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An amplifier circuit board is the heart of an amplifier. It contains the components that accept a signal and increase its strength by passing the signal through a transistor, integrated circuit (IC) chip, or tube that blends it with additional current from a power supply. Circuit boards come in a range of sizes and capabilities, but all of them usually contain components that are soldered to a substrate.
The most prominent part of the amplifier circuit board is the board itself. Technically referred to as a substrate, the wafer on which all of the components sit is usually made of a plastic resin that is reinforced with fiberglass. The wafer is coated with copper that is etched away to leave the conductive markings that connect the various electronic components that are mounted to it.
Amplifier circuit boards typically contain a number of electronic components, though the actual amplifier is usually a single component. In addition to the amplifying tube, transistor, or IC, the circuit board will also house a number of resistors and capacitors that serve a number of purposes. It will also have both input and output terminals for the original signal and the amplified signal, respectively. Although technically not part of the board itself, many boards also carry large heat sinks that are connected to the amplification component to help cool it.
Depending on the application, an amplifier circuit board can be relatively small or quite large. Many portable headphone amplifiers are quite small, with circuit boards measuring just a few square inches. On the other hand, an amplifier circuit board for a large audiophile home amplifier or for professional audio can fill much of the component's case, measuring well over 100 square inches (645 square cm).
Most amplifier circuit boards lack one key component: the power supply. In battery powered amplifiers, the battery typically provides power and requires no intervening circuitry. Many small amplifiers use an external power supply such as a "wall wart" alternating current (AC) power adapter, which also eliminates the need for an on-board supply. Larger amplifiers that plug into an AC outlet, on the other hand, do need circuitry to convert wall power into a signal that the amplifier can use. Most of them have the power supply and its power conversion circuits on a different physical board, isolating the large and noisy AC power signals from the more delicate audio or video signals that the amplifier actually works with.