The first of these can be divided into several types:
1. Pure alpha power amplifiers
Pure alpha power amplifiers, also known as class a power amplifiers (class a), are fully linear amplifiers. When a pure alpha power amplifier works, both positive and negative channels of the transistor are open, whether with or without signal, which means that more power is consumed as heat. Pure alpha power amplifiers are relatively rare in the application of car acoustics, such as the sinfoni high-quality series in italy. This is due to the very low efficiency of the pure alpha-power amplifier, which is usually only 20-30 per cent, and its sound-crazy companions are very happy with its sound。
2. B. Power amplifiers
B power amplifiers, also known as class b power amplifiers (class b), are also called linear amplifiers, but they work in very different ways from pure alpha power amplifiers. When working, the positive and negative channels of the transistor are usually in a closed state unless there is a signal input, that is to say, only the direct channels work when a positive signal comes in, while the negative channels are closed, and the two channels never work simultaneously, so that there is no loss of power in the absence of the signal. However, when both positive and negative channels are opened and closed, cross-fiscres often occur, especially in low-altitude situations, so that a type b power amplifier is not a truly high-fiscal amplifier. In practical applications, it is true that many early car acoustics are type b because they are more efficient。
3. Enrichment of alpha-b device
The ab power amplifier, also known as the ab power amplifier (class ab), is a design compatible with the advantages of a and b power deployments. When there is no signal or when the signal is very large, both positive and negative channels of the transistor are frequently opened, at which point the power is depleted, but no a-type operation is severe. When the signal is positive, the negative channel is open before the signal becomes stronger, but the negative channel is closed when the signal turns strong. When the signal is negative, the reverse works. The weakness of the ab power amplifier is that it produces a distortion, but it is better than the a and b categories relative to its efficiency ratio and the level of authenticity, and the ab type amplifier is also the most widely used design in the current car sound。
4. C. C
In fact, it's a job that's not real! Early c is used for radio-frequency power amplification ~ because fm-type radio-frequency output can be used, and the frequency is adjusted to carry the waves, all of which are not affected by their frequency, even if they are not true ~ but there are some fever friends in the near future because of its efficiency and the direction it is being studied to apply to the audio. But it's more popular in d, too
5-d power amplifiers
The d amplifiers, unlike the a, b or a-type amplifiers described above, operate on the basis of a switch transistor that can be fully readable or completely closed in a very short period of time. The two transistor tubes will not be transistored at the same time, resulting in very little heat. This type of amplifier is extremely efficient (around 90 per cent) and, ideally, 100 per cent, compared to only 78. 5 per cent for ab type amplifiers. On the other hand, the switch working pattern also increases the distortion of the output signal. The circuits for the d amplifiers are divided into three levels: input switch level, power magnification level and output filter level. Category d amplifiers work in a pulsed (pwm) mode with switches. Using pwm to convert audio input signals to high frequency switches, a comparison of audio signals with high frequency triangles is made by a comparator, with output being low level when the reverse end voltage is higher than the same end voltage, and high level when the reverse end voltage is lower than the same end voltage。
In the d type amplifiers, the output of the comparator is linked to the power magnification circuit, where the metallic oxide field effect tube (mosfet) replaces the bipolar transistor (bjt) because the former has faster response times and therefore applies to high frequency working patterns. Category d amplifiers require two mosfets, which can be fully operational in a very short period of time under a conductor or deadline. When a mosfet is fully steered, its pipe pressure is low; when the mosfet is completely closed, the current through the tube is zero. The two mosfet rotations are very fast on the switch in the conductivity and cut-off state, resulting in high efficiency and low heat generation, so that the d type amplifiers do not need a large radiator。
There are many other terms of reference for category d, such as category t, which are a deformation of category d. In practical applications, it was not until 1980 that this switch was rapidly developed as a result of the presence of mosfet. In real development, while efficient, there are also high levels of distortion, noise and poor resistance. As technology develops, such deficiencies will become fewer and it is expected that future d-type work will be more widely applied in the field of car sound。
Description of category a, b, a, c, d 5
Category a (also known as category a)
