The Nexus Distortion/Sustainer is based on the Catalinbread Manx Loaghtan, a mouthful of a pedal whose name is taken from a British breed of sheep native to the Isle of Man. This, of course, is a reference to the Big Muff and more specifically the Ram’s Head.
As expected, the Manx Loaghtan shares a lot in common with the classic Big Muff topology, but with two notable changes that make it stand out.
First, the tone control has been replaced with a passive Baxandall tone control (also called a James tone stack) allowing independent adjustment of bass and treble frequencies. With the right settings, you can get a very close approximation of the mid-scoops of several different Muff variants, or you can come up with something entirely your own.
Second, a JFET-based gain recovery has been added to help counteract the ~20dB signal loss of the tone stack. This JFET stage is placed between the tone control and the stock Big Muff recovery stage (Q5 in this project).