|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING The block of adjustments of the portable radio tape recorder. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment Improving the sound quality of medium-class sound reproducing equipment is one of the areas of application for the skilled hands of a radio amateur. And often this brings interesting results. The article describes one of these studies and the implementation of the task. The proposed option can be applied in any other equipment of a similar purpose. It is known that portable equipment (radio tape recorders, cassette recorders) is not distinguished by high sound quality. There are objective reasons for this - small size, limited acoustics. But that's not all. As the analysis of the circuit design shows, the electrical path of the named equipment is often performed unsatisfactorily. So, most models, not only minor firms, but also leading corporations SONY SHARP, LG, do not have tone controls or have only one treble control that works to block the frequency response [1]. As a result, the boost in high and low frequencies that is so necessary to compensate for the reduced sensitivity of the human ear to them and eliminate the roll-off in acoustics with limited capabilities is absent. A typical view of the frequency response of portable radio equipment in two extreme positions of the RF tone control is shown in fig. 1.
The characteristic has a constant decline in the low-frequency region and an adjustable one in the high-frequency region. Consequently, the sound spectrum turns out to lie in the mid-frequency region, with a monotonous booming tone. The mentioned tone control can only worsen the sound, finally cutting off the high frequencies. In the vast majority of wearable equipment, loudness is also absent. But it is precisely the thinly compensated volume control (TKRG) that is able to improve the sound quality at low volume, when there is still a sufficient margin for the overload capacity of a low-power UMZCH. True, the lack of loudness compensation can partly be explained by the unsatisfactory operation of TKRG circuits using a single-tap variable resistor, which do not provide the necessary limits and smoothness of correction, especially in the low frequency region. The well-known circuits with variable resistors without taps also have a small range of LF correction or, otherwise, narrow the volume control range [2]. From the foregoing, it becomes clear that in order to improve the sound quality of the radio, it is necessary first of all to form a frequency response with a smooth rise in high and low frequencies and correctly working loudness. The proposed block of adjustments is simple in design, economical and at the same time effectively solves the problem. Main Specifications
Block diagram (one channel) is shown in fig. 2. Its first feature is the use of variable resistors of the device being finalized in their design (which simplifies further modernization and retains the design), but with changed functional purposes. There are two variable resistors, but now one of them (R2) has a TKRG, and the other (R10) has a bass tone control.
Note that in small-sized equipment, it is first of all necessary to adjust the low frequencies. With their lack, the sound becomes flat and inexpressive, and with an excess, the low-power UMZCH is instantly overloaded. To find a compromise, you need a bass tone control, and with sufficient depth. As for the high frequencies, their level is chosen by the listener close to the maximum and is rarely regulated. In addition, high frequencies are well approximated by the simplest loudness circuits, which also reduces the need for their separate adjustment. In practice, it is only advisable to set a certain fixed level of RF. The TKRG (Fig. 2) is based on a well-known circuit with a T-shaped filter R3C2R4C1, which lowers the level of mid frequencies. The filter parameters are chosen to provide maximum bass boost and sufficient treble boost. The latter is determined by the capacitance of the capacitor C1 and slightly exceeds the required one according to the equal loudness curves, which favorably affects the sound quality. The proposed TKRG is supplemented with an amplifying stage based on the VT1 transistor. A frequency-dependent OOS is introduced from its collector through capacitor C4 and resistor R5. Its circuit also includes elements of the original TKRG: capacitor C2 and resistors R3, R2. Since the OOS signal is applied to point "a", its depth depends on the position of the slider of the resistor R2. In its lower position according to the diagram, the effect of the environmental protection is practically not manifested, since the point "a" is connected to the common wire through a small resistance compared to the resistors R3, R5, the resistance of the introduced part of the variable resistor R2. In this case, the frequency response of the regulator (Fig. 3, curve 1), taken from the collector of the transistor VT1, has the most concave shape with the greatest rise in the low-frequency region.
As the slider of the resistor R2 moves up, i.e., the volume increases, the depth of the OOS increases, moreover, it is selective in frequency due to the filter formed by the resistor R5 and the capacitor C2. Since the specified filter is a first-order low-pass filter, the depth of the feedback increases with decreasing frequency, which leads to a decrease in the gain of the VT1 stage in the inverse dependence formed by the passive circuits of the TKRG. Thus, with an increase in volume, the excessive rise in low frequencies is compensated and the characteristics straighten out, acquiring the required form (Fig. 3, curves 2 and 3). For comparison, in Fig. Figure 3 shows (dotted line) these TCRG curves at the break of the introduced NF chain. It is clearly seen that without environmental protection, the former shortcomings return to the regulator. From the collector of the transistor VT1, the signal goes to the tone control, which is also non-standard in the device (see Fig. 2). It is an adjustable filter R12C6R11R13C7, in which the bass rise depends on the degree of shunting of the capacitor C6 by the introduced part of the variable resistor R10. The filter achieves a great depth and smoothness of bass adjustment even when using a variable resistor of group A. The rise of high frequencies is fixed and is set by capacitor C7. The circuit is suitable for radio tape recorders that have a variable resistor with only two leads. 10.
If the variable resistor R10 has three terminals, the more traditional circuit shown in fig. 5.
This is a conventional bridge tone control, but in an abbreviated form, without treble control. Its frequency response (Fig. 6) is smoother, with less steep slopes, but also, accordingly, with less rise in bass and treble.
In battery equipment, it is especially important to limit those signals whose frequency lies below the resonant dynamic heads. Otherwise, distortion increases and the energy of the power supply is wasted. In typical paths of radio tape recorders, the simplest high-pass filter is used for this, which is already effective starting from a frequency of 200 ... 250 Hz (see Fig. 1). As a result, part of the useful signal is also attenuated. This device has a high-pass filter with a cutoff frequency of about 60 Hz. One of them is formed by a capacitor C3, a resistor R6 and the input impedance of the cascade VT1, the other is obtained by installing an isolation capacitor at the UMZCH input with a capacity of C = 1/2πRBXFcp, where Fcp = 60 Hz is the cutoff frequency; RBX - input impedance of the UMZCH microcircuit (given in the reference books). Two simple HPFs form a second-order filter with a sufficient slope at the lowest frequencies. For the manufacture of the device, non-polar capacitors KM are suitable, oxide - any imported, MLT-0,125 resistors. Instead of the KT3102D transistor, you can use a similar one with the letter index E, as well as KT342B, KT342V. The static current transfer coefficient of the transistor VT1 must be in the range of 350 ... 500. Setting up the device comes down to setting the trimming resistors R1 of the left and right channels of such a signal level at which the UMZCH operates without overload in the maximum position of the TKRG. The same resistors can be used to equalize the stereo balance within a small range, since the initial gains of the channels are often different. After that, instead of trimming resistors, it is advisable to solder the constants of the nearest value, which are more convenient for surface mounting. The sound of the radio with the new block of adjustments is fundamentally different from the previous one: the monotonous, "telephone" tone disappears, the bass part begins to be heard, the upper frequencies appear, which are characteristic of high-quality sound reproduction. In conclusion, we note that it is possible to fully appreciate the possibilities of modernization only by using a higher-quality UMZCH and better acoustics. Literature
Author: A.Pakhomov, Zernograd, Rostov Region
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Smartphone Microsoft Lumia 430 ▪ Impact of electric cars on the environment ▪ UP Xtreme i11 Single Board Computer ▪ A quantum computer that does not use qubits
▪ section of the site Application of microcircuits. Article selection ▪ article How much sleep do we need? Detailed answer ▪ article Operator of hydraulic lift and telescopic tower. Standard instruction on labor protection
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page