A product of the Latvian industry, Radiotehnika U-101-stereo (later, Radiotehnika U-7101) was a desirable acquisition for any music lover in the mid-eighties. The complete set of Radiotehnika equipment consisted of at least four units - an amplifier, a tuner, a cassette deck, and a vinyl player. There might be something else, but I didn’t come across it.
Some time ago, I found myself alone with a Radiotehnika U-101-stereo amplifier, a Radiotehnika M-201-stereo cassette deck and a pair of Romantika 25AC speakers. There was a lot of time, there was nothing to do, next to the dream of a music lover of the mid-eighties there were cassettes with recordings of The Beatles and Al Bano & Romina Power. It was decided to listen to Felicita and Let it be, but that was not the case. The cassette deck didn't play cassettes, and the amplifier produced such background noise that it was scary for the speakers.
With the cassette deck, everything was resolved quite simply - a little liquid lubricant, a bottle of cologne and a splash of vodka brought the old lady to her senses. Here is a small photo report:
Just pour alcohol and oil on top of everything, and glue the cracked plywood body together. This, of course, will not last long, because... and the gears were brought up and the belts stretched
With the amplifier, in principle, everything is also quite simple. All the salt is in the electrolytes :) As it turned out after five minutes of studying the problem via Google, it is enough to replace a couple of electrolytes in the HF unit and it is possible to replace the electrolytes at a high level. Here is a small photo report:
Since I didn’t remember which pair of electrolytes to change in the RF unit (such a small shielded box with a cold contact plugged into the main board), I had to replace everything. Likewise with high electrolytes. Everything was aggravated by the fact that I didn’t have a multimeter, and I didn’t have a soldering iron either. I had to buy everything in the same place where I came for electrolytes. DIN 5 pin and TRS 3.5mm connectors were also purchased just in case.
As a result, everything took about 40 minutes of work and the dream of a music lover of the mid-eighties began to sing first in the voice of Al Bano, and then with the Moby synthesizer, taking the signal from a mobile phone.
It is soldered, disassembled and assembled quite easily, I soldered with a decent Chinese 100W soldering iron. All parts are available and distributed, for high - six pieces 50V 2000uF, for low - a pair of 6.3V 50uF, a pair of 10V 20uF and a pair of 50V 2uF. You just need to keep in mind that the tracks from the RF block board peel off easily and naturally, and you need to solder carefully so as not to tear anything. Otherwise, you will have to “duplicate” the tracks with electrolyte legs.
Yes, I almost forgot, the amplifier circuit:
- (PDF, 100KB)
- (PDF, 100KB)
Amplifier "Radio engineering U-101-stereo" designed for high-quality amplification of signals both from devices included in the complex and from external sources of sound programs. The amplifier has electronic switch inputs, electronic output power level indicators separated by channels, a device for protecting the output stages when short circuit under load; protection of the loudspeakers is also provided against the possible contact of a constant voltage component in the event of amplifier malfunctions, as well as protection of the output stage transistors from overheating.
Rice. 1. Layout
Rice. 2. General amplifier circuit
Nominal output power, W... 2x20
Nominal range of reproduced frequencies, Hz... 20...20,000
Nominal input voltage, mV, input:
pickups... 2
the rest... 200
Harmonic coefficient in the nominal frequency range, %, no more than... 0.3
Signal/background ratio, dB... 60
Signal-to-noise ratio (weighted), dB, with an output power of 50 mW 83
Output voltage for connecting stereo phones (Rн=16 Ohm), V... 0.9
Power consumption, W 80
Dimensions, mm... 430x330x80
Weight, kg... 10
The electronic switches of the amplifier inputs are made on DA1-DA3 microcircuits (Fig. 4), controlled by a constant voltage coming from the input selector - the SA1 roller switch. This circuit design simplified installation, eliminated crackling noises when switching inputs, and reduced interference input circuits. The microcircuits are located directly next to the input connectors, and the switch is on the front panel of the amplifier.
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 dubbing phonograms. The switching is purely mechanical, which allows, in the absence of the need for control listening, to carry out this work without connecting the amplifier to the network.
Rice. 5. Pre-amp board
Unified ULF-50-8 modules were used as the final amplifiers of Radiotekhniki U-101-stereo. The input stage of the module (Fig. 5) 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), providing symmetrical drive of the output stage. High linearity of amplification of large signals by this part of the module is ensured by an increased (compared to the output stage) supply voltage.
The output stage (VT13-VT20) is symmetrical, based on composite emitter followers with parallel connection of transistors in the last stage. Temperature stabilization of the cascade operating mode is ensured by a device based on the VT9 transistor.
Rice. 5. Final amplifier board
The amplifier overload protection device is assembled on transistors VT11, VT12 and diodes VDЗ-VD6. When the load is short-circuited, it limits the output current to 2 A. As already mentioned, Radiotekhnika U-101-stereo also provides protection for loudspeakers from contact with DC voltage in the event of an amplifier malfunction and protection of the output stage transistors from overheating. Voltage 34 is supplied to the speakers through the contacts of relay K1 (Fig. 6). If the amplifier is working properly, it operates 3... 5 s after turning on the power, which eliminates clicks caused by transient processes in the amplifier. The delay time for connecting loudspeakers is determined by the parameters of the R10СЗ circuit. With the appearance of a constant component (more than 2. In any polarity), transistors VT1, VT2 generate a voltage that goes to the base of the transistor VTZ and closes it. As a result, the winding of relay K1 is de-energized, and its contacts disconnect the speakers from the amplifier.
