I want to build this electric guitar output to phone mic input converter:
From my limited knowledge on the subject, it looks like a simple JFET preamplifier (actually, I've simulated the circuit in LT Spice and it seems to attenuate the signal, not amplify), but I do not understand the role of the 100pF (gate to ground) and 470 pF (drain to ground) capacitors, are they used for some kind of filtering of the signal ? Will it work without them ?
The circuit I used for simulation in LT Spice is:
(the parts in the red rectangle should be the circuity inside the phone, I used the reference circuitry for soundblaster mic input thinking the phone has something similar inside)
So, my question is: what is the role of C2 and C3 ?