|The Digital-Analog-Converter fetches one of 15 parallelly pressed keyboard keys from the digital bus of the synthesizer and converts it into a control voltage (1V/Octave) and a GATE signal.
The TUNE-COARSE and TUNE-FINE pots allow pitch adjustment of the voice the DAC is responsible for in polyphonic environment. The portamento pot creates a pitch slide from one key touch to the next.
The analog part of the circuit comes from the book "Formant Pro MSS 2000" by H.J. Helmstedt, but I built only a part from it, as I don't use wheels or key velocity. I developed the digital part of the circuit which reads the digital bus and makes the voice selection. Schematic:
Update 11.01.2005: This DAC is not in use anymore. Please see Simple MIDI Keyboard and Universal Control Voltage Module