Wien Bridge Oscillator
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%.
Wien Oscillator Circuit Diagram
about 1 month ago
Wien bridge oscollators can provide signals with very low distorsion. Typical < 0.1%
However if the gain control element is a fet, distorsion is caused by the nonlinear behavior of the fet and also by the ripple from the signal rectifier. Filtering the control voltage to reduce ripple makes the control circuit slow and control oscillations might occur.
With carefully selected components this circuit might work as expected. The gain set pot is a compromise between distorsion and the risk the oscillator will not oscillate at some frequencies. If the resistance of the sections of the frequency set potmeter are not exactly the same, the gain control circuit must be able to compensate the gain variations.
I prefer the oldfashened control circuit with a lamp as variable resistor in the feedback circuit.
Only for frequencies below 40 Hz the resistance of a lamp might be not constant over a period.