I know some argue facts on amplifiers while some really honeslty really dont know or understand them or their classes sho I hope this clarifies alot of it and its more understandable. Classes also referred to in audio equipment. This should help a bit in understand what the classes do or the quality.
The Class of an amplifier refers to the design of the circuitry within the amp. For audio amplifiers, the Class of amp refers to the output stage of the amp (in practice there may be several classes of signal level amplifier within a single unit). There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of.
Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half "on" when the amp is idling (this is the point at which the semiconductor devices are most linear in behavior). As a result of being half on at idle, a lot of power is dissipated in the devices even when the amp has no music playing! Class A amps are often used for "signal" level circuits (where power requirements are small) because they maintain low distortion. High end Class A audio amplifiers are sometimes used by the most discriminating audiophiles. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Some class A amps have speakers connected via capacitive coupling.
Class B: Class B amplifiers are used in low cost designs or designs where sound quality is not that important. Class B amplifiers are significantly more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion in this region of operation is called "crossover distortion"). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical. For example, a siren driver is one application of a Class B amp. Siren drivers are amplifiers that are basically driven into clipping (to produce a square wave type signal). In such a drive situation there would be little need to care about crossover distortion (the design can be less expensive due to reduced parts count).
ClassAB: Class AB is probably the most common amplifier class currently used in home stereo and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the improved efficiency of class B amps and distortion performance that is a lot closer to that of a class A amp. With such amplifiers, distortion is worst when the signal is low, and generally lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated.
Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient.
Class D: The concept of a Class D amp has been around for a long time (~ 50 years or so), however only fairly recently have they become more commonly used in consumer applications. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a completely different method of amplification as compared to Class A, B and AB. Whereas the aforementioned classes of amplifier operate the semiconductor devices in the linear mode, Class D amplifiers operate the output semiconductor devices as switches (ON or OFF). In a Class D amplifier, the input signal is compared with a high frequency triangle wave, resulting in the generation of a Pulse Width Modulation (PWM) type signal. This signal (which some people incorrectly identify as a “digital” signal) is then applied to a special filter that removes all the unwanted high frequency by-products of the PWM stage. The output of the filter drives the speaker. Please note that this is a VERY high level idea of how Class D amplifiers work! Class D amps are (today) most often found in car audio subwoofer amplifiers. The major advantage of Class D amplifiers is that they have the potential for very good efficiency (due to the fact that the semiconductor devices are ON or OFF in the power stage, resulting in low power dissipation in the device as compared to linear amplifier classes). One notable disadvantage of Class D amplifiers: they are fairly complicated and special care is required in their design (to make them reliable). Due to the high frequencies that are present in the audio signal (as a result of the PWM stage), Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace and less costly. Class D amps find use in many other applications besides audio. Class D amplifiers will probably eventually revolutionize audio power amplifiers: when they are perfected, their efficiency will allow outputs of 1000+ watts without the need for a cooling fan! They will also be small and lightweight compared to the class AB designs that are most common today.
Other classes: There are a number of other classes of amplifiers, such as G, H, S, etc. Although some experts would certainly argue with me, most of these designs are actually clever variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example). At this time I will not go into the details of all of these other classes. Suffice to note that Class D (among A, B, AB, D, S, G, H classes) is the class that represents a major delta in the way it operates as compared to the other audio amplifier classes. Sometimes the consumer marketplace promotes Class D amplifiers as being "digital". The marketplace tends to toss around the word "digital" a lot, there is no really standardized definition (that I am aware of) that deems an amp "digital". To find out what a vendor means when they use the word digital with regard to an amp requires research into the design of the amp. Most likely the vendor is just using a buzz word that the consumer may associate with a superior technology.
The Class of an amplifier refers to the design of the circuitry within the amp. For audio amplifiers, the Class of amp refers to the output stage of the amp (in practice there may be several classes of signal level amplifier within a single unit). There are many classes used for audio amps. The following is brief description of some of the more common amplifier classes you may have heard of.
Class A: Class A amplifiers have very low distortion (lowest distortion occurs when the volume is low) however they are very inefficient and are rarely used for high power designs. The distortion is low because the transistors in the amp are biased such that they are half "on" when the amp is idling (this is the point at which the semiconductor devices are most linear in behavior). As a result of being half on at idle, a lot of power is dissipated in the devices even when the amp has no music playing! Class A amps are often used for "signal" level circuits (where power requirements are small) because they maintain low distortion. High end Class A audio amplifiers are sometimes used by the most discriminating audiophiles. Distortion for class A amps increases as the signal approaches clipping, as the signal is reaching the limits of voltage swing for the circuit. Some class A amps have speakers connected via capacitive coupling.
