Introduction to Audio Amplifier (Introduction)

Introduction to Audio Amplifier (Introduction)

Amplifier─Amplifier, in this article is talking about audio amplifier audio amplifier. It doesn't matter if it's an amplifier or an amplifier, it's good that everyone can know exactly. Let's talk about functionality first, then gradually from shallow to deep.

Different components of the audio equipment have different functions, mismatch or incorrect positioning. Even if it costs a lot of money, it will not make a good sound. Since ancient times, when it comes to audio, the amplifier has always been listed as the heart. Although some people think that the listening room space and speakers are more important than it, but it is definitely the five internal organs, not one of the six organs.

The main function of the pre-amplifier is to amplify the input signal enough to drive the load. However, the level (amplitude) of the input signal is different, and the load impedance of the signal also has high and low. Therefore, the amplifier often appears in different appearances in response to different conditions.

Pre Amplifier─The pre-amplifier is to withstand the signals from CD, DVD or LP turntable, FM / AM tuner, recording base, etc., and then amplifies it to drive the load. We should first understand two points. First, the preamplifier may not exist alone, or it may coexist with the post-amplifier. The second is that in addition to amplifying the signal to drive the load, it also has the function of impedance transformation. Because the pre-stage has to undertake many sources, such as CD, tuner, DVD, and recorder, the impedance of these sources is very likely to be inconsistent, and it can be integrated before being sent to the pre-stage. However, with the current circuit design, these source devices all tend to have low-impedance output characteristics and are easier to match.
You must have seen the preamplifier, there are many gold-plated seats on the back panel, and there are many knobs or rocker switches on the panel, so the preamplifier is also often called a control amplifier. In recent years, the design of the preamplifier is very different from the past. Because CD turntables, tuners, recorders, and DVDs are all listed as high level sources, although there are four or five gear options on the panel, you can connect them at will, because they are all high level sources. Source, there is no substantial difference.
Of course, there are high and low, relative to the high level is the low level (low level) source, the popular LP vinyl record system in the past, is a low level source.
The LP system includes a turntable, a tone arm and a phono cartridge. The phono cartridges are mainly in the MM moving magnet type and the MC moving coil type. The output voltage of the MM cartridge is only one fiftieth of the high-level source, even one third. The output of MC cartridges is as low as one-twentieth of that of MM cartridges. Therefore, to connect the MM cartridge, its signal must be amplified separately first, and then sent to the high-level amplifier for the second amplification. It is more troublesome to connect the MC cartridge, first to amplify separately, and then to amplify through the MM cartridge, and finally send it to the high-level circuit for the third amplification. If you want to save a level of amplification, you can use a high-output MC cartridge.
Low-level sources not only have low output voltages (levels, amplitudes), MM and MC cartridges also go through the "anti-RIAA" network, and this anti-RIAA network is only subject to the standards of the American RIAA Association. All have different calculated values, which was still a feature of blooming flowers.
Looking at the current pre-stage, it is rare to have low-level amplification. Some pre-levels directly indicate high level high-level amplification on the panel, which cannot match the LP system. As for the pre-amplifier (Pre Preamp.) Or booster (Set Up Trans.) For MC cartridges, most of them have also been discontinued for many years. Beginners may only remember the past years from the pictures.
Few people think that the sound quality of LP records is not good enough, and very few audiophiles still insist on using LP. However, the CD system is very convenient in operation, has low loss, and the software is also light and easy to carry; and the famous foreign record companies, new recordings only release CDs, and no longer issue LP records, so LP quickly fades. Coupled with the recent rapid growth of DVD, if SACD or DVD audio is popular, LP is likely to have no market at all. (Note: The currently popular DVD movies have a digital audio specification of 48KHz / 16bit, not 96KHz / 24bit. Although the DVD audio specification is determined to be 192KHz / 24bit, the sampling frequency of SACD is higher than 2MHz; purely based on sound quality SACD should be better than DVD audio.)
The preamplifiers close to the 21st century have other differences. Early products were equipped with a tape monitor transcription function. At that time, audio fans often bought cassette recorders, and in order to prevent feedback from the "recording loop". Howling, there must be a tape monitor switch. A few years ago, the author was designing a pre-level, in order to prevent the recording loop, and invented a three-segment switch connection method; because the line connection method was published in the "Audio Technology" magazine, this design has also been domestically produced by Zhongrong The audio is used on their predecessor, and there is a chance to publish this design on the website.

