Reworking the S-90 filter

Having been an opponent of audiophilia as a simplification, after experiments I changed my point of view and now I’m even ready to sacrifice something for the sake of a small number of obstacles in the path of sound :). This is actually very important, even on the speakers discussed below. But this also forces you to sacrifice some things: high power and congestion of frequency bands.

I used the crossover below, broken down into pieces, for my s-90de with speakers: 30GD-2, 6GDSH-5-5, 3GD-2, where it plays simply wonderful with any genre of music. 3GD-2 (its worse analogue 6GDV-1-16) is a very old high-frequency speaker (my copy is from 1977) with a resonance frequency of as much as 4500 Hz (but there is an opinion that in this place it is quite calm), so the high frequency of the midrange section is HF is due precisely to this fact. However, most domestic tweeters have not gone far, so I consider this cut to be very good for them.

This filter will work great on good foreign mid-high-frequency speakers, which I tried myself :). But, of course, it needs to be changed taking into account everything new (including the frequency of the section) - taking the principle itself as a basis.

p.s. Still, we should not forget that everything in the world is not only relative, but also subjective :). In addition, at the moment I have absolutely no means of measuring the frequency response of my system - everything is adjusted by ear in the same room...

speakers

NC: Let's look at the generally good bass driver used in the s-90. 30GD-2 (75GDN-1-4) with a nominal resistance Z=4Ohm, sensitivity S=86dB (or dB/W*m) and frequencies F=30-1000Hz does not provide the best IFC (impedance-frequency characteristic:)) in the compartment with poor sound at frequencies above 500Hz.

Our cutoff will be at 500Hz. Ideally, to make this speaker work really well, you would cut off everything above 200Hz. After all, the main drawback of the 30GD-2 is that at these frequencies it mumbles (“sound from under the diffuser hood”) and plays very poorly. But to make such a low crossover frequency you need an excellent midrange speaker with a resonance frequency of no more than 70Hz.

MF: The standard mid-range driver 15GD-11 (20GDS-4-8), with parameters Z=8Ohm, S=89dB, F=200-5000Hz, does not stand up to any criticism either in terms of sound or the characteristics we need. Therefore, it needs to be replaced with the nice baby 6GDSh-5-4 (Z=4Ohm, S=92dB, F=150-12000Hz) which looks completely frivolous, but in fact turns out to be very good. In addition, it has the sizes we need, price (no more than $4!) and availability in Russia.
It should be noted the low power of the 6GDSH-5 (as a result, the inability to work at discos/parties) and bursts in some parts of the frequency range (“loudness”).

There were opinions that the 6GDSH-5 has poor directivity at high frequencies, which is why the stereo panorama is “unstable” at a relatively high section. It seemed to me that this was not so, so if there are problems, act according to the circumstances :).

HF: Any tweeter with parameters S=89-92dB and Z=16Ohm will do. It is important to note F (actually, the minimum operating frequency of the speaker) - it should not be more than 4500Hz, and the lower the better.
Structural dimensions and fastenings are selected on site using available means.

sensitivity

MF: To cut off the extra 7 dB (92-85 = 6), I suggest using the option of one resistor, which will avoid unnecessary elements in the circuit and at the same time reduce the ratings of the filter elements due to an increase in the speaker resistance. Resistor R2=4.3Ohm will give us a reduction of 6dB. The sensitivity is reduced by a resistor in the approximate ratio of 1 dB/0.7 Ohm. Coil L1 has its own resistance of 0.75 Ohm and will help us remove another 1 dB. Voila! :)

However, the disadvantage here is that there are no exact formulas and dependencies, and the values ​​I gave appeared as a result of my personal feelings.

VC: We use the same method, selecting the desired resistor until the desired result is achieved. However, in this circuit there are no filter elements with a high intrinsic resistance, so resistor R1 must be taken with a margin of 1 dB. We also note that the volume of the high-frequency speakers relative to others in the system strongly characterizes its “inclinations” - for example, most listeners like a slightly muffled high-frequency sound (by about 1-2 dB), the system seems to be “softer”. What is important for domestic high-frequency speakers is not of the best quality :)). For heavy music, emphasizing the high frequencies may be more important.

It's nice to know that changing the sensitivity resistors within one unit (1 Ohm) has virtually no effect on the filter itself and the cutoff frequencies, which makes it possible to experiment.

But you shouldn't cross the 0.7 Ohm difference when experimenting with R2 - the L1 coil is much more sensitive to this change.

inductors

The most difficult thing. We urgently need to find ways to measure inductance, otherwise precise tuning will not work.

In the absence of a way to measure, I suggest the following: compare the coils by their own resistance, taking into account all design parameters. Theoretically, if all the factors influencing the inductance rating coincide (there are some very interesting ones - the density of turns, the content of iron impurities in the frame :)), then you can obtain the necessary inductance, as if “following a model”.

Despite everything, this method, it must be said, is very inaccurate. There is no difference between the inductance L2, for example, 1.5 mH and 1.27 mH in terms of resistance.

LF: I’ll give you my parameters for a large coil (it also has “ears” on the sides): inner diameter of the ring: 35mm, outer: 70mm, coil height: 37mm, width of the winding area (height without sides): 30mm, wire thickness (copper, enameled ): 1mm. With these parameters, the DC coil resistance (measured with a digital tester): 0.8 Ohm.
If these parameters are observed, you should get an inductance in the region of 1.0-1.6 mH, congratulations :).

You can wind the coil the “old fashioned” way, knowing how many turns you need to make. This has recently become known: for 1.27 mH, 210 turns of “manual” (not very neat) winding are required. In this case, for every 0.05 mH there are approximately 5 turns.

