Push-Pull Power Amplifier design (High Voltage) with Op Amp and Darlington Transistors

A high-voltage Push Pull power amplifier circuit with current limiter is analyzed in this video. This power amplifier is design with one Op Amp, NPN and PNP Darlington BJT Transistor pairs and Zener Diodes. How much this circuit amplify the input signal? What is the maximum output current of this power amplifier? How does this circuit achieve both substantial voltage and power gains? For more examples including regulator circuits see    • Electrical Engineering, Analog, Digit...  
The Zener Diodes in this circuit control the positive and negative supply voltages for the operational amplifier. The Op Amp stage is properly wired to have negative feedback. The overall input to output of this circuit has a negative gain to indicate a proper negative feedback in this circuit. There are two stages in this class AB amplifier by biasing both Darlington transistor pairs via chain of four diodes so they conduct when the signal is close to zero. This helps with avoiding voltage dead zones during zero crossing of the output voltage (to minimize distortion) due to limited slew rate of the op amp. The small output resistors define the maximum allowed output current of the power amplifier and also limit the quiescent current of Darlington Transistors when output is near zero or shorted. The input-output voltage transfer function of this high voltage Push-Pull Power Amplifier is derived and then analyzed to show the overall gain and also the frequency range of operation for this amplifier.