With this new version, Catalinbread added a Bias control which gives you a little more gain and body from the stock circuit by simulating out-of-spec parts in the preamp core. They played with the early" and "later" circuits and found the differences to be a bit too subtle, so they decided to add a well-curated filter knob to take you from early to later and beyond, a tasteful hi-cut that lets you adapt the pedal to your rig. The Preamp control lets you engage a gentle filtering circuit that simulates the Volume control from the original Echoplex, acting on the tone as the echo would have. The stock EP-3 circuit adds only a trivial amount of gain by itself, so Catalinbread have included a Boost knob to wring as much gain from it as possible, giving you a real punch where you need it. Controls "¢ Preamp: Wet/Dry mix control but because there's no echo here, it sounds like a volume control until noon, then it imparts some subtle frequency enhancement, on account of the loading simulation circuit. "¢ Boost: Adds extra gain and volume to the circuit. All the way down simulates the stock EP-3 circuit. "¢ Bias: Think of it as a gain control and a body enhancer. Light crackling noises are normal. "¢ Filter: Gentle hi-cut filter for a more refined, bluesier tone."