The Ephemeris JFET Booster is based on the Xotic EP Booster, a one-knob boost first released in 2009 that is loosely based on the preamp section of the Echoplex EP-3 tape delay. There have been some minor changes to the circuit throughout production, but we traced one in 2023 to ensure that we had the most accurate version.
In addition to the gain knob, the original EP Booster also has a DIP switch on the inside with two additional settings. In the stock circuit, the minimum gain setting is +3dB above unity. One of the DIP switch settings adds a resistor at the output that essentially just turns down the volume and makes the minimum position unity gain instead. The second mode disables a treble-cut filter. This could be called a treble boost, but in practice it provides something more like a flat response while the stock mode has a slight cut above 3.2kHz for a vintage-sounding warmth.
The Ephemeris moves the treble cut to a front-panel control, and replaces the fixed resistors at the output with a true volume control. The gain and volume controls are somewhat redundant, but at high gain levels it’s possible to get the second transistor to clip, so different combinations of gain & volume can yield different tones. You can still dial back to unity gain as well, so the pedal can be used as a tone enhancer or buffer.
We have also ported the “Bass” switch from the earlier version of the EP Booster, and added a third position which cuts bass a bit, inspired by the original EP-3 preamp. More on this in the build notes.