The introduction of high-quality radio broadcasting on ultrashort waves, as well as good reproduction of magnetic sound recordings and long-playing gramophone records, creates a need for equipment that would allow high-quality sound reproduction. In the vast majority of industrial and amateur radio receivers and amplifiers, sound reproduction occurs from a single loudspeaker, which sharply reduces sound quality, especially when playing orchestral music, since the emitted sound comes from one point. In addition, conventional diffuser electrodynamic loudspeakers have uneven directional reproduction of the high-frequency spectrum, which also reduces the quality of sound reproduction, especially when the listener moves around the room. Recently, acoustic systems of so-called stereophonic sound have become widely used, in which loudspeakers are installed not only on the front wall of the box, but also on its side walls. With this arrangement of speakers, due to the reflection of their sound from the walls of the room, the directivity effect at high frequencies is sharply reduced and the playback quality is significantly improved.
To obtain sound close to natural, it is necessary that all parts of the sound-reproducing equipment have the appropriate quality indicators. First of all, the low-frequency amplifier must provide reproduction of the frequency band from 30 to 15,000 Hz, be able to rise and fall in the region of low and high frequencies, have minimal nonlinear distortion and have an output power sufficient for normal driving of the speaker system. In the current state of electronics, it is much easier to manufacture an amplification device with a wide frequency bandwidth than to manufacture a loudspeaker that provides high-quality reproduction of this frequency band.
The following description of a wide-range surround sound acoustic unit uses four loudspeakers, two of which are located one inside the other and are placed on the front wall of the box, on this wall below the loudspeakers there is a rectangular cutout for the output of the low frequencies emitted by the back of the cone of the large loudspeaker in the same phase. The placement of a small loudspeaker in the center of a large diffuser expands the overall playback bandwidth, improves the directivity characteristics and output in the high frequency region.
Two loudspeakers located on the side walls of the box give the sound reproduction a three-dimensional effect and also improve the polar pattern.
The loudspeakers are placed in a wooden box, the dimensions of which are shown in Fig. 1. The walls must be made no thinner than 10 mm from plywood or dry boards. The inside of the box must be pasted over or upholstered with sound-absorbing material (felt, cloth, velvet, etc.).
The loudspeakers used are as follows: one produced by the Riga plant named after. Popov from T-689 or Riga-10 receivers with the lowest possible resonance of the moving system. It can be either with a permanent magnet or with bias, the other three loudspeakers are of the 1GD-1 type with permanent magnets; It is desirable that one of them has a rigid diffuser (such as Whatman paper) and its own resonance at frequencies of 150-180 Hz. The remaining two loudspeakers can have conventional diffusers, but it is desirable that their resonant frequencies differ by 20-40 Hz (in the described design, loudspeakers with resonant frequencies of 100 Hz and 130 Hz are used).
To determine the intrinsic resonance of a moving loudspeaker system, a sound generator of the type GZ-1, ZG-2A, ZG-10 is required. The loudspeaker under test is connected to the output of the generator and a tube voltmeter (type LV-9, VKS-7) is connected parallel to its voice coil, to which a voltage of about 3-5 V is applied.
Slowly rotating the dial of the sound generator from the zero point towards an increase in frequency, observe the needle of the tube voltmeter and at the moment of the first maximum peak, its readings are recorded on the dial scale of the sound generator, this frequency will correspond to the natural resonance of the moving system of the loudspeaker under test. It is advisable to repeat these operations several times, clarifying the instrument readings. In the absence of a tube voltmeter, you can determine the intrinsic resonance of the moving loudspeaker system visually by connecting it to the output of the sound generator, and by rotating the dial, observe the diffuser of the loudspeaker under test. At the moment when the amplitude of the diffuser oscillations is maximum, this will indicate the onset of resonance.
