Hi,
I hope, details and schematic diagrams from attached file (polyphonic2.png),
will help you to understand my project.
Referring to anterior schematic diagram (poliphonic.png), you understood correctly, the four top middle diagrams are wired like the top left (identically),
but using the resistor values mentioned (for tuning).
P1 and P2 are adjustable resistors and they are used for instrument tuning.
The resistors seried-connected with P1 and P2 are Very important too and serve the same scope. Please read again, what Dr.EM wrote in one of his posts: "For tuning, its probably best to tune it roughtly with a potentiometer, measure its resistance, then place a resistor a little under that value in the circuit with a small trimmer in series for fine tuning/adjustments",or respect the values mentioned by me and use 10Kohms trimmmpots(It is better to use the method described by Dr.EM).
You cannot hook a speaker directly to the output of the mentioned schematic diagram, you need to use a small audio amplifier; see the new attached schematic, which is a suggested testing arrangement.
Don't worry about the number of components, you can make only one PCB from the new schematic and test it. If everything is ok and you like the produced sounds, then you can make identical PCBs for as much tones as you need or wish.
In this project, all the sound generators are working permanently but only desired tones go to the outputs, depending on the pressed keys.
The laser commutation of signals represents the second stage of the project, and we will discuss it after you finnish first parts wich consists in the tone generating module and tuning of the instrument.