Shure 55S Unidyne Dynamic Microphone

The Unidyne Model 55, introduced in 1939 by the Shure Brothers Company was the world’s first single-element dynamic cardioid microphone, a significant innovation. The modified 55S model appeared in 1951, still fitted with an impedance selection switch. The ‘S’ indicated the use of the new ‘small unidyne’ capsule. 

The stars of rock and roll, Chuck Berry, Little Richard, Elvis Presley and Bill Haley used the Shure 55S.

The Model 55S is a multi-impedance type. He may be connected directly to a 30-50 ohm line, a 150-250 ohm line or high impedance input. The selection happens through the change of the position of the switch at the rear, marked as "L" for low impedance (30-50 ohms), "M" for medium impedance (150-250 ohms) and "H" for high impedance (35.000 ohms).