However, like LP, the cassette seats that were once beautiful have long been out of fashion. Even the advanced models with three heads and dual drive shafts are almost completely discontinued. Dolby C / Dolby S has not changed the cassette seat market. Eliminate the destiny out. So when you have a budget now, ask the owner of the audio shop to combine a set of audio, his equipment list absolutely does not have LP turntables, and there will be no cassette recorder.
Omit the tape monitor, and the most important operation functions of the preamplifier are only the source switching selection and volume control. Some models still have the MM phono amplifier, which is considered a gift. As for tone control (high and low frequency tone control), and loudness (loudness control), the more Hi-End models, the less you can see.
Because the current preamp has excellent characteristics and the response is like a straight line, there is no need to add extra oil and vinegar. If you want to buy a preamp with high and bass control, you may still be ridiculed. Because the response is flat, the high-level front stage is also called a flat amplifier (Flat Amp.).

The post-amplifier is different from the post-amplifier. The post-amplifier or power amplifier can be Main Amp. Or Power Amp. Like the pre-amplifier, the post-amplifier also amplifies the input signal enough to drive the load. But in actual operation, the two are very different. (Amp. Is short for Amplifier)

The input signal of the latter stage is very simple, that is, to accept the output of the preceding stage. But the load of the latter stage is the speaker, which is what makes many audio fans and even magazine review writers unsure. The rear stage is the front stage load, which is a high impedance load; the horn is the rear stage load, which is a low impedance load. It looks almost the same, with only one word difference, but the high and low impedances result in "easy to push" or "not pushable"; the load is important, so I hope you can really understand it.
The front stage is connected to a high-impedance post stage, which mainly provides a suitable output voltage, because the input impedance of the post-stage amplifier is rarely lower than 10KΩ. There are such post-stages, but they are rare, generally about 47KΩ.
When the rear amplifier is connected to a low-impedance speaker, it should not only provide a suitable voltage, but also provide sufficient current. Except for a few special cases, the current speaker impedance is rarely higher than 8Ω, and even lower than 4Ω. And 1KΩ = 1000Ω, is the difference big?
Therefore, the Hi-End stage not only emphasizes high-power output, hundreds of watts at a time, each channel is individually packed, but also specifically notes that it is a high-current design. When the load impedance is reduced by half, the output power will be doubled. If the output current capacity is insufficient, when the load impedance decreases (some speakers are working, such as Dynaudio, its impedance will decrease as the signal frequency decreases), if the amplifier output current is not enough, it will produce cutting-clipping.

The preamplifier and post stage of the integrated amplifier are integrated together, which is the integrated amplifier (Integrated Amp.). It is very common to make mono (mono) in the back stage, and there have been mono in the front stage, but the integrated amplifier has always appeared on the market as a single machine. I have never seen the mono integrated amplifier. Maybe you will think: it is also a stand-alone, and it is also a pre-level + post-level, so the integrated amplifier is not only low in price, but also the sound quality is not very good.
Even if you are the editor-in-chief of a battle-hardened magazine, you will not be wrong. Because the integrated amplifier has limitations in size, power, and components, the price and quality of the integrated amplifier are not as high as those of the separate model. But to broaden your horizons and look around, perhaps the A brand integrated machine is better than the B brand separate model. Some integrated machines can be settled for tens of thousands of yuan. If you want to bring it home to worship, it will cost a lot of money.
Separated models seem to be more convenient when changing machines. Because the front and rear stages are independent, the power is not enough to change the power, and the front stage can still be used. Or replace the transistor pre-stage with a vacuum tube pre-stage, and the latter stage can still be used. However, the integrated machine also has ingenuity. The Pre Out and Main In jacks are added on the back panel, and the front stage and the rear stage can be used separately. During normal operation, insert a U-shaped copper rod between the Pre Out and Main In terminals. However, not every integrated machine has a front-stage output and a back-stage input terminal. Although this method is beneficial to the user than the bucket machine, it may also reduce the signal-to-noise ratio, so some manufacturers have abandoned this function.

Radio amplifier --- At present, the receiver has almost completely withdrawn from the audio market of LP and cassette, and the fate of FM / AM tuner is not better than that. I have never seen equipment reviews of magazine media in recent years. . Many years ago, some foreign manufacturers wanted to develop AM Stereo stereo AM broadcasting, but in the end it was unsuccessful. Because the receiver amplifier (Receiver) is a combination of pre-amplification, post-amplification, and tuning circuit, it is one machine with three uses.

