Two (or two) of the transistors in the output stage of the Class A amplifier are always in a conducting state, that is, they maintain conduction current regardless of the presence or absence of signal input, and make these two currents equal to the peak value of the AC, at which time the AC is at the maximum signal. In case of flow into the load. When there is no signal, the two transistors each circulate an equal amount of current, so there is no unbalanced current or voltage at the output center point, so no current is input to the speaker. When the signal goes to the positive side, the output transistor above the line allows more current to flow in, and the lower output transistor reduces the current relatively. As the current begins to unbalance, it flows into the speaker and pushes the speaker to sound.
Class A amplifiers work best in linearity, and each output transistor amplifies the full-wave signal. There is no Switching Distortion. Even if negative feedback is not applied, its open-loop distortion is still very low. It is known as the most ideal amplifying circuit design for sound. However, this design has advantages and disadvantages. The biggest disadvantage of Class A power amplifiers is their low efficiency. Because there is still full current flowing in the absence of signals, all the energy is converted into high heat. As the signal level increases, some of the power can enter the load, but many still turn into heat.
Class A amplifiers are ideal for replaying music. They provide a very smooth sound quality, a rounded and warm tone, and a high-pitched transparent opening. These advantages are enough to compensate for its shortcomings. Class A power amplifiers generate amazing heat. In order to effectively deal with heat dissipation, Class A amplifiers must use large radiators. Because of its low efficiency, the power supply must be able to supply sufficient current. A 25W Class A power amplifier is capable of at least 100 watts of Class AB amplifiers. Therefore, the size and weight of the Class A machine are larger than those of the AB class, which increases the manufacturing cost and the price is relatively expensive. In general, Class A amplifiers sell for about twice or more the price of Class AB amplifiers.
2. Class B power amplifier (Class B power amplifier)
Class B amplifier amplification works in such a way that when there is no signal input, the output transistor is not conducting, so no power is consumed. When there is a signal, each pair of output tubes is amplified by half of the waveform, and each of the output tubes is turned on and off to complete a full-wave amplification, and crossover distortion occurs when the two output transistors are rotated, thus forming a nonlinearity. Pure Class B amplifiers are less, because the distortion is very severe when the signal is very low, so the crossover distortion makes the sound rough. Class B amplifiers have an average efficiency of about 75%, which produces less heat than Class A machines, allowing the use of smaller heat sinks.
3. Class AB power amplifiers Compared with the first two types of power amplifiers, class AB power amplifiers can be said to compromise in performance. Class AB amplifiers typically have two bias voltages, and a small amount of current is passed through the output transistors when there is no signal. It uses the Class A mode of operation to obtain the best linearity in the signal hour. When the signal is raised to a certain level, it automatically switches to the Class B mode of operation for higher efficiency. The general-purpose 10 watt class AB amplifier works in class A within about 5 watts. Since the power required to listen to music is only a few watts, the class AB power is placed in class A power amplifier mode most of the time, only in the presence of music. Turned to Class B when the transient is strong. This design is a logical design with excellent sound quality and improved efficiency to reduce heat. Some Class AB amplifiers have a high bias current, allowing them to work in Class A over a wider power range, making the sound close to a pure Class A machine, but the amount of heat generated is relatively increased.
4. Class C power amplifier (C Class A power amplifier)
This type of amplifier is less heard, because it is a very distorted amplifier and is only suitable for communication purposes. Class C machines have exceptionally high output efficiency, but are not suitable for HI-FI amplification.
5, Class D power amplifier (Ding amplifier)
This design is also known as digital power amplifier. When the transistor of the class D amplifier is turned on, its load is directly connected to the power supply, and the current flows but the transistor has no voltage, so there is no power consumption. When the output transistor is turned off, all of the power supply voltage appears on the transistor, but there is no current, so it does not consume power, so the theoretical efficiency is 100%. The advantage of Class D power amplifier amplification is that the efficiency is the highest, the power supply can be reduced, and almost no heat is generated. Therefore, a large heat sink is not required, and the volume and weight of the body are significantly reduced, and the theoretical distortion is low and the linearity is good. However, this kind of power amplifier work is complicated, and the added line itself is inevitably biased, so the products that are really successful are few and the price is not cheap.
There are some Class D amplifiers that have good sound quality, but they are still only used in car audio, and some interested DIY masters have converted them into home audio.
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