1. Small cabinet volume for a woofer. The consequence is the humming of low frequencies.
2. The phase inverter is designed for a frequency of 20 Hz. The consequence is large bass distortion.
3. Worthless mid-range speaker. The consequences are disgusting midrange, overtones.
4. Low resonance frequency of the tweeter. Consequences - "quacking", hissing.
5. The filter is designed taking into account the previous shortcomings. The consequence is that when modifying any node, the filter must be changed.
6. The case is not rigid enough and is not "muffled". Consequences - vibrations, overtones, "barrel".
7. Etc. and so on. …

Learning and laughing

Drinking beer, we reach three truths. There are three ways:

1. Lightweight and efficient.
2. Medium difficulty. More shamanism and snobbery. Some sound improvements compared to point 1.
3. Super complex, time consuming and super efficient. You are actually trying to make new speakers. It all depends on the quality of workmanship and musical flair. If nothing happens, then no one promised you anything.

Attention! Attention! Attention!

1. When carrying out all work, make sure that the phasing of the speakers is correct. If you have not encountered this yourself - invite a specialist - electronics!
2. Alteration of the speaker 15 GD - 11A is an irreversible process. In case of inaccuracy, the speaker has one road - to the trash can, and you have another - to the market.

Way one. Lightweight and efficient.

1. The mids are the main focus. By altering the speaker, we will achieve its operation in piston mode, increase the upper cut-off frequency, remove overtones, increase sensitivity, improve directivity, dampen.
2. Let's translate the column into the range from 31.5 Hz, instead of 20 Hz. There will be less noise.
3. We will suppress the resonance of the high-frequency head.
4. Calm down the overtones of the hull

We buy a Soviet tennis ball in the store. Chinese and others do not fit. They have different material. The ball should be exactly the same as in early childhood for 8 kopecks. In extreme cases, you can take it from friends or in the sports section of tennis. We buy epoxy resin (a little, you can 1 cm cube), glue (Supercement, Mars, Argo, etc. - hard after hardening), a couple of simple pencils, any medical bandage and cotton wool.

Let's get creative. We cut the ball in half along the seam. The seam is visible through the light. It is overlapped and 1 - 2 mm wide. You need to cut in the middle of the seam. I sawed with the Neva blade, having previously made notches on it with a whetstone. After sawing, align the cut line on sandpaper, and process the outer surface of the ball with fine sandpaper. If there are large influxes inside in the area of ​​\u200b\u200bthe seam, then they must also be removed. When working, the ball must be fixed with plasticine on the Mars battery (case from photographic film, jars of fish food, etc., by imagination) at three points. It's enough. Plasticine is removed with sweat or with a dry cloth or rubbing with gasoline. After the surface of the ball is processed, it should not be touched by hands. Grind pencil leads on sandpaper.

Dilute epoxy with double the amount of hardener. Cover the surface of the ball with the thinnest layer. If necessary, excess glue can be removed with newsprint. Sprinkle with graphite, shake off excess. It is necessary to ensure that the white plastic of the ball does not shine through the graphite. If it shines through, then the epoxy layer was small. We must add. After everything turned out, we leave to harden.

We collect the filter at 3 kHz. To do this, we take a 4.7 Mf capacitor and a 0.6 mH inductor. You can take a capacitor from 4 to 7 mF and fit a choke under it. In order not to fill your head with unnecessary formulas, the simplest thing is that the product of the capacitance of the capacitor in microfarads and the inductance of the inductor in mH should be equal to 2.82. Let's say the capacitance of the filter capacitor is 6.6 μF (MBGO and MBM with a permissible deviation from the nominal value of ± 10%), then the coil inductance is 2.82: 6.6 = 0.43 mH, (the winding contains 150 turns of PEV-1 wire 0.8 wound on a frame with a diameter of 22 and a length of 22 mm with a cheek diameter of 44 mm). Based on these data, it is possible to assemble a circuit without an LC meter, since it is not the exact value that is important, but the "capture" of the resonant frequency, which has a certain spread. We mount the capacitor and inductor on a piece of fiberboard and solder one output of the coil to the output of the capacitor. We solder wires 40-50 cm long to the free leads.

We parse the column. We remove the low-frequency speaker, mid-frequency speaker, take out the glass from it, remove the high-frequency speaker, remove the decorative overlay, remove the phase inverter (on some speakers you will have to unscrew the filter). We take half of the dried ball, polish it on the outside with suede or newsprint and glue it over the dust cap of the midrange speaker head with hard glue. It is necessary to ensure that there are no unglued lye between the edge of the ball and the cap and that the ball is glued exactly in the center. We do the same with the second midrange. We leave to dry.

We fasten a home-made filter to the back wall of the speaker (inside) opposite the tweeter. Solder the wires from the filter to the output of the tweeter. Which one does not play a role. We remove the connectors from the rear wall of the speakers and solder the wire coming from the amplifier directly to the filter. From the pipe of the phase inverter we saw off with a hacksaw for metal 10 cm along the center line. We wrap the phase inverter pipe and the glass of the midrange speaker with a layer of gauze and bandage it. It is necessary to check whether they will enter their nests after this procedure. If not included, then reduce the layer of cotton wool with gauze. We check if there is cotton wool and gauze in the glass. Add if little to complete. We dampen the midrange speakers. To do this, we additionally fit their diffuser holders with foam rings made from blanks 10x27x355 mm. the ends of which are glued together with glue "Moment" end-to-end. We glue the bottom and ceiling of the column from the inside with felt (batting, padding polyester, etc.). We wrap the wires with a bandage.