SC: The small coils should all be the same in frame; I took the one with the smallest inductance. Inner ring diameter: 12mm, outer: 32mm, coil height: 23mm, winding area width (height without edges): 18mm, wire thickness (copper, enameled): 0.5mm. Resistance: 0.7 Ohm, inductance 0.18-0.21 mH.

At 0.18 mH the number of turns is 127 pieces. At 0.21 mH - 136.

By the way, do not repeat the mistakes of the USSR assemblers, do not fasten small coils with screws inside - the inductance will change and nonlinearity will be added; attach with glue.

For those who measure themselves: it is useless to try to rewind a small coil with a thick wire from a large one, and you probably want to do this :). Even having completely wound the entire frame, I did not get an inductance of more than 0.1 mH.

At the same time, if you build a new optimal frame (see links, “Cec”), which is not as simple as it seems, then the coil’s own resistance will allow you to gain 1 dB to the speaker sensitivity - you will need to slightly calibrate the sensitivity resistors in front of the speakers.

If you try to find the same large frames somewhere else and wind the L1 coils with thick wire, then their resistance will be approximately 0.4 Ohm - also better.

p.s. I kindly ask you not to write me letters asking for help in calculating inductance on other frames and other values ​​using this method. Assemble the “box” (see links), it is very easy and will solve all your problems with precise winding of coils.

capacitors

Everything is extremely simple. You need to find the same values ​​for decent quality capacitors, you can read about the types here, and about resistors there, by the way. Capacitors can be combined (summed) in parallel (as well as reduced according to the resistance rule by connecting in series). If you have disassembled the s-90 filters, then you should already have a good set of necessary containers :).

Among the domestic ones, instead of the film K73-xx that you probably came across, I recommend trying the metal-paper MBxx - a “softer” sound. If you have the funds and availability, it is advisable to use foreign MKP (1uF ~ $1.1, domestic equivalent - k78).

The capacitors, of course, are non-polar and for a voltage of at least 40V. The quality of the elements in Zobel circuits is just as important.

Here you can experiment with changing the “color” of the system that the capacitors give. I recommend trying to bypass all capacitors (except those in the Zobel circuit) with small (around 0.1 µF) capacitors of other, usually higher quality, types. For example, polystyrene (k71-7) or mica (SGM) - the result is more detailed sound at mid-high frequencies and increases the transparency of the system. In addition, metal-paper (MBxx) capacitors give a slightly “muddy” sound. To bypass means to combine together in parallel :).

resistors

With a power of at least 2W, with less, overheating and a change in rating are possible. Among the domestic ones, MLT-2 can be used. PEV-10 from the s-90 kit are not the best, but they will reluctantly go... I recommend Chinese ceramics - they look like white teeth, they are large, they are inexpensively sold everywhere in radio stores (power up to 15 W), but the range of ratings is fully present.

In other matters, low-power MLT resistors also work well at non-disco power levels, at least in place of R1.

Please note that the value written on the resistor is not necessarily the same as what it actually is. I strongly recommend selecting resistors by measuring them with an ohmmeter/tester. The diagram shows clearly measured resistors.

When finalizing the speakers, it is highly recommended to place resistors R1 and R2 as close to the speakers as possible - directly on the terminals. This will greatly reduce the influence of the cable (which is after these resistors, but not before them) on the sound.
Zobel chains

The reason is that the impedance of the speaker is not constant and increases as the frequency response decreases. This effect occurs in all dynamic type heads without exception, regardless of the country and year of production. More precisely, the Zobel circuit (in my filter only a simplified version of it is used; full ones allow you to adjust the impedance at low frequencies, which is not always necessary) is necessary for the normal operation of the filter inductors, with a sufficiently large self-inductance of the speaker coil. Without a Zobel circuit, the operation of the inductor as a low-pass filter is grossly disrupted and filtering is practically not carried out at all (!).

LF: Elements R4 and C4. It is advisable to set C3 to more than 60 µF, but even this is sufficient for a crossover frequency of 500 Hz. R4 is equal to 4.3 Ohm.

Compare the ICHH of 30GD-2 without and with Zobel. The graphs are approximate, but there you can see the tuning frequency of the s-90 bass reflex - the second huge rock on the left, before 100Hz :).

SC: ICHH 6gdsh-5. You can try smoothing above 3 kHz with Zobel R3, C3. For this, 10-20 µF and an 8.0 Ohm resistor are enough.

Important: a Zobel circuit on the midrange is required for the normal operation of this crossover. Without it, the “new lightweight filter” showed its complete inconsistency in the midrange and high frequencies.

HF: Due to the low inductance of the speaker's own coil and the cutoff at low frequencies, the circuit is irrelevant.

filter

In all frequency sections, a passive all-pass filter of the first order is used with an attenuation of 6 dB per octave (frequency change by a factor of two), Butterworth approximation. Actually, the filter itself was calculated by the JBL Speaker Shop program and slightly adjusted manually :)).

LF: Low pass filter. As you can already understand, the cutoff frequency is 500 Hz (for 30GD-2/75GDN-1-4, lower is desirable, but was chosen as a compromise to 6GDSH-5). Provided by element L2, speaker load, coupled with a simplified Zobel correction circuit.

Midrange: Bandpass filter. The lower part (C2) is matched with the low-pass filter and is tuned to a cutoff frequency of 500 Hz based on considerations of the resonant frequency of the 6GDSh-5. The upper part (L1) is matched with the high-pass filter and is tuned to 7500Hz, which allows for a broadband speaker structure, coupled with Zobel.
Both parts are loaded at 8 ohms (4 ohms from 6GDSH-5-4 + 4 ohms from R2).

