If given the distortion rate, the PA system amplifier can produce a maximum power output to drive an amplifier of a certain load, such as a speaker. The PA system amplifier plays the role of "organizing and coordinating" in the whole sound system, which to some extent dominates whether the whole system can output good sound quality or not. Its technical indicators are as follows:
1. Rate power
It refers to the continuous sine wave power, and the harmonic distortion will be less than 1% of the output power at 500Hz sine wave input with a certain load, marked as W/CH (watt/channel). In general, the higher the rated power, the higher the cost.
2. Total Harmonic Distortion (THD)
It refers to the ratio of higher harmonic to the base wave, and the smaller the total harmonic distortion, the better. The total harmonic distortion of a good PA system amplifier can reach 0.02%.
3. Slew rate
It refers to the voltage amplitude increased in unit time, in volts/microseconds, which reflects the PA system amplifier's ability to track transient sound signals and is a transient characteristics index.
4. Damping factor
It is defined as the load impedance of the PA system amplifier (high-power tube internal resistance together with the loudspeaker wiring impedance). For example, 8Ω:0.04Ω=200:1, in general the ratio required is relatively large, but not too large. If the ratio is too large, the sound by the speaker may sound weak. If the ratio is too small, then it will make poor audio-visual distribution.
5.Output impedance (or rated load resistance)
There are usually 8Ω, 4Ω, and 2Ω and others, and the smaller this value, the stronger the load capacity of the power amplifier. For a single circuit, a power amplifier with rated load at 2Ω o can drive 4 speakers with the impedance of 8Ω and has very little distortion.
Regardless of the strict requirements for PA system amplifiers of AV amplifiers and Hi-Fi amplifiers, there are clear requirements in terms of output power, frequency response, distortion, signal-to-noise ratio, output impedance and damping coefficients.