We place the bandage along the wire and twist it, clasping the wire. It is convenient to fix the bandage with threads. We collect the column. We coat with plasticine all the perimeters of all the speakers. It is not worth putting on protective nets, but only on the condition that there are no small children, the wife does not call in with a mop or vacuum cleaner, and that the speakers will not be transported. We turn on the columns. We don't know right. We call friends. Please come with your favorite entries. We listen. Comforting friends with beer. With a sneer, we notice how useful the bucks spent on the purchase of foreign rubbish would be useful to them.

Way two. Medium difficulty.

We do everything that is indicated in path 1, but do not collect the columns.

1. We will improve the properties of the body and kill overtones and "barrel"
2. Achieve better signal transmission
3. Hull sealing. We remove the influence of the body

So let's go. Strengthen the rear wall of the case by placing two rails with a section of 3x2 cm. vertically in full length at a distance of 15-20 cm from each other symmetrically, and attaching them with screws to the back wall. Pre-treat the attachment site with epoxy. It is necessary to take into account the possibility of installing a phase inverter later. Between the back and front walls, we install a spacer rail at the level of the midrange head, taking into account the possibility of installing a glass. We coat all the joints of the walls and corners from the inside with silicone glue such as "Bizon" or plumbing silicone putties. We paste over the entire body inside with felt (batting, synthetic winterizer, etc.). Thicker than 1.5 cm is not worth it, so as not to greatly reduce the internal volume of the case.

We reject all proposals to change 15 GD - 11A to 6 GDSH-5. Ours is already "cool", and such a replacement will lead to a loss of power, a decrease in dynamic range (very dangerous) and you will have to change the filter a lot. So when replacing 15 GD - 11A with 6 GDSH-5 for 35AC - 212, you will have to replace the following parts: L1 - 0.22mH, C2 - 1.0mF, C8 - 0.5mF, L4 - 0.1mH. New parameters are specified. When using 6 GDSH - 5 - 4, you will also have to put additional resistance in the circuit of this head at 4 ohms. Also, the appearance of the column changes. Well, if you really want to, then you can. Further. Remove tone switches. Remove unnecessary resistors R (1, 2, 4, 5, 7, 8, 9, 11, 12). We replace the wires on the filter installation with a copper wire with a diameter of 1.2 mm. We replace the wires going from the speakers to the filter with more travel ones. On a low-frequency speaker - stranded - with a cross section of 2.5 - 3 mm square, on a mid-frequency speaker - 2.5 mm square. On high-frequency - 2 mm sq. - single core. All wires are soldered to the filter directly, and not through the previous speakers. The filter is installed at the bottom of the column. All wires are laid under a layer of felt. On the side walls.

The filter controls are removable. We make wooden (chipboard, plywood) plugs in their place according to the thickness of the body. We pour them on epoxy and grind them. We cover the front panel with self-adhesive wood-like film to match the veneer of the speakers. Installing speakers. Low-frequency and mid-frequency through rubber pads. Suitable rubber from window insulation, thin rubber medical hoses, silicone hoses (worse). We process the installed speakers around the perimeter with plasticine or non-hardening window putty (it resembles a piece of laundry soap and is cheap). Checking the sound. We're just balding. Pushing back all sorts of "Pioner", "Technics", JAMO and ...

Way three. Super complex, time consuming and super efficient.

It's good to have the following instruments: an oscilloscope, an audio frequency generator, a digital multimeter, an LC meter. A person who does not repair and assemble at home - of course, does not have all this, but there is a way out - go to the workshop and ask to measure what you need, taking filters, heads, etc. with you. If they ask for a fee for this, then it is purely symbolic. You can even order filters. This, of course, will be more expensive. Let's start. We take as a basis 35AC-212 with dimensions 710x360x285. It is desirable that the case be plywood, a woofer with a rubber suspension, a tweeter with a fiberglass dome. We understand everything. We no longer need a midrange speaker. The case must be increased for a low-frequency speaker with a rubber suspension up to 100 liters. If the suspension is polyurethane foam, then up to 120-130 liters. Our body is 70 liters.

There are two options:

1. Remove the front wall from the case, so that later it can be used for the matrix for the holes for the speakers in the newly manufactured case for 100 liters. From the remains of the buildings, good boxes are obtained for potatoes and markoshka in the cellar.
2. You can try to build up the old building.

