The earlier MC500s (like the one in the OP) have the tri-sound pickups and the active EQ/boost functions. Later MC500s added a master tone control. To me, these early ones without the master tone were probably intended to be used with the active EQ in place of the tone control. 
The MC150 has split-able pickups, with 2 volume & 2 tone controls. These have a great feel to them and I find I prefer their simplicity & lighter weight compared to the MC500. YMMVStatistics: Posted by A Knight of NI — Tue Jun 26, 2012 11:32 am
]]>