Power amplifier: front stage, rear stage, pure rear stage, combined type

             Power amplifier: front stage, rear stage, pure rear stage, combined type

For power amplifiers, there is a concept of pre-amplifier, post-amplifier, pure post-amplifier, combined type, etc. Many people can't tell the type of front and back stage power amplifiers, and don't know which one to buy. In fact, the functions of the front stage and the back stage are different. The front stage is generally a differential amplifier circuit or a common collector amplifier circuit. It mainly selects the differential mode signal that needs to be amplified from the signal, and it is generally connected to a multi-stage common-emitter amplifier circuit behind it. for small signal amplification. It is the signal voltage rather than the current that is boosted most likely at the front end.

Simply put, the function of the pre-stage is to initially amplify the signal and realize volume adjustment. Most pre-amplifiers are active pre-amplifier circuits, not passive pre-amplifiers that can only adjust the volume. Of course, in addition to adjusting the volume, the active front stage can also perform preliminary amplification and reduce the internal resistance between the sound source and the rear stage to play a buffer role. The rear stage is completely different from the front stage. It sends the signal of the front stage to the speaker and drives the speaker to produce sound.

The pure post-stage input signal is very simple, which is to undertake the output of the pre-stage and increase the power of the signal. The current stage is connected to the high-impedance post-stage, which mainly provides an appropriate output voltage, and the post-stage amplifier is connected to a low-impedance speaker to provide not only an appropriate voltage, but also sufficient current. Therefore, a good post-stage system not only requires high power output, but also specifically indicates that it will be a large current design. When the impedance of the load is reduced by half, the output power is doubled.

Our most common is the integrated power amplifier, which integrates the pre-amplification and power amplification into one body. This kind of amplifier has multiple input options for information sources, and has the level control function of the front stage. It integrates the left and right channels into one. When the signal source is at a certain input level, the amplifier output can be fully loaded. Some of the consumer amplifiers we often see and use are integrated designs, which are relatively more cost-effective than using pre- and post-amplifiers alone.

But there is no doubt that the split front and rear stage design is definitely better than the integrated power amplifier, because they each have a larger space and are more refined. The design of the front and rear amplifiers together will inevitably cause some interference, which will affect the performance of details, and the separate front and rear amplifiers will give enthusiasts more choices to use with different equipment. Many high-end power amplifiers are pure front-end and pure rear-end systems with split design.