In low-frequency and audio technology, it is necessary to have a sine signal source with very little distortion.
Such a signal source can be achieved by a simple connection using an operational amplifier. Condition
small distortion in this connection is a high value of resistance R4. The connection is more complicated than the classic one
The Wien oscillator, on the other hand, gives a much better result signal.
The LM358 operational amplifier is a double operational amplifier in a DIL8 package. So they are in one case
two operational amplifiers. The first operational amplifier is used for the oscillator and the second is used as
output driver together with output transistor. The amplitude of the output signal is set by a potentiometer
R4 in the range from about 2V to 12V (peak-to-peak).
Resistors R6 and R7 have the value "Rx" and resistor R5 has half this value. So "Rx / 2"
Capacitors C1 and C3 have the value "Cx" and capacitor C2 has twice this value, ie "2 * Cx".
If a continuously tunable oscillator is required, a tuning triple capacitor can be used instead of C1, C2 and C3
from old radios. The second option is to switch either resistors R5, R6 and R7 with a switch
or capacitors C1, C2 and C3 for different fixed frequencies.
The required values of Rx and Cx are calculated according to the formula and the scheme.
The following table shows the Rx and Cx values for several frequencies.
| Fx |
Rx |
Cx |
| 500 Hz |
47kΩ |
6.8 nF |
| 1000 Hz |
47kΩ |
3.38 nF |
| 10 kHz |
47kΩ |
338 pF |
| 20 kHz |
47kΩ |
169 pF |
