Basic knowledge of popular science hifi power amplifier
A complete hifi sound system, in addition to a pair of speakers satisfied with itself, its matching power amplifier is also essential. The power amplifier in hifi system is not only simple to adjust the volume and promote the speaker, but also has many doorways. The matching combination is also one of the reasons why enthusiasts enjoy hifi music.
What is a power amplifier? Its working principle is actually very simple, which is to amplify various sound signals played by the sound source to promote the sound of the speaker. From a technical point of view, the power amplifier is like a current modulator. It converts alternating current into direct current, and then transmits different sizes of current to the speaker according to different frequencies through the sound signal control played by the sound source. In this way, the speaker will emit sound of corresponding size and frequency.
HiFi audio generally uses pure music power amplifier. Different from ordinary audio power amplifier, pure music power amplifier emphasizes the lowest signal distortion in design and most faithfully restores the scene, details and performance of music, so as to meet people's best appreciation requirements for music.
In terms of design and production, the requirements of pure music power amplifier are extremely strict. The quality of pure music power amplifier is not entirely determined by its technical indicators. We can't simply look at the power frequency response or distortion marked on it, but should pay special attention to its design and production technology and the clarity of music.
The power amplifier is generally divided into front level power amplifier, rear level power amplifier and combined level power amplifier. The front level is used to preliminarily amplify the signal and adjust the volume; The latter stage amplifies the signal from the former stage to promote the loudspeaker; The merging machine is a machine that integrates the front stage and the rear stage.
The front stage is also divided into active and passive. The active front stage uses the power supply to amplify the signal. It can also be used for preliminary amplification and reduce the difference between the sound source and the internal resistance between the rear stage, that is, it is used as buffer; The passive front stage can only adjust the volume.
The latter is to amplify the awesome signals from the previous stage to the speakers. The latter stage must have enough power to push the loudspeaker, but not louder and louder. The detailed expressive force of music is also one of the criteria for judging whether the amplifier is capable.
Generally speaking, the effect of separating the front and rear stages is better than that of the merging machine, because their independence can make the division of labor clearer and complete their responsibilities more reasonably, and there is less interference between the two and more details. Moreover, for enthusiasts, there will be more combination methods for separating the front and rear stages, and there are more possibilities for sound, which increases the playability of hifi sound.
The front stage of 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 by constant current flow in its output circuit regardless of whether the input signal is input or not, and this amplifier is usually operated 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, and the smaller the signal, the higher the fidelity. The biggest disadvantage is that the "power benefit" is low, the maximum is only 25%. When the signal is not input, the power consumption will not be reduced at all. However, due to its high fax degree, some advanced audio equipment still use class a amplifiers. It is undeniable that class a power amplifier is an ideal choice for replaying music. It can provide very smooth sound quality, mellow and warm sound, transparent and open treble. These advantages are enough to compensate for its shortcomings. The calorific value of class a power amplifier is amazing. In order to effectively deal with the problem of heat dissipation, class a power amplifier must use a large radiator. Because of its low efficiency, the power supply must be able to provide sufficient current. Therefore, the volume and weight of class a machine are generally large, which increases the manufacturing cost and the selling price is also more expensive.
Class B power amplifier is also called class B power amplifier. Its working mode is that when there is no signal input, the output transistor is not conductive, so it does not consume power. There are few pure class B power amplifiers, because the distortion is very serious when the signal is very low, so the crossover distortion makes the sound rough. The average efficiency of class B power amplifier is about 75%, and the heat generated is lower than that of class a machine. It is allowed to use a smaller radiator.
Class AB power amplifier is also called class A and class B power amplifier. Its working state is usually the cooperation of two transistors. When there is no signal, both transistors are on, but the current in them is very small. When there is signal input, the current in the transistor will increase
When one transistor is cut off due to the action of the signal, the other transistor must be on. The two tubes are always cut off and on in turn, and almost all the current flowing through them is sent to the speaker. Therefore, class A and class B power amplifiers produce less heat and much higher efficiency. Because the power required to listen to music is not large, class AB power amplifier uses the working mode of class a power amplifier most of the time, and it changes to class B only when there is a transient strong sound of music. This design can obtain excellent sound quality, improve efficiency and reduce heat. It is a quite logical design.