UMZCH for computer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers
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By supplementing a sound card with a stereo power amplifier based on cheap microcircuits and a speaker system from outdated audio equipment, one can significantly improve the quality of sound reproduction in computers and bring it closer to the level of good multimedia systems.
Specialized active or passive acoustic systems (AS) are widely used for joint work with computers. The cheapest of them do not differ in sound quality, and high-quality ones are not cheap.
If there are old domestic speakers of low power (10MAS-1, 15AC-213 and similar), then they will sound good, but connecting them directly to the output of a computer sound card is not always possible. The point is that sound
the cards have a 3H line signal output or output to low-power loudspeakers. To use speakers with a power of 10 ... 15 W, you need to make an additional ultrasonic frequency converter.
It can be assembled on the available integrated circuits of the K174 series (K174UN7, K174UN14, K174UN15).
The variant of the UMZCH on the K174UN7 microcircuits is described below, its circuit is shown in fig. 1. In each of the channels, the microcircuits are connected according to a standard simplified circuit and provide an output power of 4 W at a load of 4 ohms. There is no volume control here, since this function is implemented programmatically in the computer. To power the amplifier, a mains stabilized power supply was used, in which a step-down transformer T1, a diode bridge VD1, a smoothing capacitor C16 and an integrated voltage regulator DA3 are assembled.
Most of the parts are placed on a printed circuit board made of one-sided foil fiberglass, a sketch of which is shown in fig. 2.
Chips through the holes in the board with the help of short metal bushings are attached together with the board to a ribbed heat sink with dimensions of approximately 70x80 mm. On the same heat sink, a DA3 chip is installed next to the board. The diode bridge VD1 and the capacitor C16 are placed in any convenient place in the case. The case itself can be plastic of a suitable size.
Parts can be used in the device: oxide capacitors K50-6, K50-35 or similar imported, non-polar - K10-17, KT, KLS, resistors - MLT, S2-33. The diode bridge can be replaced by four separate diodes - KD208A, KD212A, KD212B, as well as from the KD213 or KD202 series with any letter index. Transformer T1 can be selected suitable, which should provide a voltage of 16 ... 18 V on capacitor C20 at a load current of 1,5 A. Any sockets can be used, for example, from stereo phones, or other suitable ones, switch SA1 - MT-1 or similar.
Setting up the amplifier comes down (if necessary) to setting the gain by selecting resistors R3, R4 (within -30 ... + 200% of the nominal value indicated on the diagram).
The amplifier can be equipped with a power-on LED indicator (HL1), but if the amplifier is placed behind a computer or speakers, then such an indication may not be necessary. The SA1 switch is also optional, because the UMZCH can be powered together with the computer through one "pilot". The UMZCH input is connected to the computer with a shielded wire.
Author: I. Nechaev, Kursk
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