What an Amplifier Actually Does

The basic function of an amplifier home audio component is to increase the amplitude of an audio signal. The signal from a source component is typically a low-voltage electrical signal, often measured in millivolts. The amplifier increases this signal to a level that can drive speakers, which require much higher voltage and current.

The amplifier performs this function through a series of stages. The input stage receives the signal and prepares it for amplification. The voltage amplification stage increases the voltage of the signal. The driver stage provides the current needed to drive the output stage. The output stage delivers the amplified signal to the speakers.

The quality of each stage affects the performance of the amplifier home audio system. A well-designed amplifier will provide clean, accurate amplification with minimal distortion and noise. A poorly designed amplifier may introduce distortion, noise, or other artifacts that degrade the sound quality.

The Different Types of Amplifiers

Amplifiers are available in several types, each with its own characteristics and applications.

Stereo amplifiers, also called two-channel amplifiers, are designed for music listening. They provide two channels of amplification, one for the left speaker and one for the right speaker. They are the foundation of a traditional hi-fi system.

Integrated amplifiers combine a preamplifier and a power amplifier in a single chassis. The preamplifier handles input selection and volume control, while the power amplifier provides the amplification. Integrated amplifiers are popular because they are convenient, cost-effective, and take up less space than separate components.

Preamplifiers are separate components that handle input selection, volume control, and sometimes tone control. They output a low-level signal that must be amplified by a separate power amplifier. Separate preamplifiers and power amplifiers are popular among audiophiles who want maximum flexibility and performance.

Power amplifiers are separate components that provide the amplification. They receive a low-level signal from a preamplifier and deliver the amplified signal to the speakers. Separate power amplifiers are often used in high-end systems where performance is the priority.

AV receivers are multichannel amplifiers designed for home theater systems. They provide amplification for multiple speakers, including front left, front right, center, surround, and height channels. They also include video processing and switching capabilities.

The Different Classes of Amplification

Amplifiers are classified by their operating principle. The class of amplification affects the efficiency, sound quality, and heat generation of the amplifier.

Class A amplifiers are the simplest and most linear. They conduct current at all times, which produces the purest sound but also generates significant heat and has low efficiency. They are typically used in high-end audio systems where performance is the priority.

Class AB amplifiers are the most common type. They combine the linearity of Class A with the efficiency of Class B. They conduct current for more than half of the signal cycle, which reduces distortion while maintaining reasonable efficiency. They are used in most consumer audio amplifiers.

Class D amplifiers use switching technology to achieve very high efficiency. They are small, lightweight, and generate little heat. They are used in portable audio devices, soundbars, and some home audio systems. Early Class D amplifiers had a reputation for poor sound quality, but modern designs have improved significantly.

Key Specifications to Understand

When evaluating an amplifier home audio component, several specifications determine its performance and suitability for a given system.

Power output is the most important specification. It is measured in watts per channel and indicates how much power the amplifier can deliver to the speakers. The required power depends on the sensitivity and impedance of the speakers and the size of the room.

Total harmonic distortion measures the amount of distortion introduced by the amplifier. Lower is better. A total harmonic distortion of less than 0.1 percent is generally considered good.

Signal-to-noise ratio measures the amount of noise relative to the signal. Higher is better. A signal-to-noise ratio of greater than 100 decibels is generally considered good.

Frequency response indicates the range of frequencies the amplifier can reproduce. A wider range is better. A frequency response of 20 hertz to 20 kilohertz is standard.

Damping factor indicates the amplifier’s ability to control the movement of the speaker cone. Higher is better. A damping factor of greater than 50 is generally considered good.

What to Consider When Choosing an Amplifier

The first consideration is the speakers. The amplifier must be compatible with the speakers in terms of power, impedance, and sensitivity. An amplifier that is too weak will not drive the speakers to adequate volume. An amplifier that is too powerful may damage the speakers if not used carefully.

The second consideration is the room. Larger rooms require more power to fill with sound. Smaller rooms require less.

The third consideration is the source components. The amplifier must have the right inputs for the sources being used. Phono inputs are required for turntables. Digital inputs are required for streaming devices and televisions.

The fourth consideration is the features. Some amplifiers include tone controls, balance controls, and headphone outputs. Others are minimalist, with only the essential controls.

The fifth consideration is the budget. Amplifiers range from a few hundred dollars for a basic integrated amplifier to tens of thousands of dollars for high-end separates.

The Bottom Line

An amplifier home audio system is the heart of any serious music or movie setup. It takes the low-level signal from a source component and increases its power so that it can drive loudspeakers. The quality of the amplifier has a direct impact on the clarity, dynamics, and overall performance of the audio system. Understanding the different types of amplifiers, the classes of amplification, and the key specifications will help you choose the right amplifier for your system and your budget.