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I think it was Dr. Peter Walker of Quad fame that once said "In an ideal world an amplifier would be a piece of wire with gain". Well, although electronics in the 21st century are very remarkable that idea is still a long way from fruition.
The amplifier is the heart of the system and as such it has two main tasks to perform;
- It must act as a complex switching unit.
- It has to process the electrical signals coming in and increase the volume of them sufficiently to drive a loudspeaker/headphones.
Lets take look at these tasks in more detail.
- As A Switching Unit
Switches on the front of the amplifier can be adjusted to select whichever source you want to listen to. The most common are as follows;
- CD - To select the CD player.
- Tape - To select the Tape deck. Some amplifiers have two or more tape loops.
- Video - Many amplifiers now have a video input for connection to TV / Video / DVD etc.
- Auxiliary - Auxiliary can be connected to miscellaneous units.
- Phono - To be able to connect a turntable to your amplifier you will need a phono input or an external phono amplifier.
Some amplifiers have the facility to output to more than one set of speakers. The sets of speakers are usually given letters or numbers. This allows speakers to be used independently (ie different rooms) or both sets together.
Another feature found on many amplifiers are separate record/listen selectors. Having this facility give you the option of recording one source while listening to another.
Of course, when building a system you should look for a pre-amplifier that has a neutral sound - that is one that does not impart it's own sound onto the music that is being played through it. My personal choice in pre-amps is the Audiolab 8000Q and 8000C which are both very neutral pre-amps, the Q being the best of the pair.
- As A Processor Of Electrical Signals
Amplifiers are comprised of two main components.
- PRE-AMPLIFIER
The different components (CD players, Tuners, Cassette Decks etc.) have different levels of output, therefore when they are connected to the input of an amplifier their respective levels must be matched. This is the job of the pre-amplifier. In addition to switching, it must control the level of drive to the power-amplifier.
A pre-amplifier may sometimes have tone / balance controls or a graphic equalizer to allow small alterations to be made to the sound. Personally I don't agree with such controls, as a well balanced amplifier and system should sound tonally correct without any other outside influences. Of course, the inclusion of tone controls in a system is really down to the individual and is a subjective opinion
- POWER-AMPLIFIER
After the pre-amplifier has done its job it feeds the signals to the main amplifier circuits. The main amplifier then boosts (or amplifies) the signal to a level that can be used by the loudspeakers.
The amount by which the amplifier amplifies is usually referred to as its power output and is measured in watts. There are many ways of measuring the output but the only measurement that means anything is Watts RMS. If it is referred to by PMPO (Peak Mean Power Output) then I would suggest you stay well away!
One Box or Two?
By far the most common amplifiers available, especially at the entry level and mid-priced end of the market are 'Integrated Amplifiers' which are essentially amplifiers with both the Pre and Power section contained in one main unit.
Although Integrated amplifiers are more convenient, my own listening tests have shown that they don't necessarily give as good a performance as their separate pre-power equivalents and they are certainly not as upgradeable
As the price range increases there's more of a choice available: you can still buy an integrated amplifier if you wish (you will usually find that they are neater, in terms of number of cables involved with connecting to them).
In addition to the usual two-channel amplifiers, some manufacturers produce multi amplifier systems which incorporates a second two-channel amplifier just for the reproduction of low frequencies. There are several advantages sonically in going the two box (or more) route of amplification, always assuming of course that the manufacturer has made full use of the design.
You get two advantages by separating the preamp and power amp: first the physical separation of the units helps cut down interference and second having separate power supplies stops the voltage fluctuations in one unit from affecting the other.
All electronic devices give off a small amount of energy in the form of radio waves. Because power amplifiers, by their nature, operate with big voltage swings they generate significant radio emissions. That can't be avoided, but a good design will bring the emissions down to very low levels. Preamplifiers are sensitive to small signals, so they can pick up these radio waves and cause distortion to the music that you want to hear. Careful circuit design and layout, in both the power amplifier and the preamplifier, minimizes the effects of interference but you can't beat a few centimetres of open space and a couple of metal cases to really knock interference on the head.
As one would expect power amplifiers makes heavy demands upon its power supply. The sudden surges of energy that the loudspeakers need to make a loud sound tend to cause the supply voltage to drop for a moment. If the pre-amp shares the same power supply then its supply voltage will also drop and this will have an effect on the sound. Using separate power supplies in separate units means this simply will not happen. This effect can go all the way back into the AC supply, so make sure your supply is rated for sufficient current and use a separate outlet for each unit.
