Tin the two strands of wire on the cable as you did earlier. Next, tin each leg of the 1/4" connector: Place the iron against them one at a time to heat them up and melt a bit of solder on them. Finally, attach the cable’s shield to the long leg, and the conductor strand to the short leg. Simply hold the appropriate wire and leg together and press the iron down on both until the solder melts, then allow the connection to cool. Remember to tin the tip of your iron a little before you solder each wire down, and to use the damp sponge to wipe debris off.
If there is a chance that the two wires below the plug or disc will touch each other, wrap the center connection with a piece of electrical tape so that the bare wire is covered. Otherwise, the two wires will short each other out when they touch and the contact mike won’t work. (Shorting the wires will not damage anything, so don’t worry if they accidentally touch while you’re working. Just wrap the center lead when you’re done to keep them apart.)
Now it’s time to test the contact mike by plugging it into an amp. If the piezo is wired correctly, you’ll hear a sound as you scrape it along the surface of your workbench. On the other hand, if you hear a buzz, you may have reversed the wires. Use the iron to melt the connections and remove the wires, and then re-solder them in the right place.
To finish things up, use another piece of electrical tape to wrap both wires together as close to the disc as possible (again, being sure the two bare wires don’t touch each other). The idea is to leave as little room as possible for something to catch under the wires and pull them apart.
Because this project is meant to be a drum trigger, you want to make the contact mike as sturdy as possible. One method is to cover the solder connections with a layer of silicon sealant. When it dries, the silicone will provide a modicum of protection.
A sturdier way to protect the top of the disc is suggested by Nicolas Collins in his excellent book Handmade Electronic Music. Collins suggests you start by covering the top of the piezo with a small piece of electrical tape, which you can cut to size or fold around the edges of the disc. Then, dip the entire disc assembly in Plasti Dip, a synthetic rubber paint used to create a grippable surface on hand tools. Let the unit dry for a few hours. Although the coating changes the sound characteristics of the piezo to a certain degree, Collins says it makes the contact mike more durable, not to mention waterproof, should you decide to use the piezo as a hydrophone.
Once the coating is dry, attach the pickup to the head of one of your drums and plug it into the device you want to trigger. A patch of duct or gaffer’s tape is all it takes to keep the piezo on the head, preferably near the hoop where you won’t accidentally strike it. I also recommend you secure the cable to the side of the drum so that it doesn’t get pulled accidentally. Once the trigger is connected to your drum module, you’ll have to adjust the input sensitivity settings to mitigate false or double-triggering issues.
The piezo’s sensitivity to vibration allows it to bring out the subtlest aspects of any object you attach it to. Anything that resonates is fair game — springs, wires, tables, gongs … you get the idea. There’s no need to hit the surface hard, let alone strike it at all. Clamp or tape the contact mike to a cymbal, and you’ll hear interesting timbres by simply dragging a wire brush or even your fingernail across the cymbal’s surface. Composer John Cage famously amplified the spines of cacti and other plant material using contact mikes, then played these new “instruments” using feathers, leaves, and other organic material.
Because our piezo trigger has a high-impedance output, it is well suited to processing through the various stomp boxes guitarists and bassists use. While fuzz, phasing, and flanging are interesting, I find echo, reverb, and sampling delay-pedals to be the most musically interesting. Once you hear a highly amplified sound looped with a sampling pedal and running through a distortion box, you’ll want to bring contact mikes and pedals to every gig.