The Wien bridge is shown in the sim

The Wien bridge is shown in the simplified circuit where the positive feedback handles the frequency of oscillations while the negative feedback handles the unity gain of the circuit. To maintain the oscillation without any distortion at the output signal, the gain should be higher which can be possibly handled by the positive feedback. The positive feedback consists of resistor and capacitors that will provide a gain of 3 to the circuit. The RC filter or tuning network together with the amplifier is necessary to achieve the conditions for oscillations. The increasing gain causes the net resistance to be more negative where the amplitude increases. A result of low distortion oscillations occurs when suitable amplitude is reached as the gain is reduced to exactly 3. The distortion will stay minimal as long as the amplifier and RC network are linear. With the aid of a non-linear component like thermistor, a glowing lamp, or other suitable circuit, the adjustment of the gain becomes automatic.