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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Modernization of EPU ELECTRONICS B1-01. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment Over the past quarter of a century, the design of the Elektronika B1-01 EPU, which was considered a high-quality signal source, has, of course, largely become outdated, especially in comparison with modern equipment. However, according to the author of the article, by some modernization of the EDA, it is possible not only to significantly expand its dynamic range, but also to increase the noise immunity of the device. This will undoubtedly improve the reproduction of the low sound levels not uncommon in classical music recordings. "Electronics B1-01 at one time was the "first sign" among the high-end electronic control units. Thanks to successful design solutions and operational reliability, it still serves thousands of recording enthusiasts. The long life of this device is largely due to the presence of an excellent tonearm in it: this successful a copy of the SME 30D9 tonearm, which is still fairly considered one of the best in the world. It is significantly superior to the currently popular but expensive RB 300. 1 rpm (for speed 0) powered by a low frequency generator. The main rumble frequency has been reduced to 1 Hz. However, the level of vibration generated by the drive does not meet modern standards. True, by improving the mechanical decoupling, it is easy to reduce it. Structurally, the EPU consists of two main units: a panel with a disk and a tonearm and a body with a metal chassis on which the engine and all electrical components are fixed. The engine is mounted under a permalloy screen on springs, which are tightened with screws that transmit vibration to the chassis. When finalizing the engine, it is necessary to remove and drill the mounting threaded holes in the chassis up to 4,5 mm. For a new suspension, three M3 bolts 18 ... 20 mm long with nuts, three steel washers with an outer diameter of 6 ... 7 mm and six washers with a diameter of 9 mm made of soft rubber or polyurethane 4 mm thick are needed. and even better - typesetting from layers of rubber and felt. Before assembly, it is better to stick the lower damping washers on the chassis - this will facilitate installation and ensure centering. The engine assembly must not come into contact with the chassis or screen (check with an ohmmeter), and its body is connected to ground with a separate wire. To lubricate the engine bearings, light grades of oils are used: watch, spindle, etc. In three EPU specimens examined, it turned out that the nozzle on the drive motor axis was made very poorly - it had noticeable beats. In addition, the rib in the middle of the nozzle does not at all stabilize the position of the belt. Its random displacements are limited only by a special bracket, which is accompanied by acoustic noise. To give the surface of the nozzle a barrel-shaped shape, it is polished with medium grit sandpaper glued to a hard surface, with the engine running and with minimal effort. The decoupling of the chassis from the panel is also unsatisfactory. Three plastic cups are screwed into the chassis, on which the panel springs rest. The springs are equipped with rubber cups at both ends, but are tightened with screws with plastic nuts. As a result, the vibrations of the motor and transformer are also transferred to the panel through the screws. The nuts must be removed and the height of the panel can be adjusted by turning the cups. In addition, the internal volume of the springs is stuffed with scraps of foam rubber or foamed polyethylene (it is used as a packaging material), which will reduce vibrations and the transmission of vibrations along the coils. Felt washers are placed under the lower rubber cups. It is also necessary to dampen the resonant vibrations of the panel. To do this, its lower surface is covered with a layer of vibration-absorbing mastic or, in extreme cases, plasticine. The drive and main disks are damped in the same way, with obligatory lubrication of the edges (skirts) with mastic. With the help of a medical stethoscope, pressing it against the top side of the panel, they are convinced of the effect of the measures taken. In the "muted" EPU, the roar of the engine is not heard at all. To reduce the sensitivity of the EPU to acoustic feedback (AOS), the bottom of the device, made of hardboard, is removed, and "legs" of four to five layers of thick soft rubber are glued to the corners of the case. For the same purpose, it is desirable to install the EPU on a massive base with a soft suspension (the so-called subchassis). In the modified EPU, the author even used two such sub-chassis with dampers (in order from bottom to top): a sheet of polyurethane foam 40 mm thick. marble slab 20 mm thick. a sheet of porous rubber 5 mm thick, a plate made of D16Tv alloy 10 mm thick, on which the regular spring "legs" of the EPU with rubber and felt gaskets rest. To improve the damping of vibrations of the record itself, the rubber pad of the disc should be turned over and a central clamp, which can be easily made from a non-magnetic material, should be used. The tonearm is adjusted in height and azimuth by moving the bushing at the base of the tonearm, which is fixed with two screws. But in case of mounting a cartridge of a higher height, it is more convenient to use a different method: the tonearm movement handle, which is located between the cartridge and its holder, can also be fixed on top of the holder. For this purpose, the mounting holes for the Corvette-128 head are bored with a needle file "on an oval". The wiring in the tonearm is left the same, and the wire going to the corrector needs to be replaced. Unfortunately, there is no full-fledged alternative to good, but expensive audio cables. However, in amateur conditions, you can make good home-made cables from a thin MGTF wire, preferably past the stage of natural aging (up to ten years). Conductors for each channel are bundled in pairs and enclosed in PTFE tubes with a diameter of 5 mm. Screen braids are pulled over the tubes (they are connected to a common wire only from the side of the amplifier-corrector), and then ordinary PVC tubes are put on. The EPU housing is connected to the amplifier unit with a separate wire. It is more rational to connect it through an additional shielding braid, in which both cables