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Convert log pots to linear pots

Discussion in 'Electronic Basics' started by [email protected], Dec 11, 2006.

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  1. Guest

    I am getting log pots (audio pots) very cheap. Is there a way to
    convert this to linear ones?

    I've seen a few designs on the net that convert linear to logarithmic
    by adding a resistance or two, but not any for the other way round. Is
    this doable by similarly connecting a resistance?

  2. Bob Myers

    Bob Myers Guest

    In short, no. If you want linear, buy linear.

    Bob M.
  3. Don Bruder

    Don Bruder Guest

    Not that I've ever heard of. Adding resistances to convert linear to log
    is pretty easy, but as far as I'm aware, converting log to linear would
    require physically reworking the resistance element of the pot. Dunno
    about you, but that's a task that's *WELL* beyond my skill... (Well, OK,
    maybe not "beyond" - I'm sure I could hack on a pot and alter its
    performance, but I wouldn't count on the results being anywhere near
    reproducible or predictable, which probably eliminates any usefulness...)
  4. BobG

    BobG Guest

    If you are gettin em for half price, hook 2 of em up back to back to
    cancel each other out.
  5. kell

    kell Guest

    It probably won't come out perfectly linear, but you could straighten
    it out some by attaching a resistor to the wiper and one of the legs.
    Start with a resistor about one fifth the pot resistance and
    experiment. Let us know what happens.
  6. How?

    On a linear pot, each degree of rotation of the shaft has an equal resistance
    change. On a log pot, that change of resistance per degree of shaft
    rotation varies.

    You can "syntheisze" a log pot with a resistor from the arm to one of
    the fixed ends (for discussion, we'll assume the ground end) of the pot
    because that resistor will be swamped out as the arm gets closer to ground
    (where the resistance from the arm to ground becomes less). Move
    the arm up towards the free end, and the resistor from the arm to ground
    will have more of an effect on the resistance of the pot.

    But if add a resistor to a log pot, as the poster is asking, you will
    get the same effect, only magnified. Not only will the pot be logarthmic,
    but the resistor will add to the effect.

  7. kell

    kell Guest

    Listen, I know he's not going to get a true linear pot but he can fake

    Set the log pot at its physical midpoint. Take resistance measurements
    from the wiper to the endpoints of the pot, call them R1 and R2. Get a
    resistor with a value approximately equal to the absolute value of
    R1R2/(R2-R1). Connect this resistor between the wiper and the end of
    the pot where you measured the higher resistance, you now have a pot
    with a resistance centered at its physical midpoint.

    Yes, probably crappy. But what's the harm? If the guy wants to take
    log pots and try to "convert" them, let him.
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