Amplifiers and Amplification

The next, equally important part of your HiFi is the amplification. A good amplifier will produce a dynamic, accurate sound that will bring your music to life.

A cheap basic amplifier or the sort which is often found in mini-systems and cheaper AV-Receivers, will work and produce sound. It might even go very loud when you crank it up. It won’t be as satisfying. You won’t hear as much detail or texture within the music. You might not be able to pick out the individual instruments as easily. The music may even seem a bit flat or lifeless. If it is a bad amplifier, it may even distort the sound.

I won’t go into massive technical detail here about the specifics of how different amplification circuits work, but I will provide a basic overview to help you choose what to look for to get decent performance.

An amplifier comprises of three basic components; a power supply, the pre-amplifier and the power amplifier.

In electronics terms, a pre-amplifier is a circuit which receives a weak electrical signal and increases it’s power into a stronger output signal which is less prone interference and ready for further processing or amplification. When we talk about the pre-amplifier in a HiFi amplifier though, this is a little bit of a misnomer. Most HiFi audio sources already output their signal to the HiFi amp at a line level.

The pre-amplifier in a HiFi amp is the part of the equipment which allows you to switch between different different sources and set the volume. It may also feature a circuit which ‘colours’ the sound to allow for the user to apply Bass, Treble or Balance adjustments. There is usually a ‘direct’ switch. This allows you to bypass this circuit altogether to get a purer sound. If your system is set up correctly with the right components, your amp should always be set to ‘direct’ mode, the other controls are only there to compensate for flaws to your system, or the audio recording.

Although it does play an important part in the quality of the sound, the pre-amplifier stage is mostly to control the amplifier and prepare the signal for further amplification by the power amplifier.

The power amplifier is the final stage of the amplification process. It receives the volume adjusted signal from the pre-amplifier and increases the power to a voltage which will power the speakers and make the music audible.

Most HiFi amplifiers which are sold these days are integrated. This means that both the pre-amplifier and power amplifier are both built into the same box, possibly even on the same circuit board inside. There may actually be two power amplifiers, one to power the left speaker, the other to power the right. To create a stereo sound, the signal which goes to each speaker must be slightly different. I’ll go into more detail about non-integrated amplifiers at the end of this section.

The other main part of an amplifier is the power supply. All mains powered electronic devices have some kind of transformer or power supply to regulate the mains voltage to the operating voltage of the product. As this is such a simple standard process in consumer electronics, you’d be forgiven for thinking that it might not have a significant importance to the performance of the amplifier. In actual fact, the quality of the power supply is perhaps the most crucial factor in the sound quality that can be achieved from an amplifier.

Much of what marks the difference between a good amplifier; which can produce a vibrant, dynamic, punchy sound and a mediocre amp, which will in comparison sound dull and lifeless, is down to how the power is supplied to it’s circuits.

As a piece of music plays, the sound varies. The loudness of the instruments vary, the notes and sounds of instruments change and the overall tempo of the music changes. As this happens, the power that is required by the amplifier changes, sometimes quite sharply. It is the power-supply’s ability, along with the amplifier, to respond to these changes which makes all the difference.

There are two main types of power supply used in consumer electronics. Switched mode power supplies, which are found on things like phone chargers, laptops and lower end audio devices such as sound-bars and wireless speakers etc. These are small and compact and fine for low demand applications. The other type is a transformer.

EI transformers are relatively cheap to manufacture. They are usually found in domestic appliances such as microwave ovens. They are also used in most mini HiFi systems, home cinema amplifiers and entry-level HiFi amplifiers. They are called EI transformers because their main components are two pieces of metal, one in the shape of an E, the other in the shape of an I. There is a length of copper wire wrapped around the central part of the E.

If you want to be sure that your amplifier is a serious piece of kit, check that it has a toroidal transformer. These consist of a doughnut shaped piece of metal which has copper wire coiled around it. They are more costly to manufacture than conventional EI transformers, but they have advantages for HiFi amps. They are more efficient, less prone to creating noise and unwanted interference within amplification circuits and can provide their power more responsively.

