How to configure the power amplifier to achieve
To some extent, the power amplifier dominates whether the whole system can provide good sound quality output. For many friends, they do not know the amplifier very well. It is unclear which accessories are required to configure the power amplifier speaker in order to play the effect of the power amplifier to an optimal state? The first one is to install a resistor under the speaker for current sampling. Actually, the feedback is still a voltage signal, which is the analog current feedback. Most people do it, but this 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 constant voltage is not applied to the end of the horn 2. It seems that the power applied to the horn can be made constant. But do n’t forget, the sound pressure characteristic curve of the speaker is TEST under the constant voltage output, so this kind of circuit is not good, the sound is not good, it is fun, but there is an improved circuit that uses 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 under the horn. The horn is an inductor. The phase of the horn will change when the current flows through the inductor. 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 resistance amplifier, except for some special occasions, the first one used for audio and achieved success is YAMAHA. Its main role is to improve the extension of low frequencies, but it is good for 200Hz and above. However, the frequency will have the effect of degrading the sound quality, so it is generally used in ultra-low frequency active speakers. In fact, this circuit is used in conjunction with the speaker, there is no practical use alone. Its working principle is: if the speaker is a rigid body, then with a tube, it can become an ideal Holmuz resonance box, then regardless of the size of the box, the thickness of the pipe, as long as it meets the Holmoz resonance Calculation formula. Even the 20Hz resonance point can be achieved. The size of the box is just the efficiency. Due to the presence of the speaker on the speaker, the speaker is moving when it sounds, the speaker is not a rigid body, then the box will not produce Holmoz resonated. Therefore, if the horn's diaphragm is stationary when sounding. Then, the box is close to the 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 untouched when speaking is the task of the negative resistance amplifier. The working principle of a negative resistance amplifier is that when the horn is working in a low frequency band, its impedance characteristics change sharply. The amplifier circuit uses the current sampling to take out this change and feed it back to the amplifier. By performing equivalent analysis on the circuit, it can be found that the internal resistance of the power amplifier becomes a negative resistance characteristic in calculation. During dynamic amplification, the internal resistance of the speaker plus amplifier is close to zero. As a result, this kind of circuit makes the speaker be strongly damped in any direction. As soon as the sound ends, the horn will not move and the box will become rigid. The third type: current mode feedback amplifier circuit, this is a practical current amplifier circuit, and it is also a real current-type negative feedback. The feedback signal is current, not voltage, that is, it is not added at the negative feedback terminal, but added , Current flows in. This kind of circuit was first used in video transmission, or instruments and equipment like an oscilloscope or something. Due to the excellent high-frequency characteristics of the low-impedance negative current feedback input circuit, the driving capacity of the capacitive load is super strong. As long as improvements are made, it is found that it is very good to make a power amplifier, which can make up for some of the inherent shortcomings of the voltage amplifier The open-loop frequency response is low, the closed-loop transient frequency response is distorted, and the drive capacity of the capacitive load 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 the voltage amplifier. However, if you do well, the total distortion will not exceed 0.01%.