The wiring diagram in the romance amplifier at 101. A complete rework of the Radio Engineering U101 amplifier. Checking the health of the output transistors
Amplifier of radio engineering at 101— so I decided to try to write an article about the alteration of the amplifier. Well, I'll probably start with its history, namely why I decided to completely redo it. Firstly, everything is old, does not correspond to the present. And secondly, he worked very hard, before he fell into my hands, respectively, he broke more than once.
6 times they repaired the final stage, repaired the tone block 2 times, something was incomprehensible with the input selector, and besides, they burned the indicator once by connecting it incorrectly, but they put another one from another amplifier, but I also managed to burn it when I myself poked around in everything. In general, there to say, this VCL was inherited by me. Decided to end these glitches by redoing it completely.
Before the change, it looked like this:
final amplifier
I wanted to insert something more interesting there, not some kind of 7294, but something more serious. Googling for a week, I found what I needed.
The parameters are:
- THD: ~0.005% (measured) sim'd: 0.002%
- Power into 8ohm: 60 watts
- Power into 4ohm: 100 watts
- Gain: 32dB (~1:40) full output at 0.7v input (0.5vrms)
- Feedback: 57dB
- Phase margin: > 90°
- Supply voltage: +/- 36v
- Biasing: 55ma, 12.1mv across a single 0.22ohm
- Frequency response: 3.2hz to 145khz (-1db) using 4.7uf input cap
Phaseshift at 10khz:<3°
Isn't it beautiful characteristics? Without hesitation, I collected 1 channel, and there I already completed 2. The sound quality is amazing!
A huge minus is that there was no printed circuit board in the lay format for it, and I don’t know how to use it in other programs, so I had to overlay a drawing and convert the board to light. Now other people who want to build this amplifier will be able to repeat it without problems. See attachments for fees.
And the main thing is that the power is about 100W for a load of 4 Ohms when powered by + -33V. This is what you need! Although I was going to redo it, I decided to leave the transformer as it was. When rectified to DC, there was a suitable voltage. Another plus, 2 such amplifiers can work on their own radiator from u101, without overload, checked! The heating of the radiator at full output power did not exceed 70 degrees for an hour, but I like to listen to music very loudly
A small guide to assembling and configuring the final amplifier.
vintage radio engineering amplifier u 101 contains the following components at the output of the cascade: transistors output pair 2SC5200 / 2SA1943. But in the original scheme, there were MJL3281A / MJL1302A, and MJE15030 / MJE15031 were replaced by 2SA1837 / 2SC4793. BC transistors are sold everywhere, there is no need to replace them with anything, they are common. I replaced BD135 with BD139, works the same. But there may be problems with the MPSA18, if you don’t find them, then you can safely replace it with the BC550, but when soldered into the board, you need to turn it 180 degrees, because. it has a MIRROR PLUG, unlike the MPSA18.
The trimmer resistor VR1 can be a vertical type 3296 multi-turn, or you can also use a regular single-turn, I would advise you to take 3296, it’s easier to tune the amplifier, when you turn on the amplifier for the first time, this resistor should have MAXIMUM resistance.
Resistors R24 R25 0.22 ohm 5W cement. Resistors R22 R23 1.2 Ohm 1W. Resistor R26 4.7 ohm for 1-2W. Resistor R27 10 Ohm 2W, a coil of 10 turns with 0.8mm wire is wound on top of it. All other resistors are 0.25W.
Capacitors ... It's better not to put bullshit here. Electrolytic capacitors for power supply must be taken with a voltage margin, I have 50V with + -33V power supply.
Capacitor C3 470uF from 16V. The capacitor at the input of amplifier C1 needs a film capacitor, from 4.7uF to 63v, you can use polypropylene yellow, put it vertically, it will fit perfectly. It is very desirable to use a film, but if you don’t find it, then turn on 2 capacitors of 10 microfarads per volt with 50 minuses, and solder the extreme pluses into the board, and it is advisable to add a film capacitor in parallel to the prefabricated capacitor, at least 1 microfarad.
C15 47nF 63V film cap, in the power supply C9 C11 C16 C17 it is also desirable to put a film.
The rest of the capacitors are ceramic, preferably NPO, but if you don’t find it, you can plug in Chinese brown ones, but I would look for something better.
Fuses from 2.5A.
In principle, that's all, you can go collect the legendary radio engineering amplifier u 101.
Transistors must be installed on the radiator through insulating gaskets, and in no case should they be shorted!
