Measure potentiometer taper and value in circuit?

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I swear I came across a useful post by @ICBM about this, but of course can't find it anymore...

So, is there a way to measure the value and taper (log vs lin) of a pot on a guitar via the output jack? If so what's the trick/formula?

Thanks in advance!

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  • ICBMICBM Frets: 40539
    Select one pickup only if it's a two-volume-control guitar. Connect the meter to the end of the cable.

    Turn the volume to zero - the resistance should read zero.

    Turn the pot up slowly and watch the resistance reading. It will reach a peak somewhere in the middle, then fall back to the DC resistance of the pickup when it's at 10. (Usually between 5K and 20K.)

    The resistance of the pot is four times the peak reading you got. (Allowing for the tolerance, eg a reading of 120K means a resistance of 480K, which is a 500K pot.)

    If the peak was at 5 on the knob, it's a linear pot. If the peak was at 7-8, it's a log pot.

    Strictly speaking you need to do a more complex calculation to take the DC resistance of the pickup out of the equation, but since this value is always much less than the pot tolerance, you don't need to bother.


    Also - some guitars are wired with the pots 'backwards' (sometimes called 'independent') - Rickenbackers, some far-east Gibson copies etc. If so, you need to know how the switching works to tell what the pot resistance is - it will either be the same as the reading when the controls are at zero, or double that depending on which side of the switch the pots are on.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

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  • Amazing - thank you as always @ICBM ;
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