HF: High pass filter. The frequency is matched to the upper part of the midrange filter and operates at 7500Hz, which avoids problems associated with the high frequency of the main resonance of domestic high-frequency speakers. Load 21 Ohm (16 Ohm speaker + 5 Ohm from R1).

All speakers are switched on in phase, which has a lesser effect on the phase characteristics of the system.

scheme

Electrical circuit diagram. Click to enlarge :).

The arrow on the right shows the “sound input” from the amplifier. The dotted lines are bi-wiring (the low-pass and mid-high-frequency filter sections are connected to each other in parallel at the amplifier - plus the low-pass with the plus of the mid-range and high-frequency to the plus of the amplifier, the minuses are the same).

The gray numbers in brackets above the filter elements indicate their load. The gray numbers with an "r" in front of them are the element's own resistance. Gray marks -1dB - loss of speaker sensitivity on the elements.

Next to the speakers, their important characteristics are briefly written out; below are the frequencies at which the bands/links intersect.

Inductance in mH, capacitance in µF, resistance in Ohm. After assembling the filter, the nominal speaker impedance for the amplifier remains equal to 4 Ohms.

A version of the “new lightweight” filter for s-90 clones, more precisely for Orbit 35AC-016. Speakers: 10gdv-2-16, 6gdsh-5-4, 75gdn-1-4 - a fairly common set.

This page contains diagrams of Radiotehnika class S90 speaker systems (35AC-212, S90, S90B, S90D, S90F, S-90E), detailed descriptions, speaker parameters, photographs.

Quite high-quality acoustics from Soviet times, after minor modifications and restoration, I can say with confidence that it will give a head start to many modern acoustic systems.

If you have similar ones lying around or bought them somewhere cheap, then put them in order and they will delight you for a long time with powerful bass, rich mid and high frequencies in musical works of any style and direction, in general I RECOMMEND!!!

Acoustic system S-90 (first model)

Rice. 1. Appearance of Radiotehnika S-90 speakers.

The speaker system has two step playback level controls separately for mid and high frequencies in the ranges from 500 to 5000 Hz and from 5 to 20 kHz, respectively.

Both regulators have three fixed positions: “0”, “-3dB” and “-6 dB”. In position "0", the signal from the crossover filter is supplied to the corresponding head directly. In the “-3 dB” and “-6 dB” positions, the signal is weakened relative to the “0” position by 1.4 and 2 times, respectively.
With the appropriate spectral composition of the program, switching the regulator changes the timbre coloring of the sound.

Passport technical characteristics of S-90:

Rice. 2. Schematic diagram of acoustic speakers S90 35AC-212.

Acoustic system S-90 35AC-1

Rice. 3. Speaker system Radiotekhnika S-90 35AC-1, appearance, photo.

Rice. 4. Schematic diagram of the Radiotehnika S90 35AC-1 speaker.

Speaker system Radiotehnika S-90B

Rice. 5. Appearance of speaker systems Radiotekhnika S-90B.

Speaker system S-90D

Rice. 6. Appearance of acoustic speakers Radiotehnika S-90D.

The speakers have an indication of speaker head overload. The controls located on the front panel of the speaker make it possible to smoothly adjust the sound pressure level of the high-frequency and mid-frequency loudspeaker heads within the range from 0 to minus 6 dB.

There is also a model of the speaker system "S-100D", it uses a mid-frequency head 30 GDS-3 with MAHID magnetic fluid, which allows you to increase the rated power of the speaker system to 100 W. Otherwise, the designs of "S-90D" and "S-100D" are similar.

To operate, the speakers must be connected to an amplifier that has the highest (maximum) power at the output of each channel, ranging from 50 to 150 W.

If the OVERLOAD indicators start to light up when the speaker is operating, then you should reduce the level of the input signal supplied to it (by using the volume control in the amplifier to which the speaker is connected).

S-90D technical specifications:

The picture below shows

11-01-2009

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

Radiotehnika 35AS-012, Radiotehnika S-90, Radiotehnika 35AS-012, Radiotehnika S-90

Currently I am the proud owner of Radiotehnika S-90 speakers.

Consideration of acoustics in normal condition

First, you should specify the full name of the acoustics - 35AC-012. From their number it immediately becomes clear that we are dealing with top-class acoustics, by Soviet standards, that is, with acoustics that have very high characteristics. It should be noted right away that by Soviet standards this was not the best acoustics, but an ordinary ordinary workhorse. There were acoustics that had a more balanced sound, for example the same Cleaver/Corvette 35AC-008.

But as they say, we have what we have. Let's go back a little to the moment of their purchase. I bought them from a friend of mine for $50, when I came to him, when I saw the decorative grilles protecting the sound-emitting heads, I wanted to cry, they were dented and, at that, very cruelly (mainly the grilles of the high-frequency and mid-frequency speakers were damaged). But this didn’t scare 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 like 5. In general, I took these speakers to my home. When connecting them to an amplifier the sound was quite decent. But nevertheless, two drawbacks should be noted, 1 of which is inherent in all 35AC-012, and as it turned out, in all its 35AC clones, to one degree or another.

The first of the shortcomings that simply killed me on the spot was an incomprehensible overtone when the woofer was working, very similar to the fact that something was stuck to the speaker from behind, and now it was vibrating, as it turned out later it was a drop of solder that stuck to diffuser from the reverse side. 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 lie 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, the rated power is indicated (from the audio engineering course:

1. The rated power of the speaker is the power of the speaker, when supplied, it operates with harmonic distortion levels not exceeding the permissible
2. Nameplate power (often also called noise): 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 begins to resonate at high volumes and thereby spoils the sound picture, and as you know, the mid-frequency speaker is crucial in the formation of the sound picture.

