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Thread: 4 pin potentiometers, 4th pin what for?

  1. #1
    Join Date
    Feb 2014
    New Jersey

    4 pin potentiometers, 4th pin what for?

    Replaced a bunch of these (6x15mm, marshall jcm2000 for instance), 3 of the pins do what I'd expect, the 4th outer pin gives no reading one way or another, anyone know what this 4th pin is there for?

  2. #2
    Old Timer Leo_Gnardo's Avatar
    Join Date
    Sep 2012
    I've wondered that myself. Far as I can tell the 4th pin is a sort of "vestigial organ". Lucky for us it can't cause trouble. Possibly the manufacturer has made provision for a tapped pot should anyone order such a thing.
    J M Fahey likes this.

  3. #3
    g1 is offline
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Canada, somewhere north of Fargo
    I bet if you look at the datasheet for that particular series of pots, there will some optional function (like the tap Leo mentioned) for the fourth leg. In this case it is not used, but it will be in other types from that series.
    Certified Dotard

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