A Guide to Hi-Fi Amplifiers

In the world of hi-fi separates, the amplifier is perhaps the device whose function is the least well-understood.  A CD player (or other input device) produces the signal; speakers are what turns the signal into sound.  What’s perhaps more difficult to grasp is the point of an amplifier, and what effect one’s choice of amplifier might have on the ultimate quality of the sound produced. 

Let’s address this confusion by examining the different sorts of amplifier available, and seeing how these differences influence the end result.

What does an amplifier do?

The signal which exits your input devices is strong enough to drive only the smallest of speakers – namely those found in your headphones.  In order to drive larger loudspeakers, you’ll need more power.  At the most basic level, this is the function of an amplifier – take an incoming signal and make it stronger.

What sorts of amps are there?

An amplifier might do this in one of several ways.  There are valve amps, which use vacuum tubes, and there are transistor amps.  Since the middle of the 20th century, transistor-based amplifiers have been preferred thanks to their longer lifespan, sturdiness and lower levels of hiss and hum.  That said, valve-based amplifiers are still preferred by some audiophiles for their warmth and distinctive mid-range.  Some integrated designs will make use of valves at one stage of the process, and transistors at the other, thereby offering the best of both worlds.

Pre-amps and power amps:  what’s the difference?

After it leaves your input device, your signal will flow into a series of two stages of amplification.  The first of these is called the pre-amp, whose role is to prepare the signal for the next stage, bringing it to the correct level and shaping it.  A pre-amp will allow the incoming signals to properly match with one another, allow you to select between them, and provide control over volume.

The second stage of amplification is known as the power amplifier.  It’s this device that actually boosts the signal to a level high enough to drive your speakers.  The amount of amplification at this stage is fixed – that’s why a dedicated power-amplifier will come with no controls on the front.

Any small distortions picked up at the pre-amp stage will colour the sound dramatically when the signal is boosted.  Separate pre and power-amplification units are rare in most hi-fi setups, where all-in-one, combined units which run off the same power supply are often preferred.

What an integrated amplifier?

An integrated amplifier is by far the sort most commonly found in the modern household.  It’s a device that does everything under the same power supply, providing the end user with a convenient means of experiencing the benefits of both.  In terms of controls and connections, an integrated amplifier is identical to a pre-amplifier – at the rear you’ll find a host of different inputs, which can be selected via a control on the front panel, along with outputs that can be used to drive your speakers.  The downside of an integrated amplifier is that it prevents the two stages from being powered separately, and that it’s more difficult to upgrade.  Having said that, the merits of being cheaper, more convenient, and more compact would seem to outweigh these drawbacks for most users.

What should I look for in an amp?

Once you’ve decided whether to go for an integrated unit, or to go for separates, you’ll still be confronted with a wealth of options.  The features on offer are certain to influence your decision, and they’re worth examining.

Tone Controls

Many amplifiers will grant you a degree of control over the signal, offering basic equalisation controls to raise or lower the bass, treble, or mid-range.  Generally speaking, you’ll want to leave this as flat as possible – and so allow your music to play as it was intended – but having the ability to shape the sound will afford some welcome flexibility if you need to compensate for the characteristics of other components, and the room.

Inputs

Any good amplifier will come with a wealth of traditional unbalanced RCA inputs – but they might also offer digital connectivity via a coaxial, optical, or USB input.  Sometimes they might even offer Bluetooth connectivity.  Most amps will also offer a phono socket that’s designed to work with your turntable – boosting its signal to line level before it enters the amplification stage proper.

More expensive amplifiers might offer balanced inputs as well as unbalanced ones.  These work by transmitting two signals, one of them inverted, from the input device, and then inverting one of them again before combining them into a single ‘balanced’ signal where any noise is cancelled out.  This process is expensive because it requires extra components on the interior of the amp – and so it’s found only on the most prestigious equipment.

Power

The overall strength of an amplifier is popularly summarised in terms of wattage – but it’s wise to be sceptical of extravagant power claims by manufacturers; raw wattage is a figure that’s easily fudged.  Provided that the amp meets the recommendations of your speaker manufacturer, you’re unlikely to ever push the dial beyond the 12 o’clock position.

Quality

While the spec-sheet of a given amplifier might provide some important indications as to how it’s going to ultimately sound, a greater influence on performance will come from the quality of the components inside the amp, and how well they’re all laid out.  The way that power is distributed across the amp is especially important – as drops in power will result in amps that are underpowered, or which produce unacceptable distortion.

As with many things in the world of hi-fi, the ultimate test of quality comes from your ears.  Be sure to test an amp with the speakers you intend to use it with – ideally at slightly lower volumes than you intend to listen to it with.  Remember that it’ll take time (sometimes upwards of 100 hours) to really sound its best.

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