The quality factor Q of the tuned amplifier can be determined by dividing the f o value by the 3 dB width. What is the Q of your tuned amplifier. The feedback resistor reduces the gain of the amplifier so that oscillation does not occur. Try reducing its value to 1 k W and then removing it. Figure 12 Notch Filters.
Notch reject specific frequencies.
The amplifiers use twin T filters to provide band rejection. The voltage followers in the notch filter provide buffered input and output. Figure 13 Use a sine wave input of about 1 V p-p. Measure the frequency dependent response, bandwidth and Q for the notch filter using a 1 V p-p sine wave input. Choose appropriate values of R and C to make the rejection filter in Figure 13 reduce or remove 60 Hz interference.