Completion of the computer speaker system SP-P110. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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During experiments with the compact active speaker system (AC) "Genius SP-P110", it was found that the dynamic heads installed in it are capable of better sound than the two-channel UMZCH built into it can provide. This speaker belongs to the lowest price category, so it is not surprising that the manufacturer saved on everything that could be saved on. Therefore, in order to improve the sound quality and increase reliability, it was decided to modify this device.

First of all, a new power supply was made, the circuit of which is shown in Fig. 1. An old, very hot transformer with an overall power of about 2 W has been removed. Instead, a more powerful and reliable transformer TS-BP-22 (from a Soviet-made cassette recorder) was installed. The mains voltage of 230 V is supplied to the primary winding of the transformer T1 through the closed contacts of the switch SB1 and the resistor R1, which performs a protective function. Varistor RU1 together with resistor R1 protects the transformer from excess mains voltage.

Rice. 1. Power supply circuit

From the secondary winding of the transformer T1, an alternating voltage of 9 ... 10 V through a self-restoring fuse F1 is supplied to a bridge rectifier assembled on diodes VD1-VD4. Capacitor C5 smoothes the ripple of the rectified voltage, LED HL1 indicates the presence of the output voltage. The interwinding screen and the transformer housing are electrically connected to the negative wire of the power supply. Most of the elements of the power supply are placed on a circuit board made of non-foil textolite with dimensions of 30x60 mm (Fig. 2). Wired installation applied. Resistor R1 and varistor RU1 are soldered to the switch contacts.

Rice. 2. Block elements on the circuit board

UMZCH in AC SP-P110 is assembled on an integrated circuit TEA2025B, which is capable of developing power up to 2,3 W in each channel. The amplifier version implemented by the speaker manufacturer on this chip developed an output power of no more than 0,2 W, and low audio frequencies were practically not heard. Another unpleasant bonus was the low sensitivity of the amplifier, which was not enough to play phonograms from pocket MP3 players.

Since the TEA2025B chip is capable of more, it was decided not to manufacture a new amplifier, but to modify the existing one. The scheme of this variant of the UMZCH is shown in Fig. 3. The numbering of elements indicated on the board is used, the designations of additionally installed elements begin with the prefix 1 . Capacitor C12 (1000 uF) was replaced with a larger capacitor (2200 uF), C4 and C10 were replaced with 470 uF capacitors (were 220 uF each). Similarly, capacitors C1 and C6 (0,22 uF) are replaced by capacitors with a capacity of 0,47 uF. The resistances of resistors R2 and R5 are reduced to 100 ohms instead of 680 ohms, which increased the UMZCH gain. Resistor R7 (560 Ohm) is replaced by a 5,6 kOhm resistor.

Rice. 3. Scheme of the modified UMZCH (click to enlarge)

The input circuits of the UMZCH were also redone. Previously, the input voltage was supplied directly to the volume control VR1, and after refinement - through RC filters on the elements 1R12, 1C14 and 1R13, 1C15, which protects the UMZCH from high-frequency interference. Prior to the refinement at the UMZCH output, the dynamic heads were automatically turned off when the headphone plug was inserted, now they can be turned off using the SW1 button. In addition, the signal to the headphones began to flow through the current-limiting resistors 1R17, 1R18. Additional blocking ceramic capacitors 1C20, 1C21, 1C22 were installed. The output power of the modified UMZCH with a new power supply is about 0,6 W in each channel.

The device was additionally equipped with a +5 V voltage regulator, which is output to the 1XS1 USB socket. You can connect various mobile devices to this socket to power them or charge the built-in rechargeable batteries. The stabilizer is assembled on an integrated circuit 1DA2, the 1R15 resistor reduces the power dissipated by the microcircuit. Zener diode 1VD2 protects the connected load from overvoltage.

Since in some mobile multimedia devices the common terminal for connecting headphones has an electrical potential relative to the common negative power wire, elements 1R11, 1C13, 1R14 are included in the break in the common UMZCH wire to prevent damage to such devices and ensure their operability.

Schottky diodes 1 N5819, MBRS140T3, MBR150, MBR340, BYV10-40, SB140 can be used in the power supply. Diode 1N4003 can be replaced by any of the series 1 N4001-1 N4007, KD243, KD247. The LED can be of any high brightness glow color. TVR10561 varistor can be replaced by FNR-10K471, FNR-14K471, FNR-20K471, MYG20-471 varistor. Resistor R1 - imported non-flammable or P1-7. Power switch - push-button or keyboard, designed for switching voltage 230 V AC, for example, JPW-2104, RS-201-8C. All non-polar capacitors are imported ceramic, oxide - K50-35 or imported. Instead of the transformer TS-BP-22, the unified TP-112-3 is suitable.

In UMZCH, resistors C2-23 or imported, oxide and non-polar (ceramic) are used, capacitors are also imported. The voltage stabilizer elements are mounted on an additional circuit board measuring 45x45 mm. The KA7805 microcircuit is installed on a duralumin heat sink with dimensions of 68x40x2 mm, it can be replaced by any of the 7805, 78M05 series. The modified UMZCH board is shown in fig. 4. An additional U-shaped brass heat sink with a surface area of ​​about 1 cm is attached to the integrated circuit U8². Initially, heat was removed from this microcircuit using printed conductors on a printed circuit board.

Rice. 4. Modified UMZCH board

The placement of nodes in the speaker cases is shown in fig. 5. In one column there is a power supply with a switch and an indicator LED, in the other - UMZCH with a volume control, a headphone jack and a switch for dynamic heads. The speakers are connected to each other by a four-wire soft cable. The supply voltage is supplied through two wires, the signal from the UMZCH output is supplied through the other two.

Rice. 5. Placement of nodes in speaker cabinets

The refinement of the UMZCH provided an improvement in the sound quality of the speaker, it has a higher sensitivity, and the speaker itself is equipped with a USB port. As a result, the sound of the speakers turned out to be better than that of compact "kitchen" LCD TVs, laptops, tablets, and other mobile devices. There were also intentions to replace the unnamed 1 W dynamic heads with others, with a power of 3...8 W, having the same overall dimensions. To my surprise, the "proprietary" dynamic heads removed from CRT (diagonal 51 cm) TVs sounded noticeably worse.

Similarly, other computer active speakers can be improved, since it often happens that their manufacturers, in order to save money, do not realize the potential inherent in dynamic heads and integrated UMZCH.

When manufacturing a new power supply, you must strictly follow the safety rules outlined in the article "Caution! Electric current!" ("Radio", 2015, No. 5, p. 54).

Author: A. Butov

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