A properly assembled amplifier immediately turns on and you can listen to it. It is better to turn on the first time through a lamp inserted between 220v and the primary winding of the transformer, if you make a mistake somewhere, the lamp will glow, but your details will not burn out.
If you are fearless, you are confident in yourself and nothing is a hindrance to you, then good luck, turn it on without a lamp, if something is phoning, buzzing or burning, we immediately turn it off and look for errors. But still, it’s better to assemble without errors, google carefully for each plug, because if you make a mistake, then an error can come out expensive.
Amplifier setting
Already collected? Wow! Congratulations. Now there is little left to do.
It is necessary to set the quiescent current in the range of 50-70mA. I set it to 70mA.
For a successful setup, radio engineering amplifier u 101 you need to warm it up, just turn it on and listen to music for 30 minutes, the fact is that until we set it up, it works in mode B, so it will not heat up itself.
Well, how's the sound? Excellent, of course. Now we need a multimeter. We set millivolts to the measurement mode, and turn on the probes between the EMMITTERS of the first and second transistors, and set the desired quiescent current, slowly twisting the resistor VR1. For 70mA, this is 30.8mV (U=I*R, U=70mA*(2*0.22 Ohm)=30.8mV).
That's it, congratulations! We do the same with the second channel.
Tone block
Slightly modified scheme:
We solder the variable resistors from the timbre block from u101, bite off the additional leads, and solder them into the board, after inserting the mounting plate.
The operational amplifier here needs a “musical” one, NE5532 is recommended, but you can look for analogues, for example, I used the RC4580IP, it was extracted from audio equipment.
All capacitors in the sound path are film! But in the power supply, electrolytes are 470 microfarads per 25V. Resistors in the power supply 1kΩ at 0.5W. The remaining resistors are 0.25W each. Zener diodes were used by 1N4743, unfortunately there were no other less powerful ones.
No configuration required, works immediately.
Attention! The board has an SMD jumper, or a 0 ohm resistor on the side of the tracks. Don't forget to post!
Payment in *.lay is in applications.
power unit
Here you can choose what you prefer. I preferred caps of 22000uF, but here it is desirable to parallel several capacitors so that the total is about 20000uF, the total ESR of the capacitors will be less than that of a large one, therefore, at the peak, it will be able to give more current. Soft start was not needed here. I have diodes KD2997. Film capacitors for 1-4.7uF at 63V.
See the appendices for the power supply board.
How to connect a transformer?
Conclusions 2 and 2 are interconnected. And 220 connect to pins 1 and 1.
Now ... We connect pins 7 and 7, and we will connect pins 8 and 8 to the indicator.
Protection block
Although you can leave your own, but I still decided to replace it. I used Mikruham, a slap in the face ready from the amplifier, by Ilya S. (Nem0). Protects against overload and constant at the output, and from constant both from plus and minus relative to the ground.
All resistors are 0.25W. Transistor BD135 can also be replaced by BD139, it must be installed on a small radiator. Zener diodes for 12V and 13V, prefabricated, it turns out for 25V. Relay for 24V.
Capacitors C1 C2 C3 C4 25V. C5 to 50V.
Payment is also in applications. One board already has protection for two channels.
Indicator
Here I would have left my native indicator, but since I burned it when it was connected incorrectly, the fact is that another indicator was put there, I did not find a diagram for it anywhere, presumably it was a radio designer.
All resistors are 0.25W. The outer LEDs "100W" are red, the rest are green. It is configured as follows: we connect to the output of the radio engineering amplifier at 101 and turn the tuning resistor, at maximum volume, so that it shows the entire indication scale, and at minimum volume, so that the “0.2W” LED winks.
We do the same with the second indicator. When you turn on the indicator for the first time, set the variable resistor to the middle position.
Installation
Now we stuff everything into the body. I came up with such fasteners for the speaker terminals. So, I cut it out of textolite.
First of all, we will deal with the most important element of any system - its heart. The amplifier has, you guessed it, a power supply. We will finalize it following the advice of Nikolai Vasilievich + add a few features from ourselves.
All wires inside are assembled with special ties. For the first time I see such accuracy in Soviet technology. Although, most likely, I simply did not come across such samples.
Loosen clamping screws
disconnect the cable with power from the preamplifier
display unit, while unfastening the tie
and final amplifiers, while also removing a couple of couplers.
That's it, the easy way is over, now you have to pick up a soldering iron. Unsolder the power supply from the input board. Yes, kids, never solder on the couch.
