[sdiy] MIDI-CV retrofit

[rsdio at sounds.wa.com]

One possibility is to use the local keyboard to transpose incoming  
MIDI, which would be particularly interesting for arpeggio or  
sequencing. Here I'm thinking of the Sequential Circuits Pro-One,  
which does not deactivate the keyboard when either of the two  
sequences is playing, but rather allows the sequences to be  
transposed up (or down?). This works because the Pro-One keyboard is  
scanned by a microprocessor, allowing the firmware to combine the two  
sources intelligently.

In other words, you don't really need a switch. There's no reason to  
allow only one at a time.

I realize that it's possible you may not have a scanned keyboard, but  
might have a priority-encoded monophonic keyboard. Personally, I  
would design a synth so that the MIDI and keyboard scanning were  
handled by the same processor, and then MIDI commands, System  
Exclusive if necessary, could be used to select between multiple modes.

You'll probably need a Sample-and-Hold, though, because the VCO  
should not change pitch on Gate off, but should hold the old pitch  
until the next Gate on. Then you can let non-overlapping Gates select  
which source is in control, only mixing the CV when Gate turns on  
from a source before Gate turns off from another source. The logic  
could be a little tricky for a pure analog circuit, which is why I'm  
thinking it would be easier with a CPU to handle MIDI-to-CV and  
keyboard scanning as well as mixing the multiple sources. This  
implies an OR of the Gates.

Brian Willoughby
Sound Consulting


On Sep 17, 2013, at 00:03, GGG wrote:
> Dear collegues,
> 	I need the expert advice! I'm about to add MIDI2CV conventer to my
> DIY synth that, as most analogue synths, has CV and Gate controll.
> 	I built several desktop synths without a keyboard, where I used
> external CV and Gate jacks with normaling switch lugs - when no  
> external CV
> or Gate is plugged in, CV and Gate from MIDI2CV conventer is routed  
> to VCO
> and ADSR correspondingly. When I plug in CV and Gate form analoue  
> sequencer,
> MIDI gets disconnected. That is easy.
> 	But with built in keyboard things are getting more complicated -
> external CV and Gate jacks with switching lugs now disconnect CV  
> and Gate
> from the keyboard. So I added a switch that allows me to switch  
> between
> external CV/Gate and CV/Gate from MIDI conventer.
>
> 	But I wonder, if there is some more advanced solution to select
> between controll sources, preferably automatically. I mean - when a  
> MIDI
> signal appears a device automatically switches to CV and Gate form  
> MIDI
> conventer and ignores signals from the keyboard. For CV I  
> considered a DC
> mixer - I just mix a CV from Keyboard, External CV and CV form MIDI
> conventer. But how to manage Gates? Maybe someone has got across  
> similar
> case and can advice me a solution.
>
> Girts