It makes use of the ICL8038 signal generator chip, manufactured by Intersil. An improved version, made by Exar corp. is available (XR8038A). It can be used to produce three types of waveforms, sine, square and triangle. The frequency, amplitude and duty cycle can be varied, and selection of waveform is done digitally.
http://wiredworld.tripod.com/tronics/signal_source.html
As a piece of test equipment, an audio oscillator has to be considered essential for anyone working in with hi-fi gear. Together with an audio millivoltmeter, and even better if you have access to an oscilloscope, you will be able to make proper measurements on everything from preamps, RIAA equalisation stages (for vinyl disks), tone controls, crossover networks, etc.
http://sound.westhost.com/project22.htm
outputs around 1 kHz sinewave at 10mV..1Vrms levels
http://www.geofex.com/FX_images/q+dosc.gif
To speed testing, the circuit generates a composite audio signal comprising 10 sine waves of 10 different equal-amplitude frequencies across the audio band. Values stored in EPROM determine the frequencies.
http://www.edn.com/archives/1994/070794/14DI7.htm
This is an ICL8038 based function generator that gives out square wave, saw wave and sine wave outputs.
http://www.lh-electric.4t.com/bin/8038gen.gif