Let us now consider in order all the speakers that we have in stock:

1)Low frequency - 30GD2, also known as 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. The loudspeaker head is of electrodynamic type, low-frequency, round, with an unshielded magnetic circuit. The diffuser holder is made by injection molding from aluminum alloy. The cone diffuser is made of impregnated paper pulp. The suspension is toroidal-shaped and made of rubber. The centering washer is made of impregnated fabric.

I would also like to add that the speakers have a relatively heavy dome and a rubber surround, which spoils the quality of the bass; it becomes less continuous and booming than speakers with a lighter moving part and a foam surround. But it should be borne in mind that the bass is influenced not only by the design, but also by the acoustic design itself; for this reason, these problems can be eliminated a little 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 indestructible, while the foam suspension soon crumbles due to the presence of sulfur in the air and the speaker requires repair.

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. The loudspeaker head is of electrodynamic type, mid-frequency, round, with an unshielded magnetic circuit. The diffuser holder is made by injection molding from aluminum alloy. The conical diffuser and spherical cap are made of impregnated paper pulp. The toroidal-shaped suspension is 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 significantly distorts the sound, but as practice has shown, this problem is very easily solved and, at that, quite simply.

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

In general, they sound good, but the filters are tuned close to the 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 it. 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 anyone interested, here is the acoustics diagram:

Revision 35AS-012

I will describe in order all the stages of improvement that my speakers 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 accessible to children (if any) and other family members. We lay the speaker system on its back and begin to disassemble it.
• Now remove the decorative covers from all the speakers and put them aside.

Here they are:

Then we take out the speakers. ATTENTION: when unscrewing the bass speaker (the treble and midrange speakers are secured with the same screws as the decorative trim, and the woofer is mounted separately from the trim), be extremely careful, because if the screwdriver comes off, you will disfigure it. Then we use a soldering iron to unsolder the wires connecting the filter and the speakers, and safely hide the speakers in a secluded place.

• We remove the bass reflex cover and take out the bass reflex 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 let's take on the regulator/controllers of the HF/MF sections. To dismantle them, you need to remove the decorative plug in the center of the regulator, then unscrew the exposed screw and remove the regulator handle. After this, carefully pry up the remaining plastic lining using two chisels and carefully remove it, then unscrew the 4 screws securing the attenuator itself and now it can be pushed inside the case. We push it out and unsolder it from the filter. We put it aside, in the future you will need to work a little magic on it. By the way, the joint between the attenuator body and the speaker body is generously covered with a viscous sealing substance; I personally reused it when putting it back into place, but you can use sealant or plasticine.
• We take out the cotton wool bags that are supposed to be in your speaker system and set them aside.
• We dismantle the panel with filters; it is screwed to the body with screws, having previously unsoldered the wires from the output at the back of the speaker system. We put it aside, since we will spend a lot of time working with them.
• Finally, remove the terminal panel from the back cover of the speaker and set it aside.

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

2. Restoration of appearance:

For this purpose, we take the grilles and covers from the speakers that we removed earlier, level them, carefully sand them, degrease them and paint them in several layers with car paint (which is in spray cans) several times and leave them 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 simplest solution would be to abandon the grilles as such, since they only introduce disadvantages into the sound, think for yourself.

3. Refinement of the speaker system housing:

Here everything is actually very simple, and is carried out in several stages:

• If desired, the body can be strengthened. What will this give us? Clearer and smoother bass, since the cabinet panels will vibrate less and, accordingly, will introduce less overtones into the bass component of the sound. How to do it? This is purely a matter for everyone, since as many people there are as many decisions. In general, it all consists of installing spacers, installing additional corners at the joints of the walls of the speaker system, and installing stiffeners on the walls of the speaker. Personally, I limited myself to gluing in additional corners at the joints. You can also tightly glue all joints. Unfortunately, I can’t show you a photo since the entire speaker system is already damped with foam rubber.
• Sealing all joints and seams. It is done very simply using various materials. For example, I used plumbing sealant. The procedure is simple: cover the joints with sealant and carefully smear it with your finger, thereby tightly sealing any cracks.
• At a hardware store we buy foam rubber 10mm thick (personally, I chose this thickness, don’t take too much as it will suffocate the body) and glue it to all the walls except the front. In this way we dampen the body, thereby increasing its virtual volume.

To do this, we buy terminal blocks with gold-plated universal-type connectors in the store. Since the S-90 terminal block itself is large, and the new ones are small, we remove the connectors from the terminal blocks and install them on the body of the S-90 terminal block. Then we lubricate the installation area with sealant (don’t be sorry, wipe off the excess later) and put it all in place, tighten the screws. Here's a photo of what you should get:

5. Let’s move on to reworking and replacing the filter:

• First of all, carefully examine the filter, pay attention to the fastening of the parts, since often the inductors were fastened with metal screws, which immediately disrupts the filter settings.
• If there were problems with the fastener, complete it by eliminating metal parts from the fastener. There are also cases of assembling the filter on a metal plate, then transfer the filter to a plywood panel.
• We pick up a piece of paper, a pen, and carefully redraw all the elements of the circuit, restoring, so to speak, the filter circuit itself, because the parameters of the speakers were wrong and for this reason the filter circuit could have been changed at the factory. By the way, we exclude the attenuator from the circuit, it simply spoils the sound.
• Now we take 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 a cable made of oxygen-free copper 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 buy a very expensive cable, as the changes in sound quality will be insignificant, but the costs are simply colossal.
• After assembling the filter, we solder the wires that will go to the speakers based on: for the low-frequency link 4 mm 2, for the mid-frequency link 2.5 mm 2, for the high-frequency link 2 mm 2.
• We put the filter in place, and then 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, secure them and cover the filter with foam.

