The Gaia Preamp Drive is an adaptation of the Catalinbread Galileo, their pedal emulation of treble-boosted Vox® AC30 tone made famous by Brian May of Queen.
The Galileo is essentially a combination of two other Catalinbread pedals, the Naga Viper (a hot-rodded silicon Rangemaster treble booster) and the CB30, their take on the AC30. In fact, the first version of the Galileo was just these two circuits in the same enclosure with separate controls and footswitches for both circuits.
The second version of the Galileo was a complete redesign, taking the same basic building blocks of a treble booster + amp-style overdrive, but reducing it down to 3 knobs: treble booster gain (just called Gain), tonestack treble (just called Tone), and master volume. The amp section’s gain control and bass knob are internally fixed. This 3-knob Galileo is the version that this project is adapted from.
The original 3-knob Galileo used MPF4393 JFETs, which are no longer produced. Aion FX sells 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 project documentation for more details.
The Gaia Mk. II 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.
Note: There is not currently a Gaia Mk. I project available, but a project based on the CB30 is underway and will have this name once it is released.