Principle of the Wien bridge oscillation circuit
The basic composition
The figure on the left is the basic form of the Wien bridge oscillator which used the operational amplifier.The part which is composed of C1, C2, R1, R2 becomes the positive feedback circuit of the operational amplifier. With it, the operational amplifier works in the oscillation. Also, the circuit sets the oscillation frequency in the damping time constant of the CR.On the other hand, the circuit of R3, R4 controls the mu factor of the operational amplifier.This oscillator begins the oscillation when it makes the mu factor equal to or more than 3. At less than 3, it doesn't oscillate. The beautiful signal doesn't come out by output's being saturated when the mu factor is more than 3.The mu factor must be controlled to 3.Because it is, only this basic circuit can not use for the practical use.

Where is the bridge?The part of the circuit diagram becomes the figure on the left when it changes the position.The balance condition of this bridge becomes the oscillation condition.The oscillation frequency can be calculated by the following formula.In case of C=C1=C2, R=R1=R2, the formula becomes the following.The condition of the operational amplifier which is necessary to do the stable oscillation is the mu factor=3.It becomes the following when finding the relation between R3 and R4 from the mu factor.Gain 3=(1+R4/R3) That is, the condition of R4=2xR3 is necessary.

Principle of the oscillator Have you brought the microphone close to the speaker and have made an unpleasant sound? This is the phenomenon, the HOWLING.
As for some oscillators, the principle which is the same as the howling is used. It is the way of returning the output of the amplifier to the input.
The feedback circuit of the oscillator has the following role mainly.
It fixes the oscillation frequency.
It controls to oscillate at the specific frequency. It returns only the specific frequency signal to the input.
It controls the input level which is necessary to oscillate.
The amplifier becomes the saturation state when the signal which returns to the amplifier through the feedback circuit is too big and the beautiful signal doesn't come out.
It adjusts the phase of the frequency which is necessary to oscillate.
The phase means the position of the signal. At the electronic circuits, phase of the input and the output depends on capacitors, the coils, the amplifier itself. Because it is, it doesn't oscillate when not adjusting the phase of the input signal.
There is a circuit to be making have the role of the oscillation frequency's, output's not changing by the temperature in addition to above-mentioned, too.

Sine wave is what? The one to have shown the height which changes when moving the circumference in the time is the sine wave. It returns to the original place when going around the circle.At present, it uses the unit, the hertz (Hz), to show the frequency. It was using the word, the cycle per second, before as the unit which shows the frequency.This shows the 1-second number of rotations.(The once is the 1 cycle) The many turns occur in the high frequency.With the figure on the left, 0V positive 0V negative 0V is called the 1 cycle.There is "a period" in the word which is related with the frequency. This is the time which the 1 cycle takes. It becomes the frequency reciprocal.Period(T) = 1 / Frequency(F) and Frequency(F) = 1 / Period(T)In case of Japan, the electricity to be using in the home is 50 Hz or 60 Hz. In case of 50 Hz, the 1-cycle sine wave occurs the 50 times for the 1 second. 60 Hz are the 60 times.Because it is, the 1 period becomes 1/50 = 0.02 seconds (the 20 milliseconds). In case of 60 Hz, it is the 16.67 millisecond.There is a way of making make the Lissajous as the way of understanding that the sine wave relates to the circle. In case of the sine wave which doesn't have the distortion, the Lissajous becomes the true circle.

We have found some of the information about electronic piano.

The sine wave oscillator is introduced which used the operational amplifier in this page.The Wien bridge sine wave oscillator to introduce is the oscillator which works in the oscillation by returning(positive feedback) the oscillation output to the input.Because there are few parts, the Wien bridge oscillator is the often used circuit.The point of this circuit is the negative feedback circuit to make the oscillation operation be stable. The circuit to be using this time changes the resistance value of the Field Effect-type Transistor(FET) at the d.c. voltage which rectified the oscillation output in the full wave and is making the oscillation operation be stable. The sine wave oscillator is the oscillator which is difficult to make because the distortion of the oscillation signal occurs compared with the square wave oscillator, the triangular wave oscillator.
In case of C=C1=C2, R=R1=R2, the oscillation frequency can be calculated by the following formula.
The example of the circuit which was made this time is shown below.
f=1/(2 x 3.14 x 0.01 x 10-6 x 15 x 103)
=1/(0.942 x 10-3)
=1.062 x 103
=1,062 Hz
The frequency in the actual circuit was to 900 Hz be.
You can change the frequency when you change C1, C2, R1 and R2 of the circuit diagram. In the relation of the balance at the bridge, you had better make C1=C2, R1=R2.Even if it is different little, it is possible to oscillate.