giuliomoro to be able to route it at the same time to R23 and the jack's normalled contact.
but that's not what you're doing, as far as i understood it? might be wrong though, but that scenario doesn't seem to happen in either of the modes?
if it were the case that you ever make both those connections simultaneously (= J20 installed AND J12 1+2 installed), that uses up both jumpers, so that would leave J12 pin3 floating - meaning the input jack (or its switched contact) doesn't go anywhere. making the J20 connection redundant.
unless you were to introduce a third jumper, which then connects the jack to R15, which would put the steady Voltage on a digital input that already is kept steady by the R2 pulldown?
again, correct me if i'm wrong.
i thought that in the analog mode:
- voltage select output routes to the jack switch (J20)
- either that or whatever is plugged into the jack routes to the pot (J12, pins 2+3)
J12, pins 1 and 4 are unused, aka digital input is unavailable on the front panel.
and in digital mode:
- voltage select output connects to the pot (J12, pins 1+2) for standalone use
- input jack (with nothing on its switch) connects to R15 (J12, pins 3+4). no need for the switched contact, because of R2.
that would mean that Voltage Select goes to either jack switch or R23 - not both.
and jack tip goes to either R23 or R15.
therefore you could have a 5 pin header. say you added J12 pin0 at the bottom for the jack switch.
analog mode is (pins0,1) and (pins2,3). digital mode is (pins1,2) and (pins3,4) as it is now.
totally academic, obviously