By the way, I still have not figured out where to find the corrective amplifier for the player here. It seems like a separate block is located on the input board, but at the same time, some additional microcircuit is on the preamplifier. Okay, we'll figure it out along the way. We solder the zeros going to the output to the speakers and to the case. Soldering is hard, my 25 watt soldering iron can handle it with difficulty.
Okay, of course, you can still solder off from the transformer and the protection unit, but something is too lazy for me, especially since the power supply has already received more than sufficient mobility for further manipulations with it. The girl moves to the table.
Well, let's start by soldering the capacitor into the network circuit in order to protect our baby from all sorts of unnecessary interference. This one from an old monitor is fine.
We proceed with the finalization of the PSU itself. As Nikolai Vasilyevich wrote in his newer article, it is not at all necessary to transfer all power to 31 volts, it is enough to power the terminals to the maximum to get the maximum return, and put all other consumers on a 26-volt "diet". Among other things, this will help avoid many problems, in particular with overheating of resistors in the display unit.
I will not breed zero as Nikolai Vasilyevich advises. Something seems to me that there will be much less tangible benefits than hemorrhoids with new wires. Moreover, the iron case should already protect against interference, according to what we were told in physics.
Let's start by swapping the 26 and 31 volt leads from the transformer to apply more voltage to a more stabilized section. (Although, given that 10,000 microfarad capacitors will be used, this benefit becomes slightly doubtful, because everything will be in chocolate anyway, but nevertheless)
Swap the wires on both 4th and 5th terminals of the transformer. Now, as expected, more voltage flows through the wires of a larger cross section.
We cut out (anti)filtering capacitors MBM. Never loved them.
We proceed to the replacement of the main "barrels". It's a pity, but they will have to be thrown away. It is unlikely that even a third of the declared capacity remained in them.
As it turned out, the process is much simpler if you remove the plastic gasket.
And now we are washing down our 10 milifarad monsters here. Jackcon, of course, is not the most expensive brand, but for our purposes - just right.
What do we end up with. The capacity has increased by 5 times, while the volume has decreased by 2. Progress, epta!
And now - the promised trick. We solder in parallel to each direction along a non-polar capacitor of the k73-17 type. Nikolai Vasilievich does not have this, but according to many close to the topic, this increases the quality of the return at high frequencies. Yes, yes, the power supply in the amplifier is a very important sound-forming element! What did you think? The world is not at all what catches the eye at first sight.
After the third inclusion, it became clear that the diodes of the small rectifier were smoking. When measured, two of them were broken. Who knows, maybe when you first turned on something unsuccessfully shorted, or 10 millifarads for them is too much of a burden, but, in any case, there is no turning back. There are no diodes either, so tomorrow I need to run to the store.
But, we will not be stopped by this minor nuisance! Muahaha! We continue to test a larger rectifier.
At first, the author was very surprised why the larger rectifier outputs 66 volts instead of the expected 31. But then he guessed to look at the circuit and saw that -31 and +31 were written on it, i.e. the total potential difference is 62 volts, which is the same as 66, only under load.
Well, hallelujah, brothers and sisters, the engine is almost ready to carry us into a bright future filled with divine sound. There are a couple of small but necessary details left, and we will move on to the most interesting part of our story. Amen.
At the dawn of my receiver activity, Speedola 232 was considered the best amplifier, Ishim was one step lower. Then came "VEF 216" - small, wildly stylish, with a built-in power supply and excellent sound, it brightened up gray everyday life and sometimes the same gray weekend. Then "Wilma" appeared, a little later - columns to her. Life has become more fun: firstly, stereo, and secondly, sound, as we say, can be “heaped”, although I don’t like loud music.
And all of a sudden, just recently, I realized that she had a very small margin of volume control, so let's say “quiet -> normal -> loud -> I-start-to-compensate-Freud-like -> no longer spinning” (2 x 4 W) . I wanted something more powerful.
But how are we usually? We say "normal available amplifier" - we mean "Radio engineering U-101" (2 x 20 W), we say "Radio engineering U-101" - we mean "normal affordable amplifier". Maybe the "duckling syndrome" also played an important role - I came across one of these for repairs, what's inside, I know about it.
In general, I found and bought.
Yes, the shed is still the same, it takes up a lot of space on the table, mainly because of the depth.
Only the interconnect cable DIN5 - DIN5 was included in the kit, so for the initial check I also had to get Wilma. We played. The sound is normal, nothing out of the ordinary. I was even a little upset that I did not know how to hear "airiness", "warmth" and "transparency". Still, the first class, it seems to be like it's time.