Class B: Class B amplifiers are used in low cost designs or designs where sound quality is not that important. Class B amplifiers are significantly more efficient than class A amps, however they suffer from bad distortion when the signal level is low (the distortion in this region of operation is called "crossover distortion"). Class B is used most often where economy of design is needed. Before the advent of IC amplifiers, class B amplifiers were common in clock radio circuits, pocket transistor radios, or other applications where quality of sound is not that critical. For example, a siren driver is one application of a Class B amp. Siren drivers are amplifiers that are basically driven into clipping (to produce a square wave type signal). In such a drive situation there would be little need to care about crossover distortion (the design can be less expensive due to reduced parts count).
ClassAB: Class AB is probably the most common amplifier class currently used in home stereo and similar amplifiers. Class AB amps combine the good points of class A and B amps. They have the improved efficiency of class B amps and distortion performance that is a lot closer to that of a class A amp. With such amplifiers, distortion is worst when the signal is low, and generally lowest when the signal is just reaching the point of clipping. Class AB amps (like class B) use pairs of transistors, both of them being biased slightly ON so that the crossover distortion (associated with Class B amps) is largely eliminated.
Class C: Class C amps are never used for audio circuits. They are commonly used in RF circuits. Class C amplifiers operate the output transistor in a state that results in tremendous distortion (it would be totally unsuitable for audio reproduction). However, the RF circuits where Class C amps are used employ filtering so that the final signal is completely acceptable. Class C amps are quite efficient.
Class D: The concept of a Class D amp has been around for a long time (~ 50 years or so), however only fairly recently have they become more commonly used in consumer applications. Due to improvements in the speed, power capacity and efficiency of modern semiconductor devices, applications using Class D amps have become affordable for the common person. Class D amplifiers use a completely different method of amplification as compared to Class A, B and AB. Whereas the aforementioned classes of amplifier operate the semiconductor devices in the linear mode, Class D amplifiers operate the output semiconductor devices as switches (ON or OFF). In a Class D amplifier, the input signal is compared with a high frequency triangle wave, resulting in the generation of a Pulse Width Modulation (PWM) type signal. This signal (which some people incorrectly identify as a “digital” signal) is then applied to a special filter that removes all the unwanted high frequency by-products of the PWM stage. The output of the filter drives the speaker. Please note that this is a VERY high level idea of how Class D amplifiers work! Class D amps are (today) most often found in car audio subwoofer amplifiers. The major advantage of Class D amplifiers is that they have the potential for very good efficiency (due to the fact that the semiconductor devices are ON or OFF in the power stage, resulting in low power dissipation in the device as compared to linear amplifier classes). One notable disadvantage of Class D amplifiers: they are fairly complicated and special care is required in their design (to make them reliable). Due to the high frequencies that are present in the audio signal (as a result of the PWM stage), Class D amps used for car stereo applications are often limited to subwoofer frequencies, however designs are improving all the time. It will not be too long before a full band class D amp becomes commonplace and less costly. Class D amps find use in many other applications besides audio. Class D amplifiers will probably eventually revolutionize audio power amplifiers: when they are perfected, their efficiency will allow outputs of 1000+ watts without the need for a cooling fan! They will also be small and lightweight compared to the class AB designs that are most common today.
Other classes: There are a number of other classes of amplifiers, such as G, H, S, etc. Although some experts would certainly argue with me, most of these designs are actually clever variations of the class AB design, however they result in higher efficiency for designs that require very high output levels (500W and up for example). At this time I will not go into the details of all of these other classes. Suffice to note that Class D (among A, B, AB, D, S, G, H classes) is the class that represents a major delta in the way it operates as compared to the other audio amplifier classes. Sometimes the consumer marketplace promotes Class D amplifiers as being "digital". The marketplace tends to toss around the word "digital" a lot, there is no really standardized definition (that I am aware of) that deems an amp "digital". To find out what a vendor means when they use the word digital with regard to an amp requires research into the design of the amp. Most likely the vendor is just using a buzz word that the consumer may associate with a superior technology.
