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Demands regarding audio power and audio fidelity of today’s speakers and home theater systems are constantly growing. At the heart of these systems is the audio amplifier. Today’s audio amps have perform well enough to meet these ever growing demands. With the ever increasing amount of models and design topologies, such as “tube amps”, “class-A”, “class-D” and “t-amp” designs, it is becoming more and more difficult to pick the amp which is ideal for a particular application. This article will explain some of the most common terms and clarify some of the technical jargon which amplifier manufacturers often use.

An audio amp will convert a low-level audio signal which often comes from a high-impedance source into a high-level signal which can drive a loudspeaker with a low impedance. Depending on the type of amp, one of several types of elements are used to amplify the signal such as tubes and transistors.

Tube amps were commonly used a few decades ago and utilize a vacuum tube which controls a high-voltage signal in accordance to a low-voltage control signal. Tubes, however, are nonlinear in their behavior and will introduce a fairly large amount of higher harmonics or distortion. A lot of people prefer tube amps because these higher harmonics are often perceived as the tube amp sounding “warm” or “pleasant”.

Another drawback of tube amps, though, is the low power efficiency. The majority of power which tube amps consume is being dissipated as heat and only a fraction is being converted into audio power. Also, tubes are quite expensive to make. Thus tube amps have mostly been replaced by solid-state amps which I will look at next.

The first generation models of solid state amps are known as “Class-A” amps. Solid-state amps use a semiconductor rather than a tube to amplify the signal. Usually bipolar transistors or FETs are being used. In a class-A amp, the signal is being amplified by a transistor which is controlled by the low-level audio signal. In terms of harmonic distortion, class-A amps rank highest amongst all types of audio amps. These amps also usually exhibit very low noise. As such class-A amps are ideal for very demanding applications in which low distortion and low noise a crucial. Class-A amps, however, waste most of the energy as heat. Therefore they usually have large heat sinks and are fairly heavy.

By using a series of transistors, class-AB amps improve on the low power efficiency of class-A amps. The operating working area is divided in two separate areas. These two areas are handled by separate transistors. Each of these transistors works more efficiently than the single transistor in a class-A amp. The higher efficiency of class-AB amps also has two other advantages. Firstly, the required amount of heat sinking is reduced. Therefore class-AB amps can be made lighter and smaller. For that reason, class-AB amps can be made cheaper than class-A amps. Class-AB amps have a drawback though. Every time the amplified signals transitions from one region to the other, there will be some distortion generated. In other words the transition between these two areas is non-linear in nature. Therefore class-AB amps lack audio fidelity compared with class-A amps.

Class-D amps improve on the efficiency of class-AB amps even further by using a switching transistor which is constantly being switched on or off. Thereby this switching stage hardly dissipates any power and thus the power efficiency of class-D amps usually exceeds 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. Due to non-linearities of the pulse-width modulator and the switching transistor itself, class-D amps by nature have amongst the highest audio distortion of any audio amplifier.

To solve the problem of high audio distortion, newer 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 type of feedback is known as “class-T”. Class-T amps or “t amps” achieve audio distortion which compares with the audio distortion of class-A amps while at the same type offer the power efficiency of class-D amps. Thus t amps can be made extremely small and still achieve high audio fidelity.

You can find additional information concerning t-amps as well as stereo amplifiers from Amphony’s website.

Looking at some of the technical specs of today’s power amplifiers, one cannot help but be at a loss in trying to compare different models and terms, such as “t-amp“, “THD” etc. I will give a short overview of the output power spec in order to help you better understand the meaning of this term and how they relate to the performance of an amplifier.

If you are looking to buy an audio amplifier to set up your home speakers, you will often be confronted with a number of strange terms describing its performance. But how do these numbers relate to how the amplifier sounds and how are these to be interpreted? Let me now go ahead and explain the wattage rating of audio amplifiers.

“Wattage” shows how loud your amp can drive your speakers. Depending on your application, you can go with a small amp delivering only a few watts or a larger one delivering several hundred watts. Most home stereos only come with amplifiers that have a few watts power which usually is enough for a small room. If you plan to shake your walls then you obviously want to opt for an amp that has up to several hundred watts. Most amplifiers will have increasing audio distortion as output power increases. Therefore, you want to pick an amp that has higher output power than you will actually need. This will assure that you will never drive the amp into areas of high distortion.

There are two common ways to display amplifier wattage. These are “peak power” and “rms power”. “Peak power” describes how much power the amp can deliver to your speakers for a short burst. On the other hand, “rms power” describes how much power the amp can output for a prolonged amount of time without being damaged. The peak power rating in the past often led to manufacturers showing large wattage ratings for small amplifiers. However, in reality those amps would not be able to sustain larger amounts of output power for larger amounts of time.

Today most amps will specify rms power which gives a better indication of the amps true performance. However, please ensure that your amp has enough headroom to avoid clipping of the audio. Having enough headroom is essential since music signals differ a great deal from sine wave signals which are used to measure rms power. Short bursts of high power are often found in music signals. These bursts will drive the amp into high distortion unless the peak power is high enough.

Usually the impedance of the speakers which you connect to the amp will determine how much power the amp can deliver. Speaker impedance is measured in Ohms. Typically speakers have an impedance between 4 and 8 Ohms. Amps have a limited output voltage swing due to the fixed internal supply voltage. As such the maximum output power will vary depending on the speaker impedance. The lower the speaker impedance the higher the maximum power the amp can deliver. If the maximum power is not referenced to a speaker impedance, you should contact the manufacturer. Usually a 4-Ohm speaker is used as a reference.

You can find more information about t-amp models in addition to power amplifier products at Amphony’s website.