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!