+-----+             +--------+ Buffered,   +--------+
 noisy 50Hz signal  |     | Amplified   |        | Amplified   |        |
------------------->+ Amp +------------>+ Buffer +------------>+ Filter +---> Output
                    |     | Noisy 50Hz  |        | Noisy 50Hz  |        |
                    +-----+             +--------+             +--------+