Toroidal transformer
Most modern amplifiers have
toroidal transformers - with a toroid-shaped core, in other words, a donut. This type is considered optimal for amplifiers of any level up to Hi-End: it creates a minimum of "extra" electromagnetic radiation and, accordingly, interference. Some time ago, E-core transformers were also widely used, but they are considered obsolete and are becoming less common today.
Frequency range
The range of audio frequencies that the amplifier is capable of handling. The wider this range, the more complete the overall picture of the sound, the less likely it is that too high or low frequencies will be “cut off” by the output amplifier. However, note that the range of sound audible to a person is on average from 16 Hz to 20 kHz; There are some deviations from this norm, but they are small. At the same time, modern Hi-Fi and Hi-End technology can have a much wider range — most often it is a kind of "side effect" of high-end circuits. Some manufacturers may use this property for promotional purposes, but it does not carry practical value in itself.
Note that even within the audible range it does not always make sense to chase the maximum coverage. It is worth, for example, to take into account that the actually audible sound cannot be better than the speakers are capable of giving out; therefore, for a speaker system with a lower threshold of, say, 70 Hz, there is no need to look for an amplifier with this figure of 16 Hz. Also, do not forget that a wide frequency range in itself does not absolutely guarantee high sound quality — it is associated with a huge number of other factors.
Signal to noise ratio
In itself, the signal-to-noise ratio is the ratio of the level of pure sound produced by the amplifier to the level of extraneous noise that occurs during its operation. This parameter is the main indicator of the overall sound quality — and very clear, because. its measurement takes into account almost all the noise that affects the sound in normal operating conditions. A level of 70 – 80 dB in modern amplifiers can be considered acceptable, 80 – 90 dB is not bad, and for advanced audiophile-class devices, a signal-to-noise ratio of at least 100 dB is considered mandatory.
If the specifications do not specify for which output the signal-to-noise ratio is indicated, it usually means its value for the linear input (see "RCA (par)"). This is quite enough to evaluate the quality of the device for this parameter. However, some manufacturers indicate it for other inputs — Main, Phono; see below for more on this.
Signal to noise ratio (Phono MM/MC)
signal-to-noise ratio when the amplifier is driven through the Phono input. This interface is for connecting turntables; its features are described in the “Inputs” section below, and for the meaning of any signal-to-noise ratio, see the corresponding section above.
Damping factor
The damping factor describes the quality of interaction between the amplifier and the speaker system connected to it.
Due to the design features, any speaker is prone to the occurrence of so-called parasitic oscillations — oscillations that continue after the main impulse from the amplifier has ceased (similar to how a string continues to vibrate after a pluck). This phenomenon has a negative effect on sound quality, and manufacturers use various means to reduce it to an absolute minimum; suppression of parasitic oscillations is called damping.
The most effective type of damping is electrical, by reducing the output impedance of the amplifier. The lower this resistance, the better the amplifier keeps the speakers from unnecessary vibrations. To evaluate this effect, they introduced the concept of “damping factor” (damping factor) — the ratio of the load resistance (impedance) to the output resistance of the amplifier. The minimum value of such a coefficient for Hi-Fi class equipment is 20; indicators at the level of 100 – 120 can be called good, and among the Hi-End segment there are numbers of the order of several thousand.
At the same time, it is worth noting that when increasing to three-digit numbers, the original meaning of this parameter is, in fact, lost, and other points appear. The most important of them from a practical point of view is that models with a high damping factor are very demanding on the quality of the connection to t...he speakers — the high resistance of cables and connectors can negate the damping properties of the amplifier itself. There are other nuances associated with this indicator (in particular, recommendations for choosing an amplifier and speakers for each other); they are described in detail in specialized sources.
Harmonic distortion
This indicator describes the amount of non-linear distortion introduced by the amplifier into the processed signal. Such distortions are not necessarily perceived as extraneous noise, but they degrade the quality of the sound anyway — for example, they can make it more deaf. It is almost impossible to avoid them, but it can be reduced to levels inaudible to the human ear.
As a result, the harmonic distortion factor (harmonics) is one of the main parameters describing the overall sound quality in Hi-Fi and Hi-End amplifiers. The lower it is, the clearer the sound. Hundredths of a percent are considered a good indicator for modern amplifiers, thousandths and below are excellent. The exceptions are tube and hybrid models, for which rather high harmonic coefficients are allowed; see "Element base" for more details.
Line input
The sensitivity and dynamic impedance of the amplifier when a signal is applied to the RCA line input.
Under the sensitivity of any input (except optical) is meant the lowest signal voltage at this input, at which the amplifier is able to provide normal nominal power values (see "Power per channel (8Ω)"). This parameter determines, first of all, the requirements for the signal source. On the one hand, the voltage provided by this source must not be lower than the input sensitivity of the amplifier, otherwise the latter simply will not give the claimed characteristics. However, a significant excess in voltage should not be allowed, otherwise the sound will begin to be distorted. More detailed recommendations on choosing an amplifier by sensitivity are described in special sources.
For any input other than optical, it is believed that the higher this indicator, the less distortion the amplifier introduces into the signal. The minimum level of input impedance in modern models is considered to be 10 kOhm, and in high-end devices it can reach several hundred kOhm.
Phono MM/MC
The sensitivity and dynamic impedance of the amplifier when a signal is applied to the Phono MM/MC input.
Under the sensitivity of any input (except optical) is meant the lowest signal voltage at this input, at which the amplifier is able to provide normal nominal power values (see "Power per channel (8Ω)"). This parameter determines, first of all, the requirements for the signal source. On the one hand, the voltage provided by this source must not be lower than the input sensitivity of the amplifier, otherwise the latter simply will not give the claimed characteristics. However, a significant excess in voltage should not be allowed, otherwise the sound will begin to be distorted. More detailed recommendations on choosing an amplifier by sensitivity are described in special sources.
For any input other than optical, it is believed that the higher this indicator, the less distortion the amplifier introduces into the signal. The minimum level of input impedance in modern models is considered to be 10 kOhm, and in high-end devices it can reach several hundred kOhm.
Preout
Signal level and dynamic impedance provided by the device at the preamplifier output (see "Outputs" for details).
The signal level must not be lower than the sensitivity of the power amplifier (see "Type") to which the signal is received — otherwise the power amplifier will not be able to provide a normal signal level already at its outputs.
Dynamic resistance (impedance) of the preamplifier output. This value is exactly the same as the input impedance of the REC output — see the relevant paragraph above. For more information about the exit itself, see "Exits".
