I have been doing some experiments with Wien-Bridge Sine Wave Oscillators, specifically trying to make one where frequency can be controlled via a single knob, using a dual ganged potentiometer. I am basing my design on the following circuit from page 29 of Analog Devices App Note 43:
I am replacing the two 1.6k resistors with each of the gangs of a 100k dual potentiometer.
I have been noticing some strange behavior. Rather than creating a variable frequency oscillator the circuit only oscillates when the potentiometer is set to a very specific range of values (~1k ohms). As I turn the knob away from this range the oscillation first becomes unstable (very jittery in oscilloscope) then disappears. Does anyone know the reason for that this is happening?