Question

How many stages needed to have powerful amplifier?​

Answer 1

Generally you should pick an amplifier that can deliver power equal to twice the speaker's program/continuous power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load.

Answer 2

Power amplifier stages in a real circuit. Circuit diagram of a three stage practical audio power amplifier is shown in the figure below. Small signal transistor Q1 and its associated components form the voltage amplification stage.