On the type and structure of audio power amplifier

Amplifier ? Power amplifier is referred to as power amplifier, commonly known as 'amplifier', is the most basic equipment in the audio system, its task is to amplify the weak electrical signal from the signal source (professional sound system is from the mixer) to drive the speaker to emit sound . ? The role of the power amplifier is to amplify the weak signal from the sound source or pre-amplifier, and promote the speaker to play sound. The function of a good sound system amplifier is indispensable. ? Amplifier is the largest family of all kinds of audio equipment. Its function is to amplify the weak signal input by the audio equipment and generate enough current to drive the speaker to reproduce the sound. Due to the consideration of power, impedance, distortion, dynamics, and different use ranges and control adjustment functions, different power amplifiers have different internal signal processing, circuit design, and production processes. ? Amplifier classification ? In addition to the function of the amplified signal of the ordinary power amplifier to drive the speaker to amplify the sound, the frequency-shifting power amplifier can also effectively suppress the on-site howling and ensure the transmission quality of the voice. Protect audio equipment from being burned out by howling. ? Frequency-shifting power amplifiers are widely used in high-end multimedia classrooms, training rooms, small meeting rooms or other simple sound reinforcement occasions. The microphone can be directly connected to the frequency-shifting power amplifier, which can also effectively suppress the howling of the microphone on the speaker and support background music connection. Into the sound reinforcement. ? According to the conductive method ? 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 A and B power amplifier (also known as Class AB) and D class ? Amplifier (also known as Class D). ? Class A power amplifier refers to a type of amplifier that does not have current cutoff (ie, stops output) in any power output element of the amplifier during the entire period of the signal (positive and negative halves of the sine wave). Class A amplifiers generate high heat during operation, and the efficiency is very low, but the inherent advantage is that there is no crossover distortion. Single-ended amplifiers are all Class A working methods, and push-pull amplifiers can be Class A, B, or A or B. ? Class B amplifier refers to a type of amplifier in which the positive and negative half cycles of the sine signal are amplified 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 amplifier is high efficiency, the disadvantage is that it will produce crossover distortion. ? Class A and Class B amplifiers are between Class A and Class B. The on-time of each 'arm' of the push-pull amplifier is greater than half a cycle of the signal and less than one cycle. Class A and Class B amplification effectively solves the crossover distortion problem of Class B amplifiers, and the efficiency is higher than that of Class A amplifiers, so it has been extremely widely used. ? Class D amplifiers are also called digital amplifiers. They use extremely high frequency transfer switch circuits to amplify audio signals, which has the advantages of high efficiency and small size. Many D-type amplifiers with a power of up to 1000W are only as large as VHS tapes. This type of amplifier is not suitable for use as a broadband amplifier, but it has more applications in active subwoofers. ? By number of components ? According to the number of power amplifier output stage amplification components, it can be divided into single-ended amplifier and push-pull amplifier. ? The output stage of a single-ended amplifier is amplified by a positive and negative signal for two and a half cycles by one amplifying element (or multiple elements but connected in parallel). single ? The end magnifying machine can only take the Class A working state. ? The output stage of the push-pull amplifier has two 'arms' (two sets of amplification elements). When the current of one 'arm' increases, the current of the other 'arm' decreases, and the state of the two switches in turn. To the load, it seems that one 'arm' is pushing and one 'arm' is pulling 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 A amplifiers. ? According to the power amplifier tube type ? According to the type of power amplifier tube in the power amplifier, it can be divided into tube amplifier and stone amplifier. ? Amplifier is a power amplifier using a tube. ? Shiji is a power amplifier using transistors. ? Press function ? According to different functions, it can be preamplifier (also called pre-stage), power amplifier (also called post-stage) and combined amplifier. ? Power amplifier is referred to as power amplifier, which is an electronic device used to enhance the signal power to drive the sound of the speaker. Without signal source selection, volume control ? Power amplifiers with auxiliary functions such as are called post-stage. ? The pre-amplifier is the pre-amplification and control part before the power amplifier. It is used to enhance the voltage amplitude of the signal, provide input signal selection, tone adjustment and volume control. The preamplifier is also called the pre-stage. ? Amplifiers with pre-amplifier and power amplifier installed in the same chassis are called combined amplifiers. Common power amplifiers in our home are generally combined. [1] ? By use ? According to different uses, it can be divided into AV power amplifier and Hi-Fi power amplifier. ? AV amplifier is an amplifier specially designed for home theater use. Generally, it has more than 4 channels and surround sound decoding function, and has a display screen. The main purpose of this type of power amplifier is to truly create the sound environment of the film and let the audience experience the theater effect. ? With the popularity of large-screen TVs and a variety of image carriers, people's demand for 'sitting at home to watch movies' is increasing day by day, so a multifunctional power amplifier that integrates various audio and video functions has emerged. 