A transistor circuit containing two stages of amplification is known as TWO STAGE AMPLIFIER. Successful application of feedback around an amplifier having large amounts of open-loop gain is done most readily if the amplifier has a simple frequency response (preferably one with a single dominant pole), and input and output impedance levels which minimize the interactions with the source and load. For many applications, a high input impedance and a low output impedance work well. The “two-stage” does a good job of meeting these requirements in applications ranging from general purpose op-amps to wide-band video amplifiers to audio power amplifiers.
It has excellent frequency response. The gain is constant over the audio frequency range which is the reason of most importance for speech, music etc.It has lower cost since it employee’s registers and capacitors which are cheap.The circuit is very compact as the modern resisters and capacitors are small and extreamely light.
They tend to become noisy with age , particularly in moist climates.Impedance matching is poor.
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