AR3109: exact replacement for the IR3109 IC

Introduction

Upcoming AR3109. An exact sounding replacement for the since long obsolete Roland IR3109. Used in SH101, MC202, Jupiter4/Promars (late version), Jupiter 6, Jupiter 8, Juno 6, Juno 60, JX3P, MKS80 (early version) and maybe others.

Been working on this one for a few years now and it's almost finished.

Sound is already spot on. Expect the same level of accuracy as my latest AR80017A's. Inaudible and impossible to measure any differences in the 20-20KHz range.

However, I still see a small dip in the resonance response around 30KHz. Outside of the audible range, but some of it gets reflected back in that range by modulation with other voices in the polysynths and the clocking of the chorus in the juno's. Now working on some extra phase compensation that should get rid of this.

Power consumption is also still a bit on the high side atm. Final version will consume a lot less. This for not stressing the power supplies when you replace all of them in the polysynths and to save batteries in the portable ones.

Also, for the above battery-powered synths, special care was taken that the sound still matches on these lower supply voltages. Even when the batteries run flat.

DC accuracy is on the same level as the IR3109, this is needed in the Jupiter 4 where besides VCF usage, it also generates the portomento.

Making this one small enough, to fit in all synths that use it, sure was an exercise in compactness: 6-layer pcb with buried parallel plate capacitors was needed to fit everything on 2cm²