I have put up a circuit for Wien bridge oscillator using 741 op amp, with R= 390 ohm and C = 2.2nF, for operation around 200 khz ( gain is 4). However, it did not work so I switched the resistor in parallel branch with potentiometer. This is the closest I could get.
Here is the circuit, with Rf = 8.2K and Rs = 2.2K
Any change in potentiometer does not yield any output.
Can someone please tell me some way to improve this to get good sine wave ?
The problem is the 741, which doesn't have enough gain at 200kHz to overcome the loss of the bandpass filter.
Here's a schematic of the identical circuit with a decent opamp, which works, and the LTspice circuit list is here if you want to play with the circuit.
To Plutonium Smuggler: I think, it is more appropriate to respond to your last comment in this way.
1.) Undoubtly, the nominal frequency for the Wien oscillator is fo=1/(2*Pi*RC). The other "resources" resp. formula you have found will, certainly, belong to another type of oscillator circuit.
2.) The above formula for the Wien type assumes an amplifier having a gain of "3" (without any parasitic phase shift). However, this cannot be provided by a 741 type opamp at a frequency of 200kHz.
3.) Does this mean, that this opamp cannot be used for oscillating circuits around 200kHz? No - it can be used. However, one must be aware of the consequences: It is not possible to DESIGN such an oscillator; it will be - more or less - a trial-and-error process because the opamp introduces additional phase shifts (which are not known with sufficient accuracy). More than that, these non-ideal opamp properties are different for the various opam types.
4.) Example: Using your values (220ohms and 2.2 nF) I have tried to produce oscillations (Spice simulation) for two different 741 types:
a.) µA741: 400mV at 135kHz for a gain of 1+3=4.
b.) AD741: 180mV at 142 kHz for a gain of 4.
5.) Evaluation: Of course, it was possible to create oscillations - however, at much lower frequencies as desired (335kHz) because the additional opamp phase shift must be compensated by a corresponding inverse phase shift of the Wien network. The required gain was found by trial and error.
6.) Question: Is it possible to derive the necessary gain values from the BODE diagram (loop gain ac simulation)? The answer is NO!. The reason is as follows: The oscillating circuit provides - as can be observed (400mV, 180mV) - automatic amplitude limitation caused by slew rate limitation. This is a non-linear effect (additional phase shift in the time domain) and cannot be seen in the ac simulation.
