Operational Amplifier or OpAmp is a DC coupled amplifier with differential inputs and usually with a single output. An OpAmp can deliver an output voltage hundreds or thousand times greater than the voltage difference between its inputs. OpAmps may be single, dual, quad etc. In single OpAmps only one OpAmp is present while in dual type two OpAmps with separate inputs and outputs are present. In quad OpAmp, four OpAmps are present in the single package. Some of the OpAmps like CA3130, CA3140, TL0 71, LM311 etc have excellent performance with very low input current and voltage.
An Audio amplifier needs to give an output waveform exactly similar to the input waveform even though the output is amplified. Op Amps are widely used to amplify signals mainly in the Preamplifier stage. The input can be signal from an audio device or from a microphone. The Pre Amplifier stage uses either a Non inverting amplifier or Inverting Amplifier. This note will help you to design an amplifier based on JFET input Op Amp TL0 71.