Pro Series heads feature single or multi-tube preamps, five position mid frequency selection, and Neutrik Speak-On(r) connectors that lock and provide better conductivity. A Mute button lets you change instruments in the middle of a set without the annoying 'pop,' and a Tuner Out jack that stays active even with Mute button on. Pro Series heads are built for the long haul. The units remain cool with variable speed fans that only turn as the temperature dictates. DC supplied filaments ensure noise-free tube performance. And the 1/8' thick extruded aluminum front panels not only allow safe racking, the contoured fronts have an awesome look.