The use of power amplifier
The audio input is an audio signal input port, and all three are. The next three are the audio input ports of channel 5 and 1. Generally, one of the three sets of audio inputs can be used for listening and singing. The stereo effects of 5 channels and 1 are good, which is suitable for watching movies, but it needs to be input in several groups. The output is five groups of speaker systems on the right. From left to right, they are right channel, left channel (left and right are the main channels), center, surround right and surround left. Five speakers can be connected, with red as the positive pole, black as the negative pole and negative pole. The output signal line of the computer sound card is connected to the audio input end of the power amplifier, and the output end of the power amplifier is connected to the speaker. The wireless microphone is connected to the wireless microphone receiver, and the output signal is connected to the power amplifier. It is more convenient to have a front-end effector. It is better to input the sound card signal and the signal received by the wireless microphone into the front-stage effector, and the output of the effector is connected to the power amplifier. It will be better to adjust the sound quality through the effector.
Function of power amplifier
The function of the power amplifier is to amplify the weak signal from the sound source or preamplifier and push the speaker to make sound. A good set of audio system power amplifier plays an important role.
Power amplifier is the largest family of all kinds of audio equipment. Its main function is to amplify the weak signal input by audio equipment and generate enough current to drive the speaker to play back the sound. Considering the differences in power, impedance, distortion, dynamics, application scope and control and adjustment functions, different power amplifiers have different internal signal processing, circuit design and production technology.
Maintenance method of power amplifier
1. Users should put the power amplifier in a dry and ventilated place to avoid working in humid, high temperature and corrosive environment with oil fume chemicals.
2. Users should put the power amplifier in a safe, stable table or cabinet, so as not to damage or fall to the ground, damage the machine or cause greater man-made disasters, such as fire and electric shock.
3. Users should keep the power amplifier away from the environment with serious electromagnetic interference, such as the aging of fluorescent lamp ballast, which will lead to the disorder of the CPU program of the machine and the failure of the machine to work normally.
4. When wiring the 4.PCB, be careful that the power pin is not too far away from the water. If it is too far away, you can add 1000-470U and put it at its foot.
Key points of power amplifier purchase
One is to see if the interface is complete.
An AV amplifier should have the following basic input and output interfaces: coaxial, optical fiber and RCA multi-channel input interfaces for inputting digital or analog audio signals; The speaker output interface is used to output signals to audio.
The second is to see if the surround sound format is complete.
The popular surround sound formats are DD and DTS, both of which are 5 and 1 channel. Now these two formats have been developed to DD EX and DTS ES, both of which are 6, 1 channels.
The third is to see if the power of all channels can be adjusted separately.
Some cheap power amplifiers divide two channels into five channels, a loud channel and a small channel, while truly qualified AV power amplifiers can adjust each channel independently.
The fourth is to look at the weight of the amplifier.
Generally speaking, you should try to choose a heavier model, because the power supply of heavier equipment is stronger, and most of the weight of the power amplifier comes from the power supply and chassis. Heavier equipment means that he uses a large transformer or a large capacitor, which is a way to improve the quality of power amplifier. Secondly, the case is relatively heavy, and the material and weight of the case have a certain influence on the sound. The housing made of certain materials helps to isolate the circuit inside the housing from the external radio waves. The weight of the chassis is relatively high or the structure is relatively stable, which can also avoid the equipment from being affected by unnecessary vibration. The third type is the heavier power amplifier, which is usually rich and solid in materials.
Power is the most important parameter in a sound system, which indicates the ability of the sound system to carry loads. This is also the first place we should pay attention to when buying. However, if each manufacturer uses different measurement benchmarks to determine product performance, it is often difficult to make an objective comparison without sufficient understanding. The same is true for power amplifiers. Check the identification of power amplifiers and pay attention to the following three points:
First, the battery voltage.
