An audio amplifier is a device used to enhance the volume and power of an audio signal in order to reproduce the input sound on the output audio device. Its goal is to achieve ideal sound quality, ensuring signal fidelity, effectiveness and minimal distortion. The frequency range of audio is typically between 20 Hz and 20 kHz, so amplifiers must have excellent frequency response to accommodate a wide range of sounds in this range, including bass and treble, especially when driving band-limited speakers. Such as a subwoofer or tweeter.

 

What is an Audio Amplifier

An audio amplifier is an electronic device specifically designed to amplify audio signals. It receives low-level, low-power audio signals from a source such as a CD player and amplifies them to high-level, high-power signals suitable for driving speakers or headphones. Typically, an audio amplifier consists of components such as a preamplifier, power amplifier, output stage, and power supply, and its structural design may vary depending on specific requirements.

 

Working Principle of an Audio Amplifier

The core of an audio amplifier is the power amplification circuit. This circuit, based on the input low-level, low-power audio signal, amplifies and processes the electrical signal using semiconductor devices such as bipolar transistors, field-effect transistors, or triode transistors at the output stage to achieve a significantly larger output power. The performance parameters of an audio amplifier primarily include amplification gain, output power, frequency response, distortion, signal-to-noise ratio, and more.

 

Purpose of an Audio Amplifier

The main purpose of an audio amplifier is to enhance the audio output power of an audio system, thereby increasing the volume and clarity of the sound. By using an audio amplifier, not only can the input signal be amplified sufficiently to drive speakers or headphones, but it also allows for the adjustment of characteristics like volume level and frequency response of the audio output to meet various user requirements.

 

 

Types of Audio Amplifiers

There are many types of audio power amplifiers, but the main four types suitable for audio applications are Class A, Class B, Class AB and Class D.

 

Class A amplifier

The characteristic of Class A amplifier is that the operating point Q is set near the midpoint of the load line, and the transistor is turned on during the entire input signal cycle. It can work as a single tube or push-pull, with small transient distortion and alternating distortion. The circuit is simple and easy to debug. However, Class A power amplifiers usually require large quiescent current and have low efficiency. The theoretical maximum efficiency is 25%, so heat dissipation is required.

 

Class B amplifier

Class B power amplifiers are composed of two complementary transistors. Each transistor is turned on during half of the signal cycle and turned off for half of the signal period, with a conduction angle of 180 degrees. Since there is no quiescent current, it has high efficiency, with a theoretical maximum efficiency of 78%. However, when the input signal approaches zero, there is crossover distortion.

 

Class AB amplifier

Two diodes are inserted into the input end of the Class AB amplifier to make the conduction angle of each amplifier tube greater than 180 degrees but less than 360 degrees, thereby overcoming the crossover distortion of the Class B amplifier. The efficiency is between Class A and Class B power amplifiers. Usually, the power consumption is higher at medium output voltage, and the efficiency is not very high.

 

Class D amplifier

Class D (digital audio power) amplifiers convert input analog audio signals or PCM digital information into PWM (pulse width modulation) or PDM (pulse density modulation) pulse signals, and then use these pulse signals to control high-power switching devices to adjust audio power. Class D power amplifiers are usually composed of two complementary power tubes. They work in a switching state without static power consumption and have high efficiency. Theoretically, the maximum efficiency can reach 100%, and in practice it is usually above 80%.

The advantages of Class D amplifiers include high efficiency, small size, no switching noise, low distortion and good frequency response. It usually requires fewer peripheral components and is easier to design and debug. Class D amplifiers are digital amplifiers that have more advantages than Class A, Class B, and Class AB amplifiers.

Taken together, different types of audio power amplifiers are suitable for different applications and scenarios. Choosing the appropriate type of power amplifier depends on requirements such as sound quality, efficiency, power consumption, and space.

 

The Difference Between an Audio Amplifier and an Audio Power Amplifier

Terminology Distinction

Audio Amplifier: This term refers to an amplifier designed to produce the maximum power output required to drive a specific load, such as speakers, while maintaining a specified level of distortion.

Audio Power Amplifier: This refers to a device that reconstructs the input audio signal on the output component responsible for generating sound.

 

Varied Operating Principles

Audio Amplifier: It operates by utilizing the current control effect of transistors or the voltage control effect of field-effect transistors to convert power from the power supply into a current that varies in response to changes in the input signal.

Audio Power Amplifier: This type of amplifier efficiently and with minimal distortion reproduces the audio input signal at the desired volume and power level on the sound-producing output components. Given that the audio signal's frequency range is 20Hz to 20kHz, the audio amplifier must exhibit excellent frequency response.

 

Distinctive Characteristics

Audio Amplifier: It plays a pivotal role in the entire audio system by serving as an "organizer and coordinator," effectively influencing the system's ability to deliver high-quality sound output.

Audio Power Amplifier: Its primary purpose is to provide the necessary current-driving capacity to the load for achieving power amplification. Class D power amplifiers operate in a switching state and theoretically do not require static current, resulting in very high efficiency.

Final Words

This article offers a concise overview of several commonly employed audio amplifiers in contemporary design. It is clear that in the process of crafting audio circuits for various device types, meticulous consideration of the audio amplifier structure that aligns best with the specific application is paramount. Gaining a profound understanding of the diverse audio amplifier types can be instrumental in pinpointing the most fitting choice for a given design.

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