Here's what I have built on breadboard so far: http://www.oldcrows.net/~jhaible/matrix_fx/jh_quad_vco.pdf Ian's saw core, modified with 3 BF256C's, two waveshapers for two triangle waves that are 90 deg apart EMS style diode waveshaper - good for low k2 and k3, needs tracking filters to get rid of higher harmonics and glitches. JH.