This audio amplifier design approach employs TMOS Power FETs operating in a complementary common- source configuration. They are biased to cutoff, then turn on very quickly when a signal is applied. The advantage of this approach is that the output stage is very stable from a thermal point of view. U1 is a high slew-rate amp that drives Q3, Q4,and Q6 (operating class AB) providing level transition for the output stage consisting of Q7, QS, Q9,and QlO.
50W-audio-power-amplifier - schematic

The positive temperature coefficient of the TMOS device enables parallel operation of Q7, QS, and Q9 and provides a higher power complementary device for QlO. These TMOS Power FETs must be driven from a low-source impedance of 100 0, in order to actually obtain high turn-on speeds.

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