A voltage follower, also known as buffer amplifier, is a special case of the non-inverting operational amplifier (op amp), where the output connects directly to the inverting input providing negative feedback. In this configuration, the amplifier does not provide voltage gain and therefore the output voltage follows the input voltage. The most important features of the follower are that the op amp has very high input impedance and very low output impedance, therefore it can supply a sizeable load current, whilst drawing zero current from the signal source. These features make it an ideal buffer amplifier for interfacing high impedance sources with low-impedance loads.

Microphone Buffer

One typical use of a buffer amplifier is with a high impedance microphone. The output current from such a microphone is extremely small, and therefore we use a buffer amplifier, which matches the output resistance of the microphone to its input so that it does not draw current from the microphone.

Since the operational amplifier has unity gain (Gain = 1), the amplitude of the audio waveform at its output remains the same as that at its input. However, the advantage here is that the op amp output can supply a sizeable current to feed the input of another op amp.

Another point to note, especially if you are a student, is that since we are using the non-inverting input of the op amp, we are not inverting the waveform, and therefore the input and output waveforms remain precisely the same. In audio electronics, this is an important aspect to understand.