Category Archives: electronics

fet testing/preamps

In between a lot of other things, I am back to making piezo preampsĀ  based onĀ  Alex Rice’s design. They impedance match piezo discs (notoriously tricky things), giving a much better response at low frequencies than when they are just plugged into a mixer/recorder.

preampsNov15

The preamp requires a matched pair of JFETs. I used to do this by ear, testing pairs in the circuit through a mixer, but I finally got my head around the matching process a couple of years ago thanks to SmudgerD’s Stompville blog. In a fit of madness I even sat down at the time and built a (point-to-point soldered) fet matcher based on SmudgerD’s PCB overlay.

fetTest2

I’m so proud that this thing still works, given it looks more like a sculptural work than a proper circuit. I am, however, going to treat myself to a new tester to be more future proof.

fetTest3

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noisy textured discs

Not long after I first armed myself with a soldering iron, I started playing with DC motors, and rigged up a turntable of sorts which read zip discs and cassette tape with a tape head.

This new turntable is an arduino and servo arrangement which lets me control its speed and direction (built with John McAreavey). In this video, I have a contact mic reading the texture scratched into a CD, which is then fed through a WMD Geiger Counter and analog delay pedal for added noise. The setup needs a bit of practice yet but it is nicely hands-on and expressive to play. The video below mixes the desk audio with a room mic, as the servo is a noisy thing in itself.