I will conduct a tour for those who are not at all in the subject of what is under the hood of the 101st. The closest thing to us is the pre-amplifier-tone block and the board of the vacuum luminescent indicator. The second row is a capacitor bank (6 x 2000u, 63 V), two diode bridges (small for small economic needs(+/- 31 volts) and powerful (+/- 26 volts) for powering final amplifiers) and a transformer. The third row is the input-switch board, the protection board (you can see the relay over there) and the final amplifiers. "Electrolytes" are full, so
Only who knew that I was guessing and this my favorite phrase would still come out sideways.
Okay, now more about blocks.
preamplifier. The suspect dog almost fell off his chair when he saw this. I read on the Internet - it turns out that there is such an alteration when the first K157UD2 in the timbre block is removed. If you do not listen to records, then it is quite possible to do without it, there will be less distortion. Looks like the previous owner thought so.
The shielded phono preamp box should be on the switchboard directly below the colored wiring harness from the PSU. The previous owner definitely decided that the time for vinyl had passed (as well as the time for four-legged devices - “Radio Engineering” turned out to be lame-footed, without a back right one). However, one of the simplest and most effective alterations of the "101st" is just to remove the phono stage, it sometimes starts to make wild noise and even receive the radio. So who knows, maybe it's for the best - I still don't have a "turntable" and it's not expected.
A little to the right is the protection board. "Electrolytes" were replaced with 85-degree ones. At first glance, everything is fine here. But this is only a first glance.
I was wildly outraged that all the boards were made of getinax (“Wilma” is a second-grader wholly on textolite).
Final amplifiers, or, as they are also called, "ends". A little dusty. Also with traces of replacement containers.
indicator board. There are two extra resistors on the side of the foil - I didn’t take pictures.
In general, what can I say: life dragged a Latvian. Nothing, the white horse is already on its way, right now we will save you, princess.
I was surprised how discrete the volume control was made: with a ratchet. Those who are accustomed to "analogue" regulators can remove the spring or press and fix the "dog".
Tests after replacing almost all containers showed: clapping speakers. Both when turned on and when turned off. And first class too! Strange, where does the defense look? Although what is it? It's nothing! Then something interesting began.
Turned on the amplifier, listened for about ten minutes. Suddenly 50 Hz appear in the right channel, louder and louder, they do not react to the sound reduction. The indicator dances with the right channel, the amplitude of the waves is increasing. By ear, it is perceived as a motorcycle idling. I turn it off, scratch my turnips, go to regulate the quiescent currents of the “ends”.
I set it to 45 mA. In the left channel, don’t understand what happened at all, the multimeter went off scale at 200 mA.
I turn it on again. It works for about ten minutes, the right one starts to growl again. I pull off the input plug from the right “terminal” - the rumble and the “motorcycle” go to the left. I pull off the input from the left - almost immediately the indicator goes off scale, so much so that the S-30 shines with an overload (even though I saw these LEDs in action). The multimeter shows that the “constant” rises at the output (up to 13 volts), then the relay clicks like a bad one. Began to understand.
Well, the coolest alteration in this "Radio Engineering" - attention!- the output wires of both ULFs are soldered to the output wires of the protection board. IN detour protection, Carl! The relay can click as much as you like, but if a "permanent" comes, then without thinking twice, it will go directly to the acoustics. No wonder the overload indicators were on. After the restoration of the status quo, the protection began to correctly process the "motorcycle", that is, not to let it go to the speakers when the indicators were already dancing almost under the "ceiling". "Motorcycle" also changed - I found myself a warm, I would even say, hot garage in the left ULF, and settled there, almost immediately after turning it on, starting a fifty-hertz song.
I decided at my leisure to still pick up the "terminator". Here, as with periodontitis, you can pull out a sick tooth, or you can treat it. Our dentist friend says that always, as long as there is an opportunity, it is better to treat. Something native is closer to the body.
It didn’t take long to look into the ULF-50-8 saloon, but as soon as he arrived, he immediately broke their chairs and tables, broke the dishes, challenged all three-legged cowboys in turn to a duel with a transistor tester. I didn’t like KT837N with h21 more than three hundred (50-150 according to the reference book and 60 from another of the same). I replaced it with KT818G, but it burned out from the power supply, even a fragment of some track annihilated.
Yes zadolbala this "Radio engineering"! Such a hard break!
