot to pop in there for the tone. Guess I just have to settle for the logs in the volume department. :)

    More input, mods etc..

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