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22K Log conductive plastic pot

Discussion in 'Electronic Design' started by Ian Bell, Mar 11, 2010.

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  1. Ian Bell

    Ian Bell Guest

    I am looking for a UK source of a 22K or 25K log panel mounting
    conductive plastic or cermet pot. I have checked Farnell, RS, Rapid and
    Maplin to no avail.


  2. Phil Allison

    Phil Allison Guest

    "Ian Bell" <

    ** Use one of these 50K dual linear pots:

    Connect the two sections in tandem - ie, the wiper of the first goes to the
    top of the second.

    The law is then close to log.

    10% = -40dB

    25% = -24dB

    50% = -12dB

    70% = -3dB.

    ...... Phil
  3. Ian Bell

    Ian Bell Guest

    Thanks for that Phil, it is something I had considered and it has the
    advantage that the law is much more repeatable. Unfortunately I should
    have been more specific about the application and in this case I need
    the log(ish) law but it is not to be used as a potentiometer but as a
    variable resistance (in an equaliser). As far as I can see, cascaded
    linear pots do not give that - for example the total resistance from the
    second wiper to ground at the 50% point is 10K. Is there some other way
    of connecting a pair of linear pots to give an approximate log law
    resistance between two terminals??

    Ah, I just realised if I connect the second wiper to its upper terminal
    I get 6.25K at the mid point - that might just do it.


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