Progress…
Long time no post. Sorry, real-life is sometimes getting in the way ;)
Recently I bought a Leaflabs Maple R5 to replace my Arduino’s. I really like it. Eventually I ported ChibiOS (realtime OS) to it and tried some software filter algorithms from musicdsp.org. Didn’t make me happy; 72Mhz isn’t enough to do serious audio filtering (at least not using my prototype coding).
New plan: use the Maple for the VCO’s (kind of DCO). Number of voices to be determined. Anti-aliasing virtual analog oscillator code will be constructed using research by Valimaki and Huovilainen. The first hardware voltage controlled versions of the VCF(s) and VCA(s) will be based on my own research regarding the VCF/VCA filter chip in the Roland Juno series. These original Roland chips last usually 15 to 20 years. Right now I’m working on a to be open sourced hardware version of these filterchips. The VCA part is solved using a BA6110 voltage controlled opamp. These aren’t in production anymore (as I know of) but easily obtainable via ebay. I used mooger5’s very valuable research to construct a BA6110 based VCA. His solution (using an SSM2044 for the VCF part):
mooger5, http://www.electro-music.com/forum/topic-17995-25.html, 15 march 2011
The VCA part like drawn by mooger5 is working perfectly! In the next few weeks (busy, busy) I’m going to start working on a VCF part using the LM13700 OTA. Fingers crossed! Resources are the great courses of Aaron Lanterman (Georgia Tech) and, ofcourse, the 80017 VCF/VCA teardown from obsoletetechnology. When the VCF part is working, my plan is to replace the BA6110 with, probably, a LM13700 OTA. This solution will be the base on which I’ll build my own hardware filter and amplifier.
To be continued!