Keeping it Simple: Amplifiers

Imagine that you hand me a large heavy flag attached to a long heavy pole and you ask me to wave the flag in a controlled way. Being quite puny I start to stagger around as I bust my butt trying to wave the flag; it’s all very messy, but eventually I get a fairly erratic rhythm going with very little movement of the flag. Then you ask me to stop and yet again there is a lot of grunting and groaning as I eventually bring the flag to a stop. I then pass the flag to my mate Dave, who is built like a grizzly bear. Dave starts waving the flag in a much smother and quicker fashion with very little wobbling around and with large swings than I could not manage. He then brings the flag to a stop, again much quicker and smoother than I could. You may have already guessed that you could consider me and Dave as amplifiers and the flag as the diaphragm in a speaker or headphone that moves the air that makes the sound.

It could be said that we can both ‘drive’ the flag, but with very different levels of control and magnitude.

Amplifiers vary greatly in their complexity and sophistication and in general the more complex they are the more they are able to get rid of unwanted ‘wobble’ and the more powerful they are the easier it is for them to create greater swings of the diaphragm, and just as importantly the better they are at stopping it in a controlled manner. It is the start and stopping of the diaphragm that defines the naturalness and tonal quality of each musical note that is produced and it is the ability to deliver power that increases the dynamic headroom allowing larger swings from low to high.

Flags can vary in size and weight from little flags (in-ear monitors) to headphones and on to large floor standing speakers and it’s not just about ‘driving’ the speaker but how controlled that driving is.

If we consider mobile phones and even portable music players they may be able to drive high quality headphones (usually heavy flags) but there is no way that one can cram a sophisticated amplifier into a fag packet powered by a small battery that is also powering lots of other stuff. The best chance such mobile devices have of sounding at their best is to use IEMs’ as the amplifier has more chance of being able to wave the flag in a controlled way. To my ears not even portable players costing thousands of pounds can drive really expensive headphones to their full potential. So my advice is to not go spending hundreds let alone thousands on headphones or IEMs’ to listen to your phone, or your music player because you may only be hearing 50% of the potential of your expensive headphones. A basic rule would be to not spend more than £100 on headphones if it is connected to your phone or £700 if it is connected to a digital player, whatever the cost.

Too many people who review headphones and portable devices don’t get this. They bang on about the ability to ‘drive headphones of 600Ω’ without considering that the sound is less than optimal, which makes the headphones unsuitable and a waste of your money.

So what can we do to realise the true potential of our music player or phone? Well for those of you who use a phone then IEMs’ are the way to go. If you want to use headphones then an amp/DAC combo is a good idea, but these devices tend to compromise either on the amp or the DAC but it will be far better than the phone. For those of you with a good quality music player I would buy a dedicated headphone amplifier. It surprises me how few dedicated portable headphone amps there are in the market, but in my opinion you can’t go far wrong with the Ifi Ican (£175). This is a small box that you can strap to your portable player and contains a well-designed amplifier and a huge capacity battery and it is easily capable of not only driving most headphones, but do so in a controlled and very musical way. The Ican can be used with a mains supply and for many it may well be the only amp you will ever need. In my opinion my Onkyo DP-X1 player and ican at a total cost of £800 is more musically satisfying than a £2000 plus Astell and Kern player directly plugged into the same headphones.

This is also true of large hi-fi systems. You should always try to have speakers and an amplifier of comparable quality so as to maximise the musical potential of both, otherwise you are not getting value for money and what’s worse depending upon the quality of your music player one components can show up the weaknesses of the other.

The next stage is to move to a desktop amplifier that is mains powered. These are physically larger and have the ability to have more complex circuit designs and greater electrical isolation between components and the mains.

Before having a very simple look at different types of amplifier I want to try to very simply explain how an amplifier works with yet another simple model.

We can think of an amplifier as a hose pipe that is connected to a very sensitive tap that can be turned by a gentle but swirling stream of water that flows all around it. The actual water supply to the tap has a very high pressure behind it so as the tap oscillates in the gently changing stream water bursts out of the hose at varying levels of high pressure and it is this high pressure flow that hits the diaphragm. In an ideal situation the continuous high pressure water coming out of the hose follows the much smaller changes in the water flow across the tap, in amplifiers this ability to accurately follow the input variation is often termed, ‘linearity’.  In this model the gentle stream of water passing the tap is the small signal coming from the player, the thing that creates the water pressure in the tap is the amplifier’s power supply and the tap and hose act like a transistor or valve (tube).

Even in our hose pipe amplifier you can see that the result depends upon such things as the sensitivity of the tap, the consistency of water pressure, the diameter of the hose pipe and such like so it’s not surprising that designing and building good amplifiers is complicated.

Let us have a quick look at the main types of amplifier that you may come across:

Valve or Tube Amplifiers.

Everyone should hear a good tube amplifier. It may be old technology but there is a lovely smoothness and analogue-like sound quality to valve amplifiers. The best and cheapest way to experience valves amps is with headphones. One of the characteristics of valve amps is that they create a wider and deeper sound-stage, which can be of benefit to headphones. Even cheap valve amps now tend to be ‘plug and play’ and you can tinker by trying different valves combinations (valve rolling), which can make a significant difference in the musicality.

Solid State Amplifiers.

These come in several basic configurations.

Class A

I am not alone in thinking that class A amps are generally the best sounding and usually the most expensive. Basically in class A the transistors are working all of the time so they tend to generate a lot of heat, especially for large power amps. This requires expensive transistors that are very stable with temperatures. Class A solid state amps operate in a similar way to valve amps that are also on all of the time. The advantages of class A include eliminating certain types of noise caused by other types where the transistors are switching on and off. If you are looking for a new amp and can afford it then I recommend you have some class A amps on your short list. The ifi Ican is a class A amplifier, as is the Arcam Rhead headphone amp.

Class B

Class B amps have two identical circuits for each channel (left and right) and one amplifies positive swings of the signal and then rests whilst the other circuit amplifies the negative swing. This means that transistors are only working half of the time and hence you don’t have to use such expensive transistors and other components that are stable with high temperatures. There are some very good class B amplifiers around but in general you have to work hard to find one that is better than a class A amp. This switching of transistors can cause noise and distortion if not done well.

Class A/B

Class B amps can introduce a lot of types of distortion and so the Class A/B amplifier uses both modes to help reduce this distortion whilst still reducing heat. This is probably the most common type of audio amplifier.

Class C

These do exist but they are not used for audio so if you see a class C audio amplifier steer clear.

Class D

Class D amplifiers have started to appear on the audio scene and my hose pipe model no longer applies as the transistors are used in a completely different way such that they are near 100% efficient and very little heat is generated. This means that they can be very compact and cheap to produce. My understanding and my own experiences suggest that they are not generally as good as an old style transistor or valve amplifiers and are often used in modern mobile phones, which is a big limiting factor in the sound quality of a phone. They are also used in AV amps where you need five or more amplifiers in the unit to power all of the speaker channels and in desktop speaker that include the amplification.

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