European and American manufacturers seem to have never been keen on the production of receivers. Even if there are products on the market, there are not many models. This is a patent of a Japanese manufacturer, and each brand has multiple models. The Japanese company is desperately engaged in receivers. About two decades ago, it used to get into trouble. The power is getting bigger and bigger. You are 60W, he is 80W, and I am 100W. After playing with each other to the end, a 330W super high power receiver per channel appeared! In the end, consumers and manufacturers couldn't play because of the poor sound quality, which caused both losses.
If there is such a receiver on the market and the price is not high, it is really suitable for personal use. Japanese products have appeared in the front class + FM tuner model, well-conceived, but not popular, audio fans who are not experienced may not know that there is such a machine.

Home theater surround --- AV amplifier This AV amplifier is the mainstream of audio amplifiers from the end of the 20th century to the 21st century. Today's audio beginners have seldom focused on pure music, and their interest is outside the DVD home theater Bring karaoke. The AV surround amplifier integrates all the controls in one body, such as the old buckle of LKK, holding the remote control in hand, you may not know which button to press. Complete AV amplifier, including MM phono low level amplification, high level amplification, and multi-channel power amplification, in addition to the most important Dolby AC-3 and dts 5.1 channel surround processors .
The main feature of the AV amplifier is the combination of audio and video. The sound quality may be compromised, but it is indeed the favorite of general consumers. Wouldn't it be more comfortable to listen to the CD while listening to multi-channel surround sound than to just listen to music?
The advancement of surround processing technology and the diversification of controls have a direct impact on the sales of AV amplifiers. Dolby Pro-Logic oriented logic surround is no longer attractive. The new Dolby AC-3 is the focus of everyone's talk. The addition of dts has increased the enthusiasm. Suppose you watch movies with dts and listen to records with DSP. If a machine has this function, why not spend money on it for enjoyment? Japanese manufacturers are right on this point, AV amplifiers have always been the protagonist of production online.
One point should be mentioned specifically: the DSP developed by Yamaha in Japan, although it is also a multi-channel surround system, is originally intended for listening to music and has nothing to do with the video part of the video. However, if the DSP theory is directly added to the general listening environment, there is a conflict. Because your listening space must be planned to be similar to a silent room before you can use the DSP to simulate the effects of various concert halls. Many audio commentators are not aware of this truth until now.

European and American manufacturers claim to be Hi-End, originally producing AV surround amplifiers, but seeing the market growing, they finally can't bear it, and also invested in AC-3 / dts processors and multi-channel post-stage production. But they still uphold the supremacy of sound quality, the product pattern is not as good as Japanese products, but the price and quality are higher than Japanese products.
The control characteristics of the Japanese-made AV amplifier are dazzling, and it also has Y / C separation S input and output terminals, and the top color difference terminal; it must be connected to the TV during operation. Although diehard audiophiles despise AV, but AV surrounds have swept the world, and it is not easy to hide it. In fact, when audio collides with video, the importance of audio must inevitably decline significantly, or only be an accessory to video. Who says watching DVD movies must be accompanied by 5.1 channel surround? Wouldn't it be possible to use two speakers?
I once said: The eyes grow in front of the ears. When you watch a movie or a disc, once the eyes are attracted by the picture (the film complex), your ears have no effect. He vigorously promoted the AC-3 and dts editor writers in the magazine, and his home almost has only a pair of speakers! I don't care about the surround sound at all.

Transistor or vacuum tube?
Not only the audio, but even the more popular computer, the original components are vacuum tubes. Therefore, in a certain period of time, the amplifiers are all tube machines, and the horns it matches are also high-efficiency types. After the rise of semiconductor components, vacuum tubes gradually faded out of the market. In contrast, semiconductor solid-state components have the advantages of long life, low heat, and high output power. Therefore, many manufacturers also gave up vacuum tubes and began to use solid-state components to design amplifiers. Some vacuum tube manufacturers closed their factories and went to other businesses.
The world is unpredictable. The vacuum tubes that have been eliminated in recent years have turned back, and not quietly, but in groups to fight against the transistors and come in a menacing manner. Not only has the production of tube machines sprung up, but some vacuum tubes that have been extinct for many years have also come to the market again.
In the face of crystal machines and tube machines, consumers often feel at a loss, which sound is better? Some people criticize that the crystal machine is cold and hard, without the warmth of the machine, and even the reporters of many domestic newspapers have reported this. This argument is absolutely wrong! No matter the transistor or the vacuum tube, as long as the design is good, it can be beautiful. The design is improper, and even the most expensive vacuum tubes can't get Bel Canto. Some people abandoned the crystal machine and switched to a tube machine, but after listening to the tube machine for more than ten years and then changing to a crystal machine, there are also many people. For example, a few years ago, the deputy director of a certain hospital in Mie, after changing the Brumaster crystal back grade, only realized that the listening machine had been wrong for more than ten years!

