This signal generator provides a sinusoidal output signal with a frequency of 440 Hz, at two voltage levels. Power can be made with a voltage between 1.5 V and 16 V. IC1a works as wave generator, the values of R4 and C1 determine the frequency of tipping the AO output. Potentiometer P1 allows to obtain a perfectly rectangular signal (setting can be done by listening and adjusting for low distortion signal).
Network R5-R6-C2 reduces output by 3 dB IC1a's (50%), after which half the signal is superimposed voltage.
IClb form a third order Cebasev filter with cutoff frequency of 400 Hz, which eliminates most harmonic of rectangular signal, thus resulting in an output waveform close enough of a sinusoidal.
The output signal S1 is selected with the voltage divider R9-R10-R11, depending on the needs of the test circuit. Powered by 16 V, output level is 1.5 or 30 mVef VEF, with 1.5 V supply, output levels are 150 mV and 3 mV. Output frequency range from about 440 Hz to 16 V, at about 370 Hz to 1.5 V.