Checking Impedance

Rick Collins · From: Claremont , CA USA

This is really embarrassing; but the only thing I know about electrons is that they whiz around in shell-like orbits about the nucleus.

I need to check the impedance of a pickup coil with a digital VOM:

Can this be done with the direct current from the VOM's batteries? I'm not getting a proper reading.

Many thanks, Rick

[This message was edited by Rick Collins on 11 February 2005 at 09:20 AM.]

Erv Niehaus · From: Litchfield, MN, USA

I've got a Radio Shack meter and I just put the two probes on the two pickup wires and take a reading. I don't know what kind of meter you have but I have to set mine for ohms.
Erv

[This message was edited by Erv Niehaus on 11 February 2005 at 11:34 AM.]

Dave Grafe · From: Hudson River Valley NY

Rick,

Impedance is similar to direct current resistance (what your VOM measures) but is an alternating current phenomena consisting of the DC resistance in combination with the counter-electromotive force induced within the coil as the magnetic field rises and falls across the windings. Impedance also changes with AC frequency, increasing as the frequency rises.

Your VOM can measure the DC resistance of a pickup or a speaker. The DC reading will be a bit lower than the AC impedance, but should give you a decent ballpark estimate.

Hope this helps -- dg

Mark Herrick · From: Bakersfield, CA

Set your meter to the resistance (Ohms) scale at 20K. There should be a little omega symbol (last letter of the Greek alphabet) identifying this scale.

If the pickup is still in the guitar, put an open (unwired) plug in the output jack. Touch the end of one probe to one tab of the plug and the other end to the other tab. You should get a reading of the pickup's resistance. If you don't get a reading the resistance is higher than 20K. Set the scale selector to the next highest setting (probably 200K).

If the pickup is out of the guitar touch the probes to the bare wires.

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Donny Hinson · From: Glen Burnie, Md. U.S.A.

Use, and refer to, the DC resistance. Right now, the only maker I can think of that doesn't is George L..

He's still using the "Henry" (impedance term).

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