The Asteria Preamp Drive Mk. III is an adaptation of the Catalinbread® Formula 55, based on the Fender 5E3 Tweed Deluxe amplifiers from the 1950s. It was originally released in 2017, the third version of the original Formula No. 5, but different enough that they changed the name.
The Formula 55 replicates the quirks of the original Deluxe amp, including a tone control whose effect diminishes as the gain is turned up, with almost no change across the sweep at maximum drive. While the original amp only had Gain and Tone knobs, this circuit adds a master volume, Presence control, and a toggle switch to increase the gain.
Like several other Catalinbread pedals, this circuit blurs the line between a preamp and an overdrive. Like a true preamplifier, it’s very reactive to what comes before it, so it’s best placed after other drive pedals but before modulation. However, it also generates more than enough drive on its own and can be used as a standalone overdrive pedal just like any other.
The original Formula 55 used MPF4393 JFETs, which are no longer produced. Aion FX carries the original MPF4393 in sets of 5. The PCB also has an extra pad so that surface-mount JFETs can be used (part number MMBF4393), which are still in production and perform identically to those used in Catalinbread pedals. See build notes for more details.
The Asteria Mk. III is compatible with the 18V Voltage Doubler / Bypass module if you want to run the circuit at 18V without an external adapter. The higher voltage provides increased volume and clarity.