Piezo contact microphone hi-Z amplifier – low noise version – Richard Mudhar
Measuring the Electrical Properties of Guitar Pickups | GuitarNutz 2
The Mint-box Piezo Buffer
operational amplifier - High output impedance piezo guitar pickup is better attenuated by a shunt capacitor than an inverting opamp attenuation circuit - Electrical Engineering Stack Exchange
piezoelectricity - Maximum Resonant Impedance of a piezo disc - Electrical Engineering Stack Exchange
Measuring Electric-Guitar Pickup Impedance with Digilent Analog Discovery