The frequency of the AF oscillator can be varied over a wide range. It can therefore be used for AF amplifier testing and also as a code practice oscillator.
The circuit of variable audio frequency oscillator using op-amp 741 is mainly a Wein Bridge oscillator whose frequency is varied using the gang condenser. While using the IC1 741 (operational amplifier), the use of split power supply has been avoided by using capacitors C1 and C2, for R4*, a 150-Ω resistor, we can use thermister or even a bulb which control the amplitude of the oscillation.
While using the oscillator, an 8Ω speaker with a 10 µF capacitor connected as in the circuit will provide a good amount of volume. While using for testing, the output pin number 6 of the IC1 I connected to the input of the instrument to be tested via a 0.01 µF capacitor. The circuit works off a 3V to 9V supply satisfactorily.
PARTS LIST OF VARIABLE AUDIO FREQUENCY OSCILLATOR USING OP-AMP 741
|Resistor (all ¼-watt, ± 5% Carbon)|
|R1, R2 = 390 KΩ
R3 = 100 Ω
R4* = 150 Ω
|C1, C2 = 100 µF/15V
C3 = 10 µF/15V
VC1 = 2J GANG 35pF-365pF
|IC1 = 741|
|LS1 = 8 Ω speaker|