Two (or two groups) transistors in the a-cell output stage remain permanently in conductivity, that is to say, they maintain the transmission current regardless of whether the signal is entered, and equal the peak of the communication, at which time the communication flows into the load with the maximum signal. When there is no signal, the currents of the two transistor tubes are in circulation in equal quantities, so there is no imbalanced current or voltage on the output centre point, so there is no current input into the speaker. When the signal tends to be positive, the output transistor above the line allows more currents to flow, while the output transistor below reduces the currents in relative terms, and, as the currents begin to be uneven, it flows into the speaker and drives the speaker to sound。
The best linear method of working in category a is that each output transistor magnifies the signal in its full wave, and there is no switching distinction at all. Even if negative feedback is not applied, it is still very low in the open circuit, and is therefore known as the ideal magnification circuit design for the sound. However, there are advantages and disadvantages to this design, and the greatest drawback of the a type deployment is inefficiency, as there is still a full current flow when there is no signal and electricity is converted to high heat. When the level of the signal increases, some power is available to load, but many are still converted to heat。
The ideal option for replaying music in category a, which provides a very smooth sound, a warm sound and a transparent high, is sufficient to compensate for its shortcomings. In order to deal effectively with the problem of dissipation, large radiators must be used for power release in category a. As it is inefficient, it is essential that electrical supplies provide sufficient currents. At least 100 w a-type power is sufficient for a 25w a-type power supply. The size and weight of a-type machines are therefore larger than that of a-class machines, which increases manufacturing costs and prices. In general, the sale price for type a credits is approximately twice or more that of equivalent ab units。
2. B. B. (b)
The method of scaling up b is that the output transistor does not conduct electricity when there is no signal input, so it does not consume power. When there is a signal, each pair of output tubes is zooming in half a waveform, one full wave amplification is done at one turn to each other, and there is a distortion when two output transistors are rotated, resulting in non-linearity. Pure b is less active, as it is very serious when the signal is very low, so it makes the noise rougher. On average, the efficiency of operation in category b is about 75 per cent, generating lower heat than in category a and allowing for the use of smaller radiators. The usual working methods for type b are ocl and btl, which can provide greater power, and the majority of power integrated circuits can now form btl circuits in two blocks。
3, ab-type credits
Compared to the first two categories, ab-type performance compromises can be described. Ab-type power release usually has two depressures, with small currents passing through the output transistor when there is no signal. It uses type a work patterns for signal hours, obtains optimal linearity and automatically converts to category b work patterns when the signal is raised to a certain level of electricity to achieve higher efficiency. The ab-type machine, 10 watts, uses a-type jobs within 5 watts, and since the power required to listen to music is only a few watts, a-type work patterns are used for most of the time and are converted to b-class only when there is a musical momentary sound. It is a logical design to achieve sound quality and to increase efficiency in heat reduction. Some ab-type power releases are highly volatile, allowing them to work in category a within a wider range of power, bringing sound close to pure a-type machines, but generating a relative increase in heat。
4, c (c)
Such performance is less known because it is a very high level of distortion and suitable for use only for communications purposes. Category c output is highly efficient, but is not suitable for hi-fi amplification。
5, d (d)
This design is also called digital power. The magnified transistor tube in category d is directly connected to the electrical supply as soon as it is activated, and the current is in circulation but the transistor has no voltage and therefore no power consumption. When the output transistor is shut down, the total power supply is on the transistor, but there is no current and therefore no power consumption, so the theoretical efficiency is 100 per cent. The benefits of d-magnification are the most efficient, and the supply of appliances can be reduced to almost no heat, so there is no need for large-scale radiators, and the body size and weight of the machine is significantly reduced, with theoretical distortions low and linearly good. However, the complexity of this work and the inherent bias in the increase in the number of lines is such that there are few successful products and prices。
Ps: the majority of multimedia soundboxes are currently available in category b (b), and for both cost and space reasons, the multi-media soundbox powered circuits are more integrated and the power transformers and filtering capacity are unlikely to do much. This directly affects the sound quality and dynamics of multimedia boxes. Of course, the use of electronic tubes for multimedia soundboxes (e. G., the great oracle) is working in category a, but the price of soundboxes is not acceptable to the vast majority of people。
It is divided by output channel:
Mono, stereo double, 2. 1 channel, 5. 1 round sound
