The Alembic F-1X is the mono version of the F-2B preamp. Alembic kept the same tone section and added a few goodies like a direct output, built in effects loop and crossover. You can still use it in a simple set up since the F-1X also includes a standard full range output.
Tube warmth??? It’s in there, and with an easy interface of Bass, Mid, Treble, you’ll be hard pressed to make an undesireable sound. Maybe that’s why Bass Player Magazine gave the F-1X its highest rating!!