In summary, op amps can be used in a wide variety of applications, but their most common application is simply to increase the amplitude of an AC or DC signal. There are two types of amps available: voltage feedback and current feedback. Voltage feedback is the most common, and responds to an error voltage between the inputs, while a current feedback op amp responds to a current error on the input. There are also many specifications to take into consideration when selecting an op amp and can vary greatly whether the part is used for high or low frequency applications.