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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Homemade quality audio cable without skin effect. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers In this article, I would like to draw the attention of audiophiles to the effect that many have recently called transistor, some have been fighting it for a long time in HF and microwave technology, some in the course of the fight against it produce interconnects and speaker cables worth up to several thousand US dollars, some people try to present this effect as nothing more than just ... hallucinations of audiophiles! Below I will tell you how to make an excellent (that is, absolutely neutral over a wide frequency range) audio cable from improvised materials at home in a couple of evenings, which is not inferior in quality to the best world samples. But before everything falls into place, I will say the following: all sound and high-frequency radio equipment is designed incorrectly! Below are your likely questions. We have long suspected this without you. Well, what's the matter here? It is known that when an alternating current passes through the conductive layer of a conductor or semiconductor, the so-called surface effect (skin effect) takes place. In this case, most of the moving electric charges due to electromagnetic induction are located near the surface of the conductive layer. The negative effect of the skin effect is manifested in the fact that a large central part of the conductive layer does not participate in the transfer of electric charges, which causes an increased resistance of the conductor to electric current. In addition, the skin effect in metal wires and in capacitor plates leads to a slow redistribution of mobile electrons from the center to the surface, as a result of which undesirable effects of directivity and lapping of cables occur, and the memory effect increases in capacitors. The negative effect of the skin effect on cables and wires is aggravated by the fact that the chemical compounds of the metal of the conductive layer with oxygen and nitrogen of the air, formed on the surface of the wire as a result of corrosion, have dielectric and semiconductor properties, which, in turn, contributes to the growth of losses and distortions. The degree of manifestation of the skin effect depends on the frequency of the current. More precisely, from the instantaneous frequency of the current. As the frequency increases, the thickness of the surface layer through which the current passes decreases. In the case of a wideband signal, where the instantaneous frequency is difficult to describe, the skin effect causes a complete mess in the placement of mobile electrons along the conductor cross section. The consequence of this is non-linear, intermodulation and frequency-phase distortion of an electrical broadband signal passing through a conductor or semiconductor. In consumer and professional audio equipment, the skin effect of connecting interconnects and acoustic wires leads to audible distortion of signals that degrades the quality of sound reproduction. In radio receiving equipment, the consequences of the skin effect (for example, in the cable connecting the antenna to the input of the radio receiver) due to the intermodulation distortion of the wideband signal created by it, are to reduce selectivity, reduce the signal-to-noise ratio and reduce the actual sensitivity. It is known that when an alternating current passes through a conductor, the main (useful) electromagnetic wave propagates along the conductor in a straight line between points with different potentials. Due to the skin effect, in addition to the useful wave, an unwanted parasitic electromagnetic wave arises, directed from the central axis of the conductive element to its surface, perpendicular to the direction of the useful wave, causing phase distortions of the transmitted signal. In digital pulse devices, for example, computers, due to the skin effect in the copper conductors of printed circuit boards and connectors, the shape of short pulses is distorted, which leads to synchronization failures, failures in pulse registration. This is the main obstacle to increasing the clock frequency in motherboards and computer connectors. At ultrahigh frequencies, the skin effect sharply reduces the quality factor of reactive elements - capacitors and inductors. As a result, at frequencies above 1 GHz, the skin effect is the main factor limiting the miniaturization of electronic products, such as microcircuits. It is the skin effect that is responsible for the so-called transistor sound effect. In transistors, the cross-sectional area of the crystal is much smaller than the cross-sectional area of the electron cloud, as are the cathode and anode areas in a lamp. In addition, the contact pads on the surface of the transistor crystal are connected by thin wires (anyone who has ever seen a transistor without a case knows this), in which the skin effect lives very freely. What can be done to combat this phenomenon? I can recommend an inexpensive and effective way to neutralize the skin effect. It is based on the fact that the material of the vast majority of conductors (copper, silver, aluminum, brass) and semiconductor (silicon, germanium) elements has a relative magnetic permeability m from 0,9999 to 1,0001, i.e., about one. The surface of the conductive element 1 is covered with a paramagnetic shell 2 (see Fig.), and the shell does not have to fit snugly, some small gap is possible. The shell is made in the form of one or more layers of a solid paramagnetic m greater than 1 dielectric material (magnetodielectric), which at the macrolevel has a relative magnetic permeability m, several times greater than the permeability of the conductive element, low electrical conductivity, and low losses for magnetization reversal (hysteresis loop). On fig. for clarity, two layers of the shell are shown: layer 3 and layer 4. The shell must be fixed relative to the conductive element on its surface; in the case of a gap, its width should not exceed half the wavelength of the alternating current in the conductive element. And what does it give?
