The function of filter capacitor and sound in power amplifier

There are three functions of filter capacitor in power supply of power amplifier:

1. The DC pulse obtained after rectification is filtered to reduce the AC dry power

2. High speed power supply

3. The filtering effect of capacitor on the power supply only shows whether there is AC interference for the power amplifier; the energy storage effect of capacitor can provide power for the transient large current of the power amplifier, but the insufficient power of transformer can not charge it in time, so its energy storage effect is not obvious; And it provides the channel for the audio signal to affect the quality and timbre

For example, the positive half cycle audio signal in the figure is divided into two channels by power amplifier, emitter resistance, loudspeaker and ground. One part is formed by power transformer and rectifier, and the other part is formed by filter capacitor. Obviously, the transformer inductance is very large, which is unfavorable to the passing of the high-frequency part of the audio, and only the low-frequency audio signal with low frequency can be passed, It can only provide a channel for the subwoofer, and more audio signals, especially those in the high frequency part, will form a circuit through the power filter capacitor. The capacitor and the transformer secondary complement each other, providing a frequency band channel from DC to high frequency for audio

The production of audio capacitance can be divided into two categories and three series, one category; non "dynamic" audio capacitance, which has a lot of audio capacitance, generally high frequency is clear, medium frequency is good, but low frequency is lacking. The second category "dynamic" audio capacitance, the sound is domineering, ready-made feeling is very good, low frequency can be put and put freely, that is to say, high frequency can cause ten ears fatigue, If is not tender enough. In detail, the good audio capacitance of medium and high frequency is a series, the good one of medium and low frequency is a series, and the good one of high and low frequency is a series. It's difficult to find the three terminals that all perform well, so it's said that matching is necessary

If you don't believe it, you can also search for a series of words [capacitance's influence on sound], [capacitance's influence on sound], [capacitance's influence on sound], [capacitance's influence on sound], [a series of words] and try to find them on various browsers. There are a lot of materials, but most of them are listening. It's almost difficult to see the specific reasons why capacitance can affect sound, including checking foreign websites, which are also the majority of audiophile tests, Foreign websites haven't found a detailed explanation for the reason that the capacitance makes the sound of power amplifier circuit change, while large manufacturer Elna can only find the design and effect matters of optimizing the audio capacitance, without a very specific explanation

The following article is the only one with a little bit of its own environmental conditions in a large number of materials. It should be a person who lives in a small and medium-sized capacitor manufacturer in Guangzhou. I have carefully read the content of the article. Although I dare not say that 100% is right, most of it is worth learning and reference, But we still need to remind you that parameter indexes can only be used as reference under ordinary DIY conditions, [precisely because we can't get a whole index as comparison and reference] the help to our DIY is just to recognize a knowledge, which can't completely help us to design and adjust the sound according to the index parameters, not according to the data of parameter index characteristics, It's a matter of limited conditions. It's impossible to use these parameter index data. Why? It's very clear who has a studio dedicated to sound design in his home. There are a lot of test instruments that can test the data. He has to sort out the data to carry out test calculation, and he has to repeatedly compare the test and then sort out the data before finalizing the model. We are a civilian DIY, not a big manufacturer. So we should try our best to do what we can, Discuss the scope of your ability. Of course, if you have the basis and conditions, you can do this. No one forces you to do this. But if you force me to use this ability to DIY, it's your fault. Thank you!

Although the following materials are useful and insightful, they are still far away from the actual use. They can only roughly explain the reason. The actual use depends on the support of conditions, and can be used naturally if conditions permit. I have done a good job in receiving goods from ears if I have no conditions!

