ABSTRACT
Audio design has for many years relied on a very small number of opamp types; the TL072 and the 5532 dominated the audio small-signal scene for many years. The TL072, with its JFET inputs, was used wherever its negligible input bias currents and low cost were important. This chapter explains the opamps most commonly used for audio in order of voltage noise. The great divide is between JFET input opamps and BJT input opamps. Bipolar-input opamps not only have larger noise currents than their JFET equivalents, they also have much larger bias currents. These are the base currents taken by the input transistors. Distortion increases with loading in different ways for different opamps. It may rise only at the high-frequency end, or there may be a general rise at all frequencies. The LM741 had effective short-circuit protection and internal compensation for stability at unity gain and was much easier to make work in a real circuit than its predecessors.
