This wien bridge oscillator circuit which is normal, low distortion and can easily adjust the resonance frequency that depends on the pair of the resistors (R) and capacitors (C). Which we can calculate by the formula.
F = 1/2 p RC
How Wien bridge oscillator works
In this circuit as Figure 1 the oscillator are based by the R that include with R1 + P1a (or R2 + P1b), and C is C1, C2 or either C3 (or C4, C5 or C6). And more parts are connected with IC1, IC2 op-amp ICs.
The some output signal from IC2 is sent to the voltage attenuator circuit, that include of IC3 and T1. The T1 is FET that is used like the variable resistors as the feedback of IC2
The gain of OP-Amp is controlled by the voltage and changing the control voltage of T1 by P2. It need to tuning to the oscillation have the high efficiency, on the frequency range is selected.
When we use the value of parts as schematic diagram of wien bridge oscillator circuit will have frequencies about 20 Hz – 22.5 Khz by adjust P1 and maximum harmonic distortion approximately 2 %.
This circuit use dual voltage positive and negative so we use the voltage converter circuit as Figure 2 input is 9V to +4.5V, Ground, -4.5V.
We use principle like the voltage divider by OP-amp IC-741 and few parts.
The parts list
IC1-IC3: CA3140, 4.5MHz, Bimos Operational Amplifier With MOSFET Input/bipolar Output.
IC4: LM741, Operational Amplifier
D1,D2: 1N4148, 75V 150mA Diodes
T1: BF256,BF244, FET
P1: 47K, potentiometer
P2: 47K, Pot
C1,C4: 150nF or 0.15uF 63V
C2,C5: 15nF or 0.015uF 63V
C3,C8: 1.5nF or 0.0015uF 63V
C7: 22uF 16V tantalum capacitors
C10: 47uF 16V, electrolytic
C11,C12: 10uF 16V, electrolytic
1/4W Resistors tolerance: 5%
SW1: 3 step selector switch
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