A loudspeaker, which has its own resonance of 150-180 Hz, is located in the central part of a large loudspeaker (from T-689 or Riga-10 receivers), as shown in Fig. 2; To do this, it is necessary to make an adapter stand, the shapes and dimensions of which are indicated in Fig. 3. A hole with a diameter of 5.2 mm is drilled in the core of a large loudspeaker on the diffuser side and an M-6 thread is cut to a depth of 8-10 mm. This work requires great care, as metal shavings can get into the gap of the loudspeaker and damage it. To avoid this, it is recommended to fill the gap between the core and the coil with wet cotton. When drilling and threading are completed, the wet cotton wool with chips is carefully removed so that the chips do not fall into the gap, and the core is wiped. If individual small chips end up in the gap, they are carefully removed with a thinly planed stick or cotton wool wrapped around a match.
In some loudspeakers of the Riga plant nm. Popov, a spherical washer is glued in the center of the diffuser to cover the core. For this design, it must be removed using acetone or a solvent, thoroughly moistening the gluing area with it, and when the glue dissolves, the washer is carefully removed.
In a small loudspeaker, a hole is also carefully drilled in the center and a thread is cut to the same dimensions as in the core of a large loudspeaker, taking similar precautions against clogging the gap with chips. The prepared stand is screwed at one end into a small loudspeaker. Two ends of a PEL-1 wire 0.8-1.2 and 250 cm long are soldered to its petals of the voice coil terminals. After that, it is screwed into the hole of the core of a large loudspeaker with a thread on the stand until it stops.
The system of two loudspeakers assembled in this way is installed in the front part of the box, secured with bolts or screws, and the output ends from the small loudspeaker are straightened and pressed by the rim of the diffuser holder of the large loudspeaker to the board, making sure that they are not shorted. The remaining two loudspeakers are mounted against the holes in the side walls of the box.
When all the loudspeakers are in place, it is necessary to phase them so that their diffusers work in the same direction. To do this, you will need a 3-4 V battery from a pocket flashlight. A battery must be connected to the output ends of the voice coil of one of the loudspeakers, and at the moment of connection, its diffuser will either retract inward or eject forward. When the battery polarity is reversed, the opposite will occur. Next, the same operations are performed with the remaining loudspeakers, marking the polarity at the ends of the voice coils when throwing the diffuser forward. After this, all three voice coils of small loudspeakers are connected in series (see Fig. 4, a). Figure 4b shows the switching on of loudspeakers if they are used for operation in a two-channel amplifier.
When all the loudspeakers are installed, mounted and phased, it is advisable to cover their outer holes with decorative fabric, making appropriate frames. The unit can be turned on at the output of an amplifier or receiver, designed for a load resistance of 12-15 Ohms. Its power should be about 8-10 W.
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The KAA-100 acoustic unit was developed by V. Shorov and E. Kuznetsov in 1992, and was later demonstrated by the RTV enterprise (Moscow) as the 100AC-017 acoustic system at the international exhibitions “Telecinema and Radio Engineering” in 1994 and “Svyaz Expokomm- 95". Professionals call units of this class control units or monitors. When choosing an amplifier for this active speaker system, many options were tested. The best among them turned out to be the amplifier published by G. Bragin in Radio (1987, No. 4, pp. 28–30). Then, during the examination of the speakers by sound engineers from Melodiya, VGTRK and RTV, the quality of sound reproduction was considered preferable in comparison with professional control units HEC-12 and NES-45. The control acoustic unit KAA-100 is intended for installation in studio hardware radio centers. The control acoustic unit KAA-100 consists of a three-way acoustic system (bass reflex for low frequencies) with passive crossover filters and an audio frequency power amplifier. The UMZCH input is symmetrical differential. Specifications Rated input voltage: 0.775V |
