Power square tube classification:

1, Class A power amplifier (also known as Class A power amplifier) Two (or two) transistors in the output stage of Class A power amplifier are always in a conducting state, that is, they keep conducting current regardless of whether there is a signal input or not, and make these two currents equal to the peak value of alternating current. At this time, AC current flows into the load under the condition of maximum signal. When there is no signal, the two transistors each flow the same amount of current, so there is no unbalanced current or voltage at the output center point, so there is no current input to the speaker. When the signal tends to the positive pole, the output transistor at the top of the line allows more current to flow in, while the output transistor at the bottom reduces the current relatively. Because the current begins to be unbalanced, it flows into the speaker to push the speaker to make sound. Class A power amplifier has the best linearity in working mode, and each output transistor amplifies the full wave of the signal without switching distortion. Even without negative feedback, its open-loop distortion is still very low, so it is called the most ideal amplifier circuit design for sound. However, this design has advantages and disadvantages. The biggest disadvantage of class A amplifier is its low efficiency, because when there is no signal, all the current flows in, and all the electric energy is converted into high heat. When the signal level increases, some power will enter the load, but most of it will still be converted into heat. Class A power amplifier is an ideal choice for playing back music. Can provide a very smooth sound quality, mellow and warm tone, transparent treble. These advantages are enough to make up for its shortcomings. Class a power amplifier has an amazing calorific value. In order to effectively deal with the heat dissipation problem, class A power amplifier must adopt a large radiator. Because of its low efficiency, the power supply must be able to provide enough current. The capacity of a 25W Class A amplifier is at least enough for Class AB amplifier of 100W. Therefore, the size and weight of A-class machines are larger than AB-class machines, which increases the manufacturing cost and makes the price more expensive. Generally speaking, the price of Class A power amplifier is twice or more than that of Class B power amplifier with the same power.

2. Class B power amplifier (Class B power amplifier) The working mode of Class B power amplifier amplification is that when there is no signal input, the output transistor is not conductive, so it does not consume power. When there is a signal, each pair of output transistors amplifies half the waveform, and when they are turned on and off, they work in turn to complete a full-wave amplification. When two output transistors work in turn, cross distortion will occur, thus forming nonlinearity. There are few pure class B power amplifiers, because the distortion is very serious when the signal is very low, so the cross 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, allowing the use of a smaller radiator.

3. Compared with the first two types of power amplifiers, Class AB power amplifier can be said to be a compromise in performance. Class AB power amplifier usually has two bias voltages, and a small amount of current passes through the output transistor when there is no signal. When the signal is small, it uses Class A working mode to obtain the best linearity, and when the signal rises to a certain level, it automatically switches to Class B working mode to obtain higher efficiency. Class AB power amplifier of ordinary machine 10W works in Class A of about 5W. Because listening to music requires only a few watts of power, class AB power amplifier works with class A power amplifier most of the time, and only when there is transient strong music can it be changed to class B.. This design can obtain excellent sound quality, improve efficiency and reduce heat, which is quite logical. Some Class AB power amplifiers adjust the bias current very high, so that they can work as Class A in a wider power range, making the sound close to pure Class A machines, but the heat generated is also relatively increased.

4. Class C power amplifier (Class C power amplifier) This kind of power amplifier is rarely heard, because it is a power amplifier with very high distortion and is only suitable for communication purposes. Class C computers have high output efficiency, but they are not suitable for high-fidelity amplification.

5. Class D power amplifier (Class D power amplifier) This design is also called digital power amplifier. As soon as the transistor amplified by class D power amplifier is turned on, the 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 the power supply voltage appears on the transistor, but there is no current, so there is no power consumption, so the theoretical efficiency is 100%. The advantage of Class D power amplifier is the highest efficiency, which can reduce the power supply and hardly generate heat, so there is no need for a large radiator, and the volume and weight of the fuselage are obviously reduced, with low distortion and good linearity in theory. However, the work of this kind of power amplifier is complicated, and the circuit itself is inevitably biased, so there are few truly successful products and the price is not cheap. There are some class D power amplifier integrated blocks with good timbre and sound quality, but now they are only used in car stereos, and interested DIY experts have changed them to home stereos. Although the sound quality of the power amplifier can't be judged by its appearance, if you can observe the size of the power transformer and the filter capacitor, you will already know the performance or quality of this machine. Class A power supply certainly needs huge power supply, even if the class AB machine is bigger, the better. At present, many high-quality power amplifiers use ring transformers, which have higher efficiency and less leakage than square transformers. The filter capacitor is equal to the pool. The more water is stored, the more water is supplied, and the power supply of the power amplifier is sufficient and stable, so that there is still inexhaustible power when the output of the output transistor is maximum. Although the power of many British-made combined amplifiers is not too high, they have sufficient power supply and can achieve excellent sound with simple signal channels. In some products, except for volume, balance, sound source selection and power switch, all other controls on the panel are cancelled to shorten the signal channel as much as possible. In order to pursue the pure beauty of sound, we will sacrifice the control function. Electron tube power amplifier, commonly known as courage machine, is famous for its female voice; Transistor power amplifier, commonly known as stone machine, is called masculine. The advantages of transistor machine are large current, wide frequency band, low frequency control, resolution, layering and brightness when dealing with large scenes. However, the treble of the pipe machine is very smooth, with enough air sense and a kind of sound dyeing that quite a few people like. Although there are few details and layers in the sound, the soft and slightly fuzzy sound is beautiful.