What effect does 1 meg pot have? Also, audio vs. linear

Discussion in 'Pickups & Electronics [BG]' started by Busker, Dec 7, 2008.


  1. Busker

    Busker

    Joined:
    Jan 22, 2007
    I assume that's double the value of a 500K ohm pot.

    Does it generally make your bass sound brighter? Are they in common usage?

    Also, what's the difference between audio and linear taper?
     
  2. line6man

    line6man

    Joined:
    Jun 20, 2008
    Location:
    Close to Los Angeles, CA
    I will try to explain this in laymans terms:

    When you turn your volume knob all the way up, there is no resistance from input to output, but there is a resistance from your signal to ground. So even with a pot all the way up, some of your signal will still bleed off to ground, and cause you to lose some of your brightness.
    The greater the resistance, the less of your signal bleeds thru to ground, so thats why a higher value pot has a brighter tone.

    When you combine resistors in parallel, their resistance decreases:
    1 500K pot is 500K
    2 500K pots is 250K
    3 500K pots is 166.67K
    and so on.

    The more pots you have in your circuit (this does not apply to active tone controls), the darker your tone.
    So 1M pots are generally used when you have alot of pots in your circuit.

    As far as audio vs. linear

    Audio taper pots are generally used for anything relating to audio, because they are perceived to have a smoother response.
    Linear taper pots are generally used whenever you need the middle of the pot to be at the halfway point in the resistor.
    (for example EQs and balance pots)

    Some people prefer differently, but generally, you would probably want to go for an audio taper for volume, and a linear taper for tone
     

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  3. Busker

    Busker

    Joined:
    Jan 22, 2007
  4. PawleeP

    PawleeP

    Joined:
    Oct 8, 2012
    I have read to never use linear taper for tone! Maybe some people prefer linear for tone, or was that a typo? PP
    P bass, J Bass
     
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  6. line6man

    line6man

    Joined:
    Jun 20, 2008
    Location:
    Close to Los Angeles, CA
    I have changed my opinion considerably on this in the past four years. Linear is preferable for volume and audio for tone.
     
  7. bassbenj

    bassbenj

    Joined:
    Aug 11, 2009
    This is true. And the reason has to do with the circuit that is used. Audio taper pots are designed for typical active volume controls where there is NO loading on the pot. In that case the audio taper is set to more or less follow ear response and keeps the volume control from having any regions were it shuts down too fast.

    In a bass the situation is difference for two reasons. One is that in a passive bass the volume control is loaded by the amp. Amp input impedance can run as high as 1 meg or as low as 50,000 ohms. Typical is about 500k. That can drastically change the apparent taper of the pot. Hence the practical observation of bassists that often a linear taper volume works better than audio taper. And same for tone which is not a volume control. People have just noticed that an audio taper seems to give you more useful range on a tone control, even though it seems to fly in the face of "conventional wisdom" used when building radios and amps.

    And the other reason is that bassists, usually don't use the entire range of a volume control as you might on a radio or amp. Typically, we tend to only use the loudest end of the control range. Hence, spreading out that portion even if the rest of the pot doesn't quite work evenly is a plus rather than a negative.

    Also note that in a passive bass the amp input impedance is in parallel with the volume control. Hence the load seen by the pickups won't change much if you up the volume control resistance too high.

    500k pot loaded by 500k amp = 250k seen by pickups.

    1 meg pot loaded by 500k amp = 333k seen by pickups.

    Not as big a change as you expected! Also note this will depend on your particular amp.
     
  8. walterw

    walterw Supportive Fender Gold Supporting Member

    Joined:
    Feb 20, 2009
    well, guitar volumes work the same way vis–à–vis loading by the amp, and audio tapers are usually indicated for them.

    the difference as i see it is all about the amount of compression and distortion in the amp;

    with guitars you usually have a good amount of compression even with "clean" sounds, and of course overdrive is naturally very compressed.

    in that case, the audio volume makes for a subtle change down in the quiet end where the signal is still clean (and small changes still make a big difference); when you crank it up, it starts making big changes in level at the louder "zone" where the signal is heavily compressed or distorted, which squashes out any changes.

    the result is an even transition from "off" to "clean" to "crunchy" as you turn up.

    bass rigs don't usually have that kind of squashing going on; as such, a linear volume behaves, well, linearly from "off" to "full".

    (oh, and nice zombie thread revival [​IMG])
     

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