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A three-way speaker with a bass reflex and passive crossover filters (speaker circuit in Fig. 1) uses three dynamic heads. A 75GDN-1-4 head is used to reproduce low frequencies, a 20GDS-1-8 head for mid-frequency and a 10GDV-2-16 head for high frequencies. Band separation frequencies in the filter are 650 and 5000 Hz. The shape of the speaker cabinet makes it possible to realize the broadest characteristic of the directionality of sound radiation in the mid- and high-frequency range, and also weakens the intensity of standing waves formed inside the cabinet. For the same purpose, the inner walls of the housing are treated with sound-absorbing material. To suppress transient distortions that have the nature of an overtone, acoustic damping of the main resonance of the mid-frequency speaker head is applied. It is worth paying tribute to V.I. Shorov, who managed in the conditions of business inertia of the early 90s. to develop and achieve the introduction into production of this remarkable speaker system at that time. Under his leadership, a speaker system with inclined side panels and symmetrically located slotted bass reflexes was designed and manufactured. |
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A sketch of the speaker housing (version without amplifier) is shown in Fig. 3. The volume of the low-frequency design is about 47 liters, the bass reflexes are tuned to a frequency of 40 Hz. The variable cross-section of the body, as well as slotted bass reflexes along the side panels, made it possible to significantly - by 5.. 1 dB - reduce the unevenness of the resulting frequency response, which contributed to the improvement of microdynamics in the sound (in comparison with others assembled on domestic dynamic heads). This speaker had an expressive structured 6ac in the midrange, the sound was clear and precise, providing good localization of instruments in the spatial picture. The speaker body is made of 16 mm thick chipboard and covered with durable vinyl film "podwood". The spacer frames are also made from chipboard to increase the rigidity of the structure. The internal surfaces, except for the front panel, are lined with a sound absorber - cotton mats covered with technical gauze. The midrange head box with an internal volume of 2 liters also has a sound absorber to prevent the occurrence of standing waves. Approximate body dimensions: lower base – 350x400 mm, upper base – 150x200 mm, height – 1030 mm (without wheel supports). Passive filters for low-frequency and mid-range heads are of the first order (6 dB per octave), for high frequencies – of the third (18 dB per octave). The LF coil is made with a core made of transformer steel, the rest are ordinary, on plastic frames. Capacitors - K73-16 for a voltage of 160 V, resistors - non-inductive C5-16V for a power of 8 W. The AS was supposed to have a different set of heads - also classics of the 70-80s: 75GDN-2, 20GDS-4-8 and 10GDV-2-16. It should be noted that for the Soviet industry of that time, this speaker design with its separating filter was the most advanced product among many other speakers. The most important distinctive feature of the sound of the speakers is the open, detailed sound of musical instruments. Careful selection of dynamic drivers, along with external acoustic design, made it possible to realize, to the maximum extent, truly high-quality speakers based on Russian components. Even today, in most objective and subjective characteristics, this system is not inferior to mid-price floor-standing speakers. |
The three-band frequency corrector UMZCH allows you to make changes in the frequency response at low, medium and high frequencies of the audio range by no less than ±6 dB.
The front panel of the KAA-100 contains three LEDs, signaling that the supply voltage is turned on (“Network”), the speaker system is overloaded (“Overload”) and the protection is activated, disconnecting the load from the UMZCH output (“Protection”).
The amplifier is located at the bottom of the acoustic unit; it is inserted from the back of the case and its front panel is at the rear. Since amplifier controls in control rooms are not operational, this arrangement is accepted in many cases.
On the front panel of the UMZCH, in addition to the heat sinks of powerful transistors, there are input and network connectors, a mains switch and a fuse, as well as an input signal level regulator and frequency response regulators for high, medium and low frequencies located under the slot.
The amplifier is assembled on four boards: the input differential amplifier and three-band tone control are assembled on one board; on the second board the amplifier itself is mounted without powerful transistors located on the heat sink; The rectifier diodes and the protection device are located on separate boards.
The AC overload indicator (on elements R1, R2, C1, VD1, VD2. HL1) is connected to the input of the isolation filter.
The circuit of the built-in amplifier is shown in Fig. 2. Structurally, it is built from several nodes, in each of which (A1–A4) the elements are numbered separately. In the input stage, which receives a line-level signal from the sound engineer's console, op-amp DA1 is used to create a differential (symmetrical) input. Variable resistor R5 is located on the front panel of the amplifier and serves to correct its sensitivity. To adjust the listening volume level in control rooms, control panels are usually used.
