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Amplifier Classes
Amplifiers fall into one of several classes based on the type and layout of their components. Each design has its own strengths and weaknesses. We measure the performance of an amplifier by measuring two criteria. Two of the most important characteristics that define each class of amplifier are:
Here's a quick look at the most important classes of car audio amplifier, focusing on how each class differs in terms of sound quality.
I talked with Shawn Scarlett, Senior Product Marketing Manager at Tripath, to gain a better understanding of how Class-T® amplifiers manage to avoid the high-frequency distortion associated with the Class D design.
Amplifiers fall into one of several classes based on the type and layout of their components. Each design has its own strengths and weaknesses. We measure the performance of an amplifier by measuring two criteria. Two of the most important characteristics that define each class of amplifier are:
- Distortion — how accurately the amplifier reproduces the audio signal put into the amp. Measured as a factor of Total Harmonic Distortion. A THD figure of 1% or below is generally considered undetectable to the human ear.
- Efficiency — how much of the power going into the amp is converted to pure sonic output (vs. being lost in the form of heat)?
Here's a quick look at the most important classes of car audio amplifier, focusing on how each class differs in terms of sound quality.
- Class A amplifiers are noted for the accuracy of their output and their signature warm, pleasing sound. However, a pure class A amplifier is very inefficient (only around 20%) and runs very hot. The output transistors of a Class A amp always have current running through them, so the amp is basically always "on." The constant flow of current through the output transistors (even with no audio signal) creates lots of heat, and "wastes" input energy. Because of this, Class A amplifiers are a relatively rare design for a car audio amplifier — most car amplifiers that boast "Class A" circuitry are really Class A/Class AB hybrids.
- Class AB amplifiers run cooler, and consequently more efficiently, than Class A amplifiers. Although they also allow current to run through the output transistors when there is no audio signal, the current is at a much lower level than in the Class A design — they're also always "on", but they use a lot less energy while waiting for an audio signal, which allows Class AB amps to achieve 50-60% efficiency. Yet, since they require built-in heat sinks to dissipate heat build-up, class AB amps are housed in relatively large (and weighty) chassis. Class AB is by far the most common design for a car amplifier.
- Class D amplifiers boast higher efficiency (some approach 90% efficiency), produce less heat, and draw less current than traditional Class AB designs. They use output transistors as switches to control power distribution — the transistors "turn off" when there is too much voltage across them. Because they produce much less heat, Class D amplifiers can be housed in a much smaller chassis than a Class AB with the same power output. The downside is that the on-off switching of the transistors produces high levels of distortion, particularly in the middle and upper frequencies. Class D amps are usually used to power subwoofers, since low-frequency distortion is hard to detect.
- Tripath's Class-T® amplifier design combines the low distortion and excellent sound quality of the Class AB design with the efficiency advantages of the Class D design. Tripath uses switching transistors to achieve very high power efficiency (around 90%), low heat production, and compact chassis-size. Yet, they've managed to solve the high-frequency distortion that plagues Class D amps.
 An inside look at a Class-T® amplifier. |
I talked with Shawn Scarlett, Senior Product Marketing Manager at Tripath, to gain a better understanding of how Class-T® amplifiers manage to avoid the high-frequency distortion associated with the Class D design.
