Publisher's Synopsis
The oscillation is caused by a small part of the signal from the amplifier output being sent back to the input of the amplifier. This signal is amplified and again sent back to the input where it is amplified again. This process continues and the result is a loud noise out of the speaker. The process of sending part of the output signal of an amplifier back to the input of the amplifier is called feedback . The input signal to the amplifier from the source will be generally in the mill volt range and it is very weak to drive the succeeding stages. The purpose of the voltage amplification stage is to provide necessary voltage amplification to the input signal for the succeeding stages to process. Usually the voltage amplification stage consists of two or more RC coupled Class A amplifiers. These Class A amplifiers coupled together will make the necessary voltage gain Driver stage is the stage that is standing between the voltage amplification stage and the output stage. The output stage will usually have low input impedance and so the voltage amplification stage cannot drive the output stage alone. The purpose of the driver stage is to produce enough current gain in order to drive the output stage. Since there is sufficient current gain, the driver stage produces considerable amount of power gain too. Output stage is the stage that is connected to the loudspeaker. The output stage gives further improvement to the power gain and transfers this power to the loud speaker with minimum loss. Push-pull arrangement consisting of two transistors is often employed in this stage. Efficiency and impedance matching are the two important parameters considered while designing this stage. Push-pull arrangement is a very common type of output configuration used in power amplifiers. In push-pull arrangement a pair of active devices (transistors) alternatively source or sink the load current. Advantages of push-pull configuration over single transistor output are better efficiency, higher power output, cancellation of even harmonics, cancellation of DC current at the output etc.
