What is a power amplifier, power amplifier introduction, power amplifier classification, power amplifier performance indicators and parameters

The power amplifier is commonly known as the "loudspeaker". Its function is to amplify the weak signal from the sound source or the preamplifier to drive the speaker to soundproof. A good sound system plays an indispensable role in the power amplifier.
The power amplifier is the most basic equipment in the sound system. Its task is to amplify the weak electrical signal from the signal source (from the mixer in the professional sound system) to drive the speaker to make sound.
The power amplifier, referred to as the power amplifier, can be said to be the largest family of various audio equipment. Its main function is to amplify the weak signal input from the sound source equipment and generate a large enough current to drive the speaker to reproduce the sound. Due to considerations of power, impedance, distortion, dynamics, and different usage ranges and control adjustment functions, different power amplifiers are also different in internal signal processing, circuit design and production technology.

Amplifier Classification

According to the different conduction methods of the power amplifier tubes in the power amplifier, it can be divided into Class A power amplifier (also known as Class A), Class B power amplifier (also known as Class B), Class AB power amplifier (also known as Class AB) and Class D power amplifier (also known as Class D).

Class A amplifiers are amplifiers in which no power output element of the amplifier will experience current cutoff (i.e. stop output) during the entire cycle of the signal (positive and negative half cycles of the sine wave). Class A amplifiers generate high heat and have low efficiency, but their inherent advantage is that there is no crossover distortion. Single-ended amplifiers all work in Class A mode, and push-pull amplifiers can be Class A, Class B, or Class AB.

Class B amplifiers are amplifiers in which the positive and negative half cycles of a sinusoidal signal are amplified and outputted alternately by the two "arms" of the push-pull output stage, and the conduction time of each "arm" is half a cycle of the signal. The advantage of Class B amplifiers is high efficiency, but the disadvantage is that they will produce crossover distortion.

Class AB amplifiers are between Class A and Class B. The conduction time of each "arm" of push-pull amplification is greater than half a cycle of the signal but less than one cycle. Class AB amplifiers effectively solve the crossover distortion problem of Class B amplifiers, and their efficiency is higher than that of Class A amplifiers, so they have been widely used.

Class D amplifiers, also known as digital amplifiers, use extremely high-frequency switching circuits to amplify audio signals. They have the advantages of high efficiency and small size. Many Class D amplifiers with power up to 1000W are only as big as a VHS video tape. This type of amplifier is not suitable for use as a broadband amplifier, but is widely used in active subwoofers.

According to the number of amplifying elements in the output stage of the power amplifier, it can be divided into single-ended amplifier and push-pull amplifier.

The output stage of a single-ended amplifier consists of one amplifying element (or multiple elements connected in parallel) to amplify the positive and negative half cycles of the signal. Single-ended amplifiers can only work in Class A mode.

The output stage of a push-pull amplifier has two "arms" (two groups of amplifying elements). When the current of one "arm" increases, the current of the other "arm" decreases, and the two states switch in turn. For the load, it seems that one "arm" is pushing and the other "arm" is pulling, and they work together to complete the current output task. Although Class A amplifiers can use push-pull amplification, it is more common to use push-pull amplification to form Class B or Class AB amplifiers.

According to the type of power amplifier tube in the power amplifier, it can be divided into tube amplifier and transistor amplifier.

A tube amplifier is an amplifier that uses electron tubes.

A transistor amplifier is an amplifier that uses transistors.

Depending on their functions, they can be preamplifiers (also called front-stage), power amplifiers (also called power-stage) and integrated amplifiers.

A power amplifier is an electronic device used to increase signal power to drive a speaker to produce sound. A power amplifier without auxiliary functions such as signal source selection and volume control is called a post-stage.

The preamplifier is the pre-amplification and control part before the power amplifier, which is used to enhance the voltage amplitude of the signal and provide functions such as input signal selection, tone adjustment and volume control. The preamplifier is also called the pre-stage.

An amplifier that has the preamplifier and power amplifier installed in the same chassis is called an integrated amplifier. The power amplifiers commonly seen in our homes are generally integrated type.

According to different uses, it can be divided into AV amplifier and Hi-Fi amplifier.

AV amplifiers are amplifiers designed specifically for home theaters. They generally have more than 4 channels and surround sound decoding functions, and are equipped with a display screen. The main purpose of this type of amplifier is to create a real movie environment sound effect so that the audience can experience the theater effect.

A Hi-Fi amplifier is an amplifier designed to reproduce the original appearance of music with high fidelity. It is generally a two-channel design and has no display screen.

According to the different components used, power amplifiers are divided into "tube amplifiers" [electronic tube amplifiers], "stone amplifiers" [transistor amplifiers], and "IC amplifiers" [integrated circuit amplifiers]. In recent years, due to the use of new technologies and new concepts in tube amplifiers, the ancient vacuum device of the electronic tube has shined again. Its beautiful sound has impressed many audiophiles. Almost all senior audiophiles have one. "IC amplifiers" are rarely seen in HI-FI amplifiers because their sound quality is not as good as the above two types of amplifiers.

