piezo.preamp

Record the sound of things


This preamp can be used to amplify signals from piezo contact microphones and ensures a good bass response.

It was developed during a workshop taken out at UrbanLab Nürnberg in summer 2018. We had a lot of fun building it and playing around.

 

The preamp is powered by a 9V battery and draws a current of only about 0.15 mA.

For the workshop I layed out a couple of PCBs and ordered parts. Some kits are still left over, so just contact me if you are interested in this project!

 

Kits include:

- PCB and all necessary parts

- 3.5 mm input mono socket

- 6.35 mm output stereo socket (plugging in a mono jack switches the unit on)

- 1 piezo disc and 1.8 m audio cable

 

What you will need on top:

- Soldering equipment

- 9V battery

- case (e. g. aluminium or wood)

 

Here are the building instructions with a wiring diagram:

Download
Building instructions (German)
Aufbauanleitung_Kit_v3_8-2018.pdf
Adobe Acrobat Dokument 560.1 KB

Building a piezo contact mic


The piezo discs should be sealed with e. g. liquid rubber for isolation and to make them more robust. This also prevents the cables to break off the solder joints when the piezo is handled, so you can use it much longer.

 

Solder the Piezo to an audio cable and dip it into the rubber. Let the rubber drip off and remove excess drops. You want just enough material around the piezo so that it is protected but with minimum damping of the vibrations. After drying, the rubber can be peeled of the bottom side to ensure better contact with a surface. I mostly used double sided tape so far to attach the piezo mic to an object.


Schematics


Circuit inspired by the Mutable Instruments Ears project and modified for 9V battery supply.