5 things you always wanted to know about amplifiers
Estimated reading time: 9 minutes
5 things you always wanted to know about amplifiers – amplifiers are the beating heart of the audiovisual set-up. But they also have a habit of confusing the hell out of people.
Don’t despair, we’ll give you some insight in the world of amplifiers; make sure you know what is what when the time is right for your next purchase. And while we are at it, there is something we really need to discuss with you in regards to this topic. We sort of think you are going to thanks us for it, as the industry is playing some cheeky tricks on you. We’ll bring you up to date and explain to you how to go about it.
We give you: 5 Things you always wanted to know about amplifiers.
What are the most important attributes of an amplifier?
Many judge an audio amplifier simply by its power capability. We all want an amplifier that can handle the huge range of soft-to-loud present in just about every type of music and soundtrack. We’re thinking along the lines of 50 to 100 watts per channel or more.
There’s a big but to this however: power is one of the most misleading and most abused amplifier indicators by equipment manufacturers despite regulations mandating specific reporting for amplifier power. But more on that later.
Sneaky practices aside, it speaks that having an understanding of the most important amplifier specs and how best to interpret these is crucial to avoid costly mistakes. You also want to ensure that your amplifier will be up to your listening habits.
Power is expressed in watts. But in the case of audio amplifiers or AV receivers, there is a lot more than just watts; a typical amplifier power rating is defined as say ‘80W/Ch RMS 20Hz-20kHz, 8 Ohms 0.09% THD.’
This means that the amplifier is capable of delivering 80 watts average power per channel into an 8 Ohm (or 4 Ohm) speaker load at a maximum 0.09% total harmonic distortion over the specified frequency range. The test has to be done with at the least two channels driven to the specified power, very much as a representation of what you would get when you run your amplifier at home in normal circumstances (as opposed to lab testing).
This format was set as the standard for comparing different amplifier brands by the US Federal Trade Commission (FTC). EIA is another accepted standard, but we will stick with FTC for now. It suffices to know that EIA ratings are generally 10-20% higher than FTC. The FTC rating tends to be the more realistic one.
While amplifier power is important in that it will enable you to match the loudness in the room to your listening habits, it probably is equally (if not more important) to have great sound.
So… make sure to take into account also the other important specs relating to sound quality like distortion or smooth frequency response.
Distortion
Distortion is a measure of the amount by which an audio amplifier output is distorted, or altered with respect to the input signal. All amplifiers have a certain amount of distortion. You just don’t want it to be at a level that ruins your listening experience.
Distortion levels below 0.5-1% are not considered significant, nor would you perceive any difference between say an amplifier with a rated 0.05% THD and one with a rated 0.1% THD. At the same time, keep in mind that high levels of distortion can make an amplifier unlistenable.
Another factor that influences sound quality for audio amplifier output is smooth frequency response. A smooth, linear frequency response means that the amplifier will treat every incoming audio signal, whether it’s a bass-drum signal or a cymbal’s high-frequency harmonics at exactly the same way, increasing the electrical strength of each tiny signal by exactly the same amount. You don’t want the amplifier to change the “mix” of tones; that would ruin the timbre of voices and instruments, making them sound unnatural. Ideally, you want the sounds that are on the recording to be reproduced as they were recorded, without changing the sound.
AV receiver or separates or both?
An AV receiver puts a processor a AM/FM tuner, a pre-amplifier (or processor) and an amplifier in a single box.
The alternative is 2 separate boxes: one for the the tuner and another one for the pre-amplifier and amplifier (integrated amplifier). This is the most common scenario.
However, you can even opt for 3 separate boxes with the amplifier and pre-amplifier also as separates.
AV receivers are usually less expensive. New features are available on AV receivers at a regular rate while audio amplifiers tend to be a lot less susceptible to the latest and greatest technology. They are simply aimed at doing a job superbly well: to amplify.
By choosing for an all-in AV receiver you may be trading off amplifying power for features like HDMI processing and decoding, Multi zone functionality, multi channels input and outputs, 7.1 Channel Dolby Digital etc. And while all of these things may be extremely desirable, amplifying power is where the cost cuts are made to provide you with an AV receiver that can do all of the above at the same (or lower) cut-throat price.
And this is where we want to alert you to a recent trend with the latest Dolby Atmos/DTS:X AV Receiver releases: Remember the FTC format we talked about earlier? Instead of publishing unclipped full bandwidth power with two-channels driven into 8 ohm as amplifiers as set by the FTC ; ALL of the major AV receiver manufacturers are now cheekily touting power with only one-channel driven, at 1kHz, into a 6 ohm load and 10% distortion (This is unusable to your speakers!). This type of testing scenario inflates the power rating up to twice the former FTC way of rating power and makes you as a consumer think you are buying an exceptionally powerful AV receiver. You are not!