You'll end up with something similar to these photos:

6. Attenuator installation:

• We remove all resistance from it.
• Let's put it in its place.
• We carefully seal it.
• Additionally, we cover it with foam rubber (I only covered it on the front wall)
• We install all the decorative panels completely.

7. Installation of the bass reflex:

Everything is simple here, we put it back on the sealant, carefully make sure that it is not pinched anywhere by the foam rubber, as this will throw off its setting.

8. Reinstall the bass reflex cover:

We install it the same way as we removed it, just install it with sealant and new screws, since the panel itself often rattles in the bass. Seal the joint between the panel and the bass reflex well.

9. We proceed to installing the dynamic heads in place:

• A) Install the HF head:

1) We remove the travesty of the seal that is on it (some kind of rubber or cardboard at the back).
2) Cut out a new seal; a mouse pad, in particular a black porous base, is perfect.
3) Solder the wires to the speaker and install it in place.
4) Put the decorative trim (grid if desired) in place and tighten it tightly with the screws.

• B) Install the midrange head:

1) We make a cylinder from foam rubber, such a size that our box will fit into it. We place this cylinder inside the speaker and pass a cable through it, which we take out.

2) Pass the wire through the box (most likely you will have to widen the hole), then 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 damping the mid-frequency head. To do this, we sew a cylinder of foam rubber, such a size that it fits tightly onto the speaker frame and covers all the windows.

5) Fill the box with cotton wool, having previously fluffed it.
6) Put the dynamic head, grille (optional) and frame in place and tighten it.

1) First, put back the bags of cotton wool that were removed during 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 window of the diffuser holder.

2) We make a gasket from a porous material, for example
Apply window seal and carefully place the speaker in place.
3) Tighten the mounting screws. Do not apply much force, then the speaker will be spring-loaded by the gasket and this will reduce the energy of vibrations transmitted to the body.
4) Put the grille (optional) and decorative trim in place. If you do install a grille, then I advise you to cut out small triangles from foam rubber and place them on the speaker at the place where it is attached; this will eliminate the vibrations of the grille, and therefore eliminate overtones at high volumes.

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

Conclusion:

After the modification, all the listeners (there were not many of them, about five people, but I asked for the most honest information from them) noted more delicate and soft bass, a much cleaner middle, the highs remained practically unchanged (it seemed to me that they became a little cleaner). Also, the acoustics began to calmly reach 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 be modified or changed several times. For example, instead of foam rubber, you can use felt (natural), this, in theory, will give better results than foam rubber; it is also a good idea to use vibrating mastics. Many people advise replacing the 15GD-11A with a 5GDSH broadband receiver; in my opinion this is a bad idea, but that’s everyone’s business. 10GD-35 - it is recommended to treat it with a notch filter, 15GD-11A should be modified based on halves of a tennis ball (by the way, the idea is quite interesting, I haven’t done it myself since I don’t have such speakers in stock).

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Who doesn’t remember the famous S-90 speakers from the 70s? (In fact, there was a Latin letter S, and therefore this Riga product was called the Radiotehnika S-90 speaker system, but the habit of not trusting anything foreign also came from this time, and then not everyone knew that the Balts use the Latin alphabet.) Dance regulars in the club (called discos in the 80s) they didn’t go into such details, and therefore they still call these speakers S-90. This article will be devoted to the literally legendary acoustics of Soviet times.

Nostalgia

"Radio Engineering S-90" was considered one of the best systems of that time and was in demand everywhere. Concerts in cultural centers in the most remote corners of our country, amateur performances, school evenings with songs and dances - everywhere this equipment was indispensable. Some irresponsible comrades risked conducting rehearsals at home, and the S-90 speakers created an unforgettable sound effect in absolutely all apartments of the five-story panel building. The “gratitude” of the neighbors was also indescribable. They can be understood. Even if the owner “turned up” the medium volume, extraneous sounds simply evaporated: the howling of dogs, the knocking of neighbors on the radiators, as well as the sound of sluggish bass from ordinary speakers two floors above disappeared.

The "Radio Engineering" column heralded either an approaching earthquake or a military fighter jet touching the roof in a low-level flight. The chandeliers bounced, the crystal in the sideboards tinkled subtly, and everything in the room that was not secured was clearly vibrating. Although it must be said that the S-90 speakers were not and were not considered the most powerful in their class, an amplifier was installed to them. By the way, working versions of this equipment are in great demand today. Even heavily used retro equipment is quite expensive. A “Radio Engineering” column of any modification in working condition will cost from four thousand rubles. One!

Description

The Radiotekhnika acoustic system of the highest (zero) class 35 AC-1 went on sale in 1977 and was immediately named S-90. The speakers had the best characteristics for those times, especially considering that only Soviet equipment was used. They were developed purely for domestic use, and this was done by the Orbita design bureau at the Riga Radio Engineering Production Association. Subsequently, the entire series of these acoustic systems received the S-90 brand.

The speakers fully justified their characteristics; they were in no way inferior to imported ones, significantly surpassing all domestic ones. In order for the sound of the acoustic system to be complete, an amplifier of the “Electronics” or “Amphiton” type must be connected to it. In the frequency range from 31.5 to almost 20 kHz, the speakers operated with a nominal power of 35 Watts. Moreover, the power in the passport was ninety. The sound pressure, the results of which are described above, was 1.2 Pa.

About the disadvantages

The weight of one column sometimes exceeded thirty kilograms. They cost three hundred rubles per pair (an engineer earned from ninety to one hundred and twenty rubles a month). However, few have seen them on sale for free. Many people bought S-90 music speakers one at a time, despite the fact that there was no guarantee that buying a second one would make them a well-tuned pair. However, even if a pair was purchased, no one guaranteed its balance: for example, the right speaker of the S-90 collected all its power together and persistently sounded louder than the left. This is despite the fact that the equipment was positioned as having the highest category of quality.

