Refinement of acoustic systems Amfiton 25AC-027. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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There is a lot of information on finalizing the USSR acoustics, but I did not find one on finalizing Amphiton 25 AS-027. Since I am the owner of this acoustics, I want to share my experience in finalizing. Basically, the ideas were taken from the improvements of other speakers, tips from friends and communication on the forums.

I wanted to buy these speakers for a long time, but I bought it only in 2009, from my hands (for $ 68 at those courses). There is only one reason for buying - isodynamic treble, but you can still add 50 HDN and a good case to them. When buying, I compared it with the S-90 and S-90D, Amphiton won in bass and treble.

Passport information according to AS

Frequency response: 25 (-17dB) - 31500 Hz

Frequency response unevenness in the range of 100-8000 Hz: ± 4 dB

Sensitivity: 86dB
Electrical impedance: 4 ohms Minimum electrical resistance: 3,2 ohms

Noise power limit: 50 W Weight: 25 kg

Dimensions: (HxWxD): 60x32x27 cm

The phase inverter pipe has dimensions: diameter 55 mm and length 165 mm, tuning frequency 25-30 Hz. The internal volume of the EXPERT is 41 l. Frequency section: 500 and 3000 Hz. Speakers: 50 GDN-3, 20 GDS-3 and 25 GDV-1 (10 GI-1-4).

The shape of the frequency response of the sound pressure measured along the axis, curve 1:

The amplitude-frequency characteristics of harmonic distortions for the 2nd and 3rd harmonics are shown in the photo, curves 2 and 3. Harmonic distortions were measured at an average sound pressure level of 90 dB.

Got it in good condition, never unscrewed, only the suspension on the bass crumbled. The first listening at home was certainly impressive.

Source KENWOOD DP 1060

Amplifier ODYSSEY-U-010

Detail and refinement on treble notes, good bass, but the middle, as elsewhere, is not very good.

_

The body is made of chipboard (front and back) and plywood (sides, top and bottom). The thickness of the walls is 18 mm, except for the front, it is 38 mm. In the upper part of the body there are two sausages with cotton wool. The filter is assembled on a metal chassis, the wires are naturally thin, there are no terminals. A bandage is attached to the wire at the end of the phase inverter - rather, it is a fight against whistling. In general, the build quality is not bad, but you can’t call it good. But there is room for improvement.

Well, now to the point. After long runs on the tracks, I established the following stages of work on these speakers:

1. Work with the body

2. Replacement midrange

3. Filter recalculation

4. Replacing the suspension with bass

5. Wiring replacement

6. Improving appearance and assembly

I want to warn you that my revision is not a standard or ideal, this is just one of the possible examples of refinement of this speaker, because everyone has different tastes. And maybe my work will seem to someone incomplete, incorrect or completely meaningless, because I did it for myself and to my taste. Therefore, let my work be for you only one of the options in the knowledge of acoustics.

1. Work with the body

We disassemble everything, down to the last screws. I will not describe the process in detail, I hope no one will have problems with this.

Here the main work is to strengthen the walls and seal the seams. I sealed the seams with PVA glue, set the AC at an angle of 45 ° and filled the seam with glue (this is convenient to use a syringe), letting it dry completely. Drying of one seam lasted about 1-2 days, so this is the longest stage in finalization, but the result is worth it. As a result, I received a case without sounds on impact, almost like a stone.

In one case, I installed 3 spacers. Two on the sides, and one on the front-back. I made them from solid wood, oak and acacia, scored them tightly and put them on PVA, without screwing in screws and pasted over with batting. Spacers installed after gluing the seams. After installing the spacers, the brush went through the seams with glue again. I didn’t cover the entire body with any material, I think it’s superfluous. Odyssey does not allow the low frequencies to go much, so there is no rumble. As a result, we got such a body from the inside.

I also cut out linings from fiberboard, under the bass, 2 for each. Since the protective grid is removed, a decent distance appears between the speaker and the overlay to cover it, I pushed the speakers a little forward, besides, strength does not hurt.

The cap for the midrange speaker, I shortened the magnet of the future 30 GDS. The plug was made of 16 mm chipboard. He did it because with his magnet he closes almost the entire volume at the back. I pasted it over with batting inside, pasted it into the hole, outside, in the body - with felt. The phase inverter pipes were shortened by 1 cm, glued into the holes and pasted over with felt inside the case.

At the back, in place of the former hole for the cable, I cut out a hole for the terminal. I put it on glue and pressed it with self-tapping screws.

2. Replacement midrange

There are many options here. You can leave 20 GDS, change it to a broadband type 5 GDSh, or import. I already had a new purchased 30 GDS, with a fabric rubberized suspension. 20 GDS in my version was with a polyurethane suspension. A direct listening comparison confirmed that the 20 GDS does have a nasty sound. Therefore, I consider the replacement to be quite justified, despite the fact that 30 GDS has such a suspension. The HDS sounds brighter and more colorful, the sensitivity is the same, the sound of 30 HDS can only be called more linear.