Transistors and vacuum tubes have been debated for more than two decades. The author's opinion is that the tone of the two is getting closer and closer; the tube machine has the transparency of the crystal machine, and the crystal machine has the warmth of the tube machine. The hybrid design that combines the vacuum tube and the transistor is expected to have the advantages of both. But not so lucky, if it is not a real master design, it is possible to get four different sound performance. However, the output power of the rear stage of the tube machine is generally low, and the high efficiency and constant impedance type should be used with the speaker. If you play AV, there is no choice, because the AV amplifier is 100% transistor machine.
In the audio amplifier circuit, many components require pairing, especially the active components of the output stage. For vacuum tubes, the accuracy of their matching is usually lower than that of transistors. Taking the common bipolar transistor example of 6922 / E88CC, the error of the two internal triodes is often more than 10%. For semiconductor components, if they are of a composite type, the characteristic error will rarely be higher than 5%. For some super-matched FETs, the factory-set internal error is even only 0.3%; the vacuum tube cannot have such resistance. There is a domestic Mr. Wen Yanping who had previously opened a fighter plane. In recent years, he has specialized in vacuum tube testing and matching. His matching is very accurate. Interested netizens can contact Mr. Wen, telephone: 2931-1530.

Active or passive front-stage active-acTIve (active), the simplest way is to eat electricity; passive (passive) passive does not eat electricity. Therefore, this source is the source of power supply, not a signal source. The post-amplifier cannot be passive because the passive components cannot provide sufficient voltage and current amplification. The MC moving coil phono can be connected to a booster. This booster is a standard passive or passive device, which has a voltage amplification function. The front stage can not be passive, although its output voltage and output current are lower than the rear stage, but passive components can not easily achieve the output current. There is a passive front stage without any components inside, only the input signal source selection and volume attenuator, plus the output and input base and wiring, it is combined into a front stage. To say that it is a passive predecessor is theoretically unreasonable because it has no amplification effect. In industry, there are similar equipment, directly called volume attenuators. If the passive front stage uses a high-priced volume attenuator, such as the British Penny + Giles (P & G), the input and output terminals use WBT. If it is an imported brand, it is guaranteed that the price of one unit will exceed NT $ 30,000!
In actual operation, we really don't need a pre-amplifier, and some integrated amplifiers do not have a pre-amplifier. At this time, the gain of the post-amplifier should be set relatively high. The volume attenuator has an absolute impact on the sound quality. A high-quality volume is sometimes more expensive than an inexpensive pre-amplifier. Whether it is a resistance progressive type or a continuous rotary type, there are high-grade and low-grade products. Some people insist on the Holco resistance progressive type, but the P & G continuously adjustable type is also used by the Hi-End factory. For example, when Dynaudio of Denmark produced Arbiter preamps, they tried the volume controllers available on the market, with multi-segment and non-segment types. Finally, they chose the best sound quality British-made conductive plastic stepless P & G volume. In the past, the former level of Mark Levinson in the United States also used P & G volume attenuators in the past, and never used resistance progressive volume.

Job category-category A? Class AB? Class B?
Please remember the importance of the load, because many characteristics of the amplifier are related to the load. The pre-amplifiers are all Class A. The reason is very simple. Its load (post-stage) is high impedance. Just set a little current to make it work in Class A. However, the load of the post-stage amplifier is a low-impedance horn, and the current must be set very high to make it work in class A. However, although the distortion of Class A work is low, the heat and power consumption are very high, and the static power consumption of the mono Class A 100W post-stage is as high as 270W.
The rear stage of the crystal is class AB, but the active bias is used in the design to allow the bias current to change with the input signal. This is close to the low distortion of class A, and there is no high heat and power consumption of class A. It is also 50W output. Some people think that the A-type amplifier is more powerful than the AB-type amplifier. It is not unreasonable, because when class A works, the current / loss is high, so the selection of components is especially thoughtful. But Class AB amplifiers are properly designed, especially for high currents, and the sound quality is not inferior to Class A. Because Class A is not a panacea, it solves some problems, but it also causes other problems, especially because of high heat, it is easy to cause large changes in the characteristics of power crystals, such as reduced hFE value and increased leakage current.

