Why is the power amplifier so complicated?

1 in fact, the power amplifier used in home theater is relatively more complicated than ordinary power amplifier. Power amplifiers are made big, not just because of heat dissipation. Digital power amplifiers can be made very compact.

Let's talk about why the home theater power amplifier is complicated. Home theater amplifier is also called AV amplifier. In order to restore the sound field effect, it is usually five-channel and seven-channel output. And is equipped with a decoder. For example, it is equipped with AC-3 decoder, Dolby surround decoder and digital sound field processor (dsp) to simulate and realize various scene sound effects. Moreover, even the radio functions are equipped with karaoke circuits, as well as multi-channel audio input and output interfaces and other functions. Therefore, the home theater power amplifier has many more originals than the ordinary power amplifier, such as the ordinary dual-channel power amplifier and the power amplifier, and both groups can be used. Av amplifier, miscellaneous seven channels. Ordinary power amplifier only needs simple signal processing, and av power amplifier needs a variety of complex functions such as decoding, sound field effect and preamplifier. Let's look at a diagram of a dual-channel power amplifier first.

Is it simple? There is room for compression. But in order to reach the standard size of the equipment, the internal space is not compressed too much. It is also spacious, with single-layer circuit board, dual-channel amplification and motherboard. Look at the av amplifier

Let's look at the row of power tubes in the radiator first. A channel has at least two channels. Look at the terminals behind the amplifier output, a big row. This is a highly integrated AV amplifier in recent years. Digital circuit, double-sided multilayer printed circuit board, all kinds of chips are highly concentrated, and the internal space is much better. The power amplifier imported a few years ago was dismantled, and there were rows of audio processing boards, so there was no way to start. It can be seen that the av amplifier is large, not because of heat dissipation, but because of its function. Of course, some av amplifiers are relatively simple, such as five-channel amplifiers, with discrete components for the main channel and power amplifier chips for other channels. All functions are streamlined. To put it bluntly is false. Let's look at the two channels of the stage amplifier (back stage). Why not be small? Heat dissipation is only part of it.

Look at the internal diagram, just two channels. But the power is high, and the output power on both channels is kilowatts. As shown above, there are two power boards, one left and one right. Because of the high output power, more power tubes must be used in the later stage. It is normal for a channel to have dozens of power tubes! In order to improve the quality of power supply, the transformer is huge, and the rectification and filtering are also huge. In short, the power of kilowatts comes from here, so the material will naturally not be thin. The amplifier with the same volume is naturally more compact inside. In addition, the weight of dozens of kilograms is not blowing! Real material! Finally look at a small digital power amplifier.

How's it going? It's much more spacious inside. If switching power supply is used, it can be made smaller. Of course, this power is not too great. But the operation is absolutely simple!

In the past, any power amplifier was quite simple, because the audio amplification circuit could not exceed two stages, and the ideal one was two stages (three stages of amplification would cause serious distortion). Simple negative feedback circuits are added to the first-stage audio voltage amplification and the second-stage power amplification to improve the sound quality, and various sockets (ports) such as record player, microphone and radio are connected through changeover switches. In these pre-input circuits, some simple impedance matching resistors and capacitors are added at most. The power supply and output are genuine, with heavy weight and pure sound quality. Later, some amateur radio enthusiasts joined Dolby system one after another. At that time, radio magazines also introduced various power amplifiers to improve the sound quality of each issue. With the development of society, the product amplifier has gradually entered the family, renamed as home theater amplifier, also known as Av amplifier. According to the configuration of the speaker, the output is divided into multiple outputs. Coupled with various complex functions such as decoders, in fact, except for a few people, people's ears are generally insensitive to sound details. Many of them can observe the curve changes on the instrument by adding and deleting functions, but people may not be aware that many functions are indeed added, but most of them are for commercial publicity. You said that there are so many buttons on the power amplifier that few people can really understand and use them. Now most devices are integrated. On the contrary, the quality of power supply and output transformer is the key to judge a power amplifier. Some power amplifiers are marked with the output of 100W or even 300W, and the power transformer seems to be limited to 30 W. Do you think it can output 100W? There is also a speaker, no matter how good the power amplifier is, it can't reflect its quality without a pair of good speakers.

In addition, when the power amplifier was popular at that time, it was amazing to talk about the fashion of cooking machines, saying that the ultimate role of power amplifier could only be played through cooking machines. I'm at a loss. The cooking machine has a little effect, but it is not as magical as it is said. The key is the choice of equipment. Why do many enthusiasts choose to do it themselves? It is the mixing of good equipment that can really produce the timbre with thick bass, delicate treble and penetrating midrange. And it should be more powerful. When working, adjust the volume to the output power of the whole machine110 or 1/6, and the timbre effect will be better.

Audio power amplifier seems to have many function buttons, which are somewhat complicated. In fact, it is not only a power amplifier, but also circuits such as preset, input selection, sound processing and equalization processing are integrated in it. In fact, it is a combined power amplifier, but it is not called this in household heating audio equipment, but called HIFI power amplifier.

Although there are many functions, not many can be used in actual use, because the adjustment is relatively complicated and difficult, and it is better not to use it if it is not well adjusted. The sound system is just a fever, and you gradually improve your level in the process of "playing". If it is too simple, you won't "play", don't you think? So the more complicated it is, the better the market performance will be. When you "play" for a period of time, you will find that it is not so complicated, that is, you will soon "play" thoroughly, so why not upgrade and buy a better one? This is the reason why the power amplifier is more complicated.

There are many components and functions, so it is naturally complicated to do. In the early days, when we played power amplifier, we just found two or four tubes and made transformers around the coils. There is no shell, two pipes are exposed, and two large transformers are lined up. Turn off the lights and turn on the lights at night. We look at the slightly shining lights. Everyone smokes and drinks tea and enjoys their own achievements.

