On Audio Cables

On audio cablesIn the audio industry, in addition to the amplifier, speaker, sound source and other equipment, signal connection cables are also very particular. The price of each cable ranges from hundreds to thousands or even tens of thousands of yuan. Some people do not agree with this, believing that it is a great waste to invest money and energy in cables to improve sound quality. The improvement of cables on sound quality is very small, which is seriously unbalanced compared with its price. So how much influence does the signal cable have on the sound quality? I am not an audiophile, so I do not have the obsession with cables that audiophiles have, but I also deny the theory that cables are useless. I will discuss my views on audio cables with a pragmatic attitude. Any transmission cable can be equivalent to a distribution system composed of resistance, capacitance and inductance. Due to the existence of capacitance and inductance, the transmission cable has its special frequency characteristics, that is, it has different time delays (that is, so-called different transmission rates) and presents different impedances for signals of different frequencies. Obviously, this will cause certain distortion of the signal. In addition, the resistance of the cable will also cause signal loss, but since the audio signal connection cable is usually relatively short, this loss can be ignored. However, the speaker connection cable cannot be ignored, because the connection cable between the power amplifier and the speaker is long and the power transmitted is large, and the resistance of the connection cable will have a direct impact on the output stage of the power amplifier (the load impedance becomes larger). Another very important parameter of the transmission line is the characteristic impedance. Although the impedance matching in the small signal matching of the audio electronic circuit is not as particular as that of the high-frequency circuit or the large signal circuit, if the difference is too large, it will also affect the sound quality of the playback. The sound sources of the audio power amplifier are roughly: radio head, tape player, CD player, record player, etc. The output impedance of these sound sources is different, so the characteristic impedance of the wire should be close to the output impedance of the sound source device when matching. We can divide the signal line into strong signal line, weak signal line and standard signal line for discussion: 1. Strong signal line refers to the connection line between the speaker and the power amplifier. This type of line often has no shielding layer. For this type of wire, the key is to reduce its resistance. Because the output resistance of modern power amplifiers is very low, the requirements for speaker wires also increase accordingly, such as using large cross-sectional area or multi-strand twisted wire. The wires range from pure copper to silver. The more expensive speaker wire is oxygen-free copper speaker wire. Its main features are good conductivity and low resistivity. The sound quality is greatly improved when it is used to reproduce the sound. Since the transmission line has different impedances for signals of different frequencies, this characteristic is manifested as unclear sound in the restoration of sound. For this reason, people have produced a high-end speaker connection wire called smart signal line. The characteristic of this line is that the signal is divided into two channels according to the frequency. The outer layer of a certain thickness passes the signal above 5KHZ, and the signal below 5KHZ is transmitted through the inner layer of the line. This greatly improves the frequency characteristics of the transmission line and makes the reproduced sound clear and transparent. However, if your amplifier has a small output power or the speaker cable is short, don't waste money on this expensive wire. In this case, the effect is not outstanding. 2. Weak signal line refers to the connection between the microphone and the preamplifier, which is usually a shielded line. 3. Standard level signal line refers to the connection between the sound source and the power amplifier. Its transmission level is about 1V, and it is also a shielded transmission line. This type of wire is the most widely used in the audio industry. Interestingly, wires made of different insulating media and metal materials have a subtle effect on the sound quality. For this reason, manufacturers have produced a variety of wire models and specifications to meet people's different requirements for music appreciation. High-end finished wires use a nylon braided sleeve coated with an anti-static layer as the outer layer, a metal shielding sleeve as the inner lining, and then oxygen-free pure copper as the core wire, and are equipped with gold-plated plugs to prevent noise caused by poor contact of the plug. The brands of standard level signal wires include: MONSTER STANDRDINTERLINK (Monster), AUDIO0UEST (Line Saint), SUPRA (Turtle), M0NITERPC (Magic), SPACE&TIME (Super Time and Space), MISSION (Beautiful Voice), PATRDNICS (Bo Li), etc. Japan's MAKURAWA (Mai Luhua), DENK0 (Climbing), PATRD NICS (Bo Li), etc. Japanese MAKURAWA, DENKO, OSONIC, PC O CC, ACROTEC, HISAGO, Lux, Golden Voice, etc., as well as European PHILIPS, VDH, IXOS, 0RT0F0N, etc., all use different materials and processes to change the frequency characteristics and improve the playback sound quality, and at best they only improve the music expression. If you are not a music fan or your amplifier is too low, you must not spend money to buy these expensive audio cables, because if your amplifier is inherently deficient in music expression, the effect of using ordinary cables and expensive cables is the same. According to one of my audiophiles, if