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pick up value question

Discussion in 'Pickups & Electronics [BG]' started by quarternote, Nov 9, 2012.

  1. quarternote


    Jan 31, 2009
    I know very little about electronics or I would not be asking this question: Can I measure the resistance of a pickup wired in place, or do I need to disconnect it. I have one pickup that has a very low signal output and would like to know why. Thanks
  2. iiipopes


    May 4, 2009
    Low signal can be from a variety of things. An imperfect coil is one of them. Yes, if you know what the nominal dc resistance of the coils should be, you can measure it from the jack with a short patch cord, knowing that with the loading of the volume and tone circuit with the controls turned all the way up that the dc resistance reading on a meter will be marginally less.

    The best way to measure the dc resistance of the coils is to undo the hot lead from the tone or switch circuits, wherever it is attached, and measure from the disconnected hot lead to ground.

    If it is a steady reading give or take about 20 percent of the nominal value, then the coil is good. If it is much higher or lower than that, or won't "settle down" to a reading, then it is possible a coil is bad, but it's also possible the coil winding is not soldered properly to the pickup lead, or that there is something else going on.
  3. If you know the value of the pots, you can just measure at the jack of a passive bass and use the following formula to get the pickup's DCR: R[SUB]1[/SUB]=1/([1/R[SUB]Total[/SUB]]-[1/R[SUB]2[/SUB]]), where R[SUB]1[/SUB] is the resistance of the pickup, R[SUB]2[/SUB] is the resistance of the pot(s), and R[SUB]Total[/SUB] is the resistance at the jack. If there are multiple volume pots or a blend pot in the circuit, be sure the pickup selection is set to solo the pickup in question, and then account for the total resistance of the pots as: R[SUB]Total[/SUB]=1/([1/R[SUB]1[/SUB]]+[1/R[SUB]2[/SUB]]+...[1/R[SUB]n[/SUB]]), where R[SUB]1[/SUB] is the first pot, R[SUB]2[/SUB] is the second, and so on. Be sure to account for variations in pot tolerances as you average out a resistance, however. Tolerances are often 20% for pots. Or, simply desolder the pickup and measure it.

    Note that DCR probably won't tell you anything. It is very unlikely for pickups to develop internal shorts, and once wound, the number of winds doesn't change. DCR will change if there are differences in the temperature of the coil, but it will not be significant to change the output impedance. DCR bears no inherent relation to output anyway.