27/01/2011 How to buy a new amplifier.

Tagged under Amplifiers, Hi-Fi, Stereo Amplifiers
Posted by Len | 1 Comment

by Len Wallis

(This article has previously appeared in Limelight Magazine)

When you are looking to invest in a new amplifier there are three primary considerations that you must be aware of:

Firstly any quality audio system, be it two channel Hi-Fi or a Home Theatre system, must be balanced, i.e. all the components must be as closely matched in quality as possible. Do not be fooled into thinking that a good amplifier is going to make an inferior pair of speakers’ sound great – or vice-versa.

Secondly, it is important that it physically serves its purpose. Work out what you want the amplifier to do, is it going to be used in a Home Theatre environment, are you intending to run speakers in other rooms, how many source components do you intend to play through it – and do these include digital files?

Finally the perfect amplifier is described as being a ‘straight wire with gain.’ This means that the sole role of an amplifier is to take the source signal fed to it, and amplify that signal without adding any signature of its own; i.e. the output of the amplifier is identical to the input, only louder. The drawback is few of us know what the input actually sounds like.

There are some other factors that must also be taken into account. The main one is your choice of speakers. Speakers vary enormously in the level of difficulty taken to drive them. One of the better guides (but not the only one) is the speaker measurement called efficiency.  This is expressed in dB, and today most speakers are rated at around 89dB efficiency. A variation of only 3dB equates to twice the audible volume. This means that a loudspeaker that has a efficiency rating of 92dB will play twice as loud for the same volume input as one rated at 89dB. In this instance the amplifier you choose does not need to be a powerhouse, particularly if you are in the habit of playing your music at moderate volume levels. However if you have a loudspeaker with an efficiency level of 86dB or less, it will be necessary to invest in some serious power.

Your listening habits will also have a big impact on the amplifier that you need to purchase. If you are in the habit of playing your music at very high levels your power requirements are going to be far greater. Most speakers that are damaged by overdriving are the victim of an underpowered amp rather than too much power. As you turn an amp up beyond its comfort zone it starts to distort, and in most instances it is this distortion, not sheer volume, that causes the voice coils in the speaker to burn (a condition not covered by the manufacturer’s warranty!)
While we are on this subject it is becoming increasingly difficult to get an honest published specification for the rated power of an amplifier. Once this information was fairly well controlled, but in recent times it appears that the more outrageous your claim is the better. The greatest culprits in this are the Home Theatre receiver manufacturers. One magazine recently tested the published specifications of a number of Home Theatre receivers and found that none came anywhere near their rated power, the worst of the bunch only achieving 28% of their claim. Admittedly some manufacturers are forthcoming – in the fine print – as to how they measure power. Usually this measurement is taken while only driving one channel, with all others turned off. Hardly a real life scenario.

There is a considerable variety of amplifiers on the market, with the more obvious split being between old fashioned valves, and solid state. Valve amplification is very much alive and well, and is the amplifier of choice for many audiophiles. They have a beautiful open transparent sound with beautiful midrange. Some may be critical of the bass response, although this can be a design issue rather than a failing in the concept. They are also usually low powered, being more suitable for more efficient loudspeakers. While many find solid state to be tonally a little harder this is the most common form of amplifier. They are more powerful, run far cooler, with a tighter and more controlled bass, and are considerably less expensive.

One variation on solid state that is hard to beat is a form of amplification called Class ‘A’. These amplifiers are again low powered, although higher than valve amps, they also run warm, but less so than valve amplification, are very controlled in the bass, but have all of the other attributes of valve.

Finally the new frontier for amplifier manufacturers are those designed to be equally at home with both analogue (radio, phono etc) and digital files. These amplifiers include high quality DAC’s (digital to analogue converters) and can accept any digital feed, including high-definition audio formats, and replay them in the conventional manner.

1 Comment

Comment

* All fields marked with an asterisk are mandatory

Please enter a name.

Please enter your e-mail.

Please enter a comment.

Name*

Email*

Website

Please enter the total/sum of these numbers (6 + 9)

Comment*