The same device is used for automatic shutdown loudspeakers when installing a stereo telephone plug into an XS17 socket equipped with a SAZ switch and overheating powerful transistors. The thermal relay is assembled on the DA1 chip. The functions of the thermistor are performed by the VT transistor, connected to one of the arms of the bridge R12R13R16R17. The bridge is powered by a stabilized voltage through resistors R14, R15. In the initial state, with the appropriate choice 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 ± 5 mV, and there is no voltage at its pin 10. When the VT transistor (it is located on the heat sink of the output stage transistors) is heated to 85...90°, the bridge is balanced, and the voltage at the output of the microcircuit jumps up to the supply voltage (+26V). As a result, the transistor switch VT4 opens, and the protection system disconnects the speakers from the final amplifiers.
Rice. 6. Protection board
Schematic diagram an electronic indicator of the output power level with information output on a vacuum cathodoluminescent two-color display is shown in Fig. 7. When the output power is less than the nominal one (-20...0 dB), the green bar lights up, and when there is an overload (0...+5) dB, the red bar lights up. The operation of the HL1 display is controlled by the DD1 chip, which provides analog-positional conversion of the output signal of each amplifier channel into the corresponding code. The threshold voltages for operation of the switching elements of the microcircuit are stabilized by a current generator on transistor VT2. The inverter on the transistor VT1, together with the elements of the DD1 microcircuit, forms a generator of paraphase pulses arriving at 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 to be 150 Hz, it is determined by the ratings of the elements R11, C6. Processing information from both channels with one analog-position converter ensures perfect consistency of display characteristics. Microcircuit DA1 amplifies signals coming from rectifiers on diodes VD1, VD2 through integrating circuits R1С1R4, R2С2R5 (indicator integration time is about 30, reverse- 500 ms). Parametric stabilizers (VD4, VD5) provide stable indicator readings with significant changes in supply voltages.
Rice. 7. Indicator board
Electric player "Radiotekhnika-EP101-stereo" made on the basis of an electric player 1EPU-70S-02 with a magnetic head GZM-105D.
The player has a device for fine-tuning the disc rotation speed with its control via a built-in strobe, an electromagnetic micro-lift, and a mechanism for automatically returning the pickup to the rack at the end of playing the record. It also provides for monitoring and setting the downforce of the pickup, fixing and holding the pickup in an inoperative state, adjusting the rolling force using a lever-type compensator, and auto-stop. Basic
specifications
Disc rotation speed, rpm... 33.33; 45.11
Detonation coefficient, %... 0.15
Relative rumble level (with weighting filter), dB... - 60
Relative level of electrical background, dB... - 60
Pickup sensitivity, MV-s/cm... 0.7 – 1.7
Voltage at the universal output, mV... 250
Operating frequency range, Hz... 31.5... 18000
Crosstalk attenuation between channels, dB. at a frequency of 1000 Hz... 20
Pickup clamping force, mN... 15±3
Power consumption, W... 25
Weight, kg... 10
Dimensions, mm... 430x330x160 “Radiotekhnika-EP101-stereo” consists of three components: an electric player 1EPU-70S-02, a pre-amplifier-corrector board and a stabilizer board for the engine power supply device. The preamplifier-corrector (Fig. 8) is built on the 548UN1A op-amp. To protect against noise resulting from power-on transients, the amplifier output is bypassed
electronic keys
on transistors T1, T2 (Fig. 9), opening with some delay after turning on the electric player. The delay time is determined by the circuits R4С2, R5СЗ, included in the control voltage circuit of +15 V. The supply voltage of the preamplifier-corrector (+ 24 V) is stabilized by a device based on the transistor TZ and the MC1 microcircuit.
Rice. 9. Stabilizer board
Rice. 8. Amplifier-corrector board
V. Papush, V. Snesar
Riga "RADIO" No. 9, 1984 I would like to tell you about my story of repair and modernization of the Radiotekhnika U-101-stereo amplifier. It seems like a completely ordinary amplifier originally from the USSR, but there is some inexplicable appeal in it (
for me personally
When I first saw/heard Radio Engineering I can’t even remember. But it stuck in my memory, and not just a wild desire to buy and listen, no, just a pleasant image. And then the other day the thought materialized and fate gave me RT 101 as a gift. Tired, tormented by everyday life and lack of attention.
I wish my wife didn’t read these lines, otherwise she’ll get jealous and call her crazy
:love: To put up with malfunctions and terrible things technical condition I can’t, I have no peace. Therefore, instead of flowers and sweets for my wife, I regularly buy capacitors, microcircuits, resistors, etc....
I decided to bring RT back to life. To begin with, the following had to be overcome:
1. Transformer hum.
2. The same terrible hum in the speakers.
3. Clap when turned on and some kind of scary sound when turned off.
4. Signal indicator not working.
5. Rustling regulators.
The first step was to replace all electrolytic capacitors. Everything is according to the original ratings, the only thing in the power supply is that the capacity has been slightly increased: 2x2200+ 2x4700 uF to power the final stage (C3, C4, C8, C9 in the diagram). KD209A diodes are replaced with “ultrafast” UF4007.
I’ll say right away that this operation almost eliminated the first three points of problems.
It was not possible to revive the indicator by simply changing the capacitors, but that’s what I wanted little blood... He continued to show the