I don't know if the Due can output exactly 1.2345 VDC. However, since it's DAC has 12-bit resolution that means there are 4,096 distinct voltage levels it can output between 0 and 3.3 VDC. So even if it cant output that specific value it can get very close
That is good enough, it doesn't need to be very close. From the early description of the DAC I thought this might only output a wave, for example, a smooth wave between 0 and 1.2345 V at a specific frequency.
Or you could use an op-amp based non-inverting amplifier with a voltage gain of about 3.85
Can you tell me more about this? I am a software guy. I see some very cheap op-amps online, but they all have much larger voltage gains. Also, why 3.85? 3.3V (or 5V) + 3.85V is less than 10V