In the first case, you need to focus on the dimensions - 1100x360x350 and manufacturing in a furniture workshop according to your drawings, with swearing and nitpicking about quality. We will consider the second way. So, you can try to get by with little bloodshed. We make it ourselves, or we order two boxes with tightly fitting walls and lids made of double 10-layer plywood with external dimensions - 380x360x285. In the bottom of the column and in the lid of the box, we cut out the same holes of approximately 270x210. Cover the inside of the box with felt. After assembly, it will be unrealistic to do this. We drill holes in the lid of the box and in the bottom of the column through which we fasten them together with bolts. The heads of the bolts should sink into the potai. Falling asleep a little - 10 kilograms of shot does not hurt, we throw a gauze bag with cotton wool on top. Pre-spill the connection with epoxy with a normal hardener content. We glue the junction with felt. The rest of the movements with the body, as in paths 1 and 2. We take the mid-frequency head 30 GDS-1. You just need to check them - a lot of marriage. Purely mechanical property. Further. We measure the resonance f of all speakers. You can sign with a felt-tip pen directly on the magnets so as not to get confused and not to measure everything again.

It would be nice if the resonance frequency of the paired speakers did not differ much. If the speaker makes extraneous sounds at any of the audio frequencies, then it must either be cleaned or changed if normal operation was not achieved by cleaning. We calculate and make filters for our case. The fewer inductances, the better. We continue to deal with the body. We remove excess resin at the junction. We grind it. We make two wooden boxes for filters. We will mount them on the back wall from the outside. We solder the wires from the amplifier directly to the filters. And we will drag the wires to the speakers through the fastening of the speaker connectors. All wires are branded audiophile. Choose your price range. Just take very expensive ones - it makes no sense. It is better to convert the phase inverter to a frequency of 31.5 - 40 Hz. If the dome of the high-frequency head is made of lavsan, then, having removed the crosspiece, it is necessary to smear the suspension and the outer third of the dome with perchlorovinyl. We paste over the entire body with a self-adhesive film. For the rest, see path 1 and path 2. With mandatory step-by-step verification - better - worse. The best method, if there is no obvious result, is blind listening.

Literature

1. Zhagirnovsky M., Shorov 8. Improving the sound of 35AC-1 and its modifications. - Radio, 1987, No. 8, p. 29, 30.
2. Shorov V. Improvement of loudspeaker heads. — Radio. 1986, no. 4, p. 39-41.
3. Aldoshina I., Voishvillo A. High-quality acoustic systems and emitters. — M.; Radio and communication. 1985.
4. Zhbanov V. Mechanical damping of diffusers. - Radio, 1988, No. 5, p. 41-43.
5. Maslov A. Once again about the alteration of the loudspeaker 35AC-212 (S-90). - Radio, 1985. No. 1, S. 59.
6. Zhbanov V. On the damping of dynamic heads. - Radio, 1987, No. 8, p. 31-34.
7. Gennady and Karen Arzumanov. To the question of the modernization of acoustic systems. Vestnik A.R.F. №6" 2000

11-01-2009

Finalization of acoustic systems Radiotehnika 35AC-012 (S-90)

Radiotehnika 35AC-012, Radiotehnika S-90, Radio engineering 35AC-012, Radio engineering S-90

At the moment I am the happy owner of the Radiotehnika S-90 speakers.

Consideration of acoustics in normal condition

To begin with, the full name of acoustics should be specified - 35AC-012. From their issue, it immediately becomes clear that we are dealing with high-class acoustics, by Soviet standards, that is, acoustics with very high characteristics. It should be noted right away that by Soviet standards it was not the best acoustics, but an ordinary ordinary workhorse. There were acoustics that had a more balanced sound, for example, the same Cleavers / Corvettes 35AC-008.

But as they say, we have what we have. Let's go back a little to the moment of their purchase. I took them from my friend for $ 50, when I came to him, at the sight of the decorative grilles protecting the sound-emitting heads, I wanted to cry, they were dented and very cruelly at that (mainly the grilles of the tweeter and mid-range speaker suffered). But this did not frighten me, since what was sold on our market cost at least $ 100, and the quality of the speakers deserved no more than 3, and in these speakers the speakers looked at 5. In general, I took these speakers to my home. When connected to an amplifier, the sound was quite decent. Nevertheless, two shortcomings should be noted, one of which is inherent in all 35AC-012, and, as it turned out, all of its 35AC clones, to one degree or another.

The first of the shortcomings that just killed me on the spot is an incomprehensible overtone during the operation of the woofer, very similar to the fact that something was stuck to the speaker at the back, and now this is something vibrating, as it turned out later, it was a drop of solder that stuck to diffuser on the back. The second drawback was precisely in the mid-frequency dynamics 15GD-11A - according to the old standard and 20GDS-1-8 according to the new one (these speakers came in a large number of modifications, for this reason it is extremely difficult to track which one you have). And again, a small digression, in which I will say that the differences in the standards are in the designation of power, that is, according to the old standard, the rated power of the speaker was indicated, and according to the new standard, nameplate power is indicated (from the sound engineering course:

1. The rated power of the speaker is such a power of the speaker, when summed up, it works with harmonic distortion levels not higher than the permissible
2. Passport power (often also called noise power): this is the level of power supplied to the speaker, at which the level of harmonic distortion is equal to ten times the level at rated power).

An additional division into the frequency ranges of the heads was also introduced, which was now indicated in the name of the speaker, in particular, this is the third letter.

