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What is an Audio Power Amplifier? – Amplify That Sound!

Love listening to your favourite music through speakers? Looking for the right equipment to amplify your music? There are a number of essential equipment that every audio engineer needs to know, when setting up a sound system. Whether be it home entertainment systems or professional ones, you will still need to ask yourself – What is an Audio Power Amplifier?

Don’t worry too much, as you have come to the right place to learn more about this vital audio equipment. In this article, we will go through the basic concepts surrounding the audio power amplifier. Understand the fundamental principles of its design and function. Also learn more about its application in the audio world. Excited yet? Then let’s begin!

Integrated Power Amp

Photo by Fred von Lohmann / CC BY 2.0

Introduction – Why Use It?

Simply referred to as a power amp, the audio power amplifier is essentially an electronic amplifier which amplifies electrical audio signals that has low power, (signals with frequencies of 20Hz – 20kHz, the human audible range) to a level that is strong enough to drive loudspeakers and ultimately resulting in the signal being audible to the audience or listeners.

In a typical sound system chain, it is known as the final electronic stage, before the signal is transmitted to the loudspeakers. The stages before this, consists of low power audio amplifiers which are involved in pre-amplification (usually applied to microphone or instrument signals), equalization, tone controls, mixing various audio signals or adding effects (such as reverberation).

The input signals can come from various audio sources such as CD players, digital music players and electronic musical instruments. In order to adhere to line-levels, these low-level signals are needed by most audio amplifiers.

Pro Power Amp

Photo by Emilian Robert Vicol / CC BY 2.0

A power amp’s input signal usually measure around a few hundred microwatts, but its output can range from a few watts for small electronics devices (like portable radios), to hundreds of watts for a home theatre system.

A nightclub’s sound system may consume several thousand watts and the sound reinforcement systems used in large concerts may require tens of thousands of watts. Standalone power amp units, are usually catered to the hi-fi audiophile and professional sound reinforcement market.

As for most consumer level audio products, such as TVs and car stereos, the power amplifiers are integrated within the chassis of the main component.

Let us now look at the various topics that we will be discussing:

  • History
  • Design parameters
  • Filters and pre-amplifiers
  • Further developments
  • Applications

History – Tube Amplification

Tube Amp

Photo by Anthony Crawford / CC BY 3.0

Invented by Lee De Forest in 1909, the triode vacuum tube (or valve) was the core component in the early audio amplifiers. Essentially a three terminal device with a control grid, the triode is designed to modulate the flow of electrons from the filament to the plate. The first AM radio was engineered to include the triode vacuum amplifier.

All audio power amplifiers used to be based on vacuum tubes and some of them are designed to be of notably high quality (such as the Williamson amplifier in 1947-9). Today, the majority of modern audio amplifiers are build using solid state devices (transistors such as BJTs, FETs and MOSFETs), however tube-based amplifiers are still in demand by people who prefer the “valve sound”.

Transistor-based audio power amplifiers became practical, when a variety of cost-effective transistors were widely available in the late 1960s.

Design Parameters

Audio power amplifiers have a couple of major design parameters which includes frequency response, gain, noise, and distortion. The functions of these parameters are intertwined. For example, an increase in gain may result in an unwanted increase in noise and distortion. While “negative feedback” causes gain reduction, it also reduces distortion. Most audio amplifiers are linear amplifiers operating in class AB.

Stereo Power Amp

Photo by Chi Bellami / CC BY 2.0

Filters and Pre-amplifiers

Most modern digital devices such as CD and DVD players, radio receivers and mp3 players already provide a “flat” signal at line level. Hence, a preamp is only needed to serve the function of a volume control and source selector. An alternative to a separate stand-alone preamp is the integrated amplifier, which integrates passive volume and switching controls, into a power amplifier.

Further Developments

The opinions surrounding solid state power amplifiers (some years after its introduction) were very poor, as they were believed to be unable to produce the pristine audio quality of the best valve amplifiers. This shaped the opinion among audiophiles that “tube sound” or valve sound had a unique value due to the vacuum tube technology itself.

In 1970, a new form of distortion was observed in solid-state amplifiers, which is called transient intermodulation distortion (TIM). TIM happens when there are rapid increases in amplifier output voltage. Problems with TIM stem from reduced open loop frequency response of solid state amplifiers. This issue was finally solved by decreasing the preamp frequency bandwidth, and inserting a lag compensation circuit in the amplifier’s input stage.

Solid State Amp

Solid State Stereo Amplifier / Photo by Justin Davis / CC BY-SA 2.0

The Baxandall Theorem was the next step in audio amplifier design. Created by Peter Baxandall in England, this theorem explains the comparison (in ratio) between the input distortion and the output distortion of an audio amplifier. This new concept allowed audio engineers to more accurately observe the distortion processes in an amplifier.

Applications

Audio power amps are used in PA systems, live sound reinforcement systems, and home systems such as hi-fi or home-theatre system. They also drive instrument amplifiers like an electric guitar amplifier. Some instrument amplifier designs require the power amplifier to be integrated into a single “head” unit, which consists of a preamplifier, tone controls, and electronic effects.

Amp Head

Guitar Amp “Head” / Photo by Graham Niven / CC BY-SA 3.0

Standalone power amplifier units are typically used by audio engineers for the setting up of PA systems and sound reinforcement systems. Power amps in stereo systems have two channels, in order to drive left and right speakers and a single channel power amplifier for the subwoofer. The size of the venue and audience determines the number of power amplifiers needed in a sound reinforcement system.