'AV' is the English acronym for AudioVideo, that is, audio, video. 'AV power amplifier' has gone through the process of Dolby surround, Dolby directional logic, AC-3, DTS, the difference between AV power amplifier and ordinary power amplifier is that AV power amplifier has AV select Dolby directional logic decoder, AC-3, DTS Decoder, and five-channel power amplifier. And the digital sound field (DSP) circuit, which is the finishing touch, provides different sound field effects for various programs. However, because the AV power amplifier is placed on the signal flow link of the circuit, too many and complicated processing circuits have passed, so that the purity of the sound has been 'stained' too much, so the effect of the AV power amplifier compatible with HI-FI playback is not Ideal. This is why many HI-FI enthusiasts disdain AV amplifiers. ? Hi-Fi amplifiers are amplifiers designed to reproduce the true colors of music with high fidelity. They are generally designed for two channels and do not have a display. ? 'HI-FI power amplifier' is the power amplifier of our enthusiasts, and its output power is generally below 2X150 watts. Designed with 'sound quality ? 'Beauty, high fidelity' is the purpose. Various high-tech technologies are concentrated on this kind of power amplifier. The price also ranges from more than a thousand yuan to hundreds of thousands of yuan. The amplifier is independent), and 'merged' (the front stage and the rear machine are integrated). Generally speaking, among the models of the same grade, the 'split' has higher indicators such as signal-to-noise ratio and channel division It is used for 'combination machine' (not absolute). It is easy to pass the signal line. The merger machine has the advantages of easy use and relatively low cost. The output power of the parity merger is generally designed below 2X100W, and many manufacturers produce it. High-end merger with 2X100W and above. [1] ? According to the use of components ? According to the different components used, the power amplifier has 'tube amplifier' (tube power amplifier), 'stone machine' (transistor power amplifier), 'IC power amplifier' (integrated circuit power amplifier). Due to the use of new technologies and new concepts in tube amplifiers, the ancient vacuum device, the electronic tube, shines again, and its beautiful sound makes many fans fall in love. Almost all experienced audiophiles have one. 'IC power amplifier' because his tone is not comparable to the two power amplifiers, so he rarely sees his shadow in the HI-FI power amplifier. [1] ? By user group ? Amplifiers can be divided into three major categories: 'professional amplifiers', 'civilian amplifiers' and 'special amplifiers'. ? 'Professional Amplifier' is generally used for the amplification of conferences, performances, halls, halls, venues, and halls. The design is based on large output power, perfect protection circuit and good heat dissipation. Most 'professional amplifier' sounds are used for HI-FI playback ? When, the sound is hard and unbearable. ? The detailed classification of 'civilian power amplifiers' includes 'HI-FI power amplifiers', 'AV power amplifiers', 'KALAOK power amplifiers' and so-called 'comprehensive power amplifiers' that integrate various common functions. ? The difference between 'KALAOK power amplifier' and general power amplifier is that 'KALAOK power amplifier' has a reverb developed from BBD analog reverb to DIGETAL (digital reverb), translator, microphone amplifier. In order to meet market demand, some manufacturers combine various functions including AV amplifier and KALAOK amplifier into one, so-called 'comprehensive amplifier'. This is a kind of hodgepodge amplifier. Low-end power amplifiers do not pursue sound quality, only rich functions. ? 'Special Power Amplifier', as the name implies, is a power amplifier used in special occasions, such as an alarm, a low-voltage power amplifier for vehicles, etc., and will not be described here. On the type and structure of audio power amplifier Audio amplifier, as the name suggests, is an amplifier that amplifies the power of audio signals. From the early simple A and B types, it has developed to the current G type, and even W type. Audio input and output have evolved from the early pure analog signals to the current digital / analog coexistence. The efficiency is getting higher, the harmonic distortion is getting smaller, and the fidelity is getting higher. This article analyzes the development of the power amplifier from the structure and basic characteristics (part of the text comes from the network). Definition of power amplifier Power amplifier is called power amplifier for short, commonly known as 'amplifier', is the most basic equipment in the audio system, its task is to amplify the weak electrical signal from the signal source to drive the speaker to emit sound. The main function is to amplify the weak signal input by the sound source equipment, and generate enough current