UIUC Physics 498POM
Physics of Music/Musical Instruments
Guitar Pickup Measurements
We have developed a PC-based DAQ system that enables us to measure the complex impedance of electric guitar and bass
pickups. A PC talks to a Wavetek-81 function generator via GPIB (General Purpose Instrumentation Bus) controlling
its frequency (10 Hz to 20 KHz) and amplitude (nominally 1.0 volt).
The sine-wave signal from the function generator (a near-ideal voltage source) is
converted to a near-ideal constant current source, simply by sending the signal through a 1.5 meg-ohm resistor.
The sinusoidal signal after the resistor is connected to the guitar pickup. We independently record the
in-phase ("real") and out-of-phase ("imaginary") components of the voltage and current using two lock-in
amplifiers, both of which are referenced to the sinusoidal signal from the function generator.
ADC's (Analog-to-Digital Converters) on a National Instruments LabPC+ DAQ card are used to digitize the
signals output from the lock-in amplifiers. These are Re(V), Im(V), Re(I), Im(I). We then compute, on-line
the magnitudes of the voltage and current, |V| and |I|, respectively. We also compute, on-line, the in-phase,
out-of-phase, magnitude and phase of the complex impedance, Re(Z), Im(Z), |Z| and phi_Z at each
frequency, as well as the complex power, Re(P), Im(P), |P| and phi_P at each frequency
We also measure the DC resistance of the guitar pickup using a Fluke 77 DMM (Digital Multimeter).
We measure the Inductance and so-called Dissipation, D at 120 Hz, 1.0 KHz and 10.0 KHz (when possible)
using a Hewlett-Packard LCR meter. We measure the polarity of the magnet poles (north or south) at the
top of the pickup, using a simple compass. We record the type of permanet magnets used in the pickup
and measure the strength of the magnetic field at the poles of each of the magnets in the pickup,
using a Hall probe. We record the winding direction/sense of the pickup coil (CW/CCW) viewed from the top of the pickup.
A pix of the Guitar Pickup Test Stand in the UIUC Physics 498POM Lab:
Here is a pix of main display panel for the Guitar Pickup DAQ setup in the P498POM Lab:
The following document summarizes the various methods and equipment we use
to obtain the various physical measurements that we make on various electric
guitar, electric mandolin and bass guitar pickups, and the definitions and
conventions that we use for the various quantities that we measure.
The following is a Microsoft Excel file that summarizes the various physical measurements
we have made for various electric guitar, electric mandolin and bass guitar pickups.
We show (here) the representative complex impedance vs. frequency curves for
e.g. a Lindy Fralin Vintage Hot Strat Bridge Pickup,
with Callaham Booster Plate, obtained with our
PC-based Guitar Pickup Impedance Measurement DAQ System.
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