Amplifier Designs

May 26, 2019

There are many choices when it comes to choosing a suitable power amplifier(s) for your speaker system(s). For example do you want a heavy but smooth analogue sounding Toroidal design which can often (but not always) be cheaper or would you prefer one of the designs listed below which are often less than half the weight of the old back breaking Toroidal powered power amplifiers?

Matching the power of the amplifier to the loudspeaker is covered in another article in our ‘Help and Support’ section so have a look at that article if you want to know more on ‘Amplifier and Speaker Matching’.

We have deliberately left out ‘Valve’ or some refer to as ‘Tube’ power amplifiers as though they can produce a superb sound by their nature they are not usually high power in terms of volume output compared to other designs and are far more susceptible to being damaged transporting them from one venue to another and therefore not really suitable for main PA Systems or Monitors.

Lets get started with a brief basic description of the more popular variations of the different classes of ‘Switch Mode’ power amplifiers you will find for sale in today’s marketplace.

Class A:

This type of power amplifier isn’t found that often these days. It is only around 50% efficient at best and therefore doesn’t make the best use of available power. It is a design a design favoured by some HIFI enthusiasts due to the very high audio quality produced.

Class B:

These amplifiers only use half the input signal and they create a fairly high distortion figure. They are quite efficient though with a rating approaching 80% which makes them considerably better than class A as far as converting electricity into what comes out of your speaker system.

Class AB:

As you may guess these power amplifiers basically use the advantages of both class A and class B designs while minimising their disadvantages and are therefore regarded as a very good design producing near HIFI quality. This design can produce high power outputs up to around 600w RMS and beyond @ 8ohms per channel. Above these power ratings they can start to run too hot to function as well as they should and therefore other classes of power amplifier are often preferred to avoid excessive heat build up leading to possible shut down.

Class C:

This class of amplifier is very efficient with figures around 90% however it produces a relatively high distortion figure. OK for something like a Megaphone but possibly not much else so lets move on.

Class D:

Now we are getting further into digital processing with this design. It offers good value for money and is one of the most efficient amplifier designs you can get with figures of up to 95%. Along with class AB amplifiers the class D amplifier is one of the more popular designs you will find in use today. Class D amplifiers are good all round performers producing a clean crisp sound at HF signals as well as Bass and they will happily tackle Sub Bass Speakers without any problem. You could say this design is a ‘Jack of all Trades’ though you will have to decide for yourself via a good listening test if this design turns out to be the ‘Master of Nothing’.

Class E:

This design dates as far back as the early 1970’s however is not something you are likely to come across very often these days.

Class F:

Another amplifier design rarely found these days and a little like class E designs can be compared with a pinch of salt to class D.

Class G:

Here we are getting into the heavy weight division of power amplifiers aimed more towards the Sub Bass speakers due to the high power output levels on offer. This particular design like class H below takes the class AB design and makes it even more efficient. While not as efficient as class D it is a design you should consider against a class D amplifier if you want the extra power on offer without the heat problems that could be associated with a class AB design.

Class H:

This class of power amplifier is very similar to class G. In terms of voltage supply a class G amplifier uses more than one voltage rail as it switches up or down the rails as and when necessary. A class H amplifier works on a constantly variable voltage rail principle. The class H output stage operates at it’s maximum efficiency all the time. As with class G amplifiers class H is a serious contender to class D especially at the higher end of the power ratings.

There are other designs such as class TD which is a variation of class D. There is also a class I design and so on. Some power amplifier designs use a combination of some of the above classes etc. However the class AB and class D designs of power amplifier are usually the most commonly used.

The best advice we can give you is to first of all match the power output of the amplifier(s) to the loudspeakers correctly and then listen to the audio quality of a particular amplifier for yourself through your own sound system as there is a wide choice out there and we all have a personal preference as to the quality of audio we want to hear from our own loudspeaker systems. Remember power amplifiers affect the audio quality in the same way audio mixers, loudspeakers, microphones and other system components do.