The alternating current flowing in the conductive element 1 perpendicular to the plane of the pattern creates an undesirable transverse electromagnetic field of the skin effect inside the conductive layer of the element 1. The lines of force 6 of this field act on elementary moving charges 5 inside the conductive element 1 and are directed from the center of the conductive layer to its surface. At the same time, the main (useful) alternating signal current flowing through the conductive element 1 creates an opposing magnetic field in layers 3 and 4 of the paramagnetic shell 2, the lines of force 7 of which are directed from the surface of the conductive element 1 to its center and also affect the elementary moving charges 5 inside the conductor 1. The intensity of both fields increases with increasing current strength and with increasing frequency. In this way, compensation for the action of a parasitic transverse field and a uniform distribution of electric current over the entire cross section of the conductive layer are achieved. For most low-current conductive elements, in order to achieve a positive effect, the paramagnetic shell can be made of a material with a relative magnetic permeability index of 1,5 to 20 with a thickness of several tens of microns or more. For power conductive elements, with small conductor sizes, as well as for low-frequency devices, the sheath can be of similar thickness with a value of m from 1,5 to 50, if the sheath material has an index m greater than 50, and the length of the conductive element is significant (several meters), then along with the parasitic transverse wave, the useful wave will also be suppressed, the cable's own inductance and losses in the sheath itself will increase, and the transmitted signal will receive phase shifts. For clarity, the principle on which this method of combating the skin effect is based can be compared with magnetic or electromagnetic focusing of an electron beam in a cathode ray tube, for example, a television kinescope. In a kinescope, the flow of electrons moves with acceleration in vacuum under the action of a high anode voltage from the cathode to the anode (screen). In this case, due to the mutually repulsive action, the electron beam incident on the screen forms a blurry spot. Therefore, forced focusing of the beam is necessary, for which coils are used that create an annular electromagnetic field around the electron beam. This is how focus and convergence are achieved. I suggest using a mixture of a dielectric (for example, varnish, resin or polyvinyl chloride) with a powder of an electrically conductive magnetically soft material (for example, ground permalloy or oxyfer) for a paramagnetic shell. The volume ratio of the dielectric and the magnetic material is chosen such that the electrical conductivity of their mixture is negligible compared to the electrical conductivity of the conductive element. I also suggest using a mixture of a dielectric polymer with powders of substances such as chromium dioxide CrO2, gamma iron oxide Fe2O3, cobalt gamma iron oxide CoFe2O3. These magnetic materials have a relative magnetic permeability of 1,5 to 2,0 and have a short magnetization reversal time. They are produced by the industry for audio and video tapes, their cost is low, although in a strong magnetic field these materials have a relatively high coercive force, in most radio-electronic elements the current passing through them is not high enough to manifest the magnetic properties of these materials. Therefore, in this case, the hysteresis losses in the shell are small, which makes it possible to achieve a positive effect. In the manufacture of a flexible high-quality (audiophile, as it is now fashionable to say) unshielded interconnect or speaker cable (the author used a conventional chromium dioxide video tape 12,7 mm wide on a lavsan base). uenta is wound with an overlap of 6 - 10 layers on the main metal (copper or silver) conductive core. As a result of such an operation, the non-linear distortions introduced by the cable are sharply reduced, and the upper transmission frequency of the cable is increased from 30 MHz to 120 - 250 MHz and higher, depending on the thickness of the wire. In this case, the cable is made in the form of three braided conductors (similar to how Kimber Cable does it). In addition to the manufacture of cables, the described method of combating the skin effect can be applied at the industrial level in relation to conductive elements of any shape and type, made of conductors, superconductors and semiconductors with a relative magnetic permeability index of about one, designed to transmit current and control current in a wide range of strength and frequency. The claimed method can be applied, for example, in the production of communication cables, mounting and connecting wires, transistors, diodes, integrated circuits, contact devices, connectors, resistors, electrical capacitors and high-frequency inductors. And what will we get as a result of applying the method you proposed? Let's enjoy listening to music. Author: Sergey Podolyak, Vinnitsa, Class A; Publication: audio.ru/class_a/home.php
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