Wien bridge oscillator

In the circuit the frequency trimming component is arranged so that the voltage across it is in quadrature with the voltage V0 from the bridge so that as it is adjusted the attenuation of the bridge only changes a little, avoiding the need for a two gang component. The range of variation of frequency is very limited.
Wien bridge oscillator  - schematic

By using a high gain amplifier and metal film feedback resistors the loop gain can be set so that the unit just oscillates and the use of an automatic gain setting component, a thermistor for example, is eliminated.

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