And just then friend Andrey, a big troublemaker in the field of electronics, comes, looks at all this (and the sluggish repair has been sluggish for a couple of weeks) and says that he would buy ready-made boards for the TDA2030A and install instead of these problematic "ends". What's the difference - 20 watts or 18, and the hassle is many times less.
And I realized that he was right. All the same, the authenticity of "Radio Engineering" is already a big question, there is nothing to lose. Of course, the move is risky. Fans of "honest Soviet transistors" will scoff at me for replacing "cool Holton" with "soulless microcircuits." Chip fans - for not being a TDA2050 or TDA7294. Fans of tube sound will snort anyway.
Well, what am I? I am no longer restoring the amplifier, I am building a Chevy.
Ready-made scarves were found on the Internet, the question arose with food. TDA2030A can operate at voltages up to +/- 22 volts, and Chevy's native amplifiers consumed +/- 26 volts. Normal people, probably, they would have rewound the transformer or found another one. But this is long and expensive, the game is not worth the candle, especially since I specifically quarreled with this game for her boorish behavior. But what if we bring the U-101 closer to the zero class? "Odyssey U-010", for example, has stabilizers for ULF. Only there is a mountain of transistors, and I will take L7820 and L7920, and there will be +/- 20 volts. True, I did not find any mention on the Internet that someone did this, and is it legal at all, but oh well, I’ll be the first, I’ll figure it out myself, I’ll try.
I gave the left ULF board to the stabilizers and shifted it to the place of the right channel, and fixed the TDA-shki where the left one was.
LEDs indicate the presence of power. I always try to make an indication of switching on - I have come across more than once when another home-made product does not work, even if you crack, but the problem turns out not to be in transistors or even in a bobbin, but in an unconnected “plus”.
And so, I start these seven and a half liters of electrolyte ... The protection thinks for a couple of seconds, click! .. Oh, "motorcycle", hello. So you, dog, it turns out, you live not only in the ULF. It is necessary to pick the tone block.
First of all, I replaced the wires from it to the TDA-shki with shielded ones (the screen is hung on the "ground" only from the side of the tone block). Not that. I replaced the two remaining non-polar capacitors (if there are no non-polar ones, then you can connect two pieces “plus” to “plus” twice the capacity), one was nothing, one was dry. Also not that. Looked that there is such a special living in the preliminary. Two K157UD2, normal trouble-free microcircuits, how much rubbish has already been collected on them. Are they really trouble free? No one else to blame. I uprooted one of the left channel (1983, brown body) and replaced it with a fresher copy (for this I had to remove the aluminum muzzle and the entire tone block). I turn it on - but it does not buzz! But it’s too early to rejoice: the sound is vile, “sand” appears at high volume. I spit on integrated technologies, idolize Wilma's multi-transistor circuitry, and finally, I look at the paper that was attached to the TDA-shki. " If self-excitation of the amplifier is noticed, solder a 2k and 82p circuit between pins 2 and 4”(This is also in the datasheet). Well, I soldered ...
***Digression***
A hare is walking through the forest, he sees: a fox is stuck between the trees. He went, did all sorts of bad things and moves on. Meets the wolf:
- Hare, are you happy with this?
“So the fox got stuck there, well, I… I threw a couple of sticks!”
The wolf also ran there - did the same. Satisfied, a bear comes back to meet him:
- Wolf, why is your face already shining?
- Yes, the fox got stuck there, so I threw a couple of sticks ...
The bear thinks, “Let me go. Descended, returns to the wolf, the whole already glows with happiness. Wolf:
- Well, did you throw a couple of sticks?
- Not at all! There were no sticks ... So I threw cones at her!
So I still showered "Radio Engineering" with cones: not a grain of sand was left. She plays loudly, nobly, the LEDs in the acoustics can even wink - “Wilma” only clicks her teeth with envy. But she also found a job - it serves as a pre-amplifier, because the only 3.5 mm cord - DIN5 I have is not soldered the way it should be "101st". Alone, she plays quietly from this cord, but cleaner - "Wilma" brings its second-class noise.
Important point: radiator temperature. The stabilizers are cold even under a good load, the TDAs heat up, but you can completely keep your hand on them. The hottest corner of the heatsink is the one closest to the input board. But even there, the temperature is very, very far from anything exciting.
And now, it seems, everything is fine, you can sit, listen to music, watch kintso ... Stop, ep-p-ponsky tape recorder! I worked for an hour and a half or two, and suddenly pink noise appears in the right channel. Well, to hell, it seemed, with him, so he is growing! Then, by nature, it becomes like a tide on the sea. Then some wild modulation begins.