In other words, the sticker on the outside box of your receiver is a figure that is severely inflated. Only when you search for the fine print on the manufacturers websites or spec sheets do you actually find the two-channel continuous ratings.
The result is that you are buying this low-cost receiver thinking it is going to be powerful enough to drive a pair of highly regarded tower speakers, but the result is that there is no way you are going to get the sound that you had in mind.
On the contrary, a too small amplifier can easily be driven into distortion and cause “clipping” with even moderately loud playback. This can quickly cause the fine wires in the speaker’s voice coils to overheat and melt.
No need to point out the importance of getting the correct FTC power rating as well as making sure that the bargain AV receiver you have in mind, is boasting sufficient power capability for your personal set-up.
Make sure to check both of these when purchasing a new AV receiver.
Depending on the size of your room (large), the quality of your speakers (good), how loud you want the sound (loud) and what source material you use, there may even be a merit in using an external amplifier if you already use an AV receiver. In doing this, you can drive your speakers better, therefore improving sound.
What are the different “classes” of amplifiers?
If you’ve ever glanced at the specifications sheet for an amplifier, one of the things you may have noticed is the amplifier’s class. Typically referred to by a letter or two, the most common amplifier classes used in consumer home audio today are Class A, B, A/B, D, G, and H.
These classes aren’t grading systems, but descriptions of how the amplifiers function at a core level.
While each amplifier class comes with its own set of strengths and weaknesses, their job remains the same: to amplify the waveform sent to them without introducing distortion.
We won’t go into the detail of how and what makes up for the differences between the classes. There are some excellent articles to be found on the internet if you would like to read up on the electronics behind the different classes. In our blog, we just briefly wanted to introduce you to their individual merits and flaws and leave it at that.
- Class A designs are relatively simple devices and have the lowest distortion of any. However, they are extremely wasteful and inefficient, dissipating 80% of their power in heat with an efficiency of only 20%. Because of the low distortion, Class A designs are considered the gold standard for audio quality in many audiophile circles. The amplifiers are in “always on” state no matter if a signal is passing through, so they consume power at any time.
- Class B amplifiers are much more efficient (about 50% to 70%) than Class A designs, but there may be distortions that occur when one set of transistors switch off and the other set switches on, called crossover distortion. Needless to say, such distortion in sufficient amounts is audible and Class B didn’t receive much love from audiophiles.
- Class A/B amplifiers as you may guess, combines the best of Class A and Class B in order to create an amplifier without the drawbacks of either. Thanks to this combination of strengths, Class A/B amplifiers largely dominate the consumer market. Class G and H are basically a variation on the A/B theme with improved efficiency, but come with a price tag.
- Class D amplifiers are extremely efficient and very light weight.
With proper implementation, any of the above (outside of pure Class B) can form the basis of a high fidelity amplifier. The choice of amplifier class is in large part a question of cost versus efficiency. In today’s market, Class A/B dominates the scene, and for good reason: they perform very well, are relatively cheap, and their efficiency is perfectly adequate for low powered applications.
Of course, as amplifier manufacturers try to push the envelope of power delivery, they turn to Class G/H and Class D designs.
Meanwhile, on the other end of the market are Class A aficionados who can forgive a lack of efficiency in the hopes of purer sound.
Why Do Some Audiophiles Insist on Tube Amplifiers?
Tube amplifiers distort in a different manner from transistor amplifiers, generating musically agreeable even-order harmonic distortion that may lend a sense of so-called “warmth” to sound quality (the “warmth” is still a distortion or coloration; it’s not present in the source signal) and it’s this characteristic that most tube aficionados prefer.
While tube amplifiers are often not as smooth or linear in frequency response as transistor designs and have other liabilities as well, when pushed near or past their output limits, tubes tend to gracefully distort, without the harshness associated with transistor clipping.
However, tube amplifiers are limited in output power due to the tubes and output transformers.
5 things you always wanted to know about amplifiers … and the right amplifier is?
We hate to disappoint, but you guessed it, there is no one answer to this question. What is right for you may not suit your next door neighbor.
Our biggest recommendation (apart from determining what set-up works best for you) is to read specification and use FTC as your point of reference for amplifier power.
In an earlier blog that you can find here, we explained to you how to figure out the right power for your amp so it matches your speakers.
With that info under your belt combined with what we discussed in this blog, you should have the tools to deciphering the specs and get on the road to the right amplifier for your speakers.
If this is still mumbo jumbo to your ears, just get your speaker specs out, give us a ring and we will figure it out for you. We love to help.
The Rapallo Team