The voltage of automobile battery is constantly changing, and the power amplifiers of two common signs: 14, 4V/ 100W, 12V/ 100W are completely different. Because the voltage of the car during driving is basically around 12V, the measured power value under the voltage state of 12V is closer to the real situation. Moreover, the power amplifier based on the continuous voltage of 12V can achieve greater power when it reaches 12V or above.
Second, the harmonic distortion rate THD.
When comparing the continuous output power of the power amplifier, it should be carried out at the same (or close to) THD value. The difference of sound quality under different THD values is very obvious. Sometimes the maximum power of logo is high, but it is very likely that its distortion and noise are also high. Therefore, when checking the maximum power, we should also pay attention to the identified THD value.
Third, the frequency range.
The continuous power output of a power amplifier should be detected within its actual frequency range. For the power of power amplifier, it is required to identify the complete detection range, and it is meaningless to identify only the power value of a certain frequency. After determining the same benchmark, we can compare the power of the amplifier. Generally speaking, the principle of high power output is generally followed when purchasing audio systems. The greater the output power of the power amplifier, the stronger the ability to drive the speaker. The power of the power amplifier should be greater than the indicated power of the speaker. If the selected power is too small, long-term use of high-power output is easy to burn out, and it will also lead to poor sound quality, distortion and other failures.
Matters needing attention in using power amplifier
1. To ensure the use in safe voltage, it is best to use 220V AC regulated power supply or DC high-voltage regulated module for power supply.
2, V+, V- error shall not be greater than 1V, positive and negative power supply and ground wire welding is firm, confirm the welding before power on.
3. In the initial stage after the power amplifier IC is normally powered on, its stability is worse than that of the discrete component power amplifier. So, at least? Cooking machine? Or play it at a low volume for more than 10 minute, and stably and efficiently play its excellent performance.
4. In the production of power amplifier, it is necessary to strictly ground, and it is best to use multi-strand thick copper wire as the grounding wire. Even the double-bridge rectifier can use floating ground technology to maximize its signal-to-noise ratio.
5. If the local power grid is seriously polluted and the low-voltage power grid is connected to electric equipment such as welding machines and silicon rectifiers, power filters can be used. If it cannot be eliminated, the transformer can be isolated by power supply, but the power should be surplus.
6. Pay strict attention to the switching order of audio equipment. For the power amplifier made by high-fidelity power amplifier IC, remember to turn it on last and turn it off first.
7. Before the newly bought power amplifier IC is put on the computer, it is best to use socket instead of welding and fix the radiator. If the power is turned on and the fever is serious, it will output DC, which can be returned to the mail order unit after being removed.
8. In order to prevent the speaker from being damaged by the DC output of the power amplifier IC, a speaker protector must be installed.
9, system equipment must be well grounded. Because the three-phase load of low-voltage distribution line is asymmetric, the neutral line will be charged and the potential will be zero after grounding, which is very beneficial to improve the signal-to-noise ratio. The method is: use round steel ∮ 10mm long ∮ 1, 5m, weld with 2,5mm2 multi-strand copper wire (without riveting or winding), and insert it into outdoor wet ground.
Important parameters of power amplifier
1. Input sensitivity refers to the minimum input signal level required by the power amplifier, which is a necessary condition for amplifying the sound source signal enough to drive the subsequent power amplifier.
2. Harmonic distortion is an extremely important index of power amplifier. It is a kind of nonlinear distortion, which is caused by the nonlinear characteristics of amplifier when it works. The result of distortion is to produce new harmonic components, which makes the sound lose its original timbre, and when it is serious, the sound is broken and harsh. Harmonic distortion can be divided into odd and even times. Strange homophones can make people fidgety, disgusted and easily perceived. Some power amplifiers sound annoying and tired, which is caused by large distortion. The biggest influence on power amplifier is distortion. General high fidelity requires harmonic distortion below 0.05%, and the lower the better. In addition to harmonic distortion, there are intermodulation distortion, cross distortion, clipping distortion, transient distortion, phase distortion and so on, which are the chief culprit affecting the quality of power amplifier. To evaluate the curative effect, we must first look at its distortion. For example, the total harmonic distortion of Italian Sinfoni power amplifier is below 0.0 1%.
