There are all kinds of amplifiers in the world. However, the purpose of all these amplifiers is the same: to amplify a weak signal. This is true for RF amplifiers (for radio signals), for example, to be able to send them over a greater distance (think of cell phone towers or FM towers for radio, for example), or in a microwave oven, for example, to get enough energy in the waves to cook food (hence the wattage listed in the specifications).
In HiFi, the goal is the same, but then it’s to drive a pair of speakers loud enough for us to enjoy the music. And often that requires more power than a source’s output can provide. Although it is theoretically possible to drive a pair of high efficiency speakers with the 2 volt output of a line source. Practically, however, it is not. You won’t be able to control volume, for one thing.
Amplify and attenuate
Now, within hi-fi, we often name two types of amplifiers: a preamplifier and a power amplifier. However, if we look at the task of these amplifiers, the power amplifier is the only real amplifier of the two. The preamplifier is basically a switch box with an attenuator, since in most cases it attenuates the 2 volts from a line source before it enters the power amplifier. It has to, otherwise you would always be listening at full power. Something your speakers won’t like and your ears won’t like either.
If we are going to calculate what an average speaker – 88dB at 1 watt / 1 meter – would produce in volume with a 100 watt amplifier at full power, then we arrive at 108dB (ΔSPL=10×log10(P1P2)… you can immediately forget this)). In short: not very pleasant if the input cannot be attenuated… hence we have a volume control at a decent hi-fi system.
How many watts?
Now, of course, the question is: is every amplifier suitable for every speaker? This is a quick answer … no. Not every amplifier will work on every speaker. You will get sound, but it certainly does not always work well. That has largely to do with stability. And part to the power an amplifier can deliver.
Ok … so how much power do we need? We’ll get into that question later, but let’s just say that in practice we need much less power than we think. And that not the number of watts counts, but the stability and quality of the delivered watts.
But back a bit … Some speakers are notorious for being difficult to drive, so a bit more power is needed to unlock their full potential. These are exceptions though; the bulk of speakers are not very difficult. So it’s more about matching in terms of sound than in terms of power.
Front, end, integrated?
In very many cases, users will buy what is called an integrated amplifier. This contains both the pre- and power amplifier. And nowadays they often have a d/a converter and sometimes even a streamer or a hdmi connection for the TV. These products are not really just an amplifier anymore. We call them ‘all-in-ones’. However, the idea remains the same: you control both volume and amplification with one box.
Whether an amplifier works well with a speaker depends on many factors. And most of the time, the match is difficult to predict. But you can get a good impression of the basics if you look at:
- The efficiency of a speaker
- The minimum impedance
- Recommended power
A loudspeaker with extremely high efficiency usually does not need much power to play well. A speaker with very low efficiency often does need some punch to play nice.
However, a loudspeaker with a decent efficiency can still need a very stable and powerful amplifier because it “dips” very low with impedance. There are models that go toward 1 Ohm. There is almost no amplifier that likes that. Most will stop playing nice at 2 ohms. Especially if then the electrical phase is also unfavorable (see the Academy series around speakers).
Rounding
Now we have gone a bit more into the technical side. It’s still Alpha Audio. But if we summarize, an amplifier is needed to amplify a line source enough so that a speaker can do something with the signal. However, it also requires an attenuator – volume control / preamp – to make the level controllable.
Amplifiers come in many flavors: small, large, weak, strong and also with various technologies. We’ll get into that later. In the next installment: class A, class AB and class D … what are the differences?