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 and the 5532 are dual opamps; the single equivalents are TL071 and 5534. Dual opamps are used almost universally, as the package containing two is usually cheaper than the package containing one, simply because it is more popular. The opamp is today thought of as quintessentially a differential amplifier, responding to the difference of the input voltages while ignoring any common-mode component. The great divide is between junction field-effect transistor (JFET) input opamps and bipolar junction transistor input opamps. The JFET opamps have more voltage noise but less current noise than bipolar input opamps, the TL072 being particularly noisy. Bipolar input opamps not only have larger noise currents than their JFET equivalents, they also have much larger bias currents. FET input opamps have very low bias current at room temperature.