A small pub may only require a single power amp unit driving two loudspeakers. A nightclub may need several amp units for the FOH speakers, one or more units for the monitor speakers (facing the performers) and also another unit for the subwoofer.

Live sound

“Avalon” power amplifier used in live sound

Larger venues such as a stadium may utilize a large number of power amp units mounted on racks. Consumer electronics such as TVs, home theatre surround sound systems, “combo” guitar amps and car stereos, are usually designed to have a built-in power amplifier within the chassis of the main component.

That’s it friends, we have come to the end of this article. Hopefully, you now know the importance of an audio power amplifier in any sound system!

Do leave a comment or question below, and share this article if you like!

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Farhan

When I'm not rocking out to great music, I'd prefer to be sleeping on a field on a windy day =)

8 Comments

  1. Farhan, before I begin, must say, “sleeping in a field on a windy day”, sounds like short term paradise with long term results! I’ve done it, love it, and plan to again soon! Got that out. Now…When I used to play, we really didn’t think about the audio power amplifier, though I’m sure someone did! I tend to be one of those artists that need baby sitting. I get the importance of technology, but have a hard time using and dealing with it. You have clarified a lot here. So, as I understand, the audio power amplifier takes, and makes the music loud! Am I correct? What brands do you recommend? Good seeing you again Farhan, good things!

    • Hey Sam!

      Sleeping on a field on a windy day, does sound like paradise on earth indeed!

      Now, back to topic. I have been in your position as well, being a musician first, before I studied about audio in-depth. Although musicians might not have the requisite training, in order to identify audio engineering principles, the more experienced ones will still be able to tell if the overall sound quality suffers.

      Yep, you got it right. Audio power amps does just that, to amplify sound. There are a lot of brands out there, some of the ones that I have come across are – Crown, QSC, Yamaha. All these are top brands, typically used in live sound systems.

      Good seeing you again Sam. Do keep in touch!

  2. Good, straight to the point information. Manipulation of sound is a very interesting thing isn’t it. I find that once your ears are attuned to what REAL good quality sound is, it makes you a harsh critic of most places. Do you find, like me, when you go to nightclubs or bars that the sound is… well, awful. Unfortunately a full understanding of sound quality isn’t all that commonplace. Which is why we get these boy racers who believe an excess of bass equates to good sound, when in actual fact it ruins potential crispness in everything else the track has to offer. Would you recommend any mid range, good quality and affordable speakers? I like to listen to intricate dub and electronic music and these old PC speakers (Creative T20) are still going great but…they’ve definitely lost their flare now.

    • Hi Nick!

      I just simply cannot disagree with all the points that you have made. Yes, quality sound is not something that the untrained ear is able to discern right away. It requires a lot of experience in order to be able to tell the difference. However, it is important to take note that the public (audience) in general, will be able to tell instinctively, if the sound quality is really bad (for example, cracking high end frequencies).

      When I look at speakers, I will always measure it based on its transparency. This is a purely objective perspective of speakers, as I generally use them for pro audio production. Here is a great affordable set of speakers that I have reviewed: http://myaudioeducation.com/yamaha-hs5-review-grea

      Thanks a lot for your valuable thoughts. Do come back anytime!

  3. This was quite a technical article in some ways, but it definitely gave me a greater understanding of how the audio power amplifier works and what it does.

    I found the history part particularly interesting and I didn’t realise the amplifier was invented that long ago. Tubes are still used in some guitar amplifiers today, while others emulate the tube sound.

    • Hey Darren!

      Yeah, it is very interesting to learn more about the device that we use everyday when listening to music. I am glad that you got something out of it!

      Thanks for your thoughts!

  4. Hi Farhan, I have a question.. Does an audio power amplifier distort or ruin the sound in anyway? Also, can they be used with something as simple as a soundbar? I currently have a Samsung soundbar on my TV and would love to increase its volume if possible with an amplifier. I’m thinking that maybe these can’t be used since you mentioned home theater systems in your article, but I wasn’t sure. Anyway thanks for going into such depth with this article.. In terms of brands, are there ones better than others in regards to the produced sound quality? Thanks in advance!

    • Hi Peter!

      Do take note that distortion does not cause speaker damage. Distortion is actually the audible detection of the signal “clipping”. Clipping happens when the power amplifier can no longer provide enough power supply voltage to “cleanly” amplify the audio signal.

      However, although distortion produced by clipping doesn’t cause any damage to either speakers or amplifiers (it is just “dirty” or “sloppy” sounding), the excessive power produced when driving the amplifier to that level can cause speakers to fail quite easily.

      From my observations, all soundbars (regardless of brand) have built-in power amps right? Correct me if I’m wrong, as I personally don’t use soundbars. If that’s the case, then you cannot use an external dedicated power amplifier with your Samsung soundbar. The available inputs on your bar, will most likely not allow such connections anyway.

      There are many brands out there, and the quality varies depending on the price range. If you are not too geeky about audio, then perhaps the regular home theatre brands like Philips, Samsung and LG will provide you with the variety that you need. If you are looking for something on the higher-end, then look for brands such as Denon, Dynaudio, Bowers & Wilkins, and Cambridge Audio.

      Hope that helps. Thanks for dropping by!

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