Requirements concerning audio power and audio fidelity of today's loudspeakers and home theater systems are always growing. At the core of these products is the audio amplifier. Latest stereo amps have to perform well enough to meet those always increasing requirements. With the ever growing number of models and design topologies, including "tube amps", "class-A", "class-D" in addition to "t amplifier" designs, it is getting more and more demanding to pick the amp that is perfect for a specific application. This post is going to explain some of the most widespread terms and spell out some of the technical jargon which amp manufacturers frequently use.
Tube amps used to be popular a few decades ago. A tube is able to control the current flow in accordance to a control voltage which is attached to the tube. Unfortunately, tube amplifiers have a reasonably high level of distortion. Technically speaking, tube amps will introduce higher harmonics into the signal. A lot of people favor tube amplifiers because those higher harmonics are often perceived as the tube amp sounding "warm" or "pleasant".
A disadvantage of tube amps is their small power efficiency. In other words, the majority of the power consumed by the amplifier is wasted as heat rather than being converted into audio. Consequently tube amplifiers are going to run hot and require sufficient cooling. Tube amplifiers, though, a rather costly to produce and consequently tube amps have by and large been replaced with amps making use of transistor elements that are less expensive to build.
One more drawback of tube amps, though, is the low power efficiency. The majority of power that tube amps consume is being dissipated as heat and merely a part is being converted into audio power. Tube amplifiers, on the other hand, a fairly expensive to make and consequently tube amplifiers have mostly been replaced with amplifiers utilizing transistor elements that are less expensive to build.
Class-AB amplifiers improve on the efficiency of class-A amplifiers. They utilize a series of transistors to break up the large-level signals into two separate areas, each of which can be amplified more efficiently. The larger efficiency of class-AB amps also has two other benefits. Firstly, the required number of heat sinking is minimized. As a result class-AB amplifiers can be manufactured lighter and smaller. For that reason, class-AB amps can be manufactured cheaper than class-A amps. Nonetheless, this topology adds some non-linearity or distortion in the area where the signal switches between those areas. As such class-AB amps normally have larger distortion than class-A amps.
Class-D amps improve on the efficiency of class-AB amplifiers even further by using a switching transistor which is constantly being switched on or off. Thus this switching stage barely dissipates any energy and thereby the power efficiency of class-D amps usually surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered in order to remove the switching signal and recover the audio signal. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amplifiers exhibiting bigger audio distortion than other types of amps.
Class-D amps are able to achieve power efficiencies above 90% by making use of a switching transistor which is continually being switched on and off and thus the transistor itself does not dissipate any heat. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Typical switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward first-order lowpass is being utilized. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the largest audio distortion of any audio amp. To resolve the problem of high music distortion, new switching amplifier designs incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known architecture which uses this kind of feedback is generally known as "class-T". Class-T amplifiers or "t amps" achieve audio distortion that compares with the audio distortion of class-A amps while at the same time offering the power efficiency of class-D amps. Therefore t amplifiers can be manufactured extremely small and still achieve high audio fidelity.
Tube amps used to be popular a few decades ago. A tube is able to control the current flow in accordance to a control voltage which is attached to the tube. Unfortunately, tube amplifiers have a reasonably high level of distortion. Technically speaking, tube amps will introduce higher harmonics into the signal. A lot of people favor tube amplifiers because those higher harmonics are often perceived as the tube amp sounding "warm" or "pleasant".
A disadvantage of tube amps is their small power efficiency. In other words, the majority of the power consumed by the amplifier is wasted as heat rather than being converted into audio. Consequently tube amplifiers are going to run hot and require sufficient cooling. Tube amplifiers, though, a rather costly to produce and consequently tube amps have by and large been replaced with amps making use of transistor elements that are less expensive to build.
One more drawback of tube amps, though, is the low power efficiency. The majority of power that tube amps consume is being dissipated as heat and merely a part is being converted into audio power. Tube amplifiers, on the other hand, a fairly expensive to make and consequently tube amplifiers have mostly been replaced with amplifiers utilizing transistor elements that are less expensive to build.
Class-AB amplifiers improve on the efficiency of class-A amplifiers. They utilize a series of transistors to break up the large-level signals into two separate areas, each of which can be amplified more efficiently. The larger efficiency of class-AB amps also has two other benefits. Firstly, the required number of heat sinking is minimized. As a result class-AB amplifiers can be manufactured lighter and smaller. For that reason, class-AB amps can be manufactured cheaper than class-A amps. Nonetheless, this topology adds some non-linearity or distortion in the area where the signal switches between those areas. As such class-AB amps normally have larger distortion than class-A amps.
Class-D amps improve on the efficiency of class-AB amplifiers even further by using a switching transistor which is constantly being switched on or off. Thus this switching stage barely dissipates any energy and thereby the power efficiency of class-D amps usually surpasses 90%. The switching transistor is being controlled by a pulse-width modulator. The switched large-level signal has to be lowpass filtered in order to remove the switching signal and recover the audio signal. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amplifiers exhibiting bigger audio distortion than other types of amps.
Class-D amps are able to achieve power efficiencies above 90% by making use of a switching transistor which is continually being switched on and off and thus the transistor itself does not dissipate any heat. The on-off switching times of the transistor are being controlled by a pulse-with modulator (PWM). Typical switching frequencies are in the range of 300 kHz and 1 MHz. This high-frequency switching signal has to be removed from the amplified signal by a lowpass filter. Typically a straightforward first-order lowpass is being utilized. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the largest audio distortion of any audio amp. To resolve the problem of high music distortion, new switching amplifier designs incorporate feedback. The amplified signal is compared with the original low-level signal and errors are corrected. A well-known architecture which uses this kind of feedback is generally known as "class-T". Class-T amplifiers or "t amps" achieve audio distortion that compares with the audio distortion of class-A amps while at the same time offering the power efficiency of class-D amps. Therefore t amplifiers can be manufactured extremely small and still achieve high audio fidelity.
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