So the disadvantage of this speaker is that it often starts to resonate at high volume and thereby spoils the sound picture, and as you know, the midrange speaker is crucial in shaping the sound picture.

Consider now in order all the speakers that we have available:

1)Low-frequency - 30GD2, aka 75GDN-1-4 (8):

Purpose - use in closed and phase-inverted remote acoustic systems of household radio equipment of the highest complexity group as a low-frequency link when working indoors. Loudspeaker head of electrodynamic type, low-frequency, round, with unshielded magnetic circuit. The diffuser holder is made of die-cast aluminum alloy. The conical diffuser is made of impregnated paper pulp. Suspension - torroidal shape - made of rubber. The centering washer is made of impregnated fabric.

I also want to add that the speakers have a relatively heavy dome and a rubber surround is used, which spoils the quality of the bass, it becomes more solid and booming than the speakers with a lighter mass of the moving part and foam rubber suspension. But it should be borne in mind that the bass is affected not only by the design, but also by the acoustic design itself, for this reason, these troubles can be slightly eliminated and the speaker will play decently. On the other hand, due to the rubber suspension, the speaker turned out to be very reliable and practically unkillable, and the foam rubber suspension soon crumbles due to the presence of sulfur in the air and the speaker needs to be repaired.

Purpose - use in closed and phase-inverted remote acoustic systems of household radio equipment of the 1st and 2nd complexity groups as a mid-frequency link when working indoors. Loudspeaker head of electrodynamic type, midrange, round, with unshielded magnetic circuit. The diffuser holder is made of die-cast aluminum alloy. The conical diffuser and the spherical cap are made of impregnated paper pulp. Torroidal suspension - made of polyurethane foam. The centering washer is made of impregnated fabric.

Here is actually a photo of this miracle of technology:

It is worth saying that at a good volume it decently distorts the sound, but as practice has shown, this problem is very easily solved and, moreover, very simply.

Purpose - the use in closed acoustic systems of household radio equipment of the highest complexity group as a high-frequency link when working indoors. Loudspeaker head of electrodynamic type, tweeter, round, with unshielded magnetic circuit. Mounting flange and acoustic lens are made of plastic. The dome-shaped diaphragm with a suspension is made on the basis of polyethylene terephthalate.

In general, they sound good, only the filter tuning is close to resonant frequencies.

Upon closer examination of the acoustics (especially from the inside), you begin to be horrified by the build quality, for this reason we will begin to refine. We will refine it according to the simplest possible scheme, without interfering with the filters, since without specialized equipment there is nothing to do there. For those who are interested, here is the acoustics diagram:

Refinement 35AC-012

I will describe in order all the stages of improvement that my columns went through:
1. Disassembly:

• First of all, we take them to a secluded place (meaning a room) in which our experimental subjects will not be available to children (if any) and other family members. We lay the speaker system on our back and begin to disassemble it.
• Now remove the decorative trims from all the speakers and put them aside.

Here they are:

Then we get the speakers. ATTENTION When unscrewing the bass speaker (the tweeter and midrange speaker are attached with the same screws as the decorative trim, and the woofer is attached separately from the trim), be extremely careful, because if a screwdriver comes off, you will disfigure it. Then we solder the wires connecting the filter and the speakers with a soldering iron, and boldly hide the speakers in a secluded place.

• We remove the cover of the phase inverter and pull out the phase inverter itself, and this must be done as carefully as possible, since we are working with plastic, and it can easily break. Then we hide these details in a secluded place.
• Now we take on the regulator / regulators of the HF / MF links. To dismantle them, it is necessary to remove the decorative plug in the center of the regulator, then unscrew the opened screw and remove the regulator handle. After that, carefully pry off the remaining plastic lining with the help of two chisels and carefully remove it, then unscrew the 4 screws securing the attenuator itself and now it can be pushed out into the case. We push it out and solder it from the filter. We put it aside, in the future it will be necessary to conjure a little over it. By the way, the junction of the attenuator housing and the speaker housing is abundantly covered with a sealing viscous substance, I personally used it again when I assembled it in place, but you can use sealant or plasticine.
• We take out the bags of cotton wool, which, in theory, lie in your speaker system and set aside.
• We dismantle the panel with filters, it is screwed to the body, having previously unsoldered the wires from the output at the back of the speaker system. Putting it aside, as we will spend a lot of time working with them.
• Finally, remove the panel with terminals from the rear cover of the speaker and set it aside.

It seems like a lot of work has been done, but in fact it is just a drop in the ocean. More interesting and labor-intensive work lies ahead.

2. Restore appearance:

For this purpose, we take the gratings and speaker covers we removed earlier, level them, carefully sand, degrease and paint several layers of automotive paint (which is in spray cans) several times and leave to dry. I’ll make a reservation right away that I restored the grilles only for the reason that I have a small child who can damage the speakers, otherwise the easiest solution would be to abandon the grilles as such, since they only bring minuses to the sound, think for yourself.

