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250K or 500K pots for active electronics?

Discussion in 'Pickups & Electronics [BG]' started by lanzealot, Aug 27, 2005.


  1. I have a bass guitar with a J-bass on the neck and MM style passive pick-ups on the bridge with active 2-band electronics.

    I need to replace the pots but don't know if I would choose the 250K or 500K (or 25K?).

    Also, I went to stewmac.com and there are so many options:

    Bass Cut/Boost Pot: 25K? 250K? 500K?
    Treble Cut/Boost Pot: 25K? 250K? 500K?
    Blend Pot: 250K? 500K?
    Push-Pull Pot (for active to passive mode): 25K? 250K? 500K?

    (note: did not see 25K for blend pot)


    Can you help me guys? thanks!
     
  2. DavePlaysBass

    DavePlaysBass

    Mar 31, 2004
    CO
    If you like the sound you have, replace them with whatever is in there.

    250Ks will be warmer.

    500Ks will brighter.

    Dave
     
  3. Assuming the pots are between the pups and the preamp I would use 250k log. I would only use 500k with humbuckers.
     
  4. but isn't the MusicMan pick-up on the bridge a humbucker?
     
  5. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Why would one be warmer? And would this be while the pickups are fully on?
     
  6. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Because the 250K pots will have a slight high end rolloff, 500K pots will have less so.
     
  7. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    When the pickups are fully on? Why, you simply restated they will, I'm interested in any reason why. Is it anything that can be measured?

    When a pot is fully closed (or open as we bassists would say) it should act as a real tiny piece of wire. The resistance is negligible, what is causing a change so big it can be heard?

    Thanks.
     
  8. DavePlaysBass

    DavePlaysBass

    Mar 31, 2004
    CO
    The less resistance you have in parallel with a pickup, the more high frequency roll off you get. It is somewhat subtle but it is there. If your bass has too much sizzle, you could put a resistor in the 50K to 500K range in parallel with the pickups to roll off some highes.

    When using volume, blend, and tone pots with passive pickups (also active when in front of the onboard preamp), you get a parallel combination of all the pot resistances. A volume, volume, tone with 250K pots looks like a 83K load.

    Dave
     
  9. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Dave, are you aware that the resistance that comes from a pot is it's value of when it's all the way off? A 250k pot has almost no resistance at full volume (a tiny bit nothing you can hear unless you can hear wire lengths) and 250k of resistance at volume off position.

    When you have any bass with the volumes and the tones at 10 the pots are not adding the full resistance of their values. However if you want to measure the accumulative effects of the wiring in a bass with the volumes and tone fully off knock yourself out, I find my basses to be rather unplayable at that setting ;)

    And you don't put a resistor in parallel with a pickup to reduce highs, you're thinking of a capacitor. The only thing a resistor would do is somewhat short the pickup. Where did you hear this stuff?

    So are people under the impression that at full volume the pickup somehow interacts with the value of the pot at it's maximum rating and not its minimum? That would explain this misconception.
     
  10. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    So a bass with one pickup wired directly to a jack with no parallel resistance you would have maximum high rolloff?
     
  11. DavePlaysBass

    DavePlaysBass

    Mar 31, 2004
    CO
    Yes.

    Then what your connecting it too becomes important. Input impedance and cable capacitance.

    I have heard of one person brag about the response of his G&L bass when he used a push pull pot to wire both pups directly to the jack.

    Dave
     
  12. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Did you read the question? You're saying that wiring a pickup straight to the jack gives you the most treble rolloff.

    Am I being punked?
     

  13. Is it? My bad. I am not really familiar with MM basses.

    On the other issues above:

    If you have no tone circuitry between the pup and the jack you have no roll off.

    I don't know the electronics, but what the guy said about 250K pots being warmer and 500k brighter is just true.
     
  14. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    I'm no EE, but there is a noticeable difference between 250 and 500K pots to my ears.
    Is it because there's still a (minimal) load with pot fully open? Unless you use a no-load pot of course, I haven't tried those.
     
  15. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Hey David, just to be clear we are talking about different pots in the full on position right?

    My DMM set to a range of 0 - 200k gives a resistance value of 0 for all the pots I have in the full on position. There is still a minimum resistance but this is in the range of what you can get from wire or that hideously bad connection between your cord and the jack.

    I'm still convinced this is just myth like so much guitar related "knowledge". If the phenomena can not be measured with lab equipment and can only be heard by people who are expecting a difference and no one can be specific of what's changing the tone I have to conclude for myself it's just an illusion of the way we perceive what we expect to hear. Also I can take a 500k pot hooked up to a multi-meter and give you a reading that the meter cannot distinguish from a 250k pot simply by turning the knob. For a pot in the on position to change tone it would need to be rolling of some signal somewhere. This conductance path would be measurable if it exists.

    Many people claim a 3db volume change is barely perceptible. Yet it is quite easy to measure such a drastic change with test equipment. This pot "tone change" is being claimed to be very noticeable. That this effect is not testable or that there isn't even a hypothesis of what's happening from an electrical standpoint leads me to believe it is all perception and not real.

    Does anyone really market a no load pot? That sounds a bit like audiophile power cords. I remember a fad in the '80's of hooking pups straight to the jack for a more "pure" tone but this came from guitar players in hair bands playing through 3 distortion boxes ;)
     
  16. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Thank you :)

    It's inconceivable to think that no tone control will give you more treble roll off than having one.

    No, I have to correct myself because this thread shows it is conceivable ;) but it is wrong.
     
  17. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    Maybe it's more noticeable in extreme combinations? I had an ash body jazz bass with 500K pots, the sound was a bit bright for my liking. I swapped the pots for 250K pots and there was noticeable to my ears rolloff of high end, I wouldn't say it was an extreme change but noticeable.

    Could it all be stuff I'm hearing because I want to hear it? Anything is possible, but I've changed enough pickups / preamps and observed tonal differences to believe my ears in this case.

    Fender market a no load pot, never tried it personally.
    http://www.guitarelectronics.com/product/CPNL1
     
  18. Hermit

    Hermit

    May 31, 2005
    LI, NY
    Because the opposite lug of the volume pot is connected to ground. When the pickups are on full, there is still a path to ground through the entire resistance of the pot. The greater this resistance, the less signal will be drained.

    Since higher frequencies travel to ground more easily, the result is a warmer signal.
     
  19. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Hey David, thanks for staying in reality. I believe you hear it. However I don't trust any ears including mine.

    Here's a fun test, play your bass in front of someone who's heard it before. Tell them you just did a little subtle mod to the preamp and ask if their ears are good enough to hear it. If they say they can't try leading them by saying do you hear the extra clarity or fullness or some glowing positive term. Watch how often they will, and how much more often the "audiophiles" will. This is just how our monkey brains work. We simply are more likely to perceive what we expect.

    Myself, being the brutal cynic, need someone to explain how before I accept it does. I know how a cap shorting to ground will cut highs but that is not in this circuit. When we talk about long cables cutting highs we can measure the instruments impedance and the cables properties and accurately predict the amount of high roll off. And then many people can't even hear that large measurable difference.

    Heck, you can get a subtle tone change by standing up or turning in a chair.

    Thanks for the Fender link, I suspect that's a bit like the silver solder and gold plated jack marketing. If it really did something I would expect to see a stat of the resistance of a normal pot compared to this one.

    Spock was my favorite Star Trek character :)
     
  20. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Ooh, that could make sense, I'll check it with my meter and report back later what I get. This is much better than it vibrates the pickups differently :)