Build an Audio notch filter 2

 Build an Audio notch filter 2 Circuit Diagram. With the circuit shown here the response at one octave off tune is within 10% of the far out response: notch sharpness may be increased or reduced by reducing or increasing.respectively the 68 ohm resistor. Linearity tracking of R8 and R9 has no effect on notch depth. The signals at HP and LP are always in antiphase, notch will always be very deep at the tuned frequency, despite tolerance variations in R6-9 and C2, C3. 

 

 Build an Audio notch filter 2 Circuit Diagram