3. Refinement of the speaker cabinet:

It's actually very simple, and is carried out in several stages:

• If desired, the body can be strengthened. What will it give us? More precise and even bass, since the body panels will vibrate less and, accordingly, will introduce less overtones into the bass component of the sound. How to do it? This is purely everyone's business, because as many people as there are so many decisions. In general, everything consists in installing spacers, installing additional corners at the joints of the acoustic system walls, installing stiffeners on the speaker walls. Personally, I limited myself to pasting additional corners at the joints. You can also glue all the joints tightly. Unfortunately, I can’t show a photo, since the entire acoustic system is already dampened with foam rubber.
• Sealing all joints and seams. It is carried out very simply with the help of various materials. For example, I used plumbing sealant. The procedure is simple: we cover the joints with sealant and gently smear it with your finger, thereby tightly sealing possible gaps.
• In a hardware store we buy foam rubber 10 mm thick (I personally chose this thickness, do not take too much as you will strangle the case) and glue it to all walls except the front one with glue. Thus, we dampen the body, thereby increasing its virtual volume.

To do this, we buy terminal blocks with gold-plated connectors of a universal type in the store. Since the S-90 terminal block itself is large, and the new ones are small, we dismantle the connectors from the terminal blocks and install them on the body from the S-90 terminal block. After that, we lubricate the installation place with sealant (do not be sorry, then wipe off the excess) and put it all in place, tighten the screws. Here is a photo of what you should have:

5. We proceed to the alteration and installation of the filter in place:

• First of all, carefully examine the filter, pay attention to the fasteners of parts, since inductors were often fastened with metal screws, which immediately knocks down the filter setting.
• If there were problems in fasteners, bring it to the end by excluding metal parts from fasteners. There are also cases of assembling the filter on a metal plate, then transfer the filter to a plywood panel.
• We take a leaf, a pen in our hands and carefully redraw all the elements of the circuit, restoring the filter circuit itself, so to speak, because the parameters of the speakers varied and for this reason the filter circuit could be changed at the factory. By the way, we exclude the attenuator from the circuit, it just spoils the sound.
• Now we pick up a soldering iron (preferably 100 watts) and disassemble the filter, or rather, simply remove all the jumpers that were installed from the factory.
• Now we are assembling the filter, instead of jumpers we will now use an oxygen-free copper cable with a cross section of 4 mm 2, the cable can be bought at any car audio store. It should also be noted that you should not take a very expensive cable, as changes in sound quality will be insignificant, but the costs are simply enormous.
• After assembling the filter, we solder the wires that will go to the speakers based on: for the LF link 4 mm 2, for the MF link 2.5 mm 2, for the HF link 2 mm 2.
• We put the filter in place, after which we solder the terminal blocks to it (observe the polarity, otherwise you will lose the sound picture).
• The very last step is to run the wires to the speakers, fix them and cover the filter with foam rubber.

You will get something similar to these photos:

6. Attenuator setting:

• We remove all resistance from it.
• We put it in its place.
• We seal carefully.
• Additionally, we close it with foam rubber (I closed it only on the front wall)
• We install all the decorative panels to the end.

7. Installation of a phase inverter:

Everything is simple here, we put it back on the sealant, we carefully monitor that it is not pinched anywhere with foam rubber, as this will knock down its setting.

8. Install the overlay on the phase inverter:

We put it in the same way as it was removed, just put it on the sealant and on new screws, since the panel itself often rattles on the bass. Seal well the joint between the panel and the phase inverter.

9. Let's start installing the dynamic heads in place:

• A) Install the HF head:

1) We remove that parody of the sealant that stands on it (some kind of felting gum, felting cardboard, is behind it).
2) We cut out a new seal, a mouse pad is perfect, in particular a black porous base.
3) Solder the wires to the speaker and install it in place.
4) We put in place a decorative overlay (grille if desired) and tighten it tightly with screws.

• B) Install the midrange head:

1) We make a cylinder from foam rubber, of such a size that our box fits into it. We put this cylinder inside the column and pass a cable through it, which we bring out.

2) We pass the wire through the box (most likely we will have to expand the hole), after which we put the box in place, adjust the length of the wire and seal the hole into which the wire is passed.
3) Solder the wires to the speaker.
4) Now the crucial stage is the damping of the mid-frequency head. To do this, we sew a cylinder of foam rubber, of such a size that it fits tightly on the speaker frame and closes all the windows.

5) We fill the box with cotton, after fluffing it up.
6) We put the dynamic head, grille (optional) and frame in place and twist.

1) First, put back the bags with cotton wool that were removed during the disassembly of the speakers. Solder the wires to the head. I tied the wires that are soldered to the head to the frame so that they do not hit the diffuser, because there is a possibility that when you put the speaker in place, the wires will bend and fall into the diffuser holder window.

2) We make a gasket from a porous material, for example
apply window sealant and carefully place the speaker in place.
3) Tighten the fixing screws. Do not apply great efforts, then the speaker will be spring-loaded with a gasket and this will reduce the energy of vibrations transmitted to the case.
4) We put in place the grate (optional) and the decorative trim. If you nevertheless put a grate, then I advise you to cut out small triangles from the foam rubber and put it on the speaker at the place of its attachment, this will eliminate the vibration of the grate, and therefore remove the overtones at high volume.