This drawback is not the only one that the S-90 column could have. Tweeters often failed because the thin and weak wires themselves were not very practical. At mid frequencies the sound was downright bad and often spoiled the whole impression. Other electronics could not withstand the sound system next to these huge structures, and the magnetic field created by the speakers had a negative effect on humans. And yet, it was the S-90 that could ideally create surround sound in an ordinary apartment of a standard panel house. In general, there were no special complaints about the sound.

Installation

The shortcomings that the Soviet S-90 speakers had did not stop music lovers throughout Rus'. For several decades they remained one of the most popular acoustic systems. Many thousands of pages on forums are dedicated to them today. This is one of the most striking symbols of a bygone era, which also had reliability and durability, which modern gadgets do not have at all. The S-90 speakers had impressive dimensions (36 x 71 x 28.5 cm), so they required proper installation, which was not always combined with the capabilities.

The apartments were quite cramped (and the conditions are the same now), and therefore you could see the speakers half a meter from the listener. While the ideal way for better sound is to place them on a pedestal just half a meter high and maintain a distance of at least two meters from the listener’s ear. Rarely does a room have such advantages; most often the required space is not enough, and therefore only the neighbors listened to the real sound that this equipment was capable of.

Appearance

The S-90 speaker has a simple and well-made body - a non-separable rectangular box made of chipboard, trimmed with high-quality veneer from valuable wood. The wall thickness is sixteen millimeters, and the front panel is made of twenty-two millimeter aircraft multilayer plywood. The joints of the walls and internal sides are reinforced with special elements that increase the rigidity and strength of the body.

The heads have decorative black frames stamped from aluminum sheet. They are also protected by a metal mesh. On the front panel, the mid-frequency head is insulated inside with a cone-shaped plastic casing, the low-frequency head is located along the vertical axis. At the bottom of the column there is an overhead plastic panel with a nameplate. There is also a hole 100 x 80 millimeters - this is the bass reflex output. The amplitude-frequency response (AFC) is displayed on the nameplate, all curves correspond to the positions of the regulators. There is also the name of the speaker system and the brand name. The above-described frame with fabric is attached to the front panel with bushings. On the bottom rear wall there is a block with terminals.

Inside

The internal volume is filled with a sound absorber made of technical cotton wool, covered with gauze. In this way, the influence of sound pressure on the frequency response is reduced and a better sound quality of the speaker is achieved by eliminating resonances in the internal volume. Inside the case there are electrical filters on the board that separate the strips of the speaker system. The kit also included four plastic feet designed to be attached to the base of the cabinet, as well as a decorative removable frame with knitted fabric that adds acoustic transparency.

A rare acoustic system of those times has such qualities as the S-90 speakers - the sound power is simply off the charts! But at close to the maximum volume, low frequencies become inaudible and booming, and the highs begin to click - this is a characteristic feature of the 6GDV-1-16 high-frequency drivers. A little later, when similar products began to go on sale - “Amfiton 35AS-018”, “Orbita 35AS-016” and others, a different head was used. Sometimes analogues of this speaker system provided a deeper and more balanced sound than the original S-90 speakers.

S-90 line

All modifications of the S-90 and even all its analogues were certainly aimed at using cassettes. The high-frequency head reproduces sound quite well in the upper frequency range thanks to the cassette deck and Soviet amplifier. But if the lower and middle parts of the high frequency range are reproduced just fine, then the very top is different from them, and therefore receives criticism for allegedly blocking the frequency response and unevenness.

And the “Orbita” column from the S-90 line of the Moscow plant turned out to be a truly worthy alternative to the Riga “Radiotekhnika”. This modification with a similar set of acoustic heads differed only in the presence of a two-tube bass reflex at the very bottom of the body. As a result, the bass became lower and thicker. However, at high power, problems with hum and inaudibility persisted, and the upper frequencies clattered in exactly the same way as with the Radiotekhnika S-90.

Manual upgrade

Many music lovers finally realized their own dream: they bought the legendary S-90 speakers and began to modify them with a file. The solution is budget-friendly, exciting, and then the sound is the envy of everyone. Over the past thirty years, the outside of the speakers, of course, has lost its former chic in almost a hundred percent of cases, but the main thing here is that no one messes with the inside. You need to start working by enriching your arsenal with tools. You will need a basic set of screwdrivers, pliers, and a soldering iron. The first step is to remove the front panel, for which you need to unscrew a dozen or two different screws.

When disassembling, it is necessary to check whether the filling corresponds to the passport. So that at high frequencies it would be 10GD-35, at medium frequencies - 15GD-11A, and at low frequencies, for example, 35GD (well, or whatever is stated in the passport). Speakers are most often damaged, since it is possible to destroy equipment within one day, and even more so in thirty years. For example, a lot of furniture rearrangements and moves could happen. Most likely something is damaged. For example, a woofer. Resuscitating him will require additional work. You need to rewind the reel. In principle, this is not so difficult if you know some of the subtleties and have encountered the rewinding process at least several times before. After winding, centering and drying, the sound of the speaker will be perfect - all extraneous sounds will disappear.

Domes

S-90 speakers, as everyone knows, most often disappoint with the sound of high frequencies - with overtones. And at mid frequencies there is often no ringing. Craftsmen recommend basically the same thing: replace the midrange, treble and dampen the body. But it’s better not to look for easy ways. The speakers are simply covered with plastic domes. This material is completely unsuitable.

Silk domes will remove overtones and make the sound more transparent. Therefore, the speakers can be safely replaced. While one speaker is being upgraded, it is necessary to test the sound and compare it with the one that is just waiting for the upgrade, that is, with the original one. Then it becomes absolutely clear whether to leave the rework or return everything as it was. The main thing is that the owner of the speakers and golden hands also has good hearing.

