The preamplifier plays a matching role. Its input impedance is high (not less than 10k Ω), which can absorb most of the front signals. Its output impedance is low (below tens of Ω), which can transmit most of the signals. At the same time, it is also a current amplifier, which converts the input voltage signal into current signal and amplifies it appropriately.
The driving amplifier acts as a bridge. It further amplifies the current signal sent by the preamplifier and amplifies it into a medium power signal to drive the final power amplifier to work normally. If there is no driving amplifier, the last stage power amplifier cannot send high-power sound signal.
3. (commercial amplifier)
The final stage power amplifier plays a key role. It will drive the current signal sent by the amplifier to form a high-power signal and drive the speaker to sound. Its technical index determines the technical index of the whole power amplifier