Press the switch shortly. I saw someone looking for a phase shift oscillator. They usually tend to clip the wave, because there's nothing to constraint the gain after the wave has reached the desired amplitude. This does exactly that. It senses when the wave has reached a certain voltage and starts drawing away from the gain, decreasing the amplitude. As it decreases the regulating part of the circuit disables and the rising starts again. It's a cyclical process. Anyway any of these amplitude stabilization circuits introduce nonlinear noise into the wave and increase its THD. Even without measuring it i can say that the THD of the circuit ia very high (maybe 10%). Only wien bridge Oscillators and specifically bulb compensated ones offer low distortion. Any other nonlinear component like a diode for instance will introduce much noise.
