Power amplifier is an electronic device, which is used to increase sound energy.  In other words, the final stage which must driven a given load e.g mechanical indicator, a loudspeaker cathode roy tade, magnetic deflection coil, a transmitting accrual of a communication network.  Power amplifier is also used in regulation power supplies, chopper amplifier, motor controller etc.  In general the load will by its nature, demand a certain power from the amplifier and the out stage must be capable of delivering the power (large current or voltage swing).  The preceding stage to the power stage are supposed to given the input to drive the power stage so that it can produce the load requirement.

In power amplifier a large portion of active device (transistor) characteristics is used (i.e there is large alternating input voltage or current to make efficient use of the device.

The economic importance of power amplifier is know to be useful in many aspect of both social and business activities.  In the social activity, it is found that during occasions like public gathering and parties people us power amplifier to increase or enlarge their speech as to be audible.  While the business activity: during business promotion, it is found that marketing agents use power amplifier for their advertisement: for notifying the public about combating.