Wiring and housing

To improve the sound of low frequencies, the housing needs to be modified. Down with cotton gauze mattresses! Stores sell inexpensive batting that makes an excellent filling pad. And for just over a hundred rubles! All this can be done quickly and without any effort: the width of the batting is two meters, enough for two columns, but you will need a furniture stapler or a friend who has one. Before installation, just in case, it is better to change all the wiring and remove the switches. Cut out the batting in two layers and boldly sheathe the body.

The bass reflex pipe is placed on the sealant, and after that it is also covered with batting. There is also not much work to do directly with the filter. The switches will never be needed, so they can be removed, like all unnecessary elements from the board. Replace all these thirty-year-old thin wires with normal copper ones at all connections. Next, the filter, freed from everything unnecessary, must be carefully installed in the housing and covered with batting. The entire midrange box on the outside should also go under the material mentioned above.

Results

Judging by the reviews of home craftsmen, such simple modifications have changed the sound of the equipment for the better simply beyond words. The bass became clear, the top became transparent and light. After replacing the speaker, the vocals sounded completely different in the midrange.

Actually there are four ways, not three. But we will not describe the first way - throw it away. We have plenty of stuff in our dacha and garage...
The main disadvantages of the S-90 series speakers.
1. Small housing volume for the woofer. The consequence is a muttering of low frequencies.
2. The bass reflex is designed for a frequency of 20 Hz. The consequence is large low-frequency distortion.
3. Worthless midrange speaker. The consequences are disgusting midrange and 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 unit, the filter must be changed.
6. The body is not rigid enough and is not “damped”. Consequences - vibrations, overtones, "barrel".
7. Etc. and so on. ...

We study and dare

While drinking beer, we reach three truths. There are three ways:
1. Lightweight and effective.
2. Medium difficulty. More shamanism and snobbery. Some sound improvements compared to point 1.
3. Super complex, time consuming and super efficient. In reality, you are trying to make new speakers. It all depends on the quality of workmanship and musical flair. If nothing works out, then no one promised you anything. I'll describe everything. I recommend the 1st way to start. Its value is that it does not take much time, you leave all the components of the speakers. Minimum of scarce parts and costs.

ATTENTION! ATTENTION! ATTENTION!

1. When carrying out all work, ensure that the phasing of the speakers is correct. If you have not encountered this yourself, invite a specialist - electronics!
2. Remaking the speaker 15 GD - 11A is an irreversible process. If you are not careful, the speaker has one path - to the trash can, and you have another - to the market.

The first way. Lightweight and effective

1. Mid frequencies are the main emphasis. By reworking the speaker, we will make it work in piston mode, increase the upper limit frequency, remove overtones, increase sensitivity, improve directivity, and dampen it.
2. Let's move the speaker to the range from 31.5 Hz, instead of 20 Hz. There will be less muttering.
3. Suppress the resonance of the high-frequency head.
4. Let’s calm down the sounds of the building

We buy a Soviet tennis ball from a store. Chinese and others are not suitable. They have different material. The ball should be exactly the same as in distant childhood for 8 kopecks. As a last resort, you can take it from friends or in the tennis sports section. We buy epoxy resin (a little, maybe 1cm 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 saw the ball in half along the seam. The seam is visible to light. It is overlapped and 1 - 2 mm wide. You need to cut in the middle of the seam. I sawed with a Nev blade, having previously made notches on it with a sharpening stone. After sawing, align the cut line on sandpaper and sand the outer surface of the ball with fine sandpaper. If there are large deposits inside the seam area, then they also need to be removed. When working, the ball must be secured with plasticine on a Mars battery (a film case, a jar of fish food, etc., according to your imagination) at three points. It's enough. Plasticine is removed later either with a dry cloth or by wiping with gasoline. Once the surface of the ball has been treated, do not touch it with your hands. Grind the pencil leads on sandpaper. Dilute epoxy resin 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 and shake off excess. It is necessary to ensure that the white plastic of the ball does not show through the graphite. If it shows through, it means the layer of epoxy resin was small. Need to add. Once everything is done, let it harden.

Assembling a 3 KHz filter. 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 adjust the inductor to it. In order not to bother your head with unnecessary formulas, the simplest thing is that the product of the capacitor capacitance 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 inductance of the coil is 2.82: 6.6 = 0.43 mH, (the winding contains 150 turns of PEV-1 0.8 wire , wound on a frame with a diameter of 22 and a length of 22 mm with a cheek diameter of 44 mm). Using 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 attach the capacitor and inductor to a piece of fiberboard and solder one terminal of the coil to the terminal of the capacitor. We solder wires 40 -50 cm long to the free terminals.

Let's disassemble the column. We remove the low-frequency speaker, the mid-frequency speaker, take out the glass from it, remove the high-frequency speaker, remove the decorative trim, remove the phase reflex (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 mid-range speaker head with hard glue. You must ensure that there are no un-glued gaps 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 driver. Leave to dry.

