Good point about the DAC's - I'll take a look in all the DAC
databooks.
Regarding exponential CV's - this is a long-standing debate - well in
a nutshell the reason is that if you take a CV and run it into the
inputs of two linear VCO's in parallel, if you set them to the same
frequency they will be modulated identically ("track" in tune) no
matter what value the CV is. But, if you set them to an interval, like
a fifth, and change the CV, they will no longer track and go out of
diatonic tune with each other. So you need a dedicated CV for each
linear VCO if you want them to track each other, whereas you could
control the frequency of a dozen VCO's from one CV and they will
always track each other perfectly (or at least within some small
margin).
But linear VCO's are so much cheaper. But exponential VCO's have a CV
sweep range of a thousand times the range of a linear VCO. But linear
VCO's are temperature-stable without exotic components. But
exponential VCO's follow the natural musical frequency doubling for
octaves. The arguments go on...
Probably the biggest reason to build MIDI-CV converters that have
linear voltage outputs (for controlling exponential VCO's) is that
there are so many exponential synthesizers laying around to control.
- Gene
gstopp at fibermux.com
______________________________ Reply Separator _________________________________
Subject: RE: MIDI-CV converters (was: Building my first synth...)
Author: "Mikko H." <MHELIN at tne01.tele.nokia.fi> at ccrelayout
Date: 2/6/96 6:12 AM
How about serial D/A convertor on printer port, there are some 4 channel
12 bit DACs made by Analog Devices (and even octal ones), but it will be
cheaper and better to use single DAC with analog switches and S/H's.
Optoisolators between parallel port and DAC thing would reduce noise and
help with grounding problems. Paia Fatman uses voltage dividers and multiplexor
to select an octave and the DAC08 for the notes inside octave, but it generates
exponential CV for linear CV inputs.
Btw. I haven't ever understood why exponential CV inputs are so important,
what is the point, as CV's are now mostly generated by computers. Is it
so difficult to build an analog exponential EG, or what is the reason?
-Mikko