That's crazy stupid. If you let it cool down for ten minutes, the noise goes away, but then comes back again. I soldered some little things, corrected the wires (it turned out that the input of the right ULF went exactly above its output, and this is a prerequisite for creating a positive feedback and turning the amplifier into a generator), even replaced the TDA-shku (suddenly they gave a defective one). Sat down to test.
It looks beautiful and convincing (at night the indicator even blinds), but again an hour and a half or two passes, and the "sea" begins. I shorted the output of the right channel from the preliminary to the "ground" - the noise disappeared. And then I thought for the second time - what is there in the timbral block? Another K157UD2- whispered amateur radio luck, no one knows where before staggering.
The Chevy cooled down a bit, when you turned on the noise was gone. I began to drive a screwdriver over the microcircuit ... Gotcha, animal: here you have noise, and hum, and 50 Hz for tea. Change immediately! Oh, and what, ran out, or what? Exactly. I had to disassemble homemade pointer indicators but it was worth it. An hour, two, three, six - and no noise! Finally!
So believe these "rods".
The problem of lameness was solved surprisingly simply: suitable legs were found in the local radio store (foreground).
They are called "legs for quick installation." Indeed, it takes longer to pick a hole in the bottom than to fix the leg.
The pre-amplifier annoys me the most. Either I don’t understand anything in circuitry, or something else, but +/- 31 volts included in the tone block after the resistors R47 And R48(1.5 kΩ) turn into +/- 15 volts (blue dots). Where is Karl? In my Chevy, 1.2 kOhm was soldered from the factory, and +/- 22 volts went after them. I replaced it with 1.5 kOhm, and even one-watt ones. It became +/- 19 volts. Still way off the charts.
Therefore, another solution peeped from the Odyssey is 15-volt zener diodes (1N4744A) for power. Was it really so difficult to do it at the factory, at the design stage?
The input selector, which is so popular on the forums, turned out to be a very useful thing. It is already difficult to imagine the situation when more than one input cable is connected to the U-101 (unless the lucky person has the complete Radio Engineering 101 Stereo complex: tape recorder, tuner, turntable), so you can use it otherwise, as a function mute(temporary mute). By switching to another input, you can attenuate the incoming signal to a barely audible rustle, without even touching the volume control (the switch uses K190KT2P, field-effect transistor microcircuits, which, no matter how you close it, pass the signal a little - this is not a relay).
But they can play such songs with Wilma. So the hand reaches out to turn up the volume.
Maybe a little later I will replace the TDA2030A with the TDA2050. It's impossible to go "fast enough".
P.S. I listened to the Chevy for a day and a half, then carried out minor repairs to the Wilma and put it on an electric run. And the sound, and the sound! The 157s hiss (there are four of them per channel in the ULF, plus one in the recording-playback amplifier), there is no volume level “yes-I-have-serious-problems-according to Freud”, the basses are too hammering, then they are sharply lacking … It turns out that you get used to good things very quickly.
P.P.S. I smiled for a very long time when I saw this correlation on the ad site:
Refinement of the amplifier "Radio engineering U-101"
So, let's begin!
1.
Power supply.
Power supply circuits may vary slightly!
To get a decent output power, you need to have a decent power supply. Let's use the gift of the transformer manufacturers: the entire secondary winding is made with one thick wire (0.8 mm in my opinion). Therefore, it is quite possible to switch the power supply of a powerful rectifier VD5…VD 8 from pins 4 - 4* to 3 - 3*, which will increase the voltage from +/-26V to +/-31V. At the same time, a low-current rectifier VD 1… VD 4 becomes unnecessary and is removed along with the wires, and its storage capacitors C2 and C7 are connected in parallel with the corresponding capacitors of a powerful rectifier. But all connections with contacts 5,6 and 9,10 should be preserved.
Then the witchcraft begins.
1. We determine the geometric mean between the ground terminals of the capacitors C2, C3, C4 and C7, C8, C9 on the board of the filter capacitors, clean and tin it. We assign this point as the main common point of the entire amplifier.
2. From it we start up 2 thick wires to the minuses of the output connectors.
3. From it we start up common wires to the UM and UE.
4. From it we start up 2 wires to contacts 6 and 6 * of the transformer, removing the jumper between them. At the same time, we remove the connection between the rectifier board and the case.
