Jazzyvee, in response to your inquiry, " PLUTO FILTERS" were George Mundy's version of " State Variable Filters " in design application for musical instrument use, of which The Alembic Superfilter SF- 2 design, has always reigned as the most musical and useful in my opinion. George Mundy had potted in epoxy Pluto Filters installed in my bass. He also built a pedal version with a dual direction potentiometer foot controller that he let me try as well to purchase, which I did not do at the time.