This device acts as a front end signal conditioner for guitar pickup measurements. It features an adjustable high impedance input circuit, preamplifier, an integration function, and a line driver amplifier. These are implemented with a single quad JFET operational amplifier. It is designed to be used with a PC sound card or PC oscilloscope and measurement software.

Electrically, a pickup has an LCR circuit response, which can be determined either by directly measuring the two terminal impedance, or by measuring the output response when an external magnetic excitation signal is applied. This system uses an excitation coil. I use about 50 turns of AWG#26 magnet wire on a humbucker bobbin, but any similar coil should work. The coil is placed in proximity to the pickup under test, and the pickup is connected to the integrator board input.

BOM and user manual, additional information:

https://github.com/KenWillmott/integrator