5. We organize the connection of the common wire with the case at the input connectors of the amplifier.
6. And check that there are no more contacts of the common wire with the case anywhere else.
And finally, we connect a 0.047x630V capacitor in parallel with the primary winding of the transformer to suppress impulse noise from the mains. 
After removing VT 6 and VT 7, installing a jumper, replacing R 10 with a diode D 7 and shorting R 15, the D 7-VT 5-R 11 circuit turns into a diode stabilizer for the current source on VT 8, which is already powered by the swinging transistor VT 10 To reduce non-linear distortion, the swinging transistor VT 10 must be high-voltage, powerful and with a high gain. just meets these requirements, so we replace the original transistor with a more suitable one. The classical scheme. Only the R 42 resistor breaks the idyll. It is soldered from the print side into the notch of the printed conductor near the VT 2 collector. The introduction of this resistor increases the stability of the entire PA and allows you to get rid of compensating capacitors C4, C5, C9, C10, as well as resistors R 20 ,R 21. Side effects introductions of R 42 will appear when listening.
For normal operation electrolytic capacitor it needs a charging potential from 0.6V, but it is not on the C3 plate. Therefore, there should be a non-polar capacitor here, limiting the bandwidth around 5 Hz. Hence the nominal value of 22 microns NP.
The setup is normal: connect an ammeter to the power break and set the idle current to about 40 mA. Then restore contact and start working.
color removed components are highlighted.Numbering corresponds to standard schemes e.
3. Preamplifier .Djvu 60 kb
Chip DA 1 is included in the preamp solely to match the piezoceramic pickup. I think that now this is no longer relevant, but it adds noise, and therefore we boldly throw out the DA 1 chip along with all the strapping and throw a jumper using the freed holes on the printed circuit board.
Newly introduced or changed components and jumpers are highlighted in red, and blue color removed components are highlighted. The numbering corresponds to the regular scheme.
This figure shows the DA1 chip and the components that should be removed along with it on the U5 ULF-P board.
Next, we more accurately adjust the loudness circuits to the volume control. Then we expand the bandwidth of the DA 2.1 and DA 3.1 amplifiers both in HF and LF and adjust the parameters of the tone block. To return the supply voltage of the DA 2 and DA 3 microcircuits to an acceptable direction, it is necessary to correct R 47 and R 48.
The preamplifier includes trimming resistors R 24 and R 26 to adjust the gain of the entire amplifier. Setting conditions: at the input - 0.5V 1kHz; volume control - to the maximum; at the output - 14V without load, set with resistors R 24 and R 26.
rednewly introduced or changed components and jumpers are highlighted in color, and blue color removed components are highlighted. The numbering corresponds to the regular scheme.
This diagram shows the ULF-P refinement circuit, the DA1 chip is not shown.
5. Corrector UPZ-15.
To date, all known moving magnet magnetic pickups operate with a correction capacitance of 470pF. Accordingly, the capacitance of capacitors C1 and C2 is changed to 470pF. 6.Payment of inputs.
To expand the bandwidth down from 20 to 7 Hz, you can increase the capacitance of capacitors C4, C5, C14, C15 to 0.33 microns. This is at the end of the work as the cheeks puff up.
This treatise was compiled on 3.06.09.
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The amplifier "Radio engineering U-101-stereo" is designed for high-quality amplification of audio signals from both devices included in the complex and from external sources of sound programs. The amplifier has an electronic input switch, electronic indicators of the output power level separated by channels, an output stage protection device in case of a short circuit in the load; the loudspeakers are also protected from possible contact with the DC component of the voltage in case of amplifier malfunctions, as well as protection of the output stage transistors from overheating.
The main technical characteristics of the amplifier Radio engineering U-101-stereo
- Rated output power, W: 2x20
- Rated frequency range, Hz: 20...20 000
- Rated input voltage, mV, input:
Pickups : 2
others : 200 - Harmonic coefficient in the nominal frequency range, %, no more: 0.3
- Signal/background ratio, dB: 60
- Signal-to-noise ratio (weighted), dB, at an output power of 50 mW: 83
- Headphone output voltage (R H =16 Ohm), V: 0,9
- Power consumption, W: 80
- Dimensions, mm: 430X330X80
- Weight, kg: 10
Scheme of electronic switches for the inputs of the amplifier Radio engineering U-101
Fig.2.