On the same panel there is a three-band active tone control (at op amps DA2, DA3), which allows, if necessary, to correct the frequency response of the loudspeaker. Its regulators are also located on the front panel of the UMZCH under a slot to prevent unqualified intervention in the installation adjustments.
In the UMZCH (node A2), the main voltage gain is provided by a cascade based on the high-speed op-amp K574UD1B (DA1). To reduce nonlinear distortions, the pre-terminal stage, assembled on transistors VT1 - VT4, is covered by local feedback (through R14, R11, R15, R12). Temperature stability is achieved by including resistors R19, R20 of relatively high resistance (15 Ohms) in the collector circuits of transistors VT3, VT4. To compensate for possible instability of the base-emitter voltage of transistors VT1, VX2 when the temperature changes, diodes VD3, VD4 are included in their base circuits. Frequency correction and stability in the negative feedback circuit are provided by capacitors C10, C11.
The output powerful emitter follower is made of transistors VT5, VT6, operating in class B mode. The VD5 diode, connected between the bases of the output transistors, significantly reduces step-type distortion. In addition, at small signals, the current of the pre-final stage flows into the load, entering through resistor R21.
Low harmonic distortion is achieved thanks to deep overall negative feedback from the amplifier output to the inverting input of op-amp DA1 through elements R4, C5, R3, SZ (non-polar). To minimize the DC voltage at the output, you can connect resistor R8 to one of the zero balance terminals (NC), depending on the bias polarity, and select its resistance in the range of 200...820 kOhm.
Filter R1C2 limits the UMZCH passband at high frequencies.
The device for protecting the speaker and delaying the connection of the amplifier output to the speaker is assembled on a separate board (node A3). After turning on the supply voltage, a positive voltage of about 10 V appears at the output of the two-threshold comparator assembled at op-amp DA1 and capacitor C2 begins to charge through resistors R10 and R11.
At the first moment after switching on, the signal from the amplifier output to the load does not pass through the open relay contacts, and the “Protection” LED on the front panel of the KAA lights up. After a given period of time (determined by the time constant of circuit R11C2), the voltage at the base of transistor VT3 will reach a value sufficient to open it. Relay K1 (in node A3) is triggered and connects the speaker to the output of the UMZCH, simultaneously turning off the “Protection” LED - During the delay, the duration of which is usually selected about 2 s, all transient processes that can cause clicks in the loudspeaker have time to end.
When a DC voltage greater than 2V appears at the output of the amplifier, the protection unit must turn off the load to prevent damage to the speakers. A constant voltage of any polarity through transistor VT1 or VT2 is supplied to the input of comparator DA1 and switches it. Capacitor C2 is quickly discharged through diode VD8 and resistor R10, the voltage at the base of VT 4, VT5 drops, and relay K1 disconnects the speaker from the amplifier output. At the same time, the red “Protection” LED lights up.
The non-polar oxide capacitor SZ in the UMZCH can be replaced with two back-to-back polar capacitors of 22 μF each. The power supply uses K50-37 oxide capacitors, which can be replaced with imported ones, for example Jamicon. Capacitor C1 – K73-17.
Structurally, the body of the control acoustic unit is made in the form of a truncated pyramid, in the lower part of which there is a special insulated compartment for the UMZCH. The amplifier is inserted along special guide rails and secured with screws to the housing. The front panel of the UMZCH with the input and network connectors located on it, volume and tone controls, power switch and fuse is located on the rear side, which must be kept in mind when choosing the location of the KAA.
Control acoustic units KAA-100 are installed in studio control rooms in convenient places to ensure optimal listening conditions.
The UMZCH case must be grounded; for this purpose, a special terminal is provided on the front panel of the amplifier. Then connect the input cable and the network cable. It is necessary to ensure the correct phasing of signals intended for listening to stereo broadcasts.
After turning on the power supply, the corresponding indicators on the front panel of the speaker should light up.
