THis Wien bridge oscillator is very simple and as every wien oscillator has low distorsion and the resonance frequency can be easily adjusted. This frequency depends on a pair of resistors and a pair of capacitors and is defined by the formula: F = 1/2ΠRC.
In this wien oscillator circuit, R is formed by R1 + P1a (or R2 + P1b) and C is C1, C2 or C3 (or C4, C5 or C6).
Part of output signal from IC2 is send to the attenuator built with IC3 and T1. This FET transistor, used here as variable resistor it’s part of reaction circuit of IC2. The gain of this operational amplifier is voltage controlled and can be adjusted by voltage variation through P2.
This potentiometer must be adjusted in such way that the wien bridged oscillator frequency is stable. The frequency range is between 20 Hz … 22.5 kHz and the distorsions are lower than 2%.