Independent components or OP IC
Almost all Hi-End machines use independent components, such as transistors, FETs, MOS FETs, and OP op amps are rarely used. You can not like IC, but you can't say that using IC is to simplify the work of the circuit. To say simple or complex, the internal circuit of the IC is absolutely complicated, which contains hundreds or thousands of components, but when we use the IC in the circuit, its peripheral components are relatively few. There are indeed many audio designers who do not have any good feelings about ICs, and the reasons are quite good. Because the voltage and current settings of ICs have been completed on the production line, designers seem to have no use for heroes in the face of it.
Please note: Some circuits must use ICs, such as Dolby Surround decoding, D / A converter--DAC; it is completely impossible to build with transistors. Some high-quality ICs are also expensive and cost more money than using independent components. Hi-End manufacturers also use ICs in high-priced machines, such as Jeff Rowland. But don't see the 8-pin, black plastic packaging, just think it is an IC, it may be a paired FET instead of an IC.
Looking at the inside of the machine, the Japanese AV amplifier is more criticized. Because of the large number of automatic plug-ins and the many functions, the arrangement of the components is not neat and the wiring is very messy. Some hand-shelved pipe machines have beautiful and neat internal wiring, which is extremely impressive. In addition to the amplifying components, the power supply voltage regulator also has IC and independent components. In a DAC or a Japanese surround amplifier, the protagonist of the voltage stabilizing component is almost always a three-legged IC, but if it can be changed to a separate component voltage stabilizing circuit, the sound quality will often be significantly improved.

Balanced or unbalanced balanced terminals are Hi-End representatives in many audio fans. Agents and distributors also often tell consumers that balanced connection is better. Due to the long connection time of professional equipment, such as more than 30 meters, it must be able to balance the line for transmission. Audio equipment did not add a balanced connection from the beginning. Although the manufacturer said it, the balanced connector has not yet become a universal standard for home audio.
The sound balance has nothing to do with long-distance connection. It is based on high sound quality, so the circuit design must be more complicated than the unbalanced type. To achieve balance, the Cannon / XLR three-plug input terminal must be installed on the back panel. Some manufacturers take shortcuts and use simple inverter circuits. There are even some Hi-End machines, such as the famous Swiss factory Revox, which has no balanced circuit at all, and its balanced terminals are fake, purely used to bluff laymen.
True audiophiles will also know another message: a post-amplifier is connected with unbalance and balance. The horizontal and horizontal connection will cause increased noise, narrower frequency response, and improved distortion. This does not mean that the balanced connection is poor, everything depends on the design. Of course, crystal machines mostly have balanced terminals, while tube machines are relatively rare.

It is said that it is better not to shut down all year round. Audio fans who do not shut down all year round are rare, and they are always worried about this. Some crystal pre-stages are not equipped with power switches at all, and they are in a state of preparation when they are plugged in. For example, the pre-stage made by me. You'd better listen to the original advice and don't be smart enough to use the power strip to turn on and off. Be careful that the pulse when turning the machine on and off will burn the speaker through the rear stage. Even if it is not turned off, the pre-stage will not consume much power. However, it is difficult to say that the latter level, high-power pure Class A models obviously consume power. If it is a vacuum tube machine, regardless of the pre-stage or post-stage, it is best to shut down when not in use, in addition to saving power, it can also maintain the life of the vacuum tube.
The crystal machine and the tube machine must be warmed up, that is, the sound quality will be normal after a period of operation. Some components may require a long time to run in (run in). If run in is not enough, there will be no sound. You can also use tricks to make the amplifier both warm up when it is turned off, so that not only does it have no pulses when it is turned on, but also quickly allows the amplifier to reach its optimal working state after each time it is turned on. However, if it is predicted that there will be a power outage, it is better to shut it down, otherwise the fuse may be blown due to the instantaneous charging of the filter capacitor. Note: The real run in is not just to boot, let the system make a sound!
In the field of audio, there are very few laws that are invariable or "universal", especially non-data arguments such as the determination of sound quality and the matching of equipment, speaker space placement, etc., have always been in full bloom. Moreover, the opinions of various audio experts even have "contradictory" differences. This is the most confusing point for consumers, because it is difficult for them to hear the truth.

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