By applying a nominal level signal to the input of each amplifier, use its sensitivity control to set the desired listening volume level, which is approximately the same for both control acoustic units. In the future, it is advisable to adjust the level from the control room console.
The KAA-100 provides the ability to correct the frequency response of the UMZCH, taking into account the acoustic characteristics of the room and the location of the control units. After such adjustment, it is advisable to measure the frequency characteristics of the control units at the listening location using a sound level meter, although in the end the main criterion is the auditory assessment.
According to expert sound engineers, KAA-100 has less uneven frequency response, reproduces a more natural timbre coloring of vocals and various musical instruments, has better “transparency”, and does not distort “sound plans”; In comparison with the control units NEC-45 (manufactured by BEAG), the difference in the sound of the KAA-100 loudspeakers in stereo mode was smaller.
In 1994, when examining the effectiveness of introducing EMOS into the acoustic system, sound engineers found that the sound quality of the KAA-100 control unit noticeably improves, becomes more natural, and the optimal depth of EMOS is recognized to be 2 dB.
Demonstration listening to the KAA-100 on display at international exhibitions aroused the interest of domestic and foreign specialists, who highly appreciated this acoustic system.
One of the reasons for the poor response of a loudspeaker in the low sound frequency range is the interaction of radiation from the front and back sides of the diffuser. To combat this phenomenon, it is necessary to design the loudspeaker in such a way that, providing optimal acoustic load, separates these emissions. From this point of view, a bass reflex is of interest, in which the radiation from the back side of the diffuser is used to increase the output at low sound frequencies. However, a conventional bass reflex, operating at frequencies of about 40 Hz, must have a significant volume and therefore is not widely used. The search for a more successful solution to this problem led the Moscow radio amateur A.G. Presnyakov to the creation of an acoustic unit, which he called a “horseshoe” (Fig. 1).
The unit was demonstrated at the XVII All-Union Exhibition of Radio Amateur Creativity. Like a horn, it serves as a waveguide for sound vibrations propagating through it and has increased efficiency at low sound frequencies. Along with great advantages, such a unit has a significant drawback. The loudspeaker installed in it is loaded onto a pipe tapering towards the middle, so that behind the diffuser a large-volume pre-horn chamber is formed. As a result, a number of spikes and dips appear in the frequency response response of the loudspeaker, worsening its uniformity. Obviously, it is more expedient to make an acoustic unit not in the form of a horseshoe, tapering towards the middle, but in the form of a horn folded into a horseshoe (Fig. 2).
Fig.2
The horn, as in A.G. Presnyakov’s unit, has only the side walls, its upper and lower covers are parallel. The loudspeaker, installed in the narrow part of the horn, in this case is loaded onto the expanding pipe. The result is not only that unwanted resonances are eliminated, but also that the high radiation impedance of the loudspeaker is better matched to the low impedance of the environment.
The author has manufactured several such units of various sizes. Two of them are shown in Fig. 3; At the top there is a “small horn bass reflex” with a volume of 50 dm3, working with a 5GD-1 loudspeaker, and at the bottom there is a “large horn bass reflex”, with a volume of 140 dm3, working with a 6GD-1 loudspeaker.
Fig.3
Both units can be used with other loudspeakers. As shown by measurements carried out in the electroacoustics laboratory of NIKFI, the units have satisfactory frequency sensitivity characteristics. One of them - the characteristics of a small bass reflex with a 5GD-1 loudspeaker with and without an acoustic impedance panel (ARP) is shown in Fig. 4.
Fig.4
The frequency response response of a large horn bass reflex with a 6GD-1 loudspeaker was given in the magazine "Radio" No. 4, 1969, p. 28, Fig. 4.