We screw a homemade filter onto the back wall of the speaker (inside) opposite the tweeter. Solder the wires from the filter to the output of the high-frequency speaker. Which one goes where does not matter. We remove the connectors from the back wall of the speakers and solder the wire going from the amplifier directly to the filter. We saw off 10 cm from the phase reflex pipe with a hacksaw along the center line. We wrap the phase reflex pipe and the mid-frequency speaker glass with a layer of gauze and bandage it. It is necessary to check whether they will enter their nests after this procedure. If they do not fit, then reduce the layer of cotton wool and gauze. We check if there is cotton wool and gauze in the glass. Add if it’s not enough until it’s full. We dampen the mid-frequency speakers. To do this, we additionally cover their diffuser holders with foam rings made from 10x27x355 mm blanks. the ends of which are glued end-to-end with Moment glue. We cover 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, wrapping it around the wire. It is convenient to secure the bandage with threads. Assembling the column. We coat all the perimeters of all speakers with plasticine. There is no need to wear protective nets, but only on the condition that there are no small children, the wife will not come in with a mop or vacuum cleaner, and that the speakers will not be transported. Turn on the speakers. We don't know right. We call our friends. Please bring your favorite recordings. Let's listen. We calm our friends down with beer. We note with mockery how useful the bucks spent on purchasing foreign rubbish would be to them.

The second way. Medium difficulty

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

1. Let’s improve the properties of the body and eliminate overtones and “barrel”
2. Let's achieve better signal transmission
3. ?

So, let's go. Strengthen the rear wall of the case by placing two slats with a cross-section of 3x2 cm vertically along the entire length at a distance of 15 - 20 cm from each other symmetrically, and attaching them with screws to the rear wall. Pre-treat the mounting area with epoxy. It is necessary to take into account the possibility of installing a phase reflex later. Between the rear 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 wall joints and corners from the inside with silicone glue such as "Bison" or plumbing silicone putty. We cover the entire body inside with felt (batting, padding polyester, etc.). It should not be thicker than 1.5 cm, so as not to greatly reduce the internal volume of the case. We reject all proposals to replace 15 GD-11A with 6 GDSH-5. Ours is already “cool”, and such a replacement will lead to a loss of power, a decrease in the dynamic range (very dangerous) and you will have to greatly change the filter. So, when replacing 15 GD - 11A with 6 GDSh-5 for 35AS - 212, you will have to replace the following parts: L1 - 0.22mH, C2 - 1.0mF, C8 - 0.5mF, L4 - 0.1mH. New parameters have been specified. When using 6 GDSH - 5 - 4, you will also have to install an additional resistance in the circuit of this head at 4 Ohms. The appearance of the column also changes. Well, if you really want to, then you can. Further. Removing tone switches. Remove unnecessary resistors R (1, 2, 4, 5, 7, 8, 9, 11, 12). We replace the wires on the filter mounting with a copper wire with a diameter of 1.2 mm. We replace the wires going from the speakers to the filter with more traveling ones. For the low-frequency speaker - multi-core - with a cross-section of 2.5 - 3 mm square, for the mid-frequency - 2.5 mm square. For high frequency - 2 mm square. - single-core. All wires are soldered to the filter directly, rather than passing through 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 regulators are removed. In their place, we make wooden (chipboard, plywood) plugs according to the thickness of the body. We pour them onto the epoxy and sand them down. We cover the front panel with self-adhesive wood-look film to match the veneer of the speakers. Installing speakers. Low-frequency and mid-frequency through rubber gaskets. Suitable rubber from window insulation, thin rubber medical hoses, silicone hoses (worse). We treat the installed speakers around the perimeter with plasticine or non-hardening window putty (it resembles a bar of laundry soap and is cheap). Checking the sound. We're just fooling around. We push aside all sorts of “Pioner”, “Technics”, JAMO and ...

The third way. Super complex, time consuming and super efficient

It’s a good idea to have the following instruments: an oscilloscope, an audio frequency generator, a digital multimeter, an LC meter. A person who does not do repairs and assembly at home, of course, doesn’t have all this, but there is a way out - go to the workshop and ask to try on what you need, taking filters, heads, etc. with you. If they ask for payment for this, it will be purely symbolic. You can even order a filter. It will, of course, be more expensive.

Begin. We take as a basis 35AC -212 with dimensions 710x360x285. It is desirable that the case be made of plywood, a woofer with a rubber surround, and a high-frequency speaker with a fiberglass dome. Let's sort everything out. We no longer need the midrange speaker. The housing needs to be increased to 100 liters for a woofer with a rubber surround. 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 in order to later use it for a matrix for the holes for the speakers in the newly manufactured 100 liter case. The remains of the buildings make good boxes for potatoes and markoshka in the cellar.
2. You can try to build up the old body. In the first case, you need to focus on the dimensions - 1100x360x350 and production in a furniture workshop according to your drawings, with abuse and quibbles about quality. We will consider the second way.

So, you can try to get by with little blood. 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. We cut out identical holes approximately 270x210 in the bottom of the column and in the lid of the box. We cover the inside of the box with felt. After assembly it will be impossible 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 bolt heads should sink into the countersunk area. Add a little bit of shot - 10 kilograms of shot won't hurt, throw a gauze bag with cotton wool on top. We pre-fill the joint with epoxy with a normal content of hardener. We cover the joint with felt. The rest of the body movements are the same as in paths 1 and 2. Let's take the mid-frequency head 30 GDS - 1. You just need to check them - there are a lot of defects. Purely mechanical properties. Further. We measure f resonance of all speakers. You can use a felt-tip pen to sign directly on the magnets so you don’t get confused and try everything on again. It would be good if the resonance frequency of paired speakers did not differ greatly. If the speaker produces extraneous sounds at any of the sound frequencies, then it must either be cleaned or replaced if cleaning did not achieve normal operation. We calculate and make filters for our case. The fewer inductances, the better. We continue to work with the body. Remove excess resin at the joint. Let's polish 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 fastenings of the speaker connectors. All wires are branded audiophile ones. Choose your own price category. There’s just no point in taking very expensive ones. It is better to convert the bass reflex to a frequency of 31.5 - 40 Hz. If the dome of the high-frequency head is made of lavsan, then, after removing the crosspiece, you need to coat the suspension and the outer third of the dome with perchlorovinyl. We cover the entire body with 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.

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