op amp

I am working on detecting fingers being placed on guitar frets. My idea is to run a small voltage through each of the strings, a different voltage for each string. The player touches the string and makes the string touch the fret. On the end of the fret I detect the voltage with a...

http://www.generalguitargadgets.com/pdf/ggg_dist_plus_sc.pdf I'm looking to understand this schematic. Currently focussing on the input and power stages. Here's where I'm at: INPUT R1 is a pulldown resistor. It provides a path for the leakage current through C2 when the switch is in the...