I came up with this solution a long time ago, look at the photos in more detail:

Conclusion:

After the revision, all the listeners (there were not many of them, five people, but I asked for the most honest information from them) noted more gentle and soft basses, a much cleaner middle, the tops remained practically unchanged (it seemed to me that they became a little cleaner). Also, the acoustics began to quietly take higher volumes.

In conclusion, I would like to say that the proposed method is the cheapest, simplest and most accessible. All components, of course, can still be repeatedly modified or changed. For example, instead of foam rubber, you can use felt (natural), which, in theory, will give better results than foam rubber, it is also a good idea to use vibromastics. Many advise replacing 15GD-11A with a 5GDSH broadband, for me this is a bad idea, but this is everyone's business. 10GD-35 - it is advised to treat with a notch filter, 15GD-11A to modify on the basis of halves from a tennis ball (by the way, the idea is quite interesting, I didn’t do it myself because I don’t have such speakers in stock).

Register .

Refinement of 35AC-212 (S-90) with native speakers and switches.

According to the prospectus of the 90s, the Riga Radio Plant mass-produced two models of acoustic systems: 35AC-212 or "S-90" and 35AC-012 in the modifications "S-90B", "S-90D", "S-100B". The time has come to finalize the older model 35AC-212, as well as its predecessor 35AC-1, which have a similar set of speakers.
These models have switches for attenuating the power to the midrange and tweeters, allowing them to be matched to the level of the woofer and tailoring the system to your particular listening environment. All this is good, of course, but it “thumps and clicks”, no matter how you turn the switches. And I want it to be musical. Somehow, I was crucifying here with alternative thoughts about finalizing the S-90. These thoughts safely dissipated, never being realized. In their place came others, more interesting ones. It seemed the most promising to use the Nivaga 9 filter from the previous article and recalculate it for another set of speakers, and leave the midrange and treble switches in their original factory form. The resulting filter circuit for the S-90 is shown in the figure. I propose to call it "Nivaga 10".

A distinctive feature of the filter is the presence of resistors R1, R2, R3, R4, which provide direct potential contact of all speakers with the PA output and do not allow the phase characteristic to go far from a linear frequency dependence. If you look closely at the circuit, you will notice that the resistance of these resistors is close to the active resistance of the corresponding speakers. Meticulous comrades can of course add to them the inductive equivalent of these speakers. I was too lazy, because even in this form the sound quality completely satisfied me, and I don’t have the opportunity to experiment in a sound chamber. Well, if you take a closer look at the circuit of the band-pass filter leading to the midrange speaker, you can see that it was created from a previously developed filter like "Nivaga 6 or 8" by replacing the speakers with equivalent resistors. Similarly, in the low-pass and high-pass filters Resistors R1 and R3 are the equivalents of the corresponding speakers.Therefore, this parallel speaker circuit is a logical development of the previous series speaker circuit, and therefore retains all its advantages, which are written in earlier articles.And at the same time, it creates new possibilities for moving the cutoff frequency of all four filters included in the circuit independently of each other, controlling the peaks and dips in the frequency response of the speaker, which was not the case in the previous circuit.In this specific case, I sought to push the cutoff frequencies of the woofer and midrange speakers, as well as the cutoff frequencies of the midrange and treble Brilliant bass, stereo panning, volume, clear mids - everything that the music lover's ear craves is present in the modified S-90 speakers.
The fear that the introduced resistors would heat up was not justified. Their power is theoretical. In practice, it can be reduced by 2 - 3 times, but the resistors must be wire.
Practice shows that not everything that I like is suitable for others. Well, the proposed scheme is open for reasonable improvements, and I am ready for serious discussions.
This treatise was drawn up on 20.02.12.

Music lovers are constantly arguing about which speaker system to choose for comfortable listening to music at home. And this is no accident: the entire contingent was divided into two camps. The former believe that it is worth shelling out a tidy sum for buying a cool Hi-Fi (or even better Hi-End) system in order to be happy and forget about headaches about this topic for the rest of your life. But there are those who are not ready to give up their entire life's savings for expensive acoustics (instead of a car or an apartment), which is why they consider the best option to purchase simpler equipment or to refine the good old classics to good sound.

In this article, we will talk about one of the most popular audio systems from the times of the USSR, which could not leave indifferent any of its owners. The S90 speakers, whose technical characteristics are able to excite the mind to this day, have become one of the highest achievements of the Soviet company Radiotekhnika.

Speaker models

The very first thing worth mentioning is the real and full name of the speaker model - 35AC-012. An important factor is the fact that this acoustics was produced in several variations. The most popular of them are S90 and S90B. There were also models S90i, S90D and S90f, but they were not widely used and are now almost never found.

The model with the postfix "B" differed from the usual "nineties" in a wider range of reproducible frequencies. Also a significant difference was the introduction of an indicator of electrical overload of the speakers. The recommended power rating of a high-quality amplifier for these speakers is in the range of 20 to 90 watts. It is also worth noting that Radiotekhnika S90, S90B (and other modifications) were the first models of acoustic systems that met international requirements for Hi-Fi category equipment.

