1. Input sensitivity refers to the minimum input signal level required by the amplifier. It is a necessary condition for amplifying the sound source signal to a level sufficient to drive the subsequent amplifier.
2. Harmonic distortion, which is an extremely important indicator of the amplifier. Harmonic distortion is a type of nonlinear distortion. It is caused by the nonlinear characteristics of the amplifier when it is working. The result of distortion is the generation of new harmonic components, which makes the sound lose its original timbre. In severe cases, the sound breaks. Harmonic distortion can be divided into odd and even harmonics. Odd harmonics can make people irritable and disgusted, and are easily perceived by people. Some amplifiers sound irritable and tired, which is caused by large distortion. The biggest impact on the amplifier is distortion. Generally, high-fidelity requires harmonic distortion to be below 0.05%, and the lower the better. In addition to harmonic distortion, there are also intermodulation distortion, crossover distortion, clipping distortion, transient distortion, phase distortion, etc., which are the culprits affecting the quality of the amplifier. To evaluate the quality of the power, we must first look at its distortion. For example, the total harmonic distortion of the Italian Sinfoni amplifier is below 0.01%.
3. Output power. The power issue is the most unclear for car audio practitioners. Here we need to explain it one by one:
A. Rated output power, called (RMS), refers to the maximum power that the audio signal output by the amplifier can output within the total harmonic distortion range. It is generally 0.707 times the peak value of the AC signal.
B. Average power. Average power generally refers to the average power consumption at each frequency point. It is somewhat similar to the rated output power, but it generally refers to time.
C. Peak output power. The maximum music power that the amplifier can output is called peak output power. It does not consider distortion and is usually about 1.414 times the (RMS) power.
D. Peak-peak power. It refers to the power from the positive voltage peak to the negative voltage peak. It is four times the peak output power. Its appearance is for commercial purposes by the manufacturer and has no practical significance.
4. The signal-to-noise ratio, the larger the value, the better, generally expressed as (S/N), expressed in decibels of the ratio of signal power Ps to noise power Pn, S/N=10lgPs/Pn=20lgVs/Vn (db), where Vs and Vn are signal voltage and noise voltage respectively.
As the signal-to-noise ratio and input signal level increase, the signal-to-noise ratio also gradually increases, but when the input signal level reaches a certain value, the signal-to-noise ratio remains basically unchanged. According to high-fidelity requirements, the signal-to-noise ratio should be above 90dB. Imported high-end amplifiers can often reach 110-120dB, and their performance can be imagined. In short, the larger the signal-to-noise ratio, the smaller the noise mixed in the signal, and the better the playback quality, so that the music can be played back cleanly and layered.
5. Frequency response, commonly known as power bandwidth in the early days, refers to the 1/2 rated power bandwidth of the amplifier when the harmonic distortion does not exceed the specified value, that is, the frequency band included between the two frequency points with a drop of -3dB at the high and low ends, which is called power bandwidth.
6. Damping coefficient, mainly for low frequencies, is an extremely important technical parameter that directly affects the quality of bass. As we all know, the larger the caliber of the speaker, the better the bass, but the sound is often unnatural, especially at low frequencies of 100-400Hz, which can easily cause sound coloration and make people sound very unnatural.
When designing the amplifier, engineers take some technical measures, such as selecting multiple tubes in parallel, low internal resistance (milliohm level) high-power tubes, increasing the working voltage, selecting high-quality wires, etc., to try to increase the damping coefficient so that it can produce "electric damping" against the inertial movement of the speaker, so that the movement of the sound basin is synchronized with the audio signal, and the sound basin is restored to zero position (i.e. center position) as soon as possible after the driving signal ends. This blocking effect is the damping factor (Damp Factor), D=Rs/Ri, Rs=speaker impedance, Ri=amplifier output internal resistance, the larger the D, the better the synchronization effect of the sound basin and the signal, the purer and cleaner the bass, and the better the playback effect.
7. Slew rate, the slew rate of the amplifier greatly affects the quality and performance of treble playback. The faster the slew rate, the better the treble sound quality, and the more accurately it can capture the fleeting high-frequency information. High-end amplifiers can achieve dozens to tens of V/us, while low- and mid-range amplifiers generally do not indicate this. The value of this conversion rate is closely related to the design and materials, but it should not be too high. If it is too high, it will produce ultra-high frequency signals above 20KHz that are inaudible to the human ear, which will not only have no effect on improving the sound quality, but can easily burn out the tweeter.
