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Rc Oscilator with Wien Bridge

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machok3

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Hi i got a homework to pass an exam. It says like this :" Create a RC Oscilator with Wien Bridge with oscilation freq. between 3-9 KHz, output load 100Ω, automatically controlling the oscillation amplitude achieved with JFET , oscillation amplitude output 10V. I need to use bipolar, JFET, βA723 transitors.
I managed to make some schmes but i got some replyes from friends that my homework is wrong :( .
10-17a448095f.png - ampl
9-ca3366f670.jpg - block scheme

Im worried because i might fail this exam and so need to remake the year. I would be greatful if some1 could guide me, or maybe help me with scheme.
 
Try googling 'wien bridge oscillator amplitude fet'.
One of the hits is
**broken link removed**
That will guide you. Adjust component values to suit your spec.
 
machok3,

How do the responses in this thread compare with your other posting here? **broken link removed**

Ratch
 
im asking on diffrent forums bro so i can get some help from diffrent guys. For exempled i mailed 1 teacher from spain to help me with some infos about ampl. I got 1GB of infos about wien bridge so i can make now alone my homework. You dont need to be rude with me ok ? If u dont want to help me with something dont dont do it and blame me for begging help from 3 forums.
 
Last edited:
There are hundreds of circuits in Google of a Wien bridge oscillator with a Jfet controlling the output level for you to simply copy.
Texas Instruments has an entire document aboput sinewave oscillators including one.
Ask your teacher to help you to copy one.

Oh, you said you must create one? If your teacher finds out that you simply copied one then will you fail?
 
This was part of our 1st Degree project as part of a bigger project.
What appears to be missing is the word "Sinusoidal". If this is the case, set the gain to about 4 using the feedback on the -ve input of the op-amp. It will give you a square(ish)wave.
Normally a JFET on the feedback is used to control the critical gain to allow oscillation as a sine wave generator which mathematically is 3. We used a 2N3189
You rectify the output to give a -ve signal on the gate of the FET which forms part of the feedback circuit.
The output level is better set using a second op-amp.
The frequency is set using a dual gang pot which I think you seem to have worked out.
I could dig out a cct if required, but my notes are in the loft and we are talking ~30 years ago.
 
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