Just finished a couple of IR3109 filter boards.
It works fine and I basically ‘copypaste’ ordered all items, except audio jacks, from Digikey bom listed in ir3109 page (so it’s now tested also).
I think SMR-4 sound is not so very far from this. Resonance sine wave is smoother in ir3109 and tuning was easier, but I’m not sure if this filter is my favorite in Shruthi…
If someone else is considering building, I spotted some ir3109 chips on eBay: http://global.ebay.com/Roland_IR3109_Filter_IC_-_IR_3109_vintage_synth_parts/290551118244/item
I don’t know the seller, but these chips at least look genuine.