Isn't the second circuit, the band amplifying filter, just an oscillator? How do you stop it from doing that? The Twin T has a 180 deg phase shift, the op-amp inverts the signal, another 180 deg and it has plenty of gain. 2 pi around the loop and gain >1.
In a more complete implementation of that circuit as a filter there's another feedback path added. In this video I used it as a Wah filter effect and then modified it to force oscillations (first step toward drum synth) ua-cam.com/video/s6U4tN_ZrB0/v-deo.html
Isn't the second circuit, the band amplifying filter, just an oscillator? How do you stop it from doing that?
The Twin T has a 180 deg phase shift, the op-amp inverts the signal, another 180 deg and it has plenty of gain. 2 pi around the loop and gain >1.
In a more complete implementation of that circuit as a filter there's another feedback path added. In this video I used it as a Wah filter effect and then modified it to force oscillations (first step toward drum synth)
ua-cam.com/video/s6U4tN_ZrB0/v-deo.html