Class A B amplifier - a class A amplifier with class B efficiency

7-50 - elektor july/august 1982 Class A amplifiers are well-known in the audio world for their low distor- tion figures and big heat radiation. Manufacturers have always tried to design an amplifier having the advan- tages of class A without the drawback (heat). During the last few years they came up with several solutions. One of them was found by the Japanese manufacturer Matsushita, who developed an ingenious method that makes a 350 W class A amplifier possible without the "heat problems". The amplifier described here follows the same principle, but with one major modification: The output power is reduced considerably, in order to sim- plify the construction. After all this is a "summer circuit" not an "annual circuit". The circuit diagram shows a normal power amplifier at the left-hand side with an output stage consisting of a TDA 1034. The final stage (T1 ... T4) is set in class A mode. The dissi- pation remains low, because the final stage is fed by ± 5 V. However, this s...