A brief analysis of the processing of external power amplifier for the headphone channel of MTK6735 module

Amplifier

The power amplifier, also known as the PA or "amplifier", is the most basic device in the audio system. Its task is to amplify the weak electrical signal from the signal source (from the mixing console in a professional audio system) to drive the speaker to make sound.

The function of the power amplifier is to amplify the weak signal from the sound source or preamplifier to drive the speaker to make sound. A good sound system cannot be without the role of the power amplifier.

Amplifiers are the largest family of audio equipment. Their main function is to amplify the weak signal input from the audio 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 amplifiers have different internal signal processing, circuit design, and production processes.

Amplifier Classification

In addition to the function of amplifying signals and driving speakers to expand sound, frequency-shifting amplifiers can also effectively suppress on-site howling and ensure the quality of voice transmission. Even in poor environments, they can greatly suppress howling and protect audio equipment from burning out due to howling.

Frequency-shifting amplifiers are widely used in high-end multimedia classrooms, training rooms, small conference rooms or other simple sound reinforcement occasions. The microphone can be directly connected to the frequency-shifting amplifier, which can effectively suppress the howling of the microphone to the speaker and support background music access for sound reinforcement.

By conductivity

According to the different conduction methods of the power amplifier tube 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.

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 the 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.

By Component Quantity

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 an amplifier element (or multiple elements connected in parallel) to amplify the positive and negative half cycles of the signal.

The end-amplifier can only adopt Class A working status.

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.

By power amplifier tube type

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.

By function

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

Power amplifier is an electronic device used to increase signal power to drive the speaker to produce sound. It does not have signal source selection or volume control.

A power amplifier with auxiliary functions such as the post-stage is called the 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 both the preamplifier and the power amplifier installed in the same chassis is called an integrated amplifier. The power amplifiers commonly found in our homes are generally integrated amplifiers. [1]

By Application

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.

With the popularity of large-screen TVs and multiple image carriers, people's demand for "sitting at home and watching movies" is increasing, so multifunctional amplifiers with various audio and video functions have come into being. "AV" is the abbreviation of the English words AudioVideo, which means audio and video. "AV amplifier" has gone through the process of Dolby Surround, Dolby Pro Logic, AC-3, and DTS. The difference between AV amplifiers and ordinary amplifiers is that AV amplifiers have AV Select Dolby Pro Logic decoders, AC-3, DTS decoders, and five-channel power amplifiers. And the finishing touch of digital sound field (DSP) circuits provide different sound field effects for various program playbacks. 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 has been "colored" too much, so the effect of using AV amplifiers compatible with HI-FI playback is not ideal. This is also the reason why many HI-FI enthusiasts disdain AV amplifiers.

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.

"HI-FI amplifier" is the amplifier for audiophiles. Its output power is generally below 2X150 watts.

The purpose of this amplifier is to create a beautiful and high-fidelity sound. Various high-tech technologies are concentrated in this type of amplifier. The price ranges from more than a thousand yuan to hundreds of thousands of yuan. "HI-FI amplifiers" are divided into "split type" (the pre-amplifier is separated) and "integrated type" (the pre-amplifier and the post-amplifier are integrated). Generally speaking, among the models of the same grade, the "split type" is higher than the "integrated 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 integrated machine has the advantages of being easy to use and relatively low cost. The output power of the affordable integrated machine is generally designed to be less than 2X100W, and there are also many manufacturers that produce high-end integrated machines with more than 2X100W. [1]

According to the components used

Depending on the components used, amplifiers are divided into "tube amplifiers" (electronic tube amplifiers), "solid amplifiers" (transistor amplifiers), and "IC amplifiers" (integrated circuit amplifiers). The use of new technologies and new concepts in tube amplifiers has made the ancient vacuum device of the electronic tube shine again, and its beautiful sound has won the hearts of 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. [1]

By user group

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 amplification. The design is based on large output power, perfect protection circuits, and good heat dissipation. Most "professional amplifiers" are used for HI-FI playback.

When listening to music, the sound is dry and hard.

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