3. Output power, power problem is the most confusing for car audio practitioners, here need to explain:
Rated output power (RMS) refers to the maximum output power of the audio signal output by the amplifier within the total harmonic distortion range. Generally, it is 0.707 times of the peak value of AC signal.
B, average power, average power generally refers to the average power consumption of each frequency point, which is somewhat similar to the rated output power, but generally refers to time.
C. peak output power. The maximum music power that a power amplifier can output is called peak output power, which is usually about 1.4 14 times of (RMS) power without considering distortion.
D, peak-to-peak power, is the power from peak voltage to negative voltage peak voltage, which is 4 times of peak output power. It appears for commercial purposes and has no practical significance.
4. Signal-to-noise ratio, the larger the value, the better, generally expressed by (S/N), expressed by the decibel number of the ratio of signal power Ps to noise power Pn, S/N =10LGPS/PN = 20LGVs/Vn (DB), where VS and VN are signal voltage and noise voltage respectively.
With the increase of signal-to-noise ratio and input signal level, the signal-to-noise ratio gradually increases, but when the input signal level reaches a certain value, the signal-to-noise ratio basically remains unchanged. According to the current requirements of high fidelity, the signal-to-noise ratio should be above 90dB, and imported high-end amplifiers can often reach 1 10- 120B, and the performance can be imagined. Some signal-to-noise ratios are followed by the word "A-weighted", which refers to the results measured after the noise signal passes through the weighted network. Because people are relatively insensitive to noise in high and low frequency bands, this weighting method appears. Weighted noise more intuitively represents the noise signal that people actually feel. In short, the greater the signal-to-noise ratio, the smaller the noise in the signal, the better the playback quality, and the clearer, cleaner and more layered the music will be.
5. Frequency response, commonly known as power bandwidth in the early days, refers to the 1/2 rated power frequency band width of the power amplifier when the harmonic distortion does not exceed the specified value, that is, the frequency band included between two frequency points with a -3dB drop at the high and low ends, which is called power bandwidth.
6. Damping coefficient, mainly for low frequencies, is an extremely important technical parameter, which directly affects the bass sound quality. As we all know, the larger the diameter of the horn, the better the bass, but the larger the cone basin, the greater the inertia of its movement, which makes it difficult to move synchronously with the audio signal, and often leads to the phenomenon of unclear sound, especially at the low frequency of 100-400Hz, which is easy to cause sound staining and makes people sound vague and unnatural. The bass horn of some modified cars will vibrate when the low frequency signal is strong, and the bass tail is serious, which is caused by the inertia of the cone.
In the design of power amplifier, engineers take some technical measures, such as selecting high-power tubes with multi-tube parallel connection and low internal resistance (milliohm level), improving working voltage and selecting high-quality wire rods. , as far as possible to improve the damping coefficient, so that you can produce? Resist? Function, make the movement of the cone move synchronously with the audio signal, and make the cone return to the zero position (that is, the center position) as soon as possible after the driving signal is over. This blocking effect is the damping factor, D=Rs/Ri, Rs= horn impedance, Ri= output internal resistance of power amplifier. The greater the D, the better the synchronization effect between the cone and the signal, the purer and cleaner the bass, and the better the playback effect.
7. Slew rate, the slew rate of power amplifier greatly affects the quality and performance of treble playback. The faster the conversion rate, the better the high-pitched sound quality, and the more accurate the capture of fleeting high-frequency information. High-grade power amplifiers can achieve a dozen to dozens of V/u, and low-grade power amplifiers are generally not marked. This conversion rate is closely related to design and materials, but it should not be too high. Too high will produce ultrasonic signals above 20KHz that people can't hear, which will not only have no effect on improving the sound quality, but will easily burn out the tweeter.