# What's this amplifier filter configuration?

I've come across an audio amplifier circuit that contains this following configuration:

I recognize R1,C1, and R3 to be part of a first order high pass filter, but I'm not sure what C2 and R2 are for. Does it filter high frequencies?

• Where is C3? I don't see it on your schematic. – Elliot Alderson Sep 28 '18 at 14:50
• I'm sorry, I meant R3 – Rico Cahyadi Sep 28 '18 at 15:00

R2 and C2 form a first order low pass filter, the cut off frequency is $$\ Fc = \dfrac{1}{ 2 \pi R C}\$$ where $$\R\$$ is in Ohms, and $$\C\$$ is in Farads, so yes, it filters high frequencies.

C1 is probably for ac coupling the opamp, which is an inverting amplifier with output$$\Vout = -\dfrac{R3}{R1} * Vin\$$