The ripple filter circuit is specially deisgned to filter out 50 Hz ripple signals from audio lines. A 50 Hz noise is usually found in european countries. In many cases, it is not possible to remove the cause of ripple noise. The featured active filter notch filter solves the problem in suvh cases. It allows the desirable signal to pass through with minimal attenuation. The Q factor of the filter is 10 at the inductivity value of 150 H.
These values can only be achieved practically by using an electronic “coil” such as this circuit. The circuit works as an active RCL circuit. The two opamps Ai and A1 LF356A together with the resistors R2 to R5 , C2 and P1, work as the electronic “coil”. The coils inductivity value is L = R2 x R3 x C1. Potentiometer P1 varies the inductivity value. The filter circuit attenuates the ripple noise by 45 to 50 dB, if properly adjusted.