MIDI-CV converters (was: Building my first synth...)

Colin Fraser colinf at easter.euro.csg.mot.com
Tue Feb 6 09:40:14 CET 1996

On Feb 5, 10:07am, gstopp at fibermux.com wrote:
> Subject: MIDI-CV converters (was: Building my first synth...)
>      The thing that is most intimidating about a home-brew MIDI-to-CV
>      converter is the fact that you need a development system for uP
>      designs. .... etc. etc...

I built my own CV convertor originally as an add-on for a BBC Micro - a 6502
based eighties home computer. The software was written using the assembler
functions of BBC BASIC.
After the code was fully developed I built a separate processor board and blew
an eprom with the code slightly modified to suit its new home, then fitted the
whole thing into a 3u rack mount case.

It has 32 CV outputs, which can be configured as note, velocity, controller and
gate outputs, and also to control a stereo VCA - there is an eight channel
mixer hardwired to 16 outputs (as the two channel volumes are calculated by
computer from the midi volume and pan controls, its easy to make the panning
follow a true sine/cosine function).

The outputs are demuxed from a single 8 bit dac, thru' 4 4051's. Gate signals
are output from the same outputs as cv's to allow soft gate voltages (5 or
15v). 4 channels also have 303 type portamento circuits, switchable between
off, on and auto. There is also a din sync output that drives my 303 and 606.

I'm currently trying to get the source software from 40 track, 100K, 5.25" disc
onto a slightly more modern machine, so I can mail it to another list member.
If anyone else is interested in this, send me a mail.
I was going to produce schematics for it a while back, but never found a
package that made it easy enough...




Colin Fraser

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