OP amps

internal schematic: note the number of transistors

OP amps are integrated chip based amplifiers that can be used for a variety of functions such as amplification, comparing, switching and other tasks.
They are reliable predictable and inexpensive.

Why build an amplifier circuit from many components when you can use an off the shelf OP amp package with reliable results and economical pricing?

Fairchild Semiconductors developed the most popular commercial integrated circuit OP amp the 741 in 1965 and is still widely used today  

The LM 386 OP amp chip can easily be configured into a
low power amp able to amplify an mp3 player or
electric guitar

G.F.I.
Ground Fault Interuption

Schematic of GFI Circuit

A GFI uses an OP amp to compare

voltages from a small current transformer

to detect small potentially harmful currents

leaking to ground and initiating tripping

of the circuit