Amplifier selection

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Technical Knowledge

Source:

2018/11/14 15:36

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[Abstract]:

A power amplifier usually consists of three parts: a preamplifier, a driver amplifier, and a final stage power amplifier

A power amplifier usually consists of three parts: a preamplifier, a driver amplifier, and a final stage power amplifier.

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

2. The driver amplifier acts as a bridge, which further amplifies the current signal sent by the preamplifier and amplifies it into a medium power signal to drive the final stage power amplifier to work normally. If there is no driver amplifier, the final stage power amplifier cannot deliver a high-powered sound signal.

3. The final stage power amplifier plays a key role. It will drive the current signal from the amplifier to form a high-power signal, which will drive the speaker to sound. Its technical specifications determine the technical specifications of the entire power amplifier.

The main technical indicators of the power amplifier:

1. Rated power (rate power): refers to the continuous sine wave power. When the 1kHz sine wave input and a certain load, the harmonic distortion is less than 1% of the output power, expressed as W/CH (Watt/Channel) . In general, the higher the rated power, the higher the cost.

2. Total harmonic distortion (THD): refers to the percentage of higher harmonics in the fundamental wave. The smaller the total harmonic distortion, the better. The total harmonic distortion of a good power amplifier can reach 0.02%.

3, slew rate (slew rate): the voltage amplitude per unit time rise, the unit is volts / microseconds, which reflects the power amplifier's ability to track transient sound signals, is a transient characteristic indicator.

4. Damping factor: It is defined as the load impedance of the power amplifier (the internal resistance of the high-power tube plus the wiring resistance of the speaker), for example, 8Ω: 0.04Ω=200:1. Generally, the ratio is relatively large, but it cannot Too big, too big will make the speaker sound thin, too small will make the sound turbid, the sound level is poor, the sound image distribution is not good.

5, output impedance (or rated load impedance): usually 8Ω, 4Ω, 2Ω, etc., the smaller the value, the stronger the power amplifier load capacity. In the case of a single channel, a power amplifier with a rated load of 2 ohms can drive four speakers with an impedance of 8 ohms with little distortion.

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