The sound of horn bass reflexes has a pleasant, unique timbre, which is explained by the high radiation efficiency at low sound frequencies. Jazz music performed by small ensembles plays especially well. For high-quality reproduction of symphonic music, the units can be damped with PAS panels (Fig. 3). The PAS is mounted in a cover covering the large bell of the unit. Holes with a diameter of 10-30 mm or blinds 10 mm wide and the length of the entire cover must be evenly distributed over its entire area. PAS, like any other damping of a moving loudspeaker system, reduces its efficiency, so their use depends on the taste of the radio amateur and cannot be recommended as mandatory. For comparison, the table shows the efficiency values of the 4A-28 loudspeaker, measured by recording polar radiation patterns for various types of design. As can be seen from the table, the PAS panel reduces the efficiency at low frequencies, but when working with a horn bass reflex it remains quite high. Almost a horn bass reflex allows you to use one loudspeaker to sound a hall that can accommodate 50-70 people, for example, a cafe, restaurant, club or school assembly hall.
In a small room (foyer, hall), a horn bass reflex can be powered by a standard single-ended low-frequency amplifier with a 6P14P lamp at the output.
The own speakers of the device used (tape recorder, radio) must, of course, be turned off. In a living room, you can get significant sound volume by connecting even a transistor radio of the Speedol type to the horn bass reflex without an additional amplifier.
Despite the rather complex configuration, manufacturing the unit does not require special skills and is accessible to every radio amateur. To do this, you need to have two standard sheets of thick (12-15 mm) and two or three sheets of ordinary thin three-layer plywood. For a cover for a large bell, you will need an additional piece of thick plywood; a cover for a small bell can be made from the trim left after cutting out the upper or lower base of the bass reflex. You will also need casein glue and 5-6 rolls of elastic bandage (rubber tape, sold in pharmacies).
Work begins by marking the upper and lower bases. Marking the bases is the most critical operation. You can practice this on a piece of paper first. Then, placing a sheet of thick plywood on the table, the overall dimensions are drawn from the near right corner - the diameter and depth (height) of the loudspeaker that is supposed to be used in the unit. Leaving a margin of 15 mm on each side, proceed to marking (Fig. 2). After a slight narrowing immediately following the loudspeaker, there should be a gradual expansion of the base, ending with a characteristic bell in the near left corner of the plywood sheet. It is desirable that the shape of the bells be symmetrical. Having marked one base, the resulting form is transferred to another sheet of plywood. After this, both bases are cut out and nailed together. It is advisable to place the nails as shown in Fig. 5, then the holes can be reused.
Rice. 5. The dimensions of a large bass reflex are indicated in brackets
When nailing down bases, the nails should not be driven in all the way so that they can be easily pulled out. It is better to finish finishing the highlanders with a brute file, but in such a way that there are no chips of the upper layers of plywood. After treatment, the bases are separated.
The side walls are made of three layers of thin plywood, glued sequentially on top of each other. For this purpose, a sheet of thin plywood should be cut into strips across the grain of the outer layers. The length of the plywood strip should be 40-60 mm greater than the length of the forming cover (processing allowance). The width of the strip determines the height of the unit. It is found based on the diameter of the loudspeaker, double the thickness of the base, a margin of 20-30 mm and, finally, allowance for processing. After making six strips of plywood, eight posts need to be cut from wood. The length of the racks should be equal to the height of the unit from the inside, their cross-section is 60X60 mm. The racks are installed on a flat surface and one of the bases is placed on them (see Fig. 5). After this, the bases are nailed to the racks through the existing holes. To prevent the plywood from bending when gluing the side walls, the location of the racks is
The edges of the sockets must coincide with the side elements of the unit. The second base is nailed to the posts in the same way, having previously aligned it with the one nailed using a carpenter's angle. Before applying glue, it is useful to lightly moisten the plywood with water. It is more convenient to glue the first layer of the side walls together. A strip of plywood is glued to the ends of the bases prepared in the same way, starting from the middle, tightly wrapping the unit with an elastic bandage, turn to turn. Thanks to the tension of the rubber, the thin plywood fits tightly to the bases along the entire perimeter. Glue drying time is 6-8 hours. The second and subsequent layers of plywood on the side walls are glued in the same way, but now the entire surface of the strips to be glued should be smeared with glue.
