Inspired by the MOTU Volta, I wanted to design my own similar system for controlling analog synthesizers, without resorting to a standard MIDI to CV interface. If Volta was already available for Windows, or had I known about Silent Way, I may not even have bothered, but I'm glad I made the effort now as it's been a very satisfying project.
Why not just use a MIDI to CV interface?
- Limited resolution
- No (or few) modulation sources included
- Multiple channels could get expensive, even doing it DIY
- Everyone does that
- I have an audio interface with 24 DC coupled outputs, many of which were unused. Economically, it made sense to take this route as I already had this hardware.
In addition to the software part of the project, I also needed to build a new synth to try it out on, as my Pro-One and the old modular I made at college are both out of action (next project: restore life to these old synths?), plus I wanted to build some new hardware anyway :-)
The Hardware
VCO
- Twin sawtooth oscillators with coarse (+/- 1 octave) and fine (+/- 1 semitone) detune controls
- Bidirectional sync. Sync from OSC A to OSC B or vice versa.
- Squarewave sub oscillator.
- Oscillator mix control.
- One CV in for pitch only. Both oscillators share this common CV input.
- Based on the PAiA Fatman oscillator section with modifications, I put this together on stripboard.
VCF - Dual channel state-variable filter
- 3 signal outputs: 12dB low pass - 12dB band pass - 12dB high pass
- Filter Cutoff Frequency CV input
- Filter Resonance CV input
- 3 signal inputs, summed.
- Circuit designed by MFOS, built using MFOS PCB.
VCA - Dual channel amplifier
- Switchable log / lin response on each channel
- Circuit designed by MFOS, built using MFOS PCB.
L-R: VCO, VCF, VCA
Each module is self contained, and powered from a common external psu, supplying +/-12vdc. Careful thought was given to knob placement, from a performance perspective. The psu also has a gooseneck lamp which can be used to cast light on the synth in dark studios / on stage.
I didn't build any modulators as this is all done by the software!!!The VSTi
I originally did this using Reaktor, but ran into 2 problems:
1. Lack of support for multiple ins and outs when used as a VST. Up to this point I was using Cubase SX3 as my DAW, and just couldn't find a way to route the signals where I wanted them to go. This led me to try out Ableton Live, which had the same shortcomings, although that can do funky stuff like send LFO signals to the outputs, used to great effect by this guy. Then I heard about Reaper, which has an amazingly flexible routing matrix, so I tried that, which led to...
2. Reaktor 5 and Reaper don't seem to work together at all. Reaper would crash as soon as I tried to fire up Reaktor as a VST.
I was getting pretty frustrated at this point, as I'd made a working controller in Reaktor standalone with all kinds of bells and whistles, even a sequencer, but couldn't get it to work in an external application. So I decided to start over using Synthedit. This way would be more work but I'd have a compact VSTi with much less cpu load than using Reaktor.
Building the controller in Synthedit turned out to be much easier than I'd anticipated, having already worked out the high level stuff, I just had to find equivalent modules and figure out the details.
The VSTi interface
The GUI is pretty ugly, although it's sensibly laid out and I'm pleased with the wood effect! (made using Wood Workshop!). At some point I'll get round to making it look nice, possibly abandoning the wood and making it match the hardware.
I was a little dis-hearted when just as I was finishing off the software, I discovered Silent Way by Expert Sleepers which is basically the same thing (a Volta alternative) only much more professional looking, and quite reasonably priced! Still, I've enjoyed doing the software myself even if it isn't the revolutionary product I thought it might be.
I haven't even tried getting this to work in Cubase yet. I'm enjoying using Reaper so much that I'm not sure I want to bother with Cubase ever again, so it's not a priority.
Other hardware modules on the horizon (parts in, circuits designed, just need time):
- Voltage Controlled Wave Shaper
- 24db Voltage Controlled Filter Bank
I'll upload some audio samples later.
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