Analysis of the reason for the change of filter capacitance

It's often said that the filter capacitance has an impact on the sound quality, but it's rarely seen what causes the principle that a capacitor that filters the power supply will affect the sound quality, which makes many practitioners only know that it has an impact but don't know. Therefore, the blindness is self-evident. I have my own view, the purpose is to study this phenomenon with you, Find out the reason why the filter capacitance affects the sound quality. The filter capacitance is to store the energy of the rectified pulsating current smoothly, make the ripple coefficient meet the requirements, and meet the requirements of the power supply of the later stage load. But it also has an important task, that is, it also provides a common AC channel. Because the impedance of the filter capacitance in the whole audio frequency range is different, it also brings the impact on the sound quality, This is the key reason. According to this reason, we can make clear the requirements of this capacitor. Conditional friends can test the internal resistance of the power supply in the whole frequency range, and then select the capacitor characteristics (especially the latter filter capacitor is more important), or compensate, The damping factor is the ratio of the rated load (speaker) impedance of the amplifier to the actual impedance of the power amplifier. A large damping factor means that the output resistance of the power amplifier is small, and the damping factor is the ability of the amplifier to control the cone motion of the speaker after the signal disappears. An amplifier with a high damping factor, The loudspeaker is more like a short circuit, which can reduce its vibration when the signal is terminated. The output impedance of the power amplifier will directly affect the low-frequency Q value of the loudspeaker system, thus affecting the low-frequency characteristics of the system. The Q value of the loudspeaker system should not be too high, which is generally better in the range of 0.5 ~ L. the output impedance of the power amplifier is the factor that makes the low-frequency Q value rise, Therefore, it is generally hoped that the output impedance of the power amplifier is small and the damping coefficient is large. The damping coefficient is generally between tens and hundreds. The damping coefficient of the high-quality professional power amplifier can be as high as 200 or more. The damping coefficient is one of the specifications of the loudspeaker, which directly affects the operation of the loudspeaker. The damping coefficient data provided by the general loudspeaker, Only the damping coefficient of a certain frequency band is published, which is very important. It reflects the power amplifier's ability not to be affected by the horn's impedance and equivalent impedance. It is impossible for a power amplifier with a small damping coefficient to obtain a true high fidelity, Especially for the speaker with higher sensitivity. Because the speaker with higher sensitivity can output a larger back EMF when the power amplifier output is small... The damping coefficient does not represent the damping force. When the speaker (speaker) is short circuited, it has the maximum damping force, which is a finite value, corresponding to the short-circuit Q value of the speaker. The larger the damping coefficient, for example, the damping coefficient is 10, reaching 90%, 100 to 99%, 1000 to 99.9%, so too large damping coefficient is unnecessary, negative feedback is damping system

Frequency band for example: the frequency below the beginning of a certain frequency, when these frequencies are transmitted from this speaker, their diffusion image is spherical, which is called bass; from a certain frequency to some frequency, when these frequencies are transmitted from this speaker, their diffusion image is hemispherical, which is called midrange; from a certain frequency and above, when these frequencies are transmitted from this speaker, Their diffusion image is cone-shaped, which is called treble. When the sound diffuses out of the shape, it will slowly become a straight line and non-diffusion, that is, super treble. Bass and treble can also be divided into bass frequency segment, midrange frequency segment and high audio frequency segment according to human physiological auditory feeling, but the division of frequency segment is very difficult to be consistent, According to the level of language (Music) storage, human physiological auditory feeling and 1 / 3 octave sequence frequency division table, it is suggested to divide the hearing range frequency as follows: below 20Hz - ultra-low frequency; 20Hz - 63Hz - ultra low frequency; 63Hz - 200Hz - low frequency; 200Hz - 800Hz - mid low frequency; 800Hz - 1600hz - mid sound; 1600hz - 4000Hz - mid high frequency; 4000Hz - 12.5khz - high frequency; 12.5khz ~ 20kHz -- ultra high frequency; above 20kHz -- ultra high frequency; make an explanation of ultra high frequency and ultra high frequency: ultra high frequency refers to the ultra-high frequency that the human ear can hear sound, and these frequencies still have the feeling of "sound". Ultra high frequency refers to the extremely high frequency beyond the hearing (above 20kHz). These frequencies have no feeling of "sound", and can only measure the existence of frequency

