Audio Oscillators

Posted on Feb 5, 2014

A phase-shift audio oscillator with excellent distortion characteristics thanks to `softened` diode limiting provided by the 1N914 and resistor divider and degenerated gain provided by the 68 ohm emitter resistor. For minimum distortion, increase the 68 ohm resistor to a point just below where oscillation stops. A simple buffer may be adde

Audio Oscillators
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d for driving lower impedance loads. The output amplitude will be about 5 volts p-p but one of the 1N914`s 10k divider resistors may be changed for a different output amplitude. The circuit will work well with a power supply voltage other than 9 volts but the 68 ohm resistor may need adjustment. I just finished watching "Track Down, " a movie about the hacker, Kevin Mitnick. In the movie, Mitnick steals a bunch of files from a phone company named Nokitel and is looking down the list when one catches his eye. He goes back and opens it. The schematic below is what he sees! Wow, those are some valuable files he has there. I`ve been hacked by a movie about a hacker! I`m not sure how to feel about that. I`ve added a bypass cap and used a different diode symbol since the movie, but it`s mine. In the movie that schematic enabled him to convert his phone into a local scanner. I can`t say I`ve tried it. : ) Too bad it took me 12 years to see this. My 1. 5 seconds of fame is long gone. The circuit can be built in the "blobular cluster" style (to coin a phrase) and potted with epoxy mixed with a little model airplane paint. Use quick-setting epoxy and, holding the circuit by the legs, keep rotating the blob near the end of the cure cycle to get an even coat - quite an art form! The finished module looks quite professional, not unlike many dipped caps. Here is a two-transistor Wien bridge oscillator using an ordinary night-light bulb...

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