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Published on Jul 30, 2013
In this setup, a 555 timer IC --based astable multivibrator oscillator circuit (powered independently with a 5V 2A wall adapter) switches a 12V 1.2A power supply via a silicon diffused power transistor into a television flyback transformer. The high-voltage transformer secondary is allowed to arc across a spark gap made from a screw and a piece of copper magnet wire.
The frequency and duty cycle of the oscillator circuit is tuned with two 0-10kΩ potentiometers and audio-modulated by tying the 555's control voltage (Pin 5; Pin 11 on the 556) to an audio input in series with a 100nF ceramic capacitor.
The resulting hot plasma arc does an excellent job of reproducing audio above 1kHz. Two Door Cinema Club's "Something Good Can Work (The Twelves Remix)" is quite recognizable. With a larger power supply, I should be able to pull much larger, more stable arcs and improve the sound quality.
Virtually all of the parts were harvested from electronics salvaged from the Bay Area streets. Don't just throw out old electronics — donate them to your neighborhood aspiring mad scientist!