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Power Amplifier

Learn about the function of a power amplifier and how to choose the right one.

Power amplifiers are developed with a range of specifications for many uses. [©Jupiter Images, 2009]
©Jupiter Images, 2009
Power amplifiers are developed with a range of specifications for many uses.

A power amplifier is a device used in audio and radio frequency applications that delivers power to speakers. A range of power amplifiers are available on the market, including radio frequency (RF) power amplifiers, audio power amplifiers, microwave amplifiers, power acoustic amplifiers and high-power amplifiers. An RF amplifier is used to amplify radio frequency sound waves. Audio power and power acoustic amplifiers are used to deliver power for audio transmissions. A microwave amplifier is used for high frequency transmissions.

Power amplifiers are developed with a range of specifications for a wide variety of uses. RF power amplifiers are designed for both band-specific and broadband frequencies. High-power amplifiers are regularly used for compact devices. Power amplifiers can be designed to meet the needs of any industry and are regularly used in the medical, military and wireless communications sectors.

The installation of power amplifiers is regulated by Underwriters' Laboratories (UL). According to GlobalSpec, when buying power amplifiers, individuals should choose power amplifiers that offer high power and linearity, broad bandwidth, and low distortion and noise.

Power Amplifier Functionality

As a result of inertia, loudspeakers can continue to vibrate long after the signal has stopped -- often producing sound waves that were not included in the original signal. A power amplifier can help to control the vibrations of loudspeakers and reduce ringing. When the loudspeaker vibrates, it generates a signal called back Electro Motive Force (EMF). EMF causes a current that travels through the speaker cable to the power amp and back to the loudspeaker. Since EMF travels opposite the speaker's vibrations, back EMF controls speaker ringing. In short, speakers rely on power amplifiers to impede ringing.

Ohms, the measurement of resistance, are also important to the functionality of power amplifiers. Audio amplifiers are typically structured to operate with four, eight or 16 Ohms of resistance. Optimal performance will be reached only if the loudspeaker's total resistive load matches the power amp. For example, if the total resistive load is too high, the power delivered by the amp will be decreased. If the total resistive load is too low, the power delivered by the amp will be increased, which could cause speaker overload and amp damage. Individuals can connect any number of speakers to one amplifier as long as speakers are properly wired to amplifiers using a series and/or a parallel method.

Optimal power amplifier performance can also be affected by slew rate. Slew rate measures an amplifier's output voltage with respect to its input voltage. Slew rate describes an amplifier's ability to transmit complex sound waves without distorting them. A slew rate that is too fast for the power amplifier to handle can affect the sound delivered by the amplifier. According to Sweetwater, a Web resource dedicated to music and audio technology information, slew rate is a condition that should not occur with audio power amplifiers.

Using Power Amplifiers

Individuals should first define their goals before using power amplifiers. If they are looking for power that will help them play their speakers as loud as they can without damage, then they need to first determine how much power their speakers can handle. Those looking to achieve a specific level of loudness to fill a certain venue should determine how large a power amplifier they need to fill a venue with undistorted, loud, crisp sound.

To determine how much power a speaker can handle, refer to the speaker's manual, which will provide the speaker's nominal impedance specifications and power capacity. Crown Audio recommends using an amplified power of 1.6 times the speaker's power capacity for light dance music or voice. For heavy metal music, it is suggested that individuals use a power amplifier that offers 2.5 times the speaker power capacity.

Choosing the Right Power Amplifier

When choosing power amplifiers, individuals should consider several factors including cost, headroom and power. Cost can be a major concern when purchasing power amplifiers. Individuals should choose devices that offer the highest level of power they can afford. Be sure to monitor the system to ensure that it is not causing speaker damage.

Some power amplifiers are specially designed with additional headroom to assure optimal amp performance and delivery of a clean sound. According to Sweetwater, it is best to match power amplifiers with speakers by choosing an amp that can deliver power that doubles the speaker's power capacity. A quality speaker will be able to handle an amp that delivers twice as much power as the speaker's continuous power rating. Using an amp with extra power capacity will help to ensure a clean, undistorted sound.

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