Amplifiers can generally be divided into three categories: "professional amplifiers", "civilian amplifiers" and "special amplifiers".

"Professional amplifiers" are generally used for conferences, performances, halls, venues, and halls. The design is based on large output power, perfect protection circuits, and good heat dissipation. The sound of most "professional amplifiers" is dry and hard when used for HI-FI playback.

"Civilian amplifiers" are further classified into "HI-FI amplifiers", "AV amplifiers", "KALAOK amplifiers" and so-called "integrated amplifiers" that integrate various commonly used functions.

"HI-FI amplifier" is the amplifier for audiophiles. Its output power is generally below 2X150 watts. The design is based on "beautiful sound and high fidelity". Various high-tech technologies are concentrated in this amplifier. The price ranges from more than a thousand yuan to hundreds of thousands of yuan. "HI-FI amplifier" is divided into "split type" [separate the preamplifier] and "combined type" [the preamplifier and the postamplifier are integrated]. Generally speaking, among the models of the same grade, the "split type" is higher than the "combined machine" in terms of signal-to-noise ratio, channel division and other indicators [not absolute]. And it is easy to compare the sound through the signal line. The combined machine has the advantages of easy use and relatively low cost. The output power of the affordable combined machine is generally designed to be below 2X100W, and there are also many manufacturers that produce high-end combined machines with more than 2X100W.

"AV" amplifier is a dark horse that has emerged in recent years. With the popularity of large-screen TVs and multiple image carriers, people's demand for "sitting at home to watch movies" is increasing, so multifunctional amplifiers that integrate various audio and video functions have come into being. "AV" is the abbreviation of AODIOVIDIO in English, which means audio and video. From its birth to now, "AV amplifier" has gone through the process of Dolby Surround, Dolby Pro Logic, AC-3, and DTS. The difference between AV amplifier and ordinary amplifier is that AV amplifier has AV Select Dolby Pro Logic decoder, AC-3, DTS decoder, and five-channel power amplifier. And the finishing touch of digital sound field [DSP] circuit, providing different sound field effects for various program playback. However, because the AV amplifier has too many and complex processing circuits in the signal flow link of the circuit, the "purity" of the sound is too "colored", so the effect is not ideal when using AV amplifier compatible with HI-FI playback. This is also the reason why many HI-FI enthusiasts ignore AV amplifiers.

"KALAOK amplifier" is also a kind of amplifier developed in recent years. The difference between it and general amplifiers is that "KALAOK amplifier" has reverberator [developed from BBD analog reverberation in the past to DIGETAL digital reverberation now], pitch shifter, microphone amplifier. In recent years, some manufacturers have combined various functions including AV amplifier and KALAOK amplifier into one, the so-called "comprehensive amplifier" to meet the needs of the market. This is a hodgepodge amplifier that has everything but can't do anything well. It is a rural-oriented resistance amplifier.

As the name suggests, "special power amplifiers" are amplifiers used in special occasions, such as alarms, car low-voltage power amplifiers, etc., which will not be introduced here.

Performance indicators of power amplifier

The main performance indicators of a power amplifier include output power, frequency response, distortion, signal-to-noise ratio, output impedance, damping coefficient, etc.

Amplifier output power: The unit is W. Due to different measurement methods of different manufacturers, there are some different names, such as rated output power, maximum output power, music output power, and peak music output power.

Amplifier music power: refers to the instantaneous maximum output power of the amplifier for music signals under the condition that the output distortion does not exceed the specified value.

Amplifier peak power: refers to the maximum music power that the amplifier can output when the volume of the amplifier is adjusted to maximum without distortion.

Rated output power of amplifier: the average output power when the harmonic distortion is 10%. Also called the maximum useful power. Generally speaking, the peak power is greater than the music power, and the music power is greater than the rated power. Generally speaking, the peak power is 5-8 times the rated power.

Amplifier frequency response: Indicates the frequency range of the amplifier and the unevenness within the frequency range. The flatness of the frequency response curve is generally expressed in decibels [db]. The frequency response of a home HI-FI amplifier is generally 20Hz--20KHZ plus or minus 1db. The wider this range, the better. The frequency response of some top-quality amplifiers has reached 0--100KHZ.

Distortion: An ideal amplifier should amplify the input signal and faithfully restore it without any change. However, due to various reasons, the signal amplified by the amplifier is often distorted to varying degrees compared with the input signal. This distortion is distortion. Expressed as a percentage, the smaller the value, the better. The total distortion of a HI-FI amplifier is between 0.03% and 0.05%. The distortion of an amplifier includes harmonic distortion, intermodulation distortion, crossover distortion, clipping distortion, transient distortion, transient intermodulation distortion, etc.

Signal-to-noise ratio: refers to the ratio of the signal level to the various noise levels output by the amplifier, expressed in dB, the larger the value, the better. Generally, the signal-to-noise ratio of a home HI-FI amplifier is above 60db.

Output impedance: The equivalent internal resistance presented to the speaker is called output impedance.

A good performance indicator of an amplifier does not necessarily mean a good sound quality, which is something that beginners must realize. This is also what many audiophiles are struggling to explore and pursue.