Two simple UMZCH for a computer. Scheme, description

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Two simple UMZCH for a computer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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The author proposes two simple two-way stereo UMZCH with a common low-frequency channel, which work with a personal computer in a multimedia system. The same amplifiers can also be used in a car radio complex or a portable music center.

In two-band or multi-band sound reproduction equipment, the separation of the bands is carried out by filters of the second, third and higher orders. But in simple stereo devices, it often makes sense to separate the bands at the output of the UMZCH stereo channels, which in this case should be wideband. The capacitor separating the UMZCH and the midrange - HF loudspeaker can be used as a low-pass filter element. In this case, the signal necessary for the operation of the low-frequency channel is formed directly on this capacitor. An increase in its reactance with a decrease in the frequency of the signal causes the same gradual increase in the voltage of the amplified signal across this capacitor. It is worth noting that broadband channels are not loaded at frequencies below the crossover frequency, and at these frequencies the distortion in the amplifier is much lower than with a broadband load. In addition, due to more efficient electro-acoustic conversion in dynamic heads in the MF-HF band, less power is required from the amplifier than for wideband heads.

The circuit diagram (Fig. 1) shows two broadband UMZCH channels on the DA1 chip. To the outputs of the microcircuit are connected the heads of the midrange - HF acoustic system BA1 and BA2 with a common decoupling capacitor C6 of small capacity. As a result, from the active resistances of the load VA1, VA2 and capacitor C6, a first-order low-pass filter is obtained. The signal of the low-frequency component is taken from it to the LF bridge amplifier, assembled on the DA2 chip.

Two simple UMZCH for a computer

The input circuits of the device consist of low-pass filters R1C1, R2C2, attenuating overtone and radio frequency interference, and a dual volume control R3.1, R3.2. At the input of the low-frequency channel, a sensitivity control R5 is installed to adjust the tonal balance of signals in the LF and MF - HF bands.

Microcircuits of the TDA1519 series were not chosen by chance. They provide good sound quality and at the same time have a minimum of attachments. The amplifier can be put into standby mode by switch SB1. It should be borne in mind that TDA1519Q microcircuits or without a letter index have two non-inverting amplifiers inside, they are installed in place of DA1, and in microcircuits with indices A and B one of the amplifiers is inverting, which is necessary for switching on the DA2 bridge circuit.

With a load of MF - HF channels with a resistance of 8 ohms and the specified supply voltage, the rated output power is about 2,5 W, and with a load of a LF channel with a resistance of 4 - 8 ohms - 9 ... 12 W with non-linear distortions of not more than 0,1%. When the capacitance of the capacitor C6 is about 220 μF, the band separation frequency is chosen to be about 180 Hz. Its value depends on the capacitance of this capacitor. If, however, a load with a resistance of 4 ohms is used in the MF - HF channels, then the power on it will double, but to maintain the crossover frequency, the capacitance of the capacitor C6 should be doubled. Amplification of broadband channels by voltage - 40 dB.

Instead of the TDA1519 (DA1) chip, it is permissible to use the TDA1517 chip. Then the gain of broadband channels will be equal to 20 dB.

Another UMZCH (Fig. 2) is based on the same principle of band separation in the load circuits of MF - HF channels, however, it uses TDA2005 microcircuits more familiar to many radio amateurs. Here, in broadband channels, current feedback through the load is used, which provides higher UMZCH parameters and allows you to have a signal on isolation capacitors (in this case there are two of them) that is identical to the input signal, with a level independent of the load impedance (of course, at frequencies below crossover frequency). The common LF channel is also assembled according to a bridge circuit, where both amplifiers of the DA2 chip are connected in an inverse circuit. The R10 regulator, switched on by the rheostat, changes the signal gain in the bass channel.

(click to enlarge)

The UMZCH parameters are approximately the same as in the previous device, but with a load resistance of 8 ohms, the voltage gain of the broadband amplifier is 26 dB and depends on the load resistance. If necessary, its sensitivity is changed by selecting resistors R6, R8. To select the capacitance of capacitors C12, C13, the same recommendations are suitable here as for C6 in the circuit shown in fig. 1.

Both in the first and in the second amplifier, microcircuits must be installed on a heat sink with an effective area of at least 200 cm2. Printed circuit boards were not developed by the author; it is enough just to mount the amplifier elements on a suitable breadboard.

Author: M. Sapozhnikov, Ganei Aviv, Israel

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