1, when the signal source is at a certain input level, the output of the amplifier can reach full power;

2. The amplifier has multiple sets of signal source input options;

3. The amplifier has level control function;

4. The left channel and the right channel are integrated, and high and low pitch control devices can be provided. The output level of the early signal source is relatively low, generally around 0.2V, so the average input power of the combined amplifier is below 0.2V, but the modern signal source has undergone great changes. For example, CD players have been widely used, and the output levels of modern signal sources are between 0.5- 1V, so the input sensitivity requirements of modern power amplifiers have changed accordingly. Of course, no matter how it changes, as long as the first three requirements of the combined amplifier are met, it is a combined amplifier. The front and rear power amplifiers are integrated 1 signal source selection, 2-stage control and 3-stage voltage amplification (the third item is the active front stage, and the third item is the passive front stage). The pure rear power amplifier integrates the left and right inputs of voltage amplification and power amplification (or both), and there is no level control and signal source selection (the input level is between 1-2V), so the structure is feasible.