In 1965 Neumann began to introduce solid-state microphones. The first model was the KTM small cardioid, later followed by the "fet 70" series—transistorized versions of small omnidirectional, cardioid and speech cardioid microphones as well as a "U 77" transistorized version of the U 67. This series used the 12-volt A-B powering system (parallel powering, T-power or "Tonaderspeisung") as found in Nagra tape recorders, and was therefore incompatible with existing studio power supplies. However, standard two-conductor shielded cables (as were commonly used for dynamic microphones) could now be used for connecting condenser microphones as well, obviating the need for special multi-conductor cables.