(This page is part of a series See the rest of my contact microphone pages here.)
I developed this contact mic design for my students in 2020. I wanted them to have durable tools with great sound, but build time and cost were important too. I settled on stereo pairs of 27mm piezo discs glued to metal to reduce resonance. A 3D-printed back shell serves as physical protection and cable strain-relief. I have been loaning these to students for several years without much trouble, so I’d say they’re well tested.
I only cover the sensor design here. Go here (LINK COMING SOON) to build an inline stereo JFET preamp that runs on “plug-in-power” from 1/8″ mic inputs.
Parts List
- 27mm piezo discs with pre-soldered wires. I used Murata 7BB-27-4L0
- 1-1/8″ dia Aluminum discs, 16GA (About 29mm x 1.25mm). I get these from ebay sellers.
- 3D-printed back shells
- Shielded cable (4mm)
- Optional heat-shrink tubing to differentiate left and right sides
- Tools: clamps, metal file and/or sand-paper, CA glue (“Super Glue”), thick solvent glue (E6000)
Construction Steps
- Print the back shells using the STL file in this download: zlp-3dprinted-contact-mic-housing.zip
You might need to adjust the OpenSCAD files (and re-render the STL) to fit your actual cable diameter (default 4mm) and aluminum disc diameter (default 29mm). - Prepare the aluminum discs. These are usually die-cut so they have a slightly raised edge. File/sand it flat.
- Use CA glue to bond each piezo sensor to an aluminum disc. Make sure it’s centered. Clamp while drying.
- Cut, strip, and tin the red/black piezo wires to about 1″ (25mm) length.
- Strip the shielded cable. Groom and tin the ends.
- Insert stripped cable through the back shell and bend the ends so they fit into the pocket.
- Solder piezo wires to the cable in the pocket.
- Apply E6000 to the back shell. To support the cable, apply glue to the cable exit (not shown in photo) and pull the cable in/out to work the glue into the hole.
- Clamp and let dry. You’re done!
