For the implementation of my MIDI to Voltage Converter I decide me for a Arduino Board and a 12Bit Digital Analog Converter. In this case I use an Arduino Mega 2560 and a MAX525 DAC.
The DAC is controlled via SPI. Beside the DAC there are a Voltage Reference (LT1236), several OP Amp Buffer (LF356 for the Reference and the voltage output) ,a 74HC14 Schmitt Trigger inverter (for a clean triggering of the SPI bus) and a LM7805 linear voltage regulator for the Digital parts and the MIDI board.
The output ranges is 0 to 2V.
Spi to Voltage.pdf
Here a first test.
The detune in the low octave is the result of the 12Bit DAC.