then matched to achieve the same front/rear response. 1960s In 1964 Neumann developed a small cardioid capsule with considerably improved off-axis linearity; it was used in the KM 64 and U 64 microphones. 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. In 1966 Neumann adapted the "phantom powering" method that had been used for years in certain telephone systems, so that a compatible method of powering would allow tube microphones, solid-state microphones and dynamic microphones all to be connected to the same power supplies. Eventually the "fet 80" series grew to include over a dozen models, some of which are still in production as of 2018—the U 87, U 89, KMR 81, KMR 82 and USM 69. The best-known models from this series were the KM 84 small diaphragm cardioid and the U 87 three-pattern, large diaphragm successor to the U 67. 1980s and after In 1983 Neumann began to introduce microphones with balanced outputs but no output transformer, starting with the model TLM 170. Eventually this "fet 100" or "transformerless" series was expanded to include the KM 100 modular series of small microphones (with seven different "active capsules" for various directional patterns), the cardioid TLM 193 (using the capsule of the U 89 and TLM 170), the small-diaphragm KM 180 series, the large-diaphragm cardioid TLM 103, the variable-pattern TLM 127 and the TLM 49 cardioid vocal microphone. Beginning in 1995 the company introduced a series of vacuum tube microphones with transformerless output circuitry: the multi-pattern M 149 Tube, the cardioid M 147 Tube, and the omnidirectional M 150 Tube (based on the classic M 50 design, with the pressure transducer mounted in the surface of a sphere inside the capsule head). In 2003 Neumann introduced their first microphone with built-in analog-to-digital conversion, the Solution-D D-01. In 2006, the D-01 was followed with a modular, small-diaphragm series