Precision adder/transposer (2HP)
T43 by Vladimir Pantelic.
Precision CV adder and switchable transposer, inspired by vpme's T43 (note that these modules are similar only in name and function, the internal design is entirely my own).
The bottom two inputs are summed into the output. Additionally, switches set the direction (negative, none, or positive) whereby input 1 and offsets of one, two, four, twelve, or twenty-four semitones are summed into the output as well. Together these switches can transpose a pitch CV signal across 43 semitones up or down.
This module uses high-precision op-amps (250 µV or 0.3 cent typical offset) and an extremely stable voltage reference (0.05% accuracy, 3 ppm/°C)
to produce pitch-perfect CV with no need for any calibration.
(oh, I would highly recommend using 0.1% or tightly-matched resistors)
The footprint for the voltage reference has only 6 pads for a SOIC-8 package, this is not a mistake.