This circuit is a variable audio bandpass filter that has a low cutoff variable from about 25 Hz to 700 Hz and a high cutoff variable from 2. 5 kHz to over 20 kHz. Rolloff is 12 dB/octave on both high and low ends. R2-a-b and RG-a-b are ganged potentiometers for setting lower and upper cutoff fre-quencies, respectively.
The Biquad consists of two successive integration stages followed by an inverting stage. The entire group has a feedback loop from the front to the back consisting of R1 which is chiefly responsible for controlling the center frequency, ‰o. The first stage of integration is a poor integrator because R2 limits the range of integration. R2 and C fo