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.
Circuit Description of A Variable Audio Frequency Oscillator Using Op-amp 741
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 a split power supply has been avoided by using capacitors C1 and C2, for R4*, a 150-Ω resistor, we can use a thermister or even a bulb that controls 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 |
| Capacitors |
| C1, C2 = 100 µF, 15V (Electrolytic Capacitor)
C3 = 10 µF, 15V (Electrolytic Capacitor) VC1 = 2J GANG 35pF-365pF |
| Semiconductors |
| IC1 = 741 (Operational Amplifier IC) |
| Miscellaneous |
| LS1 = 8 Ω speaker |
In the circuit, the observed output waveform are rectangular rather then pure sine wave. As i have used 6V, 60mA bulb for R4.
what are the uses of a variable audio frequency oscillators ?