The Basic Composition of Professional Amplifiers

Professional Amplifiers usually consist of 3 parts: preamplifier, driver amplifier, and final power amplifier.

Here is the content list:

• Basic component

• Class A and Class B Professional Amplifiers

Basic component

1. The preamplifier plays a matching role, and its input impedance is high (not less than 10kΩ), which can absorb most of the previous signal. The output impedance is low (less than tens of ohms), and most of the signals can be transmitted. At the same time, it is a current amplifier itself, which converts the input voltage signal into a current signal and gives appropriate amplification.

2. The drive 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 driver amplifier, the final power amplifier can't send out a high-power sound signal.

3. The final power amplifier plays a key role. It will drive the current signal sent by the amplifier to form a high-power signal to drive the speaker to produce sound. Its technical indicators determine the technical indicators of the entire power amplifier.

Class A and Class B Professional Amplifiers

Class A amplifier:

The main characteristics of the class A amplifier are: the operating point Q of the amplifier is set near the midpoint of the load line, and the transistor is turned on during the entire period of the input signal. The amplifier can work as a single tube or push-pull. Since the Professional Amplifiers work in the linear range of the characteristic curve, the transient and alternating distortions are small. The circuit is simple and easy to debug. But the efficiency is low, the transistor consumes a lot of power, the theoretical maximum efficiency is only 25%, and there is a large nonlinear distortion. Therefore, the efficiency is relatively low.

Class B amplifier:

The main characteristics of the class B amplifier are: the quiescent point of the amplifier is at (VCC, 0), and when there is no signal input, the output terminal consumes almost no power. In the positive half cycle of Vi, Q1 is on and Q2 is off, and the output terminal is a positive half-cycle sine wave; similarly, when Vi is a negative half-wave sine wave, two push-pull tubes must be used to work. It is characterized by high efficiency (78%), but because a section of Professional Amplifiers works in the non-linear region, its disadvantage is that the "crossover distortion" is relatively large. That is when the signal is between -0.6V~0.6V, Q1 and Q2 cannot be turned on. So this kind of amplifier is gradually abandoned by designers.

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