Audio Signal Generator

This is an audio signal generator that I designed and built in 1993. I use it for testing audio equipment. The generator outputs low-distortion sine waves and square waves over a frequency range of 10Hz to 100KHz.

The circuit consists of a phase-shift oscillator with two integrators each providing 90 degrees of phase shift. A third variable phase-shift stage completes the feedback loop. The variable-phase shift stage is controlled by a slow feedback loop to stabilize the amplitude of the oscillator. The circuit is the electrical equivalent of the simple harmonic oscillator (spring-mass, pendulum, tuning fork, etc). It produces very low-distortion sine waves.