I am looking for a circuit that I expected to find everywhere but I don't. The "active" lowpass filter I often see in the web uses an RC filter with a buffer in series.
The alternativ version I found quite often is, in my opinion, not a true one pole lowpass but a lowpass shelving filter. The capacitor in the feedback is paired with a parallel resistor.
Now my question is, why don't I see the second variant without the additional parallel resistor in the feedback path more often? Are there any major disadvantages to the RC - buffer implementation?