Spring reverb simulator based on the legendary Fender 6G15 outboard spring reverb unit, typical of surf guitar and other great guitar sounds from the sixties. Part of its magic, and how it differs from the internal spring reverb found in most Fender-style amps, is that it is run *in front* of the amp, causing the reverb signal to distort and get more intense than the internal circuit could. It also had a Dwell knob, which controlled how hard the springs were getting hit by the guitar signal. It was also essentially a tube preamp, so it would color the sound going into the amp. All this added up to a very distinctive reverb sound that is hard to replicate. There's also a great discrete preamp that you can control via the Volume knob for a healthy amount of great clean boost when you want it.