New sound of 6AC-2. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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These miniature speakers, which were once equipped with electrophones of the first complexity group "Melody-106-stereo", are considered by many to be hopelessly outdated. The author of this article claims that they are still able to provide quite high-quality sound reproduction.

The magazine "Radio" has repeatedly published articles about the alteration of 6AC-2. Usually it was reduced to the manufacture of new loudspeakers based on the dynamic heads used in these speakers. I suggest that radio amateurs go for a more economical and, I think, more interesting bullet, trying not only to get rid of the shortcomings of the factory design, but also to make the most of its advantages.

The main defect of the 6AC-2 is the strong vibration of the cabinet walls, which not only gives the sound an unpleasant coloration, but also makes it unbearably "dirty". To eliminate this shortcoming, you must first remove the speaker grille, remove the rear panel and the head unit (in order not to break the plastic base, it is recommended to cut the sealing layer from the inside and push the block out from the back) and carefully clean the parts from the remnants of foam rubber and putty. All four walls of the case and the plane of the rear panel should be pasted over from the inside with one layer of linoleum with a fabric base using Bustilat glue. Glue it with the smooth side.

To obtain higher parameters, it is desirable to mechanically untie the heads and body. To do this, the plastic base of the head block is strengthened by gluing an overlay made of hard plastic or plywood 6 ... 10 mm thick on it from the back (Fig. 1). On the sides of the overlay, a round file made a selection for a cone with a diameter of 133 mm, as shown in the section. The final fit is done in place by sawing grooves in the overlay for the wires going to the HF head. The inner surface of the plastic base is coated with a thick layer of plasticine.

The diameter of the mounting holes must be such that the screws pass through them freely, without touching the lining and the base of the head block. A flange (Fig. 2) made of plywood should be tightly glued into the body. According to the same sketch, a gasket is cut out of a soft material (in the author's design, vacuum rubber 3 mm thick was used). Washers of the same material are placed under the screw heads. During assembly, the block of heads is centered so that it does not touch the body. The degree of tightening of the screws is finally determined by listening.

The head 25GDN-1-4 (1 OGD-34) is connected directly to the UMZCH, like 8 of the original design, and 6GDV-1-16 (ZGD-2) is shunted with a 5,4 Ohm resistor, in the author's version it is composed of four connected in parallel resistors MLT-2 (two 20 each and two more 24 ohms each). Such a shunt not only equalizes the frequency characteristics of the sensitivity and electrical resistance of the head, but also, as a current divider, serves as an effective damper of its resonances, including the main one. The 6GDV-1-16 head noticeably emphasizes the noise components of the signal, and with additional resistors it sounds much softer.

It may seem that the shunt will play the role of an unwanted low-pass filter, cutting off high frequencies as the electrical resistance of the head increases. However, the inductance of the 6GDV-1-16 head is small, and its frequency response has a noticeable rise at high frequencies, and as a result, the sound is better balanced. Thus, it became possible to connect the head through the simplest first-order filter - a capacitor with a capacity of 8 microfarads. It is made up of two capacitors with a capacity of 4.7 and 3.3 microfarads (K78 or K73-16. In extreme cases, K73-11 is also suitable). Hinged installation, with strong twisting and good soldering. It is also advisable to replace the connecting wires, at least with good copper network wires, but not in PVC or rubber insulation.

When assembling the speakers, the joints are coated with plasticine and the head block is fixed. The body itself is completely filled with a sound absorber: pieces of batting are tightly laid in layers. The rear panel of the speaker cabinet should be inserted with little force. Such a dense packing allows you to significantly weaken the resonances and eliminate the mumbling of the sound.

At the time of listening, the speakers are installed in the middle of the room or at some distance from furniture and walls, which should not strongly reflect the sound. You need to put them directly on the floor, vertically, with their heads up, for this purpose the back panel is provided with soft legs or spikes. This arrangement, in fact, is the "highlight": the elongated shape of the body and the coaxial arrangement of the heads make it possible to obtain a circular radiation pattern, with all the ensuing advantages.

It should be noted that the AS parameters are optimized after 50...60 hours of operation required for the heads to run in; in the future, with regular use, the characteristics do not deteriorate and daily “warm-up” is not required.

Since the author did not have the opportunity to remove the frequency response of the speakers. when it was tested in the presence of a group of experts, a gramophone record with a recording of sinusoidal signals with fixed frequencies (IZM ZZS 0201-02) was listened to. An extremely flat frequency response was noted, as well as invisibility to the ear of recessions at the frequency of the section of the midrange and high-frequency bands (5 kHz). The falloff of the frequency response is noticed only at a frequency of 63 Hz, and the lowest effectively reproducible frequency can be estimated at 40 Hz. The lowest frequency that can be reproduced without distortion is marked on the disc as 31,5 Hz, which makes it possible to reproduce even organ music quite naturally (!).

In general, the experts noted the surprisingly clear timbre-accurate sound of the converted speakers. The sound of the 6AC-2 was voted by all experts when compared to the sound of such renowned "shelf" speakers. like "Rogers Studio 3". Rogers LS3/5a. "B&W DM 302". The main and decisive advantage of 6AC-2 is its ability to convey the unique individuality of singers' voices and musicians' playing. By the way. 6AC-2 are quite capable of providing in a room with a volume of 50 ... 60 m3 sound pressure approaching the "disco" one.

Converted speakers with a power amplifier with load current feedback were tested (see, for example, M. Sapozhnikov's article "Non-standard inclusions of microcircuits in UMZCH" in the Radio magazine, 1998, No. 2. p. 23).

Author: R. Kunafin, Moscow

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