DIY version of Mutable Instruments CV PAL
Mutable Instruments’ CVpal is a USB MIDI to CV interface – enabling you to control an analog synthesizer or modular system from a computer or smartphone/tablet equipped with a USB port. The CVpal is class-compliant and as such, does not require any driver. It features various conversion/voice allocation modes, covering monophonic, duophonic and drums/triggers applications.
Quirks ahoy! Before moving forward, it is important to state some limitations of the CVpal – most of them due to its ridiculously simple design:
The CVpal is a USB device not a USB host! It can be connected to ‘active’ devices such as smartphones, tablets, laptop or desktop computers, but not to USB MIDI controllers. The CV output is in the 0 .. 4V range – so a tessitura of 4 octaves is covered. The CVpal does not support V/Hz conversion; only V/Oct.
The Gate output uses V-trig, has a 5V high level, and a direct polarity (note on = 5V, note off = 0V). Most Eurorack modules use a trigger level below 2.5V and can thus be triggered by the CVpal. If a module or synth requires a higher level, a level conversion circuit such as the CD4504 can be used. Polarity inversion can be implement with a CD4049 or with a software hack. S-trig conversion can be implement with a few parts. The CVpal works optimally with iOS, OS X >= 10.6.3 or Linux kernel >= 2.6. On other operating systems, the messages might be delayed by up to 8ms, causing a very jittery timing!
INSTALLATION The CVpal can either be mounted in a Eurorack system, or used as a standalone box. In both cases, it does not need any external power source as it is powered by the USB bus.
ABOUT CONVERSION MODES The CVpal interprets MIDI messages differently depending on the MIDI channel on which they are received. For example, when receiving messages on MIDI channel 1, it behaves like a monophonic synthesizer and outputs a CV/Gate pair. When receiving messages on MIDI channel 10, it behaves instead like a drum trigger converter and outputs a trigger for 4 drum instruments.