@HAGIWO or anyone: I should know better than to ask questions like this this early in the morning, they tend to have obvious answers after breakfast, but here goes: Is there some reason the pulldown resistor on each input is placed after the series resistor and not before? In that position a voltage divider is formed, reducing the level reaching the pin, which is why on the V/oct input the series resistor has to be lowered and the pulldown resistor raised. But why can’t the pulldown resistor be put first, between the jack and the series resistor?