The Lithium Analog Chorus is an adaptation of the Electro-Harmonix Small Stone chorus pedal, originally released in 1979 and produced up until Electro-Harmonix closed down in 1983. It was a more compact alternative to the Clone Theory, in the same way that the Small Stone was a reduced-footprint successor to the Bad Stone.
The Small Clone was most famously used by Kurt Cobain on “Come As You Are” as well as several other tracks on Nevermind. It has also been used by Jonny Greenwood, The Edge and several others.
The original circuit had two different variants, one using the extremely rare SAD1024 and the other using the MN3007. It’s commonly thought that the SAD1024 version came first and the MN3007 replaced it—and the factory schematic would seem to support this, showing SAD1024 as the default and then including the MN3007 changes as a modification. However, based on date codes of production units, the SAD1024 wasn’t seen until 1981 or possibly late 1980, while the MN3007 was used throughout the whole production run. Whatever the case, the MN3007 variant is far more common.
While it’s often said that Kurt used the SAD1024 version, there is no definitive proof of this that we have seen. It’s statistically much more likely that his was the MN3007 one.
The Small Clone was reissued in the early 2000s, still using the MN3007 BBD but with a few small circuit changes that cause it to sound different. The overall schematic is pretty well identical, though, so the reissues can be easily modified to vintage specs.
The Lithium is an expanded adaptation of the MN3007 Small Clone, with the addition of a Depth control (converted from a switch) and a Mix control. If you want to read more on the changes, the build notes are extensive, so there are plenty of details for the curious.