This circuit demonstrates the power of feedback.
Feedback (closed loop) has a lot of advantages over open loop. The left amplifier is open loop, while the second amplifier is closed loop. Feedback is only done with a single resistor, and the feedback gain can be adjusted by adjusting the resistor. Feedback gives you control of the output impedance too, among others.
Notice how the closed loop system removes the crossover distortion from the output. The open loop system has a gain of about 221, while the closed loop only has a gain of about 2.