The electronic switches of the amplifier inputs are made on DA1-DA3 microcircuits (Fig. 2), controlled by a constant voltage coming from the input selector - the SA1 switch. Such a circuit solution simplified the installation, eliminated cods when switching inputs, and reduced pickups on the input circuits. Microcircuits are located directly near the input connectors, and the switch is located on the front panel of the amplifier.
The switch SA2 "Copier" is also connected to the switching board. It is designed for quick switching of tape recorders (without additional manipulations with connecting cables) when re-recording phonograms. The switching is purely mechanical, which allows, in the absence of the need for control listening, to carry out these works without turning on the amplifier in the network.
Scheme of final amplifiers "Radio engineering U-101-stereo"
Fig.3.
ULF-50-8 unified modules were used as terminal amplifiers of Radiotekhnika U-101-stereo. The input stage of the module (Fig. 3) is differential on transistors VT2, VT4 with a current source (VT1, VT3) in the emitter circuit. The next stage on transistors VT5-VT10 is also differential, with a dynamic load in the form of a current mirror (VT5, VT8), which provides a symmetrical buildup of the output stage. The high linearity of the amplification of large signals by this part of the module is provided by an increased (compared to the output stage) supply voltage.
Output stage (VT13-VT20) - symmetrical, on composite emitter followers with parallel connection transistors in the last stage. Temperature stabilization of the cascade operation mode is provided by a device based on a VT9 transistor.
Amplifier protection scheme Radio engineering U-101
Fig.4.
The amplifier overload protection device is assembled on transistors VT11, VT12 and diodes VD3-VD6. In the event of a short circuit of the load, it limits the output current to 2 A. As already mentioned, Radio Engineering U 101 Stereo also provides protection for loudspeakers from direct voltage falling on them in the event of an amplifier failure and protection of output stage transistors from overheating. The AF voltage is supplied to the loudspeakers through the contacts of relay K1 (Fig. 4). If the amplifier is in good condition, it works 3...5 s after the power is turned on, which eliminates clicks caused by transients in the amplifier. The speaker connection delay time is determined by the R10C3 circuit parameters. With the advent of a constant component (more than 2 V of any polarity), transistors VT1, VT2 form a voltage that enters the base of the transistor VT3 and closes it. As a result, the winding of relay K1 is de-energized, and its contacts disconnect the loudspeakers from the amplifier.
The same device is used to automatically turn off the loudspeakers when a headphone plug is inserted into the XS17 jack, equipped with an SA3 switch, and the power transistors overheat.
The thermal relay is assembled on a DA1 chip. The functions of the thermistor are performed by the VT transistor, which is included in one of the arms of the R12R13R16R17 bridge. The bridge is powered by a stabilized voltage through resistors R14, R15. In the initial state, by appropriate selection of high-precision resistors, the bridge is unbalanced in such a way that the voltage at pin 5 (relative to pin 4) of the DA1 chip is 50 ± 5mV, and there is no voltage at its pin 10. When the transistor VT is heated (it is located on the heat sink of the transistors of the output stage) to 86 ... 90 °, the bridge is balanced, and the voltage at the output of the microcircuit rises abruptly to the supply voltage (+ 26V). As a result, the VT4 transistor switch opens, and the protection system disconnects the loudspeakers from the final amplifiers.
The scheme of the electronic indicator of the output power level of the amplifier Radio engineering U-101
Fig.5.
A schematic diagram of an electronic indicator of the output power level with information output to a vacuum cathodoluminescent two-color display is shown in fig. 5. When the output power is less than the nominal one (-20...0 dB), the green bar glows, and when overloaded (0...+5) dB, red. The operation of the HL1 display is controlled by the DDK chip, which provides analog-to-position conversion of the output signal of each amplifier channel into the corresponding code. The threshold voltages of operation of the switching elements of the microcircuit are stabilized by a current generator based on the transistor VT2. The inverter on the transistor VT1, together with the elements of the DDI chip, forms a generator of paraphase pulses that enter the display grids in time with the connection of the inputs of this microcircuit to the outputs of the op-amp DA1.1, DA1.2. The pulse frequency is chosen equal to 150 Hz, it is determined by the values of the elements R11, C6. The processing of information from both channels by a single analog position converter ensures perfect consistency of the display characteristics. The DA1 microcircuit amplifies the signals coming from the rectifiers on the diodes VD1, VD2 through the integrating circuits R1C1R4, R2C2R5 (the integration time of the indicator is about 30, the reverse run is 500 ms). Parametric stabilizers (VD4, VD5) provide stable indicator readings with significant changes in supply voltages.
