Refinement of AS imported mini-systems. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Refinement of AS imported mini-systems. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Speakers

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At present, in the Russian market of radio equipment, you will be offered many inexpensive mini-systems, their kit includes speakers of medium quality. Usually these are two- and three-band phase inverter systems with the simplest crossover filters on non-polar oxide capacitors. So. for example, the mini-system "Technics SC-EH60" of the Japanese company MATSUSHITA that I bought was equipped with an AC "SB-EH60". The quality of its sound clearly did not match the parameters of the 3H amplifier of the system itself, which became clear when a higher-class speaker was connected to it. This circumstance forced me to make an attempt to modify the "SB-EH60".

This speaker has two cone-type tweeters with paper cones. Due to their design features, such heads have very low electro-acoustic parameters, but since their cost is low, they are widely used by manufacturers in relatively cheap audio equipment. The heads are mounted on the inside of the plastic front panel, which makes the sound of high frequencies fuzzy and blurry.

LF-MF frequencies are reproduced by a head with a paper cone with a diameter of 14 cm. The sound of the MF range is tolerable, except for the spurious emissions on the frequency response of the speakers that are well perceived by the ear. As for the reproduction of low frequencies, it is accompanied by mumbling and resonant overtones introduced by an insufficiently strong speaker cabinet when operating at high power. The matter is that the case is made of a chipboard 12 mm thick, in it there is no sound-absorbing material. The AC separation filter is made on only two non-polar oxide capacitors. The filter section frequencies are 3 and 8 kHz.

When finalizing the speakers, I tried to replace the crossover filter, but this did not give positive results, mainly due to the low quality of the HF heads. Therefore, I decided to replace the HF speaker heads of a mini-system with one domestic 10GDV-2-16, which has better characteristics. Naturally, the separation filter had to be replaced. Its scheme is shown in the figure.

Refinement of the speakers of imported mini-systems

Since the LF-MF head effectively reproduces the frequency range up to 5 kHz, the filter's crossover frequency was chosen to be 5 kHz. The filter parts are mounted on a fiberglass board. Coil L1 is frameless, its winding is wound on a mandrel with a diameter of 21 mm and contains 153 turns of PEL-1 0,57 wire. Resistor R1 - PEV-3. Capacitors C1, C2 - MGBO for an operating voltage of 160 V.

Since it was not possible to install the 10GD8-2-16 head inside the speaker cabinet, a separate HF box was made for it, placed on top of the speaker of the mini-system. The dimensions of its body are not decisive, it is only important that the head is fixed on the front side of the box through a rubber or foam rubber vibration-absorbing pad. It is desirable to lay out the inner surface of the HF box with cotton mats. The HF heads of the mini-system speakers are disconnected from the UMZCH and left in their places.

Now about the further refinement of the AU. Considering that the body of the AC "SB-EH60", like most other mini-systems, is non-separable, it was necessary to remove part of the back wall with a hacksaw to strengthen it. Previously, a panel with sockets for connecting the speakers to the UMZCH and a phase inverter pipe were removed from it. Further, through any of the holes formed, you need to carefully cut out a part of the back wall along the perimeter so that 15 mm are left to its edges on each side. Instead of the removed part of the back wall, a new one made of 12 mm thick plywood is installed. Holes should be cut in it for the phase inverter pipe, panels with sockets for connecting the UMZCH and wires connecting the speakers to the HF box.

The new back wall is fixed with screws overlapping on the remaining edges of the old one. But before installing it, you should dampen the back and outer surfaces of the LF-MF head cone by soaking them with a solution of Guerlain in gasoline. To do this, you need to prepare a solution of the consistency of liquid sour cream and grease the rear surfaces of the diffuser and corrugation through the windows in the diffuser holder. Then do the same with the front surfaces of these head parts. When the solution dries, this operation is repeated again.

To strengthen the speaker cabinets of the existing speakers, I recommend installing spacers inside them made of wooden bars with a section of 20x20 mm. The length of the spacers should be chosen so that they fit snugly and without distortion between the side walls of the loudspeakers. They should be attached to the walls themselves using metal corners. All seams of the housings should be smeared with plasticine, the old ones should be removed and new separation filters should be installed. After that, the entire internal volume of the loudspeaker housings should be evenly filled with cotton wool (about 800 g), leaving free space in front of the bass reflex tube. To prevent cotton wool from getting inside the LF-MF heads, the windows of their diffuser holders should be sealed with gauze or any other acoustically transparent material.

Upon completion of the above work, it is necessary to make holes in the newly made rear walls of the loudspeakers for installing phase inverter pipes and strips with sockets connecting the speakers with the UMZCH. Then, through another specially made hole in the rear wall, pass the connecting wires of the tweeter and connect them to the outputs of the woofer-midrange head.

After refinement, the sound of the speakers has improved significantly. The mumbling and unpleasant overtones in the low-frequency range have disappeared, and the reproduction of higher sound frequencies has also improved.

According to the above methodology, the speakers of such mini-systems as "Panasonic CH40" were finalized. "Panasonic CH32". "Daewoo AMI-940", "Shatp CD-C451H" and others. Their owners were very pleased with the improved sound quality.

Author: P. Lyubimov, Bobruisk, Mogilev region, Belarus

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