You can increase the power available to the loudspeakers either by using a more powerful amplifier or by spreading the load over more than one amplifier.
As long as the gain and broad tonal characteristics are the same - as they are across all Audiolab products, you can use any two power amps for bi-amping with one amp for high frequencies (usually marked 'HF') and the other for bass/ midrange frequencies (marked "LF"). Where the amps have different power ratings, it will be a matter of taste where you should put the more powerful amplifier - so try it both ways. Whichever sound you prefer is the right configuration. Conversely you can run upto six power amplifiers depending on your speakers. The Epos ES22's have a three way crossover and sound their best when each speaker unit is driven with three separate power amps, thus six amplifiers are needed to for best results.
For example in a four amplifier system . Connect the amps as follows.
1 x Left Woofer, 1 x Left Tweeter, 1 x Right Woofer, 1 x Right Tweeter.
If you have an Integrated amplifier, the power supply is running two amplifiers, one for left and one for right in addition to the pre-amp section. When playing music through it, if a big signal occurs that will drain the power available to the amp and will invariably affect the level of power available to the rest of the system and ultimately the sound. This is particularly evident in bass heavy music such as rock etc.
As long as the gain and broad tonal characteristics are the same - as they are across all Audiolab products, you can use any two power amps for bi-amping with one amp for high frequencies (usually marked 'HF') and the other for bass/ midrange frequencies (marked "LF"). Where the amps have different power ratings, it will be a matter of taste where you should put the more powerful amplifier - so try it both ways. Whichever sound you prefer is the right configuration.
Now play the same the same track through the Four amplifier system. When that big bass signal appears on the left woofer, the rest of the system carries on as if nothing has happened this is because each component is running on its own power supply. Bi-amping won't make your system any louder but it will reproduce the sound more accurately and you will hear a marked decrease in the inherent distortion between mid to high frequencies and low frequencies, thus resulting in super sonic reproduction with a much more defined and dynamic frequency range
Additionally, it gives more scope for the components to be optimised and gives the consumer more choice in tailoring the amplifier to his/her specific needs. However, pre/power combo's aren't always better - it's what's inside that counts. The difference between connecting your loudspeakers using a pair of cables each costing 'X' or via a single higher-quality cable costing '2X' is small. However, adding a second speaker cable to an existing system is a cost-effective upgrade.
The same arguments about interference and power supplies are true for separate phono pre-amp stages and for separating the CD transport mechanism from the DAC
Facilities
It may sound a bit obvious but make sure that the amplifier you select sports all the facilities you require. There is nothing worse than having an amplifier that doesn't have enough inputs to accommodate all your equipment requirements.
If like myself, you use recording equipment regularly make sure that you get amplifier with enough recording loops. This is partly the reason why I favor Audiolab pre-amplifiers as they have three recording loops which is unusual for most hifi gear.
You will also need to make sure that you have enough pre/outs for your current needs and to accommodate any future upgrades. Pre/outs are handy for connecting extra power amps or for multi-channel amplifiers.
If you are a regular user of Vinyl and have a decent turntable, you will need to make sure that the amplifier has a decent Phono-stage built in. If not, or if you want your turntable to sound it's best, you will need to budget for a decent Phono amplifier to plug into the line-level auxiliary connections.
Tone controls are generally frowned upon by the Hifi community. The theory being that the more units you put into the signals path the more distortion you add to it. However, there are instances when tonal adjustments can become useful, for example when playing a bright or bass-heavy recording. If you do decide to get an amp with tone connections, do ensure that it has a 'tone defeat' switch so you can disable them when not in use. The principles also apply to graphic equalisers; again they are generally frowned upon and other than the nice light display they are not of much use in a good system.
Valves or Solid State?
In the dim and distant past, all amplifiers were valved, but when transistors make their appearance in the 1950's a whole new breed of amplification was born. Today, the majority of amps are of the Solid State types; for most people they offer a more cost effective solution, easier to live with and are more flexible for system building. Their greater power output makes them easier to match with a wider range of loudspeakers.
