The Thomas Henry 8038 Audio Generator device –
The audio generator operates in the the range of exactly 20 Hz to 20 kHz. It features sine, triangle and square wave outputs. The frequency control set consists of a coarse and fine tune arrangement – the coarse control obviously will move the frequency in greater increments, and the fine control allows one to set the frequency exactly at the desired point.
In addition to the front panel frequency controls, the audio generator also accepts an external control voltage in the range of 0 to +12V. An input attenuator is provided to scale this voltage to the desired range of control.
Finally, the schematics include a +/-12V power supply to power the audio generator, so that the audio generator can operate as a completely stand-alone unit.
Altogether it’s a very cool device and handy tool for audio/music use. Check Scott Stites’ site for schematic, parts list, and PCB image.
The designer, Thomas Henry, has written a number of books on the subject of electronic sound synthesis. He has become well known for his ability to push an IC’s ability beyond the manufacturer’s specifications. When it seems a chip is unable to fully perform a desired function, he begins to experiment – as with the ICL8038 in the Audio Generator:
As it turns out, what the 8038 needed was a good change of diet. Instead of junking out on positive voltage rails, Thomas fed it a steady diet of good old fashioned negative rail. For +V Thomas gave it a nice vitamin enriched ground potential, and for the pin formerly known as ground, a nice fibery -12V. That alone catapaulted the 8038 from mediocrity to true A Number One function generator-hood.
He’s used similar techniques with the 566 function generator chip, for more info see his book “Making Music with the 566”.
Audio Generator build guide –Link
Thomas Henry books on Lulu.net –Link