As per pigtronix's site: Class A Boost will fatten up and boost anything you feed it. This deceptively simple design uses discreet J-FET transistors in a single-ended “Class A” configuration to achieve the warmest possible tone. Class A Boost can deliver up to 20db of clean boost and remains effective with both instrument and line level signals. Superior signal to noise performance allows you to put the Class A Boost anywhere in your pedal chain. It can add punch and extra output to a classic overdrive sound and is able to push distortion pedals into extremely aggressive crunch land. Class A Boost is also ideal for hitting the front end of a tube amp to achieve an added layer of sweetness.