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Class A. Wikipedia has a really good set of data to give you a start on understanding amplifier classes.
Amplifiers can be binned into basic, prosumer, and professional amplifiers, with a corresponding increase in cost.
Darlington amplifier has more gain when compared to cascade amplifier .
1.differential amplifier
2.operational amplifier
3.instrumentation amplifier
4.chopper amplifier
5.isolation amplier
current series feedback amplifier=series parallel feedback amplifier or voltage to current amplifier,or TRANS CONDUCTANCE AMPLIFIER.