The small digital amplifier is a kind of amplifier with the characteristics of low distortion, low noise, and large dynamic range. It is incomparable with a traditional power amplifier in terms of the transparency and analytical power of sound quality, the quiet background and the shock strength of low frequency. The basic circuit of a small digital amplifier is an existing class D amplifier. Previously, this amplifier was used only in the laboratory or high-value testing equipment for the price and technical reasons. Advances in technology over the years have integrated digital amplifier components into one or two chips, and prices are falling. The theory proves that the efficiency of class D amplifier can reach 100%. However, the ideal switching element has not been found so far, so it is inevitable that some power loss will occur. If the device used is not good, the loss will be greater. However, its magnification efficiency is still more than 90%. In addition, the small digital amplifier has the characteristics of low distortion, low noise and large dynamic range, which is incomparable to the traditional power amplifier in terms of the transparency and analytical power of sound quality, the tranquility of background and the shock strength of low frequency. In the field of digital power, now there is a new term "pure digital power amplifier" for HIFI enthusiast, which directly transmits digital signals, then the PCM digital signal frequency and reforming the clock again after a PCM->PWM conversion, direct PWM for digital signal amplifier, PWM power output again after LPF of LC circuit to directly drive the horn after 1 bit DAC, the benefits of the digital signal in the process of transmission will not bring the phase retard, phase distortion, the distortion and so on, the advantage of the listening is sound will be more fully, more accurate positioning, closer to the truth.