45 Watt Class B Amplifier Description 4 5W into 8 Ohm - 69W into 4 Ohm Easy to build - No setup required 45 Watt Class B Amplifier 45 Watt Class B Amplifier Description The main design targets for this amplifier were as follows: Output power in the 40 - 70W range Simple circuitry Easy to locate, low cost components Rugged performance No setup These goals were achieved by using a discrete-components op-amp driving a BJT complementary common-emitter output stage into Class B operation. In this way, for small output currents, the output transistors are turned off, and the op-amp provides all of the output current. At higher output currents, the power transistors conduct, and the contribution of the op-amp is limited to approximately 0.7/R11. The quiescent current of the op-amp biases the external transistors, and hence greatly reduces the range of crossover. The idea sprang up from a letter published on Wireless World, December 1982, page 65 written by N. M. Allinson, th...