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.