This filter rejects 1 kHz signals, being suggested by the manufacturer of the operational amplifier, Motorola's MC34074. Of course, the same configuration can be used with other operational amplifiers. The double T must have components with the ratio of Vin values indicated in the diagram. The formula for calculating the rejected frequency is given next to the diagram. The amplitude of the input signal must be 200 mV for better performance of the circuit and the amplitude of the input voltage will be the same, since for the non-rejected frequencies the gain is unitary, since the operational amplifier is connected as a voltage follower.