DiMarzio DP301 Relentless J Bridge Pickup (Nickel Cover)DiMarzio introduced the world's first Fender Jazz bass replacement pickups at the NAMM show of 1977. DiMarzio invented the dual bar ceramic magnet structure for extra power and included twin hum cancelling coils for decreased noise. The DiMarzio Model J is 50 percent quieter than the original Fender Jazz bass single coil pickups, and it's 60 percent louder. DiMarzio also added adjustable pole pieces to improve the string balance and designed them in