Basic knowledge of HiFi amplifier

                                            Basic knowledge of HiFi amplifier

For a complete HiFi audio system, in addition to a pair of speakers you are satisfied with, the matching power amplifier is also essential. The power amplifier in the HiFi system is not only as simple as adjusting the volume and driving the speakers, but also has many ways, and the combination of them is one of the reasons why audiophiles enjoy HiFi music.

What is an amplifier? Its working principle is actually very simple, that is, to amplify various sound signals played by the sound source to push the speaker to emit sound. From a technical point of view, the power amplifier is like a current modulator, which converts alternating current into direct current, and then controls the sound signal played by the audio source to transmit currents of different sizes to the speakers according to different frequencies, so that the speakers will emit corresponding volumes. , The sound of the corresponding frequency.

HiFi speakers generally use pure music power amplifiers. Different from ordinary audio power amplifiers, pure music power amplifiers emphasize the lowest signal distortion in design, and faithfully restore the scene, details and performance of music to meet people's best expectations for music. Good appreciation request.

In terms of design and production, the requirements for pure music power amplifiers are extremely strict. The quality of a pure music power amplifier is not completely determined by its technical indicators. We should not simply look at its marked power frequency response or distortion, but should pay special attention to its design and production technology and music resolution.

Power amplifiers are generally divided into pre-stage power amplifiers, post-stage power amplifiers and combined power amplifiers. The pre-stage is used to initially amplify the signal and adjust the volume; It is a machine that integrates the pre-stage and post-stage.

The pre-stage is also divided into two types: active and passive. The active pre-stage uses the power supply to amplify the signal, and can also be used for preliminary amplification and reduce the internal resistance between the sound source and the post-stage, that is, it is used as a buffer; the passive one The front stage only has the effect of adjusting the volume.

The rear stage is to amplify the signal from the front stage to the speaker. The rear stage must have enough power to drive the speaker, but not louder and more powerful. The detail expression of music is also one of the criteria for judging whether the power amplifier is powerful.

Generally speaking, the effect of separating the front and rear stages is better than that of the combined machine, because the independence of each can make the division of labor more clear, complete their respective responsibilities more reasonably, and there is less interference between the two, and the details will be more detailed. . Moreover, for audiophiles, separating the front and rear stages will allow more combinations and more possibilities for sound, which increases the playability of HiFi speakers.

The front stage in Hifi equipment is generally divided into class A power amplifier, class B power amplifier and class AB power amplifier.

Class A power amplifier, also known as Class A power amplifier, is characterized in that its output circuit has a constant current flow regardless of whether the input signal is input, and this kind of amplifier usually operates within the linear range of the characteristic curve, so that the amplified signal is not distorted. Therefore, its advantage is that the distortion is small, the smaller the signal, the higher the facsimile, the biggest disadvantage is that the "power efficiency" is low, the maximum is only 25%, and the power consumption is not reduced at all when no signal is input, but because of its high fidelity, Some high-end audio equipment still uses Class A amplifiers.

It is undeniable that Class A power amplifiers are ideal for replaying music. It can provide very smooth sound quality, round and warm timbre, and transparent and open treble. These advantages are more than enough to make up for its shortcomings. Class A power amplifiers generate astonishing heat. In order to effectively deal with heat dissipation, Class A power amplifiers must use large radiators. Because of its low efficiency, the power supply must be able to provide sufficient current. Therefore, the volume and weight of Class A machines are generally relatively large, which increases the manufacturing cost and makes the price more expensive.

Class B power amplifier, also known as Class B power amplifier, works in such a way that when there is no signal input, the output transistor does not conduct electricity, so it does not consume power. There are fewer pure class B amplifiers, because the distortion is very serious when the signal is very low, so the crossover distortion makes the sound rough. Class B power amplifiers have an average efficiency of about 75%, generate less heat than Class A amplifiers, and allow the use of smaller radiators.

Class AB power amplifier is also called Class A and B power amplifier. Its working state is usually two transistors cooperate. When there is no signal, both transistors are turned on, but the current in it is very small. When there is a signal input, the transistor The current in it will increase. When one of the transistors is turned off by the signal, the other transistor must be turned on, and the two tubes are always turned off and on in turn, and almost all the current flowing through them is sent to the speaker, so , Class A and B power amplifiers generate less heat and are much more efficient.

Because the power required for listening to music is not large, Class AB power amplifiers use the working mode of Class A power amplifiers most of the time, and only switch to Class B when there is a transient strong sound of music. This design can obtain good sound quality and improve efficiency to reduce heat, which is a quite logical design.

In addition to the different working methods of power amplifiers, its materials also have the difference between "gall" and "stone". It is much larger, and can achieve better impedance matching with a variety of signal sources, and the sound is more stretched and natural. Because it works at a high voltage of hundreds of volts, the power amplifier made with it has the characteristics of large voltage dynamic range, less clipping distortion, and good sound field extension.

"Stone" refers to transistor devices. With the development of electronic technology, it is more than 40 years later than electronic tubes, but its development is very fast. In the 1970s, the transistor has developed rapidly, and it can be compared with tube amplifiers in terms of stability and sound quality. In terms of technical indicators, the distortion of the transistor machine is much lower than that of the tube machine, and due to the low cost and high output of semiconductor device production, the price of the transistor is much lower than that of the electron tube, which is more suitable for large-scale industrial production.

What are the specific differences between the two? Compared with the transistor, the advantage of the electronic tube is that it has a strong ability to withstand overload. Even if a very strong signal is accidentally input during use, it is not easy to break down and short circuit instantly and damage the electronic tube. As long as the peripheral circuit is not damaged, its working state will automatically recover; When the output is too large, the distortion produced by the electronic tube will increase slowly, which is difficult to detect in the hearing, so that the sound field performance will not be harsh and harsh, but more delicate and gentle; the temperature characteristic of the electronic tube is very stable in normal working conditions, so its amplifier circuit It is also far simpler than a transistor circuit, in line with the principle of simplicity first.

Of course, there are also deficiencies, mainly reflected in the need for a variety of power sources when the electronic tube circuit is working, and the power supply circuit is complex, the interference generated is not easy to completely eliminate, and the efficiency and signal-to-noise are lower than those of the transistor machine; the life of the electronic tube is limited by the cathode material. After hours, it starts to age, and at the same time, the electronic tube generates a lot of heat, so other cooling measures cannot be used except air cooling, and there must be sufficient cooling.

In terms of productivity, in addition to the power transformer, the transformer used in the tube amplifier also has an output transformer, which increases the weight a lot, and the tube amplifier with larger power can weigh tens of kilograms; Make production efficiency low, and production cost is very high.

Nowadays, there are fewer and fewer manufacturers producing high-cost devices such as electronic tubes, and electronic tube devices have become rare. Even if there is no worry about the extinction of bile ducts, the high price of tube machines and unbearable post-production costs (high energy consumption, tube replacement costs) It really deters ordinary audio enthusiasts, which is also the reason why its market cannot be expanded.