"Class A", this logo may be seen in the introduction of some guitar amps, but what does this "Class A" mean in guitar amps? What are the meanings of other signs such as "AB" and "D"?
In order to answer this question, we must first understand the meaning of their speaker design. After the scientific explanation, I will use some inaccurate examples to explain by analogy. It may not be completely correct, but I hope to help you get a rough idea of the terms A/B/AB/D. Understanding.
1. Pure Class A power amplifier
Pure Class A power amplifier is also called Class A power amplifier (Class A).
When a pure class A power amplifier is working, the positive and negative channels of the transistors are always open regardless of whether there is a signal or not, that is to say, they keep conducting current regardless of whether there is a signal input, and make these two currents equal to the peak value of the alternating current. At this time, the AC flows into the load under the maximum signal condition, and this means that more power is consumed as heat.
Class A power amplifier works with the best linearity. Each output transistor amplifies the full wave of the signal, with almost no distortion, that is, there is no "switching distortion" and "crossover distortion", so it is a kind of amplifier with very good performance. Circuit. Especially the single-ended Class A amplifier, its screen flow changes very little when there is zero signal and full signal, the work is quite stable, the distortion of the linear working area is very small, and the even harmonic content is extremely rich, which gives the output guitar The audio signal adds a rich sense of layering, so the sound it produces is sweet, warm and full, with a more "vintage" feeling.
Class A power amplifier is also an ideal choice for playing music. It can provide a very smooth sound quality, a round and warm tone, and a transparent and open treble, so it is known as the most ideal sound amplification circuit design.
Analogy: You can simply and crudely think of Type A as a speaker with only one unvoiced channel. Think about it if you want to get an overdrive sound, you can only turn on the volume, and even the volume The overload degree will not be particularly large when it is opened too much. But it is undeniable that this type of single-channel speaker is indeed very clear, even the slight overdrive timbre obtained at high volume is also very pleasant.
2. Class B power amplifier
Class B power amplifier, also known as Class B power amplifier (Class B).
Its working principle is completely different from that of a pure Class A power amplifier. When the Class B power amplifier is working, the positive and negative channels of the transistor are usually closed unless there is a signal input, that is, when there is no signal input, the output transistor does not conduct electricity and does not consume power. When there is a signal, each pair of output tubes will amplify half of the waveform, and each pair will turn on and off to complete a full-wave amplification. When the two output transistors work in turn, "crossover distortion" occurs.
There are fewer pure Class B power amplifiers, because distortion has already occurred when the signal is very low, so the sound becomes rougher when "crossover distortion".
Analogy: You can simply and rudely regard Class B as a single-channel speaker without a clear sound channel. As long as you play this speaker, it is overloaded. When the output power increases, it will produce more serious distortion, and then this The channel transitions from an overloaded tone to a distorted tone.
3. Class A and B power amplifier
Class A and B power amplifiers are also called Class AB power amplifiers (Class AB).
It is a design compatible with the advantages of Class A and Class B power amplifiers. It uses Class A working mode when the signal is small to obtain the best linearity. When the signal increases to a certain level, it automatically switches to Class B working mode to obtain higher efficiency.
Analogy: We found that both A-type amplification and B-type amplification have obvious advantages and disadvantages. Then we can combine them. Don't you want both gentle unvoiced sound and wild distortion? Class AB is such a speaker. At the same time, it has an unvoiced channel and a distortion channel, and has both A and B characteristics. When in the unvoiced channel, when the volume is increased to a certain level, there will still be overload. Also in the distortion channel, when the gain is low, it will only overdrive the timbre instead of high distortion.
4. Class C power amplifier
Class C power amplifiers are also called Class C power amplifiers.
To put it bluntly, it is actually working in a distorted state. This type of power amplifier is rarely heard, because it is a very high distortion power amplifier.
Analogy: You can think of it as a speaker with only a distortion channel, a single-channel speaker with a pure distortion tone that can't even be overloaded.
5. Class D power amplifier
This design is also called a digital power amplifier.
Once the transistor of the Class D amplifier is turned on, it directly connects its load to the power supply. The current flows but the transistor has no voltage, so there is no power consumption. When the output transistor is turned off, the entire power supply voltage appears on the transistor, but there is no current, so no power is consumed, so the theoretical efficiency is 100%.
The advantages of Class D amplifier amplification are the highest efficiency, the power supply can be reduced, and almost no heat is generated, so there is no need for a large radiator, the body volume and weight are significantly reduced, and theoretically low distortion and good linearity.
Analogy: It is the latter stage of our common digital class. It is the same as boiled water, and the sound is small, but because it is not a tube after all, it is not comparable in dynamics.
Finally: At present, most of the multimedia speakers use Class B (Class B) power amplifiers, and due to cost and space reasons, the power amplifier circuits of multimedia speakers mostly use integrated circuits, and the power transformers and filter capacitors cannot be made very large. . This directly affects the sound quality and dynamics of the multimedia box. Of course, the power amplifiers of multimedia speakers (such as Dajidian) that use tube power amplifiers work in Class A, but the price of the speakers is not acceptable to most people.