It’s amazing what a little disk can do … when it’s layered with piezoelectric crystals. Piezo disks are impressively sensitive to vibration and can easily be adapted to work as a contact microphones. The trick is the preamp — a basic circuit used to match the piezo’s signal to levels compatible with modern audio gear inputs. The resulting piezo/preamp combo can be used for electrifying an acoustic guitar or simply exploring the lesser-heard world of small sound around us.