As a result, the sound has changed for the better. Appeared expressiveness and naturalness in the sound. The sound became more dynamic.

_

3. Filter recalculation

I decided to recalculate the filter due to the fact that the section of midrange and high frequencies is too low, around 3000 Hz. With the new filter, the LF and MF sections are slightly raised, the MF and HF are raised to 5500 Hz.

Here is the diagram of Amphiton's native filter:

There were no instruments for studying the frequency response, so I tuned it by ear. The only possibility of measurement was in the attenuation of the filter, here:

In blue, the attenuation graphs of the native filter are indicated, but without the load of the speakers. Red indicates my version of the filter, also without speakers. When the load (loudspeaker) is turned on, the attenuation of the filters drops, and the curves will be even steeper, plus the frequency response of the speakers themselves is also added and the final frequency response will be completely different than these graphs. Therefore, do not pay attention to too smooth recessions.

According to the native filter, it can be seen that the section of LF and MF is about 750 Hz, MF and HF - 3700 Hz. According to the new (red graphs) LF and MF - 40 Hz, MF and HF - 12000 Hz. When you turn on all the speakers, the sections will be different, especially the frequency response.

The filter setting was carried out in the place where the speakers will stand. I soldered wires to each speaker, and already on the couch, in a normal environment, I picked up the details. I achieved the final result in 4 months, even when the columns were already fully assembled.

As a result, I came up with this filter:

The phase agreement of the loudspeakers is the same. At low frequencies, the second order, a little less than the nominal value than it was. On the midrange, the first order, trimming along the bottom. Since 30 GDS does not take higher than necessary (above 5 kHz), I did not cut the top, and the sound is so much more alive. Resistance for sensitivity matching. On HF the second order. Everything is simple and clear. The woofer coil was taken from an old filter, from the midrange link. I took the HF coil from another speaker. Capacitors are also recruited from the old filter.

I used capacitors K73-11 (HF link) and MBGO (MF and LF links). I also tried K73-17, but I didn't like the sound. All parts are glued to the AC floor.

4. Replacing the suspension with bass

Old suspensions simply crumbled before our eyes, especially at high volumes, so repairs are required. Replacement is quite simple, we remove the old suspension, a new one with glue.

We clean the old suspension and everything that remains of it. I worked as a solvent. He worked especially carefully on the diffuser. I did not peel off the cap and centering washer. Even without suspension, the speaker plays as it should, without friction, but only in this position. Result:

I bought new suspensions on the radio market, $ 5 for a pair:

Caution! Do not smear suspensions with alcohol and solvents. Glue used polymer. I cleaned the gluing points on the suspension with sandpaper. First glued to the diffuser, then after drying - to the frame.

To give a decent look, I covered the outer side of the movement with clerical ink, in 3 layers.

5. Wiring replacement

I used a regular speaker cable, LF 2,5 mm2, MF and HF - 1,5 mm2. But I think that it can be limited to low frequencies - 1,5 mm2 midrange and high frequencies - 1 mm2. It will be more convenient to work with him.

I installed the usual terminals:

6. Improving appearance and assembly

Here comes the leveling of the surface, using putty. I removed the nameplates and aligned the holes. Here's what happened:

I cleaned the lining on the speakers with fine sandpaper and covered it with black matte paint from a can, in 3 layers. I bought a self-adhesive to my taste.

Next, I glued the body and proceeded to the assembly. Vatu put the one that was, did not add anything and did not take away. The photo shows lining under the woofers made of fiberboard. Grids in front of the speakers removed. Each speaker was planted on a soft window insulation. Result:

_

Sample of one of the joints

Rear view, painted, because I never look back, and there is no point in pasting over.

I did not varnish it, I painted the screw heads with black paint.

The result exceeded expectations. When properly installed, there is a full-fledged bass up to 50 Hz, then a decline, but up to 30 Hz it still presses normally. The lower audible threshold is 27 Hz. The sound is natural, not straining. Tight bass, expressive (but not protruding middle), light and clear high-frequency notes. I will not say how much they pull at the store prices of acoustics, I can only say that they sound better than they look.

Compared to the old speakers, the new version is especially distinguished by its expressive mids and light, not sibilant highs.

Another very important point. Acoustic refinement is not the full effect of good sound. The source is also very important, the noticeable difference between a computer and a normal DVD player, not to mention CD players. A good amplifier is a big step towards good sound. Well, the correct setting. Refining, of course, will change the sound, but the full effect cannot be achieved without a good source, amplifier and proper installation.

In the end, I want to thank my friends and participants of the "Acoustic Systems" forum, the "Soldering Iron" site cxem.net, who helped in creating this project, thank you very much!!!

Good luck with the upgrade everyone!

Best regards, Dmitry!

Author: Dmitry Levenets ( lds 212008); Publication: cxem.net

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