To make springs work you need a very solid box that can hold up to the hardware. I didn’t have such a box, so I used one of my Christmas tins and made this into more of an ambient pickup rather than a device that created it’s own sound. Youtube shows several hacks for the Black Fly, so all I needed was an interior photo of the build from one of those videos, and the rest was easy.
The piezo is set in place with Guerrilla Glue. The filter capacitor value was a bit tricky. First attempt with a 10pF cap showed no filtering effect. I couldn’t make out what they were using in the photo, so I checked with my dad who advised based on his experience with similar circuits, “try .01uF to .05uF. The pot could be 50K more or less… ” The second attempt with a .022uF Mylar cap works well!
What’s it for? This can be used as a pickup for all sorts of sounds around the studio, basically like a low-fi mic. The filter acts as a tone control, which is necessary to roll off some of the harshness of the piezo. Paired with a proper DI box, this can be a very effective tool for sound design. The larger form factor and thinner metal also gives this much different properties from a Black Fly, though I would still like to build one of those when I have the materials.
To hear this in action, check out some of my piezo sound scapes.