The EchoPlex Preamp emulates the input stage on the old EchoPlex EP-3. It provides up to 11dB of gain and is mostly used as an always on pedal to sweeten the user's tone. If you want to add the volume control, use a 500k pot and connect lug 1 at the junction of the 100n cap, 220k and 100k resistors, and run lug 2 to ground. This also works really well when running at 18v. Schematic for reference can be found here.