The overall power of an amplifier can be rated by wattage. However, don’t pay too much attention to this. Not only can the wattage of an amplifier be measured in different ways, which can be miss-leading; as we’ve already explained, the wattage measurement is only a small part of the story. For further explanation about this please see this post: What’s Watts?: Myths About Power and Performance in Amplification and How it Really Works

A Summary of What’s Covered in That Post:

  • Power is not just about volume. Your amplifier relies on power to provide a dynamic sound with plenty of detail, even at low-medium volume.
  • If your shopping for an amplifier, ignore ‘peak-wattage’. Only look at the wattage RMS and be wary of if this is; per-channel, or the total wattage. If the seller can’t provide you with this information, walk away.
  • Don’t obsess too much on the wattage. There are powerful amplifiers that can go loud but have under-whelming performance. There are moderately powered amplifiers that are plenty loud enough for most of us and sound amazing.
  • A 120W RMS amplifier is only a tenth louder than a 60W RMS amplifier.
  • If a bloke down the pub tells you he has a 1000w amp, he likely doesn’t know what he’s talking about.

Most of all, be aware that even if you know to look only at the watts RMS, it is only one part of the picture. To get the best idea of how an amplifier sounds, check out some reviews, get an idea of how much you’d like to spend, then go and talk to your local specialist HiFi retailer. They should be able arrange for you to listen to a couple of different systems to see what suits you best.

Non-Integrated Amplifiers

While an integrated amplifier has both the pre and power amplification built into one unit, with a non-integrated HiFi amp the pre and power amplifiers are entirely separate components in different boxes.

The pre-amp has the inputs for the different sound sources, as well as the means to select a source, a volume and other controls. This is attached to a power amp with two cables, one for the left channel and one for the right. The power amp has no controls on it at all besides a button to switch it on. This is a basic pre and power set-up.

Bi-Wiring and Bi-Amping

With a conventional integrated amplifier or a basic pre-power amp: Once the audio signal leaves an amplifier it goes along a singe cable to each of the speakers. Then the cross-over circuit in the speaker filters the signal to divert the low frequencies to the woofer and the high frequencies to the tweeter. With an integrated amplifier or basic pre-power set-up, the same power amplifier is powering the full frequency range for each speaker.

Speakers which are ‘bi-wirable’ have two pairs of terminals. One pair which goes to the woofer and the other which powers the tweeter. When the speakers are bought new they usually arrive with small metal bridging plates which connect both positive terminals to each other and both negative terminals to each other. These are left in place when wiring conventionally, using a single cable for each speaker.

To bi-wire or bi-amp, these plates are removed and an extra speaker cable is used for each speaker, to allow the high and low frequency drivers to be separately powered.

If you are using an integrated amplifier with two pairs of speaker terminals, it is possible to bi-wire your speakers. This is done by removing the bridging plates on the speakers and using one pair of terminals of the amplifier to power the high frequencies and the other to power the low.

Bi-wiring increases the performance by roughly 5%, so is fairly negligible. You will need either two lengths of conventional duel-core speaker cable or quad-core speaker cable to do this. You will see a much bigger improvement in quality by ensuring you use decent quality speaker wire. If given the choice between bi-wiring using basic speaker wire, or conventionally wiring using high quality cable, it’s best to go for second option.

Where things start to really get interesting is by bi-amping.

This is where two or even four separate power amplifiers are used, to independently power either:
Each speaker. One power-amp for the left, another for the right speaker. This is known as mono-blocking.
The Bass and Treble. Some speakers have two pairs of speaker terminals meaning the woofers can be powered by one power-amp and tweeters can be powered by a separate power amp. This is known as horizontal bi-amping.
Or for the ultimate set-up, four separate mono power amplifiers are used to independently power; the left speaker’s tweeter, the left speaker’s woofer, the right speaker’s tweeter and the right speaker’s woofer.

Bi-amping does provide better performance. By providing separate power to different parts of the frequency range, it creates a more dynamic sound to make individual instruments stand out more and create an improved sound stage.

Now we need to figure out how we’re going to actually play music through our amp and speakers.. Next: The Audio Source…