This circuit shows a twin-T network connected to an LMl02 to fonn a high-Q, 60-Hz notch filter. The junction of R3 and C3 which is normally connected to ground, is bootstrapped to the output of the follower. Because the output of the follower is a very low impedance, neither the depth nor the frequency of the notch change;
however, the Q is raised in proportion to the amount of signal fed back to R3 and C3. Shown is the response of a normal twin-T and the response with the follower added.