In view of my school project for a stethoscope (to record 20Hz to 1kHz), I was given this circuit(check picture) to study and told that it is a 2nd order low pass butterworth filter with cutoff frequency of 159Hz and 200 gain.
I am having my doubts since I remember the circuit as being an audio amplifier similar to this website (https://lowvoltage.wordpress.com/2011/04/23/lm386-audio-amplifier/)
An electret microphone with following characteristics was used as input:
Input Impedance: 10 Ohms
Sensitivity : -44dBV/PA +/- 2.5dB

The output was given to an audiojack(earphone).
Please help me in describing this circuit, its features and how the values of each components was calculated.

 

Have you searched the internet for a 2nd order Butterworth filter? A schematic and the formulas should found easily.

 

Have you searched the internet for a 2nd order Butterworth filter? A schematic and the formulas should found easily.

Yes I have. However, no 2nd order low pass butterworth filter are similar to the circuit in the diagram.

 

Good. The circuit you posted is an audio amplifier, and I suspect is is based on the LM380 audio amplifier chip.