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If you don't know characteristics of these 5 power amps, you are wrong...
According to different conduction methods of power amplifier tubes in power amplifiers, they can be divided into Class A (also known as Class A) power amplifiers, Class B (also known as Class B) power amplifiers, Class A and B power amplifiers. (also known as class AB) and class C (also known as class A) power amplifiers, referred to as class C) and class D power amplifiers (also known as class D).
1 Class A Power Amplifier (also known as Class A Power Amplifier)
The two (or two sets) transistors in output stage of a class A power amplifier are always in a conducting state, that is, they keep conducting current whether there is an input signal or not, and make two currents equal to peak value of AC B that time AC Into load under maximum signal conditions. When there is no signal, each of two transistors passes equal current, so there is no unbalanced current or voltage at center output point, so no current flows to speaker. When signal tends to be positive, output transistor above line passes more current, while output transistor below line reduces current relatively. As current starts to be unbalanced, it flows into speaker and drives it. Sound.
Class A power amplifier works with best linearity, each output transistor amplifies full waveform of signal, there is no crossover distortion (switching distortion), even if negative feedback is not applied, its open-loop distortion is still very good low frequencies , so it is called most ideal audio amplification circuit. But this design has its advantages and disadvantages. The biggest disadvantage of a class A power amplifier is low efficiency, because when there is no signal, full current still flows and all electrical energy is converted into a lot of heat. As signal level increases, some of power may go to load, but most of it still turns into heat.
It can provide very smooth sound quality, round and warm tone, transparent and open high frequencies, these advantages are more than enough to compensate for its shortcomings. Class A power amplifiers generate an astonishing amount of heat. To efficiently dissipate heat, Class A power amplifiers must use large heatsinks. Due to low efficiency, power supply must provide sufficient current. A 25W Class A power amplifier power supply is sufficient for at least a 100W Class AB power amplifier. Therefore, volume and weight of class A machines are larger than those of class AB machines, which increases cost of production and makes price more expensive. Generally speaking, price of a class A power amplifier is about twice or more than price of a class AB power amplifier of same power.
2 Class B Power Amplifier (Class B Power Amplifier)
The way a class B power amplifier works is that when there is no input signal, output transistor does not conduct current, so it does not consume power. When there is a signal, each pair of output transistors amplifies half of signal, and each of them works in turn to complete full-wave amplification. When two output transistors work alternately, crossover distortion occurs, thus producing non-linearity.
There are fewer pure class B power amplifiers because distortion is very severe when signal is very weak, so crossover distortion makes sound rough. Class B power amplifiers have an average efficiency of about 75%, generate less heat than class A amplifiers, and allow use of smaller heatsinks. The common working methods of class B power amplifiers are divided into OCL and BTL. BTL can provide more power. At present, most high-power integrated circuits can use two parts to form a BTL circuit.
3 Class AB power amplifier (Class A and B power amplifier)
Compared to first two types of power amplifiers, Class AB power amplifiers represent a compromise in performance. Class AB power amplifiers typically have two bias voltages and a small amount of current flows through output transistors when there is no signal. It uses class A working mode when signal is small to get best linearity, and automatically switches to class B working mode to get better efficiency when signal increases to a certain level.
A 10-watt class AB power amplifier of a conventional car will operate with a class A power amplifier within about 5 watts. Since power required to listen to music is only a few watts, a class AB power amplifier operates in classroom. Most of time, power amplifier mode is in operation, which only converts to category B when music is played briefly. This design can provide good sound quality and improve efficiency to reduce heat, which is quite a logical solution. Some Class AB power amplifiers adjust bias current very high so that they can operate as Class A over a wider power range, making sound close to pure Class A, but heat generated is relatively increased.
4 Class C Power Amplifier (Class C Power Amplifier)
This type of power amplifier is rarely heard because it is a very high distortion power amplifier suitable for communication purposes only. The output efficiency of Class C machine is extremely high, but it is not suitable for HI-FI amplification.
5 Class D Power Amplifier (Class D Power Amplifier)
This design is also known as a digital power amplifier. Once transistor amplified by class D power amplifier is turned on, its load is directly connected to power supply and current flows, but transistor has no voltage, so there is no power consumption. When output transistor is off, transistor has full supply voltage, but no current flows, so no power is drawn, so theoretical efficiency is 100%. The advantages of a class D power amplifier are highest efficiency, power consumption can be reduced, practically no heat is generated, so a large radiator is not needed, volume and weight of case are significantly reduced, and theoretically distortion is low, and linearity is good. However, operation of such a power amplifier is complex, and added circuit itself will inevitably have deviations, so there are very few truly successful products, and price is not cheap.
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