However there are also those, who like myself swear by Valves on the ground of sound quality. With Valves there is a certain clarity, and depth to the sound that just cannot be better or even matched with solid state equipment. Their transparent, almost liquid midrange and clean, sweet treble can be enthralling but as with most things, you can't have your cake and eat it! many valve amplifiers sound a little soft and wooly in the bass compared to high-performance solid state amplifiers. But, what they may lack in grip they more than make up for in their dynamics, ironically lower powered triode types often produce a more powerful sound than the pentode alternatives. With valves amps it is often important to partner them with sensitive speakers.
General hints and tips
Don't skimp on cables and wherever possible, use recognised methods of isolation - a good quality equipment support will help, perhaps with an additional isolation platform or equipment 'feet' of the compliant or coned variety. Amplifiers like to be stretched to attain maximum performance - they may need a week or so to run in, and could take up to an hour to warm up prior to a serious listening session.
Keep ventilation holes clear and avoid stacking components on top of an amplifier; if direct stacking is unavoidable, put the amp on the top. It's always advisable to site amplifiers well clear of source components, on a separate shelf of a dedicated hifi support if possible. Again, if there are any tone controls on your amplifier set them to zero or switch them out for best performance.
With regards to equipments supports, I can recommend those from Mana and Ash Designs.
Crank It To The Max - or the amplifier that goes to 11
Fancy recreating that PA rig feeling in your front room? Your neighbours will be pleased to know there are limits
The common view of the hi-fi enthusiast is a bit like that joke about the artillery company's record request in Good Morning Vietnam: we don't care what you play, but play it LOUD. And once you've got your new pride and joy of a system home and checked the neighbours are out, sooner or later you're going to succumb to the temptation to crank the volume.
It's not hard to work out why - many people would agree that music does sound better when you can feel it as much as hear it. Anyone who's experienced the sheer power of a big PA system driving clean and hard, or the sheer impact of an orchestra giving it some, will know just how thrilling it can be.
But as you'll have discovered if you've ever woken up the morning after that unforgettable gig or a nights clubbing with muffled hearing, listening at those kind of levels can cause problems. Even some classical players have noticed the effect - there have been reports recently of orchestras resorting to earplugs or screens to protect performers from brass or percussion and full blast. After all, in industrial situations ear-defenders have to be worn where levels exceed 85dB - the kind of level you'll experience a metre from most hi-fi speakers with an input of just a single Watt.
So why have amplifiers capable of delivering 100W or more? And why are there speakers capable of turning that power into levels of 120dB or so? Its a bit like asking why there are cars capable of exceeding sensible speed limits - it's all a matter of power in reserve. It doesn't mean you have to make use of it all the time, but it's handy for those moment when you need it.
Crank modest systems up and you'll soon discover a flattening of the dynamics of the music - if you've ever listened to a portable radio going flat-out you'll have heard the fatiguing, compressed wash of noise it can make of any music. An amp with plenty of power and speakers of high sensitivity enable the system to play cleanly at realistic levels, and have power in hand for the dynamics of the music.
It's when the sound gets hard and fatiguing that two problems can set in. One is the potential for damage to your speakers, as the amp begins to clip, but then speakers can always be replaced. That may seem like a bit of a throwaway remark, given that you've spent your hard-earned on those precious rosewood veneered boxes, but it's a much less serious matter than the other consequence.
And that's the potential, after long-term exposure to overloud sound, for temporary (and in extreme cases permanent) damage to your hearing. Once lost, hearing acuity can't be regained, however much you spend on your system - the high frequencies will go first, followed by an overall loss of sensitivity.
Think we're being killjoys? All this was brought home to us a couple of years back, at a show where a big home cinema rig was being demonstrated continuously as visitors passed through. The salesman made his pitch, signaled for the show to start, and put on a pair of ear-defenders. good gimmick, we thought, until we stumbled out ten minutes later with our ears ringing and began to imagine what spending eight hours a day in that room could do.
Your ears are the most important part of your hi-fi system - take care of them.
Crank It To The Max section adapted from http://www.whathifi.com/scripts/sadbuttrue.asp?id=22
AMPLIFIERS and their role in my system
I personally see the Amplifier as one of the most important parts of my system. Indeed I have spent a great deal of time (and money!) on setting my amplifiers up to be the best they can.
At the present moment I am using the following setup for my amplification;
2 x Tube Technology Genesis Power Amplifiers
Mick Evans 1999-2001
[email protected]
