Hi Ratch - yes, here are the results of my "fresh start:":

With reference to your post#14 (calculation in blue):

Third line from the bottom:

* Left side of the equation is __imaginary__ and right side is complex (imag. plus real).

This requires to set the __REAL__ part of the right side equal to zero.

This would immediately lead to **w=1/[SQRT(3)*RC].**

* Alternative: Continuing __your__ approach:

Shifting the left imag. part to the right side of the equation, we get: **0=Im + Re.**

In the second line from the bottom you have set all the __imaginary__ parts equal to zero **(Im=0**).

The result is given in the last line of your calculation.

* However, this is only the "first half of the story“.

Because the left side is zero you also must set** Re=0**.

Hence, we get as a __second__ equation again: ** w=1/[SQRT(3)*RC]**.

* Finally, __both__ equations must be fulfilled at the same time (because of 0=Re+Im)).

Equalizing both w expressions gives the condition: R2=8R. After inserting this requirement into

your w expression, we again get: **w=1/[SQRT(3)*RC].**

* __Comment__: To me, it was clear from the beginning that w cannot depend on R2 because only the

CR sections determine the phase properties of the loop gain. So - how can we interpret your

result (involving R2) - even if it is only 50% of the calculations?

If you - from the beginning - __replace__ the ratio R2/R by the gain A you will see that A will be __not__

part of the imaginary part and, hence, R2 would not appear as part of your result.

Why this surprising fact?

Because the resistor R at the inv. input node of the opamp plays a __double role__: It is part of the

CR network and, at the same time. part of the gain determining resistor ratio. Therefore, it is

good to use the term A instead of R2/R (and not to combine this ratio with the other R terms).

* __Final comment:__ The oscillation frequency is determined by the time constant RC only.

That means: The resistor R2 determines the gain only with the requirement: R2>8R.

Of course, the oscillation amplitude will rise until it is limited by the supply voltage or by any

additional non-linear part.