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difference between 250 and 500k pots?

Discussion in 'Hardware, Setup & Repair [BG]' started by RETSAMPALS, Feb 2, 2001.


  1. RETSAMPALS

    RETSAMPALS

    Sep 10, 2000
    hey i'd like to know what the difference is between 250 and 500k pots...i've never had my pots changed so i'm not sure....could you give me some help?
     
  2. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    O.K., Ret. This is probably more than you really wanted to know about pots, but here goes. :)

    The 250k means the resistance of the resistor is 250,000 ohms. Likewise with the 500k pot. Another very important spec is the taper of the pot. You have the choice of linear or audio taper. The audio taper corrects for the way that we hear sound. If you can grasp the fact that doubling the power of an amp only raises the perceived volume by 3db (the least amount of change that the ear normally can detect as a change in volume) it becomes clearer.

    An audio taper would be called for in a volume control while a linear taper would be more usable as a tone control.
    If you come across a bass that doesn't increase smoothly as you raise the volume it probably has the wrong taper pot in it. In other words, around 75% of the volume is achieved in the first or last 25% of knob rotation. This is a very common problem on a lot of Samick basses.

    The pots in a bass should be replaced with the ohmic value of the original. Almost all passive pup setups use 500k pots. A lot of active pup setups use 250k pots. I have known of people changing from 500k to 250k and vice versa in an attempt to change the tone of an instrument. How succesful this may or may not be I don't know.

    As always, I stand to be corrected.

    Hope this is understandable. :)

    Pkr2
     
  3. rickbass

    rickbass Supporting Member

    pkr2- I would have answered, "exactly 250k," so your post was really great to read. I'm having a custom bass spec'd out to several luthiers and I need to know this stuff!!! Thanks!
     
  4. Not a correction but an observation of a different situation. I just installed a new set of Seymour Duncan Basslines in the CAD/CAM Jazz and their instruction sheet included with the pickups specifically said use 250k ohm pots for both the volumes and tone control.

    I certainly don't know why or much more about the whole subject, just that I did what I was told.
     
  5. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Good point, Hambone. There are probably more exceptions. That's why I said "almost" always use 500k. There is usually a way to determine the right value, either by measurement, factory specs(your case) or simply reading the value from the old pot. It's usually marked with the value but very seldom with the taper.

    If you need to figure out whether you are dealing with a log taper(another name for an audio taper) turn the shaft half way thru its rotation and, with an ohm meter, measure from the center terminal to each outside terminal. If the two values are very close to the same, it will be a linear taper. If there is a considerable difference(several thousand ohms), it is an audio taper.

    T.M.I.? :)

    Pkr2
     
  6. Passive Fenders always used 250k.
     
  7. RETSAMPALS

    RETSAMPALS

    Sep 10, 2000
    ummm...does anybody know the tone difference?
     
  8. I think with the higher pot resistance of 500k you lose less highs from the pickups to ground- it's a subtle difference, and probably not noticeable at all with active pickups or active tone controls/an active preamp.

    it's similar to the difference between having the pickup at full volume using a volume pot, and having a pickup wired straight to the output (control bypass).

    the general rule for guitars seems to be 250k for single coil pickups eg. Strat , and 500k for humbuckers eg. Les Paul (the idea being to compensate for the brightness of s/c p/ups and the thick low end of h/b's).
    the same seems to be applied to basses also -the Gibson Thunderbird (2 humbucking pickups) has 500k pots.



    [Edited by The Mock Turtle Regulator on 02-03-2001 at 11:41 AM]
     
  9. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    That's interesting, MTR. I knew there was a reason for the different values but I hadn't made the connection. Tnx

    Pkr2

     
  10. Monkey

    Monkey Supporting Member

    Mar 8, 2000
    Dayton, Ohio, USA
    I've always read that 250k is better for single coil, and 500k for humbuckers, too. I put 250s in my passive bass with humbuckers, because I thought it might make the sound warmer. I play fretless and don't use a lot of highs. I do work for my guitar player who plays a Tele. That guitar has outrageous treble, and I noticed that it had 1MEG pots, so it seems that the higher the number, the more treble.
     
  11. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Did you notice much difference after the 500 to 250 mod? I've thought about playing around with the cap value in the tone circuit but it never occurred to me to tweek the pot values. Hmmmm.

    Tnx for the info, Monkey.

    Pkr2