The Emerald Resonant Phaser is based on the BOSS® PH-1r Phaser, a four-stage JFET phaser first released in 1980. The PH-1r is itself a slightly updated version of the PH-1, which was one of the first three BOSS pedals released in 1977 alongside the OD-1 OverDrive and SP-1 Spectrum.
The PH-1r changed the PH-1 circuit enough to warrant a new name, but not a full version number increase. The “r” stands for Resonance, also called “regen” in other similar circuits, which mixes some of the phased output back to an earlier stage, increasing the midrange resonance and providing a much more colorful effect. With the resonance control turned down, it is very similar to the original PH-1, but it adds another dimension to the tonal palette.
The Emerald is an adaptation of the PH-1r, converting it to true bypass and adding a volume control so that it can be adjusted to match unity gain regardless of setting. Other than these changes, it’s an exact replica of the original pedal.
The PH-1r uses four matched 2SK30A-GR JFETs for the phase stages. These are similar to the 2N5457, but not identical. For convenience, Aion FX offers matched 2SK208-GR JFETs, which are the SMD version of the 2SK30A and are still in production. They are pre-soldered to through-hole adapter PCBs so they can be used with no SMD experience.