From a professional point of view, the ability to provide good sound quality output is mainly dominated by power amplifiers.

For many people who have started in the audio industry, they don't know much about power amplifiers, nor do they know what accessories are needed to configure the power amplifier speakers to achieve the best effect of the power amplifier.

The first type: install a resistor under the speaker to sample the current. In fact, the feedback is still the voltage signal, which is the analog current feedback. The most people do it, but the circuit is defective. There are two reasons.

1. It is that his output gain will change with the change of impedance. As a result, the voltage applied to the horn 2 is not constant, as if the power applied to the horn can be made constant.

But don’t forget that the sound pressure characteristic curve of the loudspeaker is tested under constant voltage output, so this circuit is not very sound, the hearing is not good, and it is fun, but there is an improved circuit with negative voltage feedback. Mainly, adding an appropriate amount of this type of current negative feedback can make a good sound, but at this time, the role of current negative feedback is to change the damping coefficient of the power amplifier, which has little effect on the amplitude-frequency characteristics.

2. The sampling point is below the horn. The horn is an inductor. The phase of the current flowing through the inductor will change. The low frequency is good, the high frequency can be shifted by 90 degrees, and the phase characteristics are extremely poor.

The second type: Negative impedance amplifier, except in some special occasions, the first one to be used in audio and to achieve success is YAMAHA. Its main function is to improve the extension of low frequency, but it can improve the extension of low frequency. The frequency will have the effect of degrading the sound quality, so it is generally used in ultra-low frequency active speakers.

Actually, this kind of circuit is used in conjunction with the speaker, and it has no practical significance on its own. Its working principle is: if the speaker is a rigid body, then adding a tube can become an ideal Holmoz resonance box, then no matter the size of the box and the thickness of the tube, as long as it meets the Holmoz resonance Calculation formula. Even the resonance point of 20Hz can be achieved. The size of the box is just the efficiency. Due to the presence of the speaker, the speaker is moving when it sounds. The speaker is not a rigid body, so the box will not produce Holmoz resonated.

Therefore, if the speaker's diaphragm is stationary when it is sounding. Then, the box is close to a rigid body, which can meet the conditions of Holmoz resonance, and the resonance point of this box can be arbitrarily designed. The job of keeping the horn stationary when sounding is the task of the negative resistance power amplifier. The working principle of the negative resistance power amplifier is that when the speaker is working in the low frequency band, its impedance characteristic changes sharply. The amplifier circuit takes out this change through current sampling and feeds it back to the power amplifier, so that the power amplifier controls the speaker in the form of current. Equivalent analysis of the circuit, it can be found that the internal resistance of the power amplifier is calculated as a negative resistance characteristic.

makes the internal resistance of the speaker plus amplifier close to 0 during dynamic amplification. As a result, this circuit makes the horn receive strong damping no matter which direction it faces. As long as the sound is over, the horn will not move and the box will become rigid.

The third type: current mode feedback amplifying circuit. This is a practical current amplifying circuit, and it is also a real current-type negative feedback. The feedback signal is current, not voltage, that is to say, it is not added at the negative feedback terminal, but added , There is current flowing in. This kind of circuit was first used in video transmission, or equipment such as oscilloscope.

Because it is a low-resistance negative current feedback input, this circuit has excellent high-frequency characteristics, and the driving ability of capacitive loads is super strong. As long as it is improved, it is found that it is very good to be a power amplifier, which can make up for some of the inherent shortcomings of voltage-type amplifiers. The open-loop frequency response is low, the closed-loop transient frequency response is distorted, and the capacitive load driving capability is extremely weak. The disadvantage is that the open-loop gain of this circuit is relatively low, and the distortion after the closed-loop will be an order of magnitude higher than that of a voltage-type amplifier.

In the audio industry, some companies do a good job with total distortion not exceeding 0.01%. It depends on the technical level of the equipment and enterprise personnel. Good equipment and technical staff's debugging can naturally bring out the best effect of the power amplifier.