An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal. It uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output.
All amplifiers in the world receive smaller electrical signal (input) from the power source (turntable, phone,CD player, etc.) and amplify it (make the same signal larger).The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input.
- What Kinds of Amplifiers Exist?
Amplifiers can be classified in numerous ways (by construction, by frequency, by voltage, power, by class from A to D, etc.). That’s not so strange considering the fact that amplifiers are widely used – they are built into all kinds of devices from hearing aid devices to the home theater speaker systems. Because of that, we have many different categories of amplifiers and different types of amplifiers. One can easily get confused when reading amplifier classification but that’s not our topic, so we won’t go into details. We are just going to say that one of the ways of classifying amplifiers is by their function.
This type of classification gives us servo amplifiers, linear and non-linear, wide-band, buffer, RF and audio amplifiers. The group called audio amplifiers is the most important for us right now. These amplifiers are used to amplify audio frequencies and we can divide them into 3 subgroups:
1) Stereo Amplifiers
2) Pre-Amplifiers
3) Home Theater Amplifier / AV Receivers
- Stereo Amplifiers
These have two output channels that they use to receive stereo output signal coming from some device and send it to the speakers that are connected to the amplifiers.
- Pre Amplifiers
These amplifiers (also known as Pre-Amps or Phono Stage) are there to receive very weak signals (signal from your turntable) and amplify them to the higher level (line-level signal) where the regular amplifiers take over. You must have a phono stage or a pre-amp if your are playing a turntable setup.
However few turntables are available which have an inbuilt pre amp which can directly be plugged into a stereo amplifier or any active/powered speakers. There are also many stereo amplifiers that have an inbuilt pre amplifiers in them.
- Home Theater Amplifier / AV Receivers (Audio Video Receiver)
An audio/video receiver (AVR) is a component used in a home theater. Its purpose is to receive audio and video signals from a number of sources, and to process them to drive loudspeakers and displays such as a television, monitor or video projector. Inputs may come from a satellite receiver, radio, DVD players, Blu-ray Disc players, VCRs or video game consoles. The AVR source selection and settings such as volume, are typically set by a remote controller.
- How do Stereo Amplifiers work?
Stereo amplifiers are one of the most popular ways of improving the sound quality in different situations and conditions. They can be used at home or office and they can amplify the signal coming from Turntable, CD and DVD players, TVs, etc.
Stereo amplifiers have 3 ports/connectors (input port for connecting the signal source, the output port that’s used to send the signal to the speakers and power source connector or power input). These amplifiers receive power from the wall socket and they convert alternating current to the direct current thanks to the device called transistor. That device is some kind of valve that enables the current to flow in specific amounts. The amount of current that the transistor allows to flow depends on the signal received from the signal source. Smaller signals will enable less current to flow and the amplification will be smaller than the amplification of larger signals that enable more current to flow.
The transistor controls not only the amount of current. It also controls its frequency. Depending on the frequency of the input signal, the transistor will work slower or faster (if the frequency is 50 Hz, the transistor will open and close 50 times per second).
- How to Choose the Right Stereo Amplifier?
As we have previously said, stereo amplifiers are the most popular way of improving the sound quality when using speaker systems. However, making a decision which model to buy is not an easy task, so we have prepared a few pieces of advice in order to help you. That way you will know which characteristics to pay attention to when purchasing a stereo amp.
Pre/Power or Integrated Amplifier
Stereo amps can be bought in two forms – in one or two boxes.
Integrated amps come in one box and they combine two devices (pre-amp and power amp) into one. They are better than the second type because they take up less space and you get everything already combined and matched together, so you don’t have to worry about these things – the perfect combination is already achieved. On the other hand, they offer lower sound quality in comparison to the pre/power amplifiers.
Pre/power amps consist of two boxes. In one box, you will find the pre-amp that has input port and volume controls while the power-amp is in the separate box. The pre-amp can be very sensitive because the signal that goes through the pre-amp is sensitive. Power-amp, however, is noisy and a great amount of current goes through it. This is why some think it is wise to keep them separate. It won’t save you any space, but the sound quality will be better. The important thing is to try to buy both devices from one manufacturer in order to achieve better results.
Compatibility (impedance/power output/sensitivity)
The most important thing about buying an amplifier is probably matching it perfectly with your speakers. In order to do that, you have to consider these three characteristics.
Power output is measured in watts (W) and it is important because it generally defines how loud your music will be. The power output you need depends on the size of the room you want to fill with music. In case you have a small apartment, even 10W will be enough but if you have really big house, you should consider some serious wattage (100 W and more). In case you use 10W amp, each of the channels will get 5W.
Impedance is measured in ohms (Ohm) and it can span from 8 to 600 ohms. Impedance is the other name for the electrical resistance and it shows what voltage you need for the best performance of the certain device. The higher the impedance of a speaker, the bigger voltage will be required by the amp to make the speaker work.
Sensitivity is measured in decibels (dB) and it shows how loud your speakers can be.
Connection (inputs/outputs)
The last but not the least is the content of the rear panel. All the input and output ports are there and based on the number and type of the connections you will know which devices you can use with that specific model. Apart from that, the rear panel tells you if your amp supports upgrading.
Let’s start with the input ports. Most stereo amplifiers have RCA inputs that can be used to connect them to different types of players (even turntables) or some other low-signal devices. This kind of connection requires high equalization level. Three-pin XLR connectors are in charge of balanced audio and they are usually used to connect the amp to the high-level devices that are often found in studios.
Although stereo amps usually use analog connection, some modern amplifiers use digital connection and have some digital inputs. Some of them can also have USB ports that come in handy when connecting your amp to your PC, notebook, phone via USB cable.
You should also pay attention to output ports. They can be used to connect some additional devices to the amplifier. For example, you can connect separately your subwoofer to add some extra bass, connect headphones using 3.5mm or 6.3mm output ports or you can connect two pairs of speakers to one amp simultaneously. However, the last one can lead to poor performance.
Many modern amps have built-in Bluetooth so you can even try connecting them to your devices using this technology and forget about all those annoying wires.