Stereo amplifiers, as a class of technology, appeared a long time ago, at first they were two-channel devices, and they worked only with sound, there was no 5.1 configuration yet. Such devices exist to this day.
Stereo amplifiers differ from receivers in fewer functions, but the sound, as a rule, is better. The main task of the amplifier is to reproduce the recording qualitatively. The emphasis is on high-quality production of the audio path. High-quality parts are used, and the circuit is made quite simple, with a minimum of functions. However, expensive devices still have some functions.
For example, a built-in phono stage, a headphone output, a USB port for a flash drive, as a rule, there is a Pure Direct button, maybe even Bluetooth. There are also not many inputs. Usually, there are analog line input, coaxial digital and optical inputs, and one or two pairs of screw terminals.
An inexpensive device will play roughly like an expensive receiver. More expensive models will give a sound that is in many ways superior to any receivers. Receivers are more popular because of their versatility, great feature set, and little compromise in sound quality.
Types of Stereo Amplifiers
There are three types of amplifiers – preliminary, full, and final. The preliminary amplifier will improve the signal, the final amplifier will simply amplify, and the complete or integral amplifier will amplify the signal and improve it.
Integral stereo amplifiers are also a small compromise. They combine two functions. If you use two separate devices – pre and post sound will be better. Separate components are always considered better than combined ones.
Amplifiers can also be analog and digital. Purely analog amplifiers are sometimes considered better than digital ones. With the right approach to design and quality details, you can achieve very good sound. Digital amplifiers must process and improve the digital signal, and then convert it to analog, and output to the speaker.
DVD and media players can have analog outputs and digital. Amplifiers have analog inputs. That is, it will be possible to connect the player to the amplifier completely analogously. If you use a digital channel, then it is better that it be coaxial or optical. Usually, there are no others in amplifiers. It will be possible to connect a player to the receiver via HDMI, but the sound will be worse since this interface also transmits a video signal.
Classes of Stereo Amplifiers
There are several classes in which amplifiers work – these are A, B, AB, and D. The classes differ in the applied technologies and details. Class A has a more accurate and balanced sound, but at the same time it is inferior in power to categories B and D. Group B will be more powerful. D is the most powerful, but at the expense of quality. It will be worse than class A or AB. The latter is a compromise between good sound and power.
According to the element base, amplifiers are:
– Transistor is the most popular type of element base. Most of all devices are made on transistors. This approach produces accurate and powerful sound. However, it can differ depending on the quality of the parts.
– On microcircuits – a cheaper and low-quality sound option, ready-made microcircuits are used. The sound will be powerful, but less clear and voluminous.
– Tube type amplifiers, highly prized for their soft, comfortable sound. Instead of transistors, they put lamps and the price of such devices is much higher than that of others.
– The hybrid type of stereo amplifiers combine tubes and transistors. The signal is improved by tubes and then amplified by transistors. The sound of such amplifiers is powerful and accurate.
Choosing the Right Amplifiers
Number of channels
Amplifiers, as a rule, have two channels for one pair of speakers. There are also devices with four channels of amplification for four speakers.
Power
The power must be selected for the speakers. Optimally, this value should be twice the power of the speaker. You also need to pay attention to the impedance of the speakers and their sensitivity. The higher the impedance, the more difficult it will be for the amplifier to swing them. Typically, the sensitivity is 90 -100 dB. Above a hundred is considered an excellent characteristic.
The speaker impedance is 4, 6, and 8 ohms. It is best to take 4 ohms, so acoustics will suit any amplifier. Also, the power of the amplifier is nominal. That is, the power for a long time and maximum – the power that the amplifier develops for short periods of time. Speakers also come with a power rating and the maximum power they can handle.
Distortion factor
There are harmonic types of distortion and intermodulation. It will be good if the harmonic distortion is within the 1 percent limit at a frequency of 50-14000 Hz, and intermodulation will not exceed 3 percent at a value of 300-10000 Hz.
Frequency range
This characteristic is responsible for the width of the reproduced frequency range. The wider the range, the better the acoustic systems will be needed, preferably approximately with the same range, so that the potential of the amplifier and speakers is fully revealed. Stereo amplifiers and speakers with a wider range reproduce every detail of the recording. For an amplifier, this characteristic should be approximately – 50-200 kHz.
Response time
This value is important when the audio signal drops, at which distortions appear. The value depends on the upper frequency limit. The higher it is, the higher the response time and will be more. The normal value for this characteristic is about 58 ms.
Resistance
The impedance of the device determines what kind of load it is designed for. That is, the impedance of the speakers. It is desirable that their impedances coincide. Acoustics are available with an impedance of 4, 6, and 8 ohms. It will be better if the amplifier is designed to operate from 4 ohms.
Signal to noise
This value determines how much useful signal and interference, noise, in the general signal. The higher this indicator, the better, it will be good if this parameter is 90-100 dB.
Damping
At high volume levels, the cones vibrate and the amplifier reduces these resonances, making the sound more accurate. The value of this characteristic should be about one hundred units.
Functions
Amplifiers have much fewer functions than receivers, but some things do happen. For example, almost all models have a Pure Direct function that turns off all digital circuits, which has a positive effect on the sound. A phono input will be useful for vinyl. For listening in popular lossless formats, the USB input is useful, as well as a headphone output.
The function of switching and redirecting signal sources is also useful. Some devices have a Bluetooth function. Outputs – inputs can additionally be an input for a power amplifier and an output from a pre-amplifier, as well as an additional pair of terminals for acoustics.
When choosing an amplifier, you need to pay attention to the power and impedance of the device so that it fits the acoustics. The amplifier normally works at half its power. Usually, the power of budget devices starts from 50 W. This parameter should be at least 70-100 W. The impedance must be matched to 4-ohm acoustics so that the amplifier can work with any acoustics.
The terminals are already, as a rule, screwed for all devices. They should be for two pairs of speaker systems. It will be better if all switches are mechanical. Electronic control is worse. It will also be better if the control panel is a system one so that you can control other components.
Of the functions, there should be tone correction, headphone output, vinyl input, and Bluetooth. Of the inputs, in addition to the linear one, you should have coaxial and optical. Budget devices may not have all these functions and inputs. First of all, you need to select an amplifier in terms of power and resistance.
