there’ s an easy way to find IR 3109s : into defective 80017A ( JUNO 106 infamous VCA/VCF chip which are prone to die because of their coating which become conductive over time) harvest dead JUNO 106 chips from owners who are replacing " dead voices " ( virtually every JUNO106 owner ) them by clones : easyly 75 to 90 % of them can be saved by dissolving the coating by soaking them into acetone for 24 hours then open the chip with small pliers . you l’ see a IR3109 fixed on a small PCB and a BA662 ( very sought after too ) VCA roland custom chips next to it , . you can find the video of the whole operation on youtube. just google " 80017A repair technique "
there’ s also the possibility of using 80017A or clones on a “playground filter board” assuming it works a bit like a cem 3379 , maybe the cem filter board could be adapted to them.
Hey people, don’t go crazy over the IR3109s please. It’s just four OTAs and an exponential converter on the same die. It’s really just that, and this is why some smart people have created near perfect clones of the Juno “chips” with just vanilla transistors and LM13700s.
My recommendation would be to grab the SMR4 mkII schematics on github, and change the resistor and capacitor values to match those of the IR3109 filter board (you’ll probably have to tweak a bit the expo converter too).
The IR3109’s and BA662’s found in the 106 that you mention are actually smaller, surface mount versions. So unless you are going to make some kind of adapter for them, they won’t fit. Plus they would be very difficult to desolder too…
1 or 2 synth parts dealers stock pulled (used) IR3109’s. Or you can just do as I did, and remove them from Boss PH-2 phaser pedals. They can be found cheap, used. And there are 2 IR3109’s in each. No BA662’s, but they do have some other potentially useful parts in there
That is currently the best way I know of to get them…