to push the speaker to reproduce the sound. Due to the consideration of power, impedance, distortion, dynamics, and different use ranges and control adjustment functions, different power amplifiers have different internal signal processing, circuit design, and production processes. Classification of power amplifier There are many ways to classify power amplifiers, which are generally divided according to the different conduction methods of the power amplifier tubes. It is usually divided into Type A (Type A), Type B (Type B), Type AB (Type A and Type B), Type D (Type D), and later developed Types G and H. Class A amplifier The characteristic of Class A amplifier is that no matter whether the input signal is input or not, its output circuit has constant current flow, and this kind of amplifier is usually operated in the linear range of the characteristic curve, in order to seek the signal after the amplification is not distorted. So its advantage is: the distortion is small, the smaller the signal, the higher the fax degree. The biggest disadvantage is its low efficiency, which is only 25% at most. It does not reduce the power consumption when no signal is input, and it is extremely unsuitable for power amplification. However, due to its high-fidelity, some advanced audio equipment still uses Class A amplifiers. No matter whether there is signal input or not, the current loss of Class A amplifiers has always been very large, and will generate a lot of heat. Therefore, when using the A amplifier, a good heat dissipation environment is required. The following figure is the schematic waveform of the working interval of the class A power amplifier, and the general implementation of the class A power amplifier, namely 'common collector' and 'common emitter'. Class A power amplifier working range Class A power amplifier output amplitude is Vp, output load average power PL, power input power is Ps, working efficiency is η, you can get the following expression: PL = Vp * Vp / (2 * Rl); Ps = 2 * Vcc * Iq; η = Pl / Ps, so it can be calculated that when Vp = VCC and Vp = IQ * RL, the class A amplifier has the largest The work efficiency is 25%. Class B amplifier Class B power amplifier is an amplifier whose operating point is at the extreme of characteristic line. When there is no signal input, almost no power is consumed at the output. According to the definition, the static operating point is 0, and the signal is connected to the original emitter follower with a PNP type BJT, forming a so-called 'complementary emitter follower', also known as 'Class B push-pull amplifier'. The operation principle is that during the positive half cycle of Vi, Q1 is turned on and Q2 is cut off. Therefore, the positive half cycle sine wave of the output terminal of FIG. 4 is formed; similarly, when Vi is a negative half cycle, Q1 is cut off and Q2 is turned on, resulting in an output The negative half-period sine wave is shown in the dotted line in Figure 4. Because the class B push-pull amplifier does not consume power when there is no input signal, it has a higher maximum efficiency of up to 78% than the class A amplifier. However, because the signal amplitude range of the push-pull amplifier is in the nonlinear region of the characteristic line, it causes severe distortion, as shown below. This distortion is called 'crossover distortion' ). Class B power amplifier implementation Class B amplifier working range Assuming that the output signal is Vp * sinωt, the output load average power PL, the power input power is Ps, and the working efficiency is η, you can get: PL = Vp * Vp / (2 * Rl); Ps = 2 * Vcc * Vp / (π * Rl); η = Pl / Ps, when Vp = VCC, the class B amplifier has the maximum working efficiency, 78.5%. Class AB amplifier The aforementioned crossover distortion of the Class B push-pull amplifier is caused by the inability of Q1 and Q2 to turn on when the signal size is between -0.6V and Vi <0.6V. Therefore, if we add two 0.6V voltages between the Vbe of Q1 and Q2, so that the input signal is between ± 0.6V, Q1 and Q2 can also be turned on to reduce distortion. This situation is Class AB amplifier, as shown above. Class AB amplifiers produce less distortion than Class B amplifiers, but the cost of this improvement is wasted static power and loss of efficiency. Therefore, the efficiency of Class AB amplifiers will be between Class A and Class B. Main points of distinction Class A amplifier Class B amplifier Class AB amplifier Working point position Load line midpoint Load line cutoff point Between load line midpoint and cutoff point Distortion The minimum distortion is slightly higher than Class AB, and there is cross distortion to eliminate cross distortion The power transfer efficiency has the lowest efficiency, and the efficiency below 50% is about 50% to 78.5%, and the efficiency is slightly lower than Class B Main application: low power distortion, low power amplifier, high power amplifier, general audio amplifier Class D amplifier The aforementioned A, B, and AB amplifiers can all be regarded as analog amplifiers. Because their input and output are analog sound electrical signals, which are amplified by the analog power amplifier, and do not involve modulation, filtering, codec and other processing processes. The class D amplifier can be called the simplest digital amplifier (some people call it a PWM amplifier, not a strict digital amplifier). Class D amplifier receives analog audio signal, and compares it with the triangle wave generated by the internal triangle wave generator, the result is a pulse width modulation signal