Design

The case, in which the S90 speakers are enclosed, is, in fact, a non-separable rectangular box made of fine wood veneer. The walls of the speakers are 16 mm thick, the front panel is made of plywood 22 mm thick. The internal joints of the walls of the case are connected by special elements that increase the rigidity and strength of the structure, but do not interfere with high-quality sound.

Looking at the device from the front, the speakers are arranged in the following order (from top to bottom): tweeter, midrange speaker and woofer. Also on the front panel of the S90 speaker you can see the frequency response graph (amplitude-frequency response) and the phase inverter hole. While the frequency response is located above or below (depending on the acoustic model), the phase inverter is always located at the bottom. This was done for reasons of proper design for better sound and giving the speakers good bass.

S90 speakers: specifications

If we take the usual S90 as an example, then they are equipped with dynamic direct-radiation heads. More precisely, a high-frequency head 10GD-35, a mid-frequency head 15GD-11A and a low-frequency head 30GD-2 (in later models - 75GDN-1-4).

Equipped with two step playback level controls for adjusting the midrange and treble in the ranges from 500 to 5000 Hz and from 5 to 20 kHz. Each knob moves in three fixed positions. In the "0" position, there is no obstruction to the signal from the crossover filter, and it is fed directly to the corresponding head. When using the "-3 dB" and "-6 dB" positions, the signal is attenuated by 1.4 and 2 times, respectively, with respect to the "0" position. By switching the selected knob, you can make changes in the timbre of the sound.

The nominal power of the S90 speakers is 90 watts, while the nominal power is 35 watts. The indicator of the nominal electrical resistance in this speaker system is at around 4 ohms, and the frequency range available for playback ranges from 31.5 Hz to 20 kHz. The nominal sound pressure of the S90 is 1.2 Pa. I would like to note the rather impressive dimensions of one column - 71.0 x 36.0 x 28.5 cm, and the total mass of the entire system reaches 30 kg.

Speaker layout and connection to the sound source

In order to understand whether it is worth refining any speaker system, you need to study all the data and aspects of the equipment. Below is the electrical diagram of the S90 speakers. Even a novice radio amateur can figure it out, you just need to have at least basic knowledge.

Another important point is the correct connection of the speaker system. After all, if something goes wrong, even when connecting, you can, unwittingly, disable the equipment. You don't have to be a pro to figure out how to hook up your S90 speakers. The main thing is to have at least 20 watts with an amplifier (in this case, most likely, the sound will not be loud enough for large rooms), but not more than 90 watts. In case of exceeding the permissible value of the amplifier power, the user runs the risk of being left without acoustics due to its breakdown. To connect, you will need ordinary acoustic wires, which must be connected to the terminals on each speaker and on the amplifier. The main condition for connection is polarity.

Refinement 35AC-012

As it becomes clear from the description above, in itself it has good technical characteristics and is capable of “building up” even small public spaces. But for home use, the most sophisticated music lover will prefer to modify the S90 speakers with their own hands. And all because, assembled more than twenty (or even thirty) years ago, the acoustic systems of the Radiotekhnika company already in those years did not have a high build quality and materials used.

Parsing

In the event that the acoustics were purchased in a used condition and are currently well-worn by life, it is worth attaching importance to the appearance. To do this, you need to disassemble the S90 speakers, after putting them on the “back”.

When removing the speakers, you need to take into account that the treble and midrange heads are attached to the case using the same screws as the lining. The woofer is attached separately, and you need to be as careful as possible so as not to damage it when unscrewing it.

Treble/midrange controls are much easier to dismantle than you think. All you need to do is carefully remove the decorative caps that are in the center of each knob. After that, using a screwdriver, it is necessary to unscrew the screw that has opened to the eye, and remove the regulator knob itself. The plastic lining must be carefully lifted from both sides with the help of flat objects and removed, and the four screws remaining under it must be unscrewed. After that, you can push the S90 column inside, not forgetting to unsolder it from the filter.

Cotton bags inside the case must be removed. Again, if the previous owner of the speakers did not forget to return them to their place in case of parsing.

You should first unsolder the panel with filters from the output from the back of the speaker, after which it must be dismantled by unscrewing the screws. Now you can remove the panel with the terminals attached to it.

Appearance and body

If the speaker grilles and decorative trims are “tired”, then it is worth straightening and painting them, having previously sanded and degreased them. This will give a fresh look to the speakers. The body of the S90 will loosen over time and can be strengthened as desired. This will result in a better sounding woofer.

This can be done in various ways, including installing spacers and additional corners inside. It is also necessary to pay attention to sealing all joints and seams with ordinary plumbing sealant. In addition, you can glue the inner walls of the case (except the front) with foam rubber, which will increase the volume of the latter.

Terminals and filter

Knowledgeable radio amateurs are advised to replace the standard speaker terminals with universal-type terminals with gold-plated connectors. The installation place must be lubricated with sealant and put the panel with the terminals in place.

Considerable attention should be paid to the sound filter. If it was attached to the body with metal screws, then the filter setting will go astray. There are cases when the filter was assembled on a metal plate. This should be fixed by transferring all the nodes to the plywood panel. The circuit of the filter itself could be changed at the factory due to different speaker parameters, so you should make sure that everything is assembled according to GOST. If there are jumpers in the filter, then they must be removed and replaced, for example, with an oxygen-free copper cable with a cross section of 4 mm 2. It is worth removing the attenuator from the circuit, as it simply distorts the sound, and replacing the wires used to connect the speakers to the filter.