"Super high frequency" highlights the characteristics of the existence of "sound"; and "super high frequency" highlights the characteristics of the existence of "frequency". The difference between super low frequency and super low frequency is the same to understand that high, mid and low frequency refer to the frequency of sound, that is, the number of sound waves per second, and the number of vibrations is called Hertz, which is consistent with Hz. Human ears are not instruments, so it is not easy to accurately determine the frequency, But you can practice slowly. Here is a table. You can make a preliminary judgment according to this table. The frequency range (Hz) listening affects the representative instrument 16k-20k, which may not be heard by many people. Therefore, not listening to this frequency does not mean that the device cannot be played back, of course, it does not mean that your listening is not good enough, Only a few people can hear 20kHz. This frequency can affect the brightness of the high frequency and the overall sense of space. If this frequency is too small, it will make people feel a little dull. If it is too many, it will produce a sense of drift and easily lead to hearing fatigue. Overtones of electronic harmony, zither piano and other instruments. 12k-16k this frequency can affect the overall sense of color, The so-called "loose fragrance" of the violin is determined by this frequency. Too dim this frequency will lead to the loss of personality of the instrument, and too much will lead to the burr feeling. In the post-processing, the high-frequency overtones of percussion instruments such as cymbals, bells, tambourines, sand hammers, copper brushes, triangle iron, etc. 8k-12k8 ~ 12khz are the high-frequency areas of the music, It is the most sensitive to the high-frequency performance of sound. Proper highlighting (below 5dB) is of great help to the level and color of sound, and also makes people feel rich in high-frequency. However, too much noise will increase the background, such as: the noise of system (sound card, sound source) will be obviously displayed, and at the same time, people will feel the sharp and hairy sound. If this section is lacking, The voice will lack of appeal and vitality. The frequency 4k-8k of flute, Oboe, trumpet, piccolo and other high pitched wind instruments most affects the clarity and brightness of the voice. If the frequency component is lack, the voice color will become flat and light; if the frequency component is too much, the voice color will become sharp, The human body may have toothed sound. This frequency is usually beautified by a pressure limiter. Some female voices and most musical instruments play. 2k-4k has a strong penetration. The resonance frequency of the human ear cavity is 1-4kHz, so the human ear is very sensitive to this frequency. If there are too few empty frequency components, the hearing ability will be poor, The voice is blurry. If the frequency component is too strong, it will produce a cough feeling. 2 ~ 4kHz has a great impact on the brightness of the voice, which is generally not suitable for attenuation. This section has a great impact on the level of music, and a proper promotion can improve the brightness and clarity of the voice, but it can not be too prominent at 4kHz, Otherwise, the female's denture will be too heavy. For some female voices and most musical instruments, 1.2k1.2khz can be a little more, but not more than 3dB, which can improve the brightness of the sound. However, if too much can make the sound hard, 1k1khz is the standard reference frequency for sound equipment testing, Generally, the parameters given in the audio equipment are tested at 1kHz. This is the most sensitive frequency of the human ear. The frequency range of 800 affects the strength of timbre. If the frequency is full, the timbre will be strong and powerful; if the frequency is insufficient, the timbre will be loose, and the component characteristics below 800Hz will be prominent, and the low-frequency component will be obvious; if the frequency is too much, If there are too many guttural sounds, the personality of the voice will be lost. A proper guttural sound can increase the sex appeal. Therefore, the sound engineer calls this frequency "dangerous frequency" and should use it carefully

The voice of vocal and part of percussion instruments 300-500 in the 300-500hz frequency band mainly represents the voice (singing and reciting), which can show the thickness and strength of the voice. If it is good, the voice is bright and clear, otherwise it is thin and muddy. The frequency of vocal 150-300 affects the strength of the voice, especially the strength of male voice. This frequency is the low-frequency fundamental frequency of male voice, At the same time, it is also the root frequency of the chord in the music. In the 80-160hz frequency band, the sound mainly shows the sense of the thickness of the music. If the playback effect of the sound is good in this part, it will feel the music is thick and has the backing