 It was also available as a head (a standalone amplifier), which could be hooked up to a number of different speaker combinations, although a 1x12" cabinet was the most common.The preamp gain on the Mark IIs occurs after the tone controls and so, according to Mesa/Boogie, the IIA has a "tighter, more focused sound" than the Mark I.The Mark IIA's control panel was extended from the Mark I's to include a separate master volume control for the lead mode, and various push/pull switches including Pull Bright, Pull Treble Shift, Pull Gain Boost, a separate Pull Bright for the lead mode, and of course, Pull Lead.