For woofers, a wire with a cross section of 4 mm 2 is suitable, for midrange speakers - with an area of ​​2.5 mm 2, for tweeters - with an area of ​​2 mm 2. After such simple actions, the filter must be returned to its place and closed with foam rubber.

Speakers and other "little things"

For speakers, new seals should be cut. This can be done with the help of cheap or simply obsolete mouse pads. This is the easiest option. After that, it is worth returning them to their seats and putting decorative trims and nets.

Before installing the regulators in place, you will have to unsolder all the resistances from them. When installing them in place, it is imperative to apply a sealant, as well as when installing a phase inverter.

Through such simple manipulations, the S90 speakers acquire a new life. The sound quality becomes an order of magnitude higher, despite the small costs. As a result, we can say that if there is no money for expensive 2.0 format acoustics, you can use this option and become the happy owner of the time-tested AS Radiotekhnika S90. If it happens that only half of the speakers are available, do not be upset. After all, it is noteworthy that the S90 column, a photo of which can be found on almost any website of acoustic lovers from the times of the USSR, can work alone and give a good result.

They are distinguished by an extended range of reproducible frequencies, the introduction of an indication of the electric overload of the loudspeakers and a new appearance. The recommended power of a high-quality household amplifier is 20-90 watts. The preferred installation option is outdoor.

A distinctive feature of the acoustic system is the use of a loudspeaker with MANGO magnetic fluid as a mid-frequency link, which made it possible to increase the nameplate power of the loudspeaker and the speaker as a whole.

Specifications: SG3.843.050 TU.

The shape of the frequency response of the sound pressure measured along the acoustic axis: a) , b) ,

Specifications:

Specifications	Meaning
Reproducible frequency range in free field conditions, Hz:
	25...25000
,	25...25000
Irregularity of the frequency response of sound pressure, dB, at the lower cutoff frequency of the reproducible frequency range relative to the average sound pressure level:
	-15
,	-14
Irregularity of the frequency response of sound pressure, dB, in the frequency range of 100 ... 8000 Hz relative to the average sound pressure level:
	±4
,	±4
Level of characteristic sensitivity (characteristic sensitivity), dB, not less than:
	85 (0,338)
,	89 (0,56)
Directional characteristics of the speakers, dB, determined by the deviation of the frequency response of sound pressure, measured at angles of 25 ± 5 ° in the horizontal plane and the vertical plane, from the frequency response measured along the acoustic axis of the speaker (0 °):
:
in the vertical plane	±8
in the horizontal plane	±6
, :
in the vertical plane	+ 2
	-4
in the horizontal plane	+4
	-3
AC harmonic distortion, %, determined by the total characteristic harmonic coefficient at an average sound pressure level of 90 dB at frequencies, Hz, not more than:
250…1000	2
1000...2000	1,5
2000...6300	1
Rated electrical resistance (nominal value of total electrical resistance), Ohm:
	4/8
,	8
	8
The minimum value of the total electrical resistance, Ohm:
	3,2/7,6
,	7,6
	7,0
Limiting noise (passport) power, W:
,	90
	100
Limiting short-term power, W:
,	600
Type of low-frequency acoustic design	phase inverter
Weight, kg	23
Dimensions, mm	360x710x285

Design features:

Cases of all AC modifications are made in the form of a rectangular non-separable box made of chipboard, veneered with fine wood veneer. The thickness of the walls of the case is 16 mm, the front panel is plywood with a thickness of 22 mm. Elements are installed at the joints of the body walls from the inside, which increase the strength and rigidity of the body.

In acoustic systems, sets of heads are used:

• : ; ; ;
• ; : ; ; ;
• : ; ; .

Heads are produced by Radiotekhnika software.

The heads that are part of the speakers are each framed with decorative blackened overlays made of stamped aluminum sheet with four mounting holes. The midrange head on the inside is isolated from the total body volume by a special plastic casing in the shape of a truncated cone. The woofer head is located on the front panel along the vertical axis, and the midrange and tweeter heads are shifted to the left or right relative to this axis. On the front panel there are also handles for midrange and treble level controls, and in its lower part there is a plastic overlay panel with a nameplate and a rectangular hole (100x80 mm), which is the phase inverter output. The nameplate shows frequency response curves corresponding to different positions of the level controls, as well as the name of the speaker and the manufacturer's logo. In addition, there are special plastic bushings on the front panel for attaching a decorative frame with fabric.

Crossover frequencies provided by filters: between low and medium frequency heads - 750±50 Hz, between medium and high frequency heads - 5000±500 Hz.

In the design of the filters and the overload indication unit, resistors of the VS, MLT, SPZ-38B, S5-35V, PPB types, capacitors of the MBGO-2, K50-12, K75-I types and inductors on plastic molded frames were used.

The removable decorative frame included in the kit is covered with a knitted fabric with high acoustic transparency.

The scope of delivery includes four plastic legs, which can be attached to the base of the case if necessary.