are placed with shields connected on one side. In some cases, ferrite rings help to reduce the level of high-frequency interference, through which cables are passed - they perform the function of a common mode choke. It is not superfluous to note that few firms produce special noise-resistant cables abroad. The main way for the penetration of high-frequency interference into the audio path is through the power supply network. As you know, the shape of the voltage sinusoid in the mains, especially during heavy hours, is highly distorted. It observes a wide range of different frequencies, including the radio band. The network acts like a giant antenna. In this case, the level of interference at individual frequencies can reach a few volts. It is they who penetrate the audio path, mainly through the power circuits of the amplifying stages. But even with complete separation of the power and signal circuits, as in a good EPU, interference penetrates through parasitic capacitances of the installation and a common wire. Note that galvanic isolation from the mains through the power transformer does not help: high frequencies penetrate into the secondary circuits through the capacitance between the windings. Once in the audio path, interference can seriously degrade the sound. They can be detected at semiconductor junctions of devices and generate noticeable intermodulation distortion. Methods for reducing noise in the power supply circuit of audio sources are often underestimated. Meanwhile, it is in them that the level of interference is most critical. So. the signal level from the magnetic head of the pickup is 7 ... 12 mV, however, with a full dynamic range of the record signal of more than 60 dB, the count must be counted in microvolts and even fractions of microvolts, and for some other sources even lower. High-frequency interference, having passed the amplification path up to and including the UMZCH, generates wheezing or, at best, harshness and shrillness in the sound. This is especially noticeable when listening to recordings of a string group. Signal sources are often to blame for the "transistor sound phenomenon"! A sure sign of the presence of such interference in the signal is an unexpected "rise" of high frequencies, caused by an increase in the level of harmonic and combination frequencies. It is characteristic that the use of tube amplifiers, which are less prone to signal detection, is also unable to solve the problem, since the combination frequencies already appear in the preamplifiers. Therefore, the only correct solution when suppressing high-frequency interference is to eliminate them in the power supplies themselves, in particular, with the help of mains filters. Network filters, as you know, consists of coils (chokes) and capacitors. In addition to their direct purpose, LC filters also perform a protective function, smoothing and limiting impulse noise in the network, the amplitude of which can reach 1.5 kV. However, not all industrial filters, including those of foreign production, work satisfactorily as part of audio equipment. As practice has shown, a high quality power supply should be equipped with a multi-stage filter with a higher order slope and a low cutoff frequency. The figure shows a diagram of a remote power supply unit for the EPU "Electronics B1-01" used by the author. In addition to the mains transformer, a rectifier bridge with filters is also placed outside the device - this also helps to reduce the level of interference. In order to further reduce them in the rectifier, you can use pulsed rectifier diodes shunted with small capacitors.
In the rectifier filter, all oxide capacitors are foreign-made, having good parameter stability and a long service life. It is advisable to select blocking capacitors in pairs or equalize their capacities by connecting additional capacitors. Capacitors C1 and C2 - any high voltage. C5-C8 - K73-9 or similar with a capacity of 0,1 ... 0.47 μF. Windings of common-mode chokes (in foreign literature - longitudinal transformers) L1. 12 on ring magnetic cores made of M2000NM ferrite with an outer diameter of 45 ... 50 mm and a cross section of about 1 cmg are wound with segments of a network or thick mounting wire with fibrous insulation, folded together. With a length of no 1,5 m, the number of turns can be in the range of 20-40. Sockets XS1. XS2 (mains sockets) are for powering other audio equipment. The MTZ toggle switch was used as SA2. Installation is carried out with a sufficiently thick (section not less than 0,35 mm2) wire. Since noise immunity deteriorates with an increase in the area of \u1,5b\u9bthe circuit, in especially critical cases, for example, when powerful radio transmitters are located close, the power wires to the EPU should be twisted, and the common wire should be made in the form of a braid. Their length must be at least 10 m in order to exclude a noticeable effect of pickups from the transformer on the EPU signal circuits. Power is supplied directly to the generator board to the capacitors C1, C2, installed in place of the former CXNUMX, CXNUMX (element numbering according to the EPU circuit diagram). The regular rectifier bridge should be removed or cut off by cutting the current-carrying tracks. The common wire leading to the motor forms a closed circuit and is therefore removed. The mains voltage for powering the stroboscope is supplied through the EPU power switch and must be turned off during listening. As an X3 connector, a multi-pin computer connector with gold-plated contacts has proven itself very well, in which 7-10 contact pairs are connected in parallel to each power wire. The measures taken, which were discussed, made it possible to significantly improve the old player. A very clear and accurate sound reproduction of the recording has been achieved. Author: R.Kunafin
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Comments on the article: petrov vladimir ... a man heard a ringing, but he does not know where he is. Unfortunately, a vivid example of non-professionalism, phrases have been pulled from various forums, but there is no understanding of what they mean. But the tone is good. Well, unfortunately we are all over the place. Guys, read the forums yourself, without such retellings, and think with your head. Otherwise, you’ll really climb to damp the disks balanced in the factory with plasticine.
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