Here's a big one, and just so happens to be the 700th layout on the blog 😎—the OKKO Dominator distortion. It's a couple of JFETs pushing an opamp with active EQ, with a charge pump. Originals use a switch to select the range of the mids control, but it's easy to swap out for a pot. Schematic can be found here on FSB for reference. Easy fit in a 1590BB.