Jim Marshall, who helped define the sound of rock and roll with the iconic amps he designed, succumbed to cancer and a series of major strokes in a hospice in England Thursday at the age of 88.  Marshall's name was well known throughout the music world as the amps produced by the company named after him have been favored by top performing musicians since the 1960s.  Because of the prevalence of Marshall amps across all types of music, Marshall is a name known by fans as well as artists because the amps can be seen behind almsot every major musician in images captured during concerts.