Pots are garbage!

Discussion in 'Hardware, Setup & Repair [BG]' started by Michael Jewels, Mar 30, 2001.

  1. Along with my Epi Jack Casady and 21 yr old Ibanez Musician, I have a year old MIM Fretless Jazz Bass. The Casady's volume and tone pots are beautiful and responsive. Ditto for the Ibanez, and it's older than a lot of members here!

    Soon, I plan to replace the pups in the MIM Jazz; I can't stand the hum! I've pretty much decided on Dimarzio Ultra Jazz for the replacements, but, in this month's Bass Player magazine they had an article about tweaking the neglected gear of three random players. This one guy has Yamaha BB 5
    string and wanted more out of it, and was thinking of dropping
    an active preamp in it. They advised him not to because it would need too much routing.

    Now I quote from the mag, " Instead, we switched out the 500k pots with 250s, giving him the ability to fine-tune his pickup blend a bit more."

    O.K. I know 500k pots have more resistance than 250k pots, but, what exactly will swithching to a lower resistance pot do?

    If used for the tone control on a Jazz Bass, will it make the transition from 0 to 10 smoother? This is another thing I can't stand about the MIM Jazz; the tone and volume pots don't work nearly as smoothly as my other two basses. What are the current (no pun intended) resistances of the volume/tone
    pots, and which ones would give me a smooth transition like my other basses?

    I posted this here because it's not really a pickup question, and it does pertain to different guitar manufacturers use of parts.

    Thanks for any feedback,
    Mike J.
  2. notduane


    Nov 24, 2000
    Hey M.J. :) . The rule of thumb (according to Stew-Mac)
    is that 500K's are for humbuckers and 250K's for single coils.
    If you were just replacin' the pots in your MIM Jazz, I'd say
    go with the 250's. But aren't the D/M Ultra-J's Humbuckers?
    Hell. They're so cheap at StewMac, I'd say get three of each
    at exper-ee-ment (stop laughin' metalarch69 :p ).

    Caps are pretty cheap too. You can get a whole wiring "Kit"
    for ~$15. But it's got the three 250K's (for single coil J-pups).

    The installation instructions at the DiMarzio site don't say
    whether you should use 250K or 500K. Huh :( .

    Whatever you decide, make double-dang sure you've got a
    good GROUND throughout...control plate, bridge, pot cases,
    output jack.

    (p.s. them bold, underlined words is click-able ;) )
  3. john turner

    john turner You don't want to do that. Trust me. Staff Member Administrator

    Mar 14, 2000
    atlanta ga
    not to change the subject, but i've heard really good things about the j-retro preamp that steve dude barr is selling at http://www.vintagebass.com for a replacement for a jazz bass. i've not played one myself, but like i said i've heard really good things about them. you might want to check them out - definitely make your life easier.
  4. Michael, this is exactly the forum to post questions like yours. We gotta whole lotta knowlegeable folks here and someone will get to the bottom of your question.
  5. the stock pot resistance values on a Fender Jazz should be 250k for both volume and tone.

    500k pots give slightly more brightness than 250k ones- that's why they're recommended for humbuckers.
    it's a subtle difference.
    I'm not sure how much smoother the transition is with 250k as opposed to 500k, but a factor that's more important is the taper of the pot ie. the way in which the resistance changes as you turn it.
    the standard pots are both logarithmic for volume and tone (i'm sure they are logarithmic for the volume).
    I'd suggest experimenting with a linear taper pot and comparing the difference.
  6. notduane


    Nov 24, 2000
    Excellent point Mr TMTR. I totally missed that one (duh).
    Here's a little essay from Stew-Mac's "Wiring 101" page :) .
  7. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Forget about trying linear pots, use logarithmic pots for audio signals.

    BTW: The 101 says experiment with the values of the pots, not the type (lin. vs. log.).
  8. yeah, in conventional hifi audio circles it's usual to go for log pots, but it ALWAYS seems in reviews of basses that they say "there's no tonal change until the last quarter turn of the pot" so surely it can't hurt to try a linear type?
  9. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    No, that's exactly typical of linear pots, not logarithmic pots. In those test basses were probably linear pots.
  10. pkr2


    Apr 28, 2000
    coastal N.C.
    There is no reason to ever use a log taper pot in the tone control circuit. The log taper is used to correct our non-linear perception of volume changes. A tone control is not dealing with volume changes, it's dealing with tonal change that I'm almost certain we hear on a linear scale.

    I've got a log pot in the tone control of my Washburn. (original part) 70% of the range of the pot is in the first 10% of shaft rotation.

    If I were designing a circuit with those characteristics I would have to use a log taper. On the other hand, if I wanted a smooth, linear change from min to max I would have to use...... yep, you guessed it. :)

    My personal belief is that the design is compromised in order to only have to stock one style of pot.

    Please note that anything I say is just my opinion. I am always open to correction.

  11. yay! it looks like I've opened a big can of worms again.
    the explanation of the logarithmic taper in several electronics books I've got is that the resistance remains fairly constant up to the last 90 degrees, where there's a substantial change- this works well for a volume control, as the human perception of loudness reads this as being an even increase.

    however, in the case of the tone pot, as pkr2 concurs, the validity of a logarithmic taper is debatable.
  12. Hey guys, thanks so much for the answers/ideas.
    This is why I love this forum.

    Notduane: Yes the DiMarzio Ultra Jazz pups are humbuckers. I haven't bought them yet, but I'm going to very soon. One of the reasons I haven't been playing my Jazz that much lately is that blasted humming. The other is the Casady; it has possesed my soul! Thanks for all the links; you're very thourough as usual.

    John Turner: Ya know, I completely forgot about that preamp. I read about it in Bass Player a few months ago and it sounded pretty good. The only thing is the price. Not that I can't afford it, but I was thinking of getting a Warmoth body because it's got standard routing for the pups. The MIM has two bridge width pups. (at least mine does)
    Also, I want to get a 5 string soon. The DiMarzios are about $125.00 for the pair. If I don't stop myself I'll wind up putting another $500.00 into a $350.00 bass.

    Mock Turtle, JMX and pkr2: The tone pot on my Casady is unbelievably smooth, so I'd guess it's a linear pot? The Casady is also passive. I'm learning a lot here.

    Thanks also Hambone, and Kurosawa, thanks for e-mailing me. I have a suspicion that my bass has little or no shielding. I haven't taken it apart yet.

    It's a shame I can't e-mail you guys a beer; but if you're ever in New York... let me know.

    Mike J.