This filter rejects 60 Hz signals and can be used as a hum filter in audio equipment, for example, at the entrance of microphones with long cables. Double T resistors and capacitors must have good accuracy to ensure operation at the desired frequency. At this frequency, we have an attenuation of 39 dB, while for the other frequencies, the gain of the circuit is unitary. Note that this circuit does not use a symmetrical power supply. The TLC271 is an operational amplifier with field effect transistors from Texas.
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