What Do Amplifier Classes Mean?
The different circuitry design within an amplifier can be determined by classes. The audio amplifier’s class refers to the output stage of the amplifier. There are several classes:
Class A – Class A amplifiers produce very low distortion. The distortion is the lowest when the volume is low. However, Class A amplifiers are extremely inefficient, thus they are not suitable for designing high power models like most multi zone amplifier in the market.
Why do they manage to produce low distortion? The transistors in Class A amp are biased in a way that they are only half working when the device is idle (at this point the semiconductor devices are most linear in behavior). From this, a lot of power is wasted even though there is no audio from the device.
Due to the working mechanism of Class A amps, they are often used for signal level circuits. Premium Class A audio amp are sometimes used by the choosiest audiophiles.
Class B: Class B amp are meant for lower cost circuit designs. Sound quality is not a priority. However,do bear in mind, Class B amplifiers are more efficient than Class A amplifier. However, distortion is rife when signal level is low (the term is called “crossover distortion”).
This is selected when design cost is emphasized. This class of amp is formerly used in pocket transistor radio, clock radio and anything portable whereby sound quality is not important.
Class AB: This class is widely used in home stereos and normal audio amplifiers. Class AB amplifiers boast about the best of A and B. Think of the efficiency of Class B and the better distortion performance of Class A amplifiers.
In AB amplifiers, distortion would deteriorates when the signal gets lower. They usually make use of pairs of transistors which are biased slightly “on”. The reason is to eliminates crossover distortion which happens in Class AB amps.
Class C: Never used for audio circuitry and usually operate the output transistor in a state that produces tremendous distortion. C amplifiers are most commonly found in RF circuits whereby such crude signal is acceptable. They are extremely efficient though.
Class D: This class of amplifier is the most employed in Multi Zone Amplifiers and Multi Zone Audios. D amplifiers use a different method of amplification as compared to earlier classes mentioned.
Class D amplifier operates the output semi-conductor devices as switches (On or OFF) which is vastly different from Class A,B, AB and C operate in the linear mode. Class D ’s input signal is compared with a high frequency triangle wave, resulting in the formation of “pulse width modulation (PWM) type signal. This type of signal is also known as ‘digital’ signal by layman.
PWM signal would go through a special filter which removes all unwanted high frequency by-products of the PWM stage. The output of the filter would drives the speaker. One of the major advantage of using a Class D amplifier is its high efficiency or low power wastage.
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