Piezo contact microphone hi-Z amplifier using a FET – Richard Mudhar
building contact microphones - john grzinich
A 5-channel mixer / preamplifier for piezo disks by Godfried-Willem Raes
Building your own Piezo-Preamp – The Center for Haptic Audio Interaction Research
operational amplifier - What is a good circuit for recording a piezo contact microphone or an electric guitar pickup? - Electrical Engineering Stack Exchange
contact microphone preamp buffer - MOD WIGGLER
Designing and building an active contact microphone for field recording and sound design — Ezra Gray Audio - Sound Engineer & Sound Artist in Dorset, UK
Make this DIY Contact MIC Circuit | Homemade Circuit Projects