Twin-T RC Notch Filter

The two T-notch filter can be used to block unwanted frequencies or if placed in an op amp as a bandpass filter. the notch frequency occurs where the capacitive reactance equals the resistance (Xc = R) and if the values are close, the attenuation can be very high and the notch frequency virtually eliminated,Insertion of the filter depends on the load, the output is connected to the subject so that the resistors must be of much lower value than the load for minimal loss.

Twin-T RC Notch Filter Circuit diagram

For audio frequencies, the filter may act as a bass and treble boost circuit by attenuating the midrange. With 1.5K resistors and capacitors 0.1 uF, the band is in stop-10dB 500 Hz to 2 kHz. The depth and breadth of the reaction can be slightly adjusted to a value of 0.5 R and adding some resistance at the C-values,If the circuit is an operational amplifier is used as a bandpass filter, the response should be reduced to avoid oscillation.