https://shop.frontpanels.de/Bus-Compressor-PCB_1
Igor Kapelevic's great bus compressor project for the 500 series. Meter, front panel, PCB... All the important parts are available for a few peanuts directly from Frank. The other parts can be found at Mouser, Digi... Already included 4K and Gyraf's GSSL compression modes, and all "super" sidechain filters. Very good piece.