In preparation for our instrument making workshop at Artspace New Haven on December 13th, your intrepid guides Brian and Scott spent a foggy Sunday afternoon making contact mics from scratch. The below is both a how-to and an advertisement for the workshop. If you are around New Haven, please follow this link to the INI site and register now as seats are limited to 10 and they will go fast. So without further ado, lets make some contact mics!
Wire stripper, X-acto knife, pliers, soldering iron, solder, helping hands (or a friend 😉 )
Grab the audio cable and cut it in half. Because you only use one end of the audio cable per contact mic, you only need half the number of audio cables as piezos.
Strip the outer shielding off revealing the wires within. What you find will depend on what kind of cable you have. We have TRS (stereo) so we have three wires. If it was a mono cable there would only be two wires or an internal wire with a shield and the ground wire layered outside it. Whatever you find, you should run a test to make sure that you have the right connections when you solder it up to your disc. To do this simply attach the leads to the piezo disc with alligator clips and plug the cable into an amplifier, audio I/O box, or laptop mic input. You should try all combinations of connections as all of them *may* produce sound, but one will be noticeably louder. After this, cut off the extraneous cables (should there be any.)
Strip the ends of the leads and tin them up with your soldering iron.
Grab your helping hands and get the cable in one side the piezo in the other, wires towards each other. When soldering the wires together, it helps to bend the ends of the leads into little hooks. This way they stay together even with a little pressure on them.
Put a piece of electrical tape around both solder points to keep them from touching and shorting out. Then, tightly (but carefully) wrap from the piezo up to the audio wire shield. This will add strength to the finished product.
Step 5b (optional):
An alligator clip makes a fine addition to the contact mic as it allows you to easily attach it to, well, just about anything. (If you do not add a clip, you will have to tape, wedge, suction cup, or find another way to attach the contact mic to whatever it is you want to amplify.) Use a pair of pliers to bend the connection end of the clip open. You can use a tack hammer to flatten it if you wish. Then just flip the pieze over and solder the clip to the back (all metal) side. *Be sure to hold the clip with pliers NOT your hand as the clip and the piezo will become very hot! Put something under the piezo (like a piece of wood) to keep it from burning the surface beneath. This step will take a little patience as the clip and disc take a while to heat up. Get the solder on there after about 20 seconds or so of just the iron. The solder will not stick initially, but eventually (another 15 seconds or so) you will see the coating on the disc dissipate and the solder suddenly spread. Make sure you get a good amount on there, you aren’t going for looks, you are going for durability.
Time to plasti dip your mic. If you haven’t properly wound and prepared your mic, it may end up looking like the above (left). You don’t want this. Evenly dip the mic all the way in up just past the tape mark. Retract it out and let the excess drip off. Just before it stops dripping I like to tilt the mic so that any excess forms around the joint at the very base of the disc and the electrical tape as this is the weakest point of the mic. Dip again (after 30 seconds) if you like, but try not to get too much dip on the disc. The more dip on the disc the less effective it will be. Blow on the disc for about a minute to set up the outer layer and hang it up over a paper towel or newspaper to dry. Takes about 4 hours to completely dry (says the tube) but I would leave it overnight.
Hopefully you now have a contact mic (or 2 or 10!)
If you have any questions please send us an email or add a comment. Also be sure to join us for the workshop on December 13th from 6-8. Registration is now, the workshop is free (with $10 suggested materials donation) but limited to 10 participants. Registered participants will walk away with an instrument of their own design AND one of the contact mics shown above! If the registration is full, you can still come and watch and learn!