It’s easy enough to buy new/replacement stereo components and hook everything up for great results. But have you ever thought about what makes it all tick? Stereo amplifiers can be a crucial element for the best audio performance.

The purpose of an amplifier is to take a small electrical signal and amplify or boost it. In the case of a preamplifier, the signal must be amplified enough to be accepted by a power amplifier. In the case of a power amplifier, the signal must be amplified much more, enough to power a speaker. Although amplifiers look like large, mysterious boxes, the basic principles of how they work are relatively simple. An amplifier takes an input signal from a source (mobile device, turntable, CD/DVD/media player, etc.) and creates an enlarged replica of the original smaller signal. The power required to do this comes from a 110-volt wall outlet. Amplifiers have three basic connections: an input from the source, an output to the speakers, and a power source from the 110-volt wall outlet.

The 110 volt current is sent to the part of the amplifier – the power supply – where it is converted from AC to DC. DC is similar to the current found in batteries; electrons (or electricity) only flow in one direction. AC flows in both directions. From the battery or power supply, the current is sent to a variable resistor – also called a transistor. The transistor is essentially a valve (think of a water valve) that varies the amount of current flowing through the circuit based on the input signal from the source.

A signal from the input source causes the transistor to decrease or reduce its resistance, allowing current to flow. The amount of current allowed to flow is based on the size of the signal from the input source. A large signal causes more current to flow, resulting in greater amplification of the smaller signal. The frequency of the input signal also determines how fast the transistor operates. For example, a 100 Hz tone from the input source causes the transistor to open and close 100 times per second. A 1000 Hz tone from the input source causes the transistor to open and close 1000 times per second. In this way, the transistor controls the level (or amplitude) and frequency of the electrical current sent to the speaker, just like a tube. This is how it achieves its amplifying effect.