If you want to build an operational amplifier and a power amplifier into one device, you can do it like this:
You don't need diodes or resistors anymore to prevent cross-over distortion; the opamp takes care of this. Since the opamp tries to keep Vp equal to Vn, the voltage gain is 2. Variable resistor (potentiometer) P1 allows you to adjust the quiescent output voltage to exactly 0V.
An appropriate symmetric power supply can be found in another chapter.