The Zircon Silicon Fuzz is a version of the “Hot Silicon” community project, itself an adaptation of the Sola Sound Tone Bender for silicon transistors.
The history of this circuit is a bit suspect, with two people claiming originality. It dates to 2003 at the very latest when Doug Hammond posted a schematic for a circuit he called the Hot Silicon, which was a hybrid of two earlier circuits from Gus Smalley and Aron Nelson.
However, an almost identical circuit was posted by Mictester in 2009 on freestompboxes.org, and he claimed he first developed it in the 1970s when he was trying to make a friend’s silicon Tone Bender from Macari’s (Sola Sound) sound good, and then tweaked the circuit over the following decades until arriving at the finalized version in 1994. (Sola Sound did make a very small number of Tone Bender Mk III’s with silicon transistors—these are different than the Jumbo Tone Bender which was basically a Big Muff clone.)
Maybe it was just parallel development that arrived at the same outcome. Regardless of true origin, though, the Hot Silicon (or Silicon Tone Bender) is a fantastic circuit that has endured as a classic in the DIY scene for many years.
The Zircon is a near-direct adaptation of the Hot Silicon circuit, with one change: the input capacitor switch (called “Fat” in the original schematic) has been changed to a potentiometer so it can be gradually blended in or out rather than being either full-on or full-off.