[00940]

I was wondering what is C2 for ? It's a 100uF, 25V cap.

It's coming from here : http://www.redcircuits.com/Page30.htm

 

[jamont]

Isn't it a low-pass filter?

 

[Nisbeth]

An LPF for bandwidth-limiting would be my guess as well though I must admit that 100uF looks a bit big for that

/U.

 

[mjw]

Technically this is a low-pass with a very low cut-off frequency, BUT it is in the negative feedback loop which means the whole circuit behave like a high-pass with the same low cut-off frequency.

Or much simpler:
C2 is used to disconnect the feedback loop for DC. This makes the circuit behave like a DC buffer (gain=1). For AC C2 is nearly a short which configures the circuit gain as R4/R1+1.

HTH,
mjw