By the current control action of triode or the voltage control action of field effect tube, PA can convert the power of the power supply to the current which varies according to the input signal. Because the sound is wave with different amplitude and frequency, the transistor's collector current is always β times of the base current. Because of this, if small signal is injected into the base, the current through collector will be equal to β times of the base current. And then the signal is isolated by the blocking capacitor to get the large signal which current (or voltage) is β times of the original signal. This phenomenon become triode amplifying function. After amplifying constantly current, power amplification is completed.
What is PA? - Power amplifier usually consists of three parts: preamplifier, drive amplifier, and professional power amplifier for sale
Preamplifier – it plays a matching role with high input impedance and low output impedance. At the same time, it is a current amplifier which can change the input voltage signal into the current signal and then amplify appropriately. Drive amplifier – it plays a role as bridge which can further amplify the current signal sent by the preamplifier. Without a drive amplifier, it is impossible for the final power amplifier to send high-power sound signal. Final power amplifier – it plays a key role. It drives the current signal sent by the amplifier to form a high-power signal and drives the speaker to make a sound. Its technical index determines the technical index of the whole power amplifier.