the price of your amplifier does not exceed 20,000 yuan, choosing expensive cables will not show the effect of improving the sound quality. In summary, for a sound system, the selection of standard level signal wires only plays an auxiliary role in the sound quality. Expensive sound wires can only be used with expensive amplifiers. It is most practical to choose the appropriate speaker wires according to the output power. Thinking draft on the key points of audio amplifier distortion Recently, I saw an article entitled "Talking about audio amplifier distortion and common improvement methods" on page 199 of the first volume of the 2002 Electronic Newsletter. I think this article is well written and worth reading for electronics enthusiasts. I will write down the key points of this article for your reference. Distortion is the phenomenon that the input signal and the output signal change in the amplitude ratio, phase relationship and waveform shape. The distortion of audio amplifiers is divided into two categories: electrical distortion and acoustic distortion. Electrical distortion is caused by the circuit, and acoustic distortion is caused by the speaker of the sound reproduction device. The types of electrical distortion are: harmonic distortion, intermodulation distortion, and transient distortion. Acoustic distortion is mainly AC interface distortion. According to the nature, there are nonlinear distortion and linear distortion. Linear distortion refers to the change in the amplitude and phase relationship between the frequency components of the signal. Only the amplitude and phase distortion of the waveform appear. The characteristic of this distortion is that no new frequency components are generated. Nonlinear distortion refers to the distortion of the signal waveform and the generation of new frequency components. The main points of distortion generated by the audio power amplifier are as follows: 1. Harmonic distortion This distortion is caused by nonlinear elements in the circuit. After the signal passes through these elements, new frequency components (harmonics) are generated. These new frequency components interfere with the original signal. The characteristic of this distortion is that the waveform of the input signal is inconsistent with the waveform of the output signal, that is, the waveform is distorted. The main ways to reduce harmonic distortion are: 1. Apply an appropriate amount of negative feedback. 2. Select amplifiers with high characteristic frequency, low noise coefficient and good linearity. 3. Improve the power reserve of the power supply and improve the filtering performance of the power supply. 2. Intermodulation distortion Two or more signals of different frequencies pass through the amplifier or speaker to generate beats and form new frequency components. This distortion is usually generated by active devices in the circuit (such as transistors and electron tubes). The size of the distortion is related to the output power. Since these newly generated frequency components have no similarity with the original signal, less intermodulation distortion is also easily perceived by the human ear. Methods to reduce intermodulation distortion: 1. Use electronic frequency division to limit the working bandwidth of the amplifier circuit or speaker, thereby reducing the generation of beats. 2. Select tubes or circuit structures with good linearity. 3. Transient distortion Transient distortion is an important indicator of modern acoustics. It reflects the ability of the power amplifier circuit to keep tracking transient jump signals, so it is also called transient response. This distortion makes the music lack of layers or transparency, and there are two forms of expression: A. Transient intermodulation distortion. When a pulse transient signal is input, the output end cannot immediately obtain the output voltage it should have due to the capacitor in the circuit, and the negative feedback circuit cannot respond in time. The amplifier is in an open-loop state at this moment, causing the output to be instantly overloaded and produce clipping. This clipping distortion is called transient intermodulation distortion, which is more serious on stone machines. Transient intermodulation distortion is a dynamic indicator of the power amplifier, mainly caused by the deep negative feedback inside the power amplifier. It is the culprit that affects the sound quality of the machine and causes "transistor sound" and "metal sound". The main methods to reduce this distortion are: 1. Select good devices and adjust the working point to maximize the open-loop gain and open-loop frequency response of the amplifier. 2. Strengthen the negative feedback of each amplifier stage and cancel the large-loop negative feedback. B. Distortion caused by too low conversion rate.As mentioned above, high-level input pulses cause clipping in the amplifier and cause transient intermodulation distortion. So will low-level input pulses cause distortion? This depends on the response time of the amplifier. The transient distortion caused by the amplifier output signal not keeping up with the rapid change of the input signal due to the long response time of the amplifier is called low conversion rate distortion. It reflects the amplifier's response speed to the signal. The amplifier with small distortion has good sound quality resolution, layering and positioning. 4. AC interface distortion AC interface distortion is caused by the feedback of the speaker's back electromotive force (the potential generated by cutting the magnetic lines when the speaker vibrates) to the circuit. Improvement methods are: 1. Reduce the output impedance of the circuit. 2. Choose a suitable speaker to make the damping coefficient more reasonable. 3. Reduce the internal resistance of the power supply.