Stable amplitude low frequency oscillator - for vibrato

Thermistors and even light bulbs have often been used in oscillator circuits to stabilise the output amplitude. The resistance of such components is dependent on temperature and there- fore on the effective voltage across the particular component. The curve of resistance versus temperature ensures that the sinewave signal generated by the oscillator is stabilised so that it is virtually distortion-free. Due to the fairly slow response of thermistors and light bulbs to rapid changes in voltage, the non-linear temperature/ resistance characteristic means that there is virtually no distortion in the sinewave signal. Things are different when the thermal inertia diminishes with respect to the time period of the signal. As far as oscillators are concerned, this normally happens at frequencies below 10 Hz, or thereabouts (for instance, the vibrato signal in electronic organs). Jfor vibrato This means that in this application a different approach will have to be taken. In the circuit des...