Having glued the body of the unit, the nails are pulled out, the fastening posts are removed, and the holes from the nails are tightly clogged with wooden sticks, the protruding ends of which are cut off flush with a knife. After this, the final finishing of the unit begins. The protruding edges of the side walls are sawed off with a jigsaw and processed with a bastard file. The openings of the sockets are processed in such a way that the lids cut in place from thick plywood can fit tightly to them. Having adjusted the covers, you need to install them in place. To do this, at the corners of the sockets from the inside, steel corners should be secured with screws or screws and threads should be cut into them for M4 screws. Screws passed through the flare covers will hold them firmly in place. The unit with installed socket covers should be sanded until a smooth surface is obtained. Finally, the outer surface of the unit can be covered with valuable wood veneer and polished. However, this work requires certain skills. If there is no veneer, you can pre-select the wood pattern on the outer layers of plywood, varnish the unit and polish it.
To ensure that the lids fit tightly to the edges of the sockets, strips of felt or thin cloth must be glued along their perimeter. If the unit is intended to be used without PAS, then a frame should be cut from the cover onto a large socket. A hole for the loudspeaker is cut out in the small cover. Both covers can be covered with a not very thick fabric, and to prevent holes from being visible through it, it is useful to paint the outer surface of the bell covers with ink diluted with water.
RADIO No. 8 1970 pp.34-35.
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"Horizon"- electroacoustic unit Minsky production association "Horizon", is a monophonic active speaker system designed to complete the same name television receivers: unified black and white first class models 107, 108 and 115, as well as unified (ULPTST) color second class models 701 and 723. All these TVs are distinguished by the absence of built-in speaker systems, and black and white ones are also distinguished by the absence of built-in UMZCH. The unit is made in the form of a cabinet with legs in a durable case that can withstand the weight of the TV, and is equipped with inputs for connecting two more signal sources: a tape recorder and a piezoceramic pickup. You can connect other monophonic signal sources to it. The output power of the unit is 6 W.
Product design
The electronic components of the unit are made on a common board. They include an input switch, a pre-amplifier on one P307 transistor and two KT315G, a simple tone block, a pre-terminal amplifier on KT201B, MP26A transistors, and a power amplifier on P307, GT402, GT404 and two KT805. Also on the board there is a parametric stabilizer on two D814D zener diodes to obtain a voltage of 24 V to power the pre-amplifier and the first pre-final stage, a rectifier bridge of the KTs405B type and two parallel-connected two-watt 1.3 kOhm resistors to limit the power supply current of the indicator light.
Outside the board there are sockets for connecting signal sources, volume and tone controls with passive elements soldered at their output, a 2.5-volt indicator light, fusible links of the primary and secondary circuits (all three for 1 A), two KT805B transistors on heat sinks, working in the final stage, power filter and crossover capacitors, output capacitor of the power amplifier, power transformer, 6GD6 and 2GD36 dynamic heads. The power switch is combined with the volume control. If the input for connecting a television receiver is selected, the signal from it arrives bypassing the volume control of the electroacoustic unit, since the TV has its own volume control.
Design and external design options
This electroacoustic unit could only be purchased complete with a television receiver, but not separately. Instances of the unit intended for completing televisions of various models differ from each other in external design in order to harmonize with the artistic and design solution of the television.
In addition, copies of the electroacoustic unit, produced in different years, as well as intended to complete various televisions, differ in the thickness and materials of the chassis and heat sinks, the types of some transistors, minor changes in the circuit diagram, the presence or absence of thermal resistors to stabilize the output stage mode, the number and types of dynamic heads, shape of legs, etc.
Precautionary measures
When operating and servicing the unit, it should be taken into account that the primary circuits of its power supply are galvanically connected to the network, and its secondary circuits contain a constant voltage of up to 40 V.
Literature
S. A. Elyashkevich, S. E. Kishinevsky. Blocks and modules of color infected televisions. M.: Radio and communication, 1982.
