GumiElectronic

The first step is to extract the piezo element from the plastic casing. It can be a little tricky opening the case because you have to be careful not to break the piezo element in the process. They are somewhat fragile. You can start by wedging a mini screwdriver into the space where the wires exit the case. Work the screwdriver around the edge of the case while prying upwards. There is usually about 1/8″ vertical space between the back cover and the element, so you have some room for prying.

Eventually the back cover will loosen. Pull it off and discard.

Now you have to cut open the rest of the case in order to pull out the piezo element. Use a razor blade or sharp wire cutters to cut a line from the center of the plastic case to the edge. Make sure the plastic is cut all the way through. Once this is done, carefully twist the plastic case until the edges of the piezo element separate from the edge of the case. This might be the hardest part of the project, so use whatever extraction technique that works best for you.

Pull out the piezo element and recycle the plastic casing.

Next, break out a 1/4″ mono jack assembly. Before soldering the wires to the mono jack (upper left in photo), remember to slip the mono jack case (upper right) over the wires first, or else you’ll have to resolder. You can also use a panel mount mono jack.

Now solder the wires to the mono jack’s solder tabs. The black wire goes to the sleeve (ground). The red wire goes to the tip (signal). With some mono jack assemblies it’s hard to tell which tab is connected to the sleeve and which is connected to the tip. Use a multimeter to test continuity if you have one. If not, you’ll have to experiment, but at least you have a 50/50 chance of getting it right first time. If you have no soldering iron, you can use a non-solder type mono jack assembly instead.

Now bend the strain relief tabs over one another and pinch them with a pliers to form a secure grip around the wires. Use an open flame or other heat source to shrink the entire length of the heat shrink tubing. Screw the mono jack into the mono jack case.

At this point your contact mic should look something like this. Test the mic by plugging it into a mixer. You’ll probably have to turn the gain up pretty high. Tap the mic and you should hear the sound. If there is no sound, first make sure the mic is connected to the mixer properly. If you still get no sound, check the solder connections on the mono jack and resolder if necessary. Also make sure the bare red and black wires aren’t touching one another or shorting out anywhere on the jack.

In order to make your contact mic more robust, apply a large dab of epoxy to the top of the element. This will prevent the piezo disc from damage and keep the wires from breaking off. Let the epoxy flow evenly to the edges of the element, but don’t use so much that it flows over the edges. This process is easiest if you use a self-mixing epoxy syringe because you can apply the epoxy directly to the element while maintaining control of the flow. Allow the epoxy to dry and you’re ready to begin recording and triggering.