The power amplifier is not complicated. The principle is to amplify the mA-mV audio AC signal to the wattage power that can drive the speaker. The simplest is a power amplifier plus an output transformer and several resistors and capacitors. The power amplifier tube works in Class A state. The so-called working class A state means that the power amplifier has been working at full load, regardless of power output. The front electron tube power amplifier circuit is. Because transistors are used, the current circuit is very complicated. The main advantage of transistor is that it can work without filament, so the power consumption is low. Because the main idea of the original amplifier is efficiency, the circuit design works in class B state. And due to the class B status, the correct tube must be used. Cross-distortion is produced on the picture tube, and the compensation circuit is complicated. Later, for the sake of high fidelity, the push-pull of the circuit should be absolutely consistent, and the couple's money should be changed to homosexuality. That work push-pull and the opposite effect, so add the circuit. In fact, the essence of complexity is to make up for the shortage of transistors relative to electron tubes and the result of efficiency, so power amplifiers are becoming more and more complicated.

Let's not talk about retro and expensive tube power amplifiers, but why are mainstream transistor power amplifiers big? A very important part of the amplifier is the power supply, that is, the transformer rectifier filter. Around the transformer is the traditional copper wire with the best effect and the most stable voltage, commonly known as "cow". A transformer weighs several kilograms! The rectifier is not heavy, but made of diodes. The purpose is to change alternating current into direct current! Filters are very important and usually consist of 4-8 supercapacitors. The purpose is to filter the current into a shape close to a straight line, and the sound is soft and noiseless. Therefore, the more filter capacitors, the better. The larger the capacitance, the better. The capacitance is not heavy, but it is very large. 10000 microfarad capacitance is similar to that of film! I'm talking about the configuration of power amplifiers with a market price of more than 3,000 yuan, but toys that are too cheap are another matter. ...

The complexity of power amplifier lies in its digital decoding system and sound reproduction system. Dolby function (AC-3) represents its grade and quality. 1996, spent nearly 7000 yuan to buy a Japanese "Tianlong" 3200G power amplifier. Up to now, no domestic power amplifier can compare with it.

Are you an enthusiast? I haven't played with this thing for years. One is to meet the power requirements, the other is to have a wide frequency response, and the third is not to be distorted, which sounds soft and relaxed. Fourth, we must sound like we are there ... meeting these requirements will of course be more complicated. It takes a lot of patience to make it, and I don't know how happy and satisfied I am when I succeed. Words are beyond description.

Large volume has little to do with heat dissipation.

The headline explained the conclusion first. Home theater power amplifiers are all multi-channel designs, and class A amplification design is not adopted for maximum sound quality like HiFi power amplifiers. In order to pursue excellent sound quality, few people will use Class A for the left and right main channels and Class A for other channels. But this is not the main reason for the large size of home theater power amplifier.

Huge function

At present, the power amplifier of home theater is very powerful, and there are also many common home stereos (the front and rear stages are integrated). Friends who have removed the power amplifier should know that the circuit board inside will have many layers, which are closely attached. It can also be seen from the dense terminals of the fuselage. The more channels supported, the larger the power amplifier. For example, the flagship combiner of Tianlong and marantz already has the post-stage output of 13 channels, and each channel in it can be an independent operational amplifier. If we want to support new technologies such as panoramic sound, Dolby vision and 8K, we need corresponding processing chips and circuits, which undoubtedly increases the space occupation.

Large size-audio and video optimization

Advanced home theater power amplifier pays special attention to the optimization of audio and video. Because the internal circuit is complex, it will produce all kinds of telecom noise, so it will shield and isolate many modules. In addition, in order to provide a stable and pure power supply, there is also a large annular transformer inside.

A few days ago, I was very lucky to experience marantz's new 80 15 8K combined flagship amplifier, which is not only big and strong, but also the price of 28,000 yuan is really exclusive to the rich. Look at the menu above, and you will find that it supports the most advanced audio and video technologies. Extremely harsh workmanship design, so that this long-established audio brand has to pay the price. No wonder it can achieve the largest market share of home theater amplifiers in the world.

From the principle analysis, it is not complicated. You are talking about AV power amplifier, because it involves audio and video decoding, processing and audio amplification, and it is amplified from several channels to more than a dozen channels with the same power, so the circuit board is naturally full. Makes you feel complicated. Take apart a low-end AV amplifier, and you will find that it is actually very simple. The higher the end, the more processing circuits and channels, which is naturally complicated.

As for why make it so big? The width of 430mm is actually the standard equipment width, following the professional equipment, and of course there are the standards of 320mm width and 240mm small chassis. However, AV power amplifiers are generally relatively standard chassis standards. Because audio equipment can't be used as a whole, it is often more appropriate to use standard chassis and standard interface when putting multiple devices together. Easy to upgrade. There are also small ones, such as Bose and B&; O I like to make my own non-standard, the fuselage and interface are exclusive and incompatible with other brands, so once the format is upgraded, all of them will be replaced.

In addition, when it comes to fever, AV power amplifiers currently include AB power amplifier modules adopted by Tianlong marantz, Qiao 'an and Yamaha, and the efficiency is about 60%. The heat is much higher than that of the pioneers who adopted D-class, Harman Kardon and Sony. But why not learn from other people's class D, and the efficiency is as high as 90%? Because at present, the performance of class D sound still cannot exceed that of class AB. Before, some brands actually used Class A as the AV amplifier, thinking that Class A sound was soft, but unfortunately they bet the wrong money. In addition to high power consumption, high calorific value and high cost, the output power is not enough for home theater.