How to make a piezo contact mic?

Question

Would I be able to turn a rather large piezo speaker I bought at radioshack into a piezo contact mic? If so how would i be able to do it?

Answer 1

A typical piezo transducer is a brass disc with a silver substance deposited on the middle of one side. I will asume this is what you have. To use it as a contact microphone solder a small diameter piece of coaxial shielded wire of appropriate length to the side with the silver center. Connect the outer shield braid to the brass border and the inner wire to the silver part. To do this precoat the stripped ends of your lead wire with solder (this is called tinning the wire) so as to keep the heat applied to the piezo to a minimum. Then using a small wattage soldering iron apply a small solder blob to the brass border and to the silver part. Now you can touch the wires to the appropriate solder blobs and apply heat. This should give you reliable connections withot applying heat for more than a few seconds at a time which may damage the piezo. To connect your new contact microphone to an amplifier you can wire the other end of the lead wire to a standard 1/4 inch mono phone jack, connecting the center wire to the tip lug of the jack and the shielding braid to the ground lug. From there you can plug in a standard instrument cable to connect to your amplifier. To attach the pickup to your instrument you have several options such as epoxy, double sided tape, or any method that holds the pickup in firm contact with the instrument. However I recomend that you use a non permanent method until you find a sweet spot on the instrument (typically near the bridge on a stringed instrument for example) that sounds the best and minimizes this type of pickup's tendancy to cause feedback. I use a pickup (microphone) just like this in my repair shop to tune acoustic instruments with my electronic tuner.