# Wien bridge sinusoidal oscillator simulate this circuit – Schematic created using CircuitLab

I would check that in the Wien bridge sinusoidal oscillator the gain A_V=1+(R5+R4)/R3) is actually A_V=3 as the Barkhausen stability criterion requires. So I build this circuit whit a potentiometer of 10k instead of R4 and I obtain that for R4=6.38K (so R3 becomes 13.7k) the oscillation starts. With this configuration the circuit should have a gain A_V=2.2 (with the formula mentioned before)but I observe a gain of 2.9-3. How can I consider the contribution of the diods to the gain formula?

• What you have shown is not an oscillator. There is no frequency-dependent feedback. Your "R3 becomes 13.7k" makes no sense. Try a better explanation. – WhatRoughBeast Dec 5 '15 at 21:24
• Of course it is not an oscillator. In order to obtain an oscillator you have to connect point A to non-inverting input V+ through a short circuit (without the sinusoidal voltage source). Now, according to the Barkhausen stability criterion the circuit sustains steady-state oscillations only for frequency for which the loop gain is=1. If you compute this condition in this case you obtain A_V=3. So I build a new circuit in order to verify that actually A_V=3 when the oscillation starts. – gilgamesht Dec 5 '15 at 21:55
• gilgameshd, why not measuring the loop gain directly? Connect node A to the non-inv. opamp input and disconnect the positive feedback path R7...C1..... Now - excite this path (via R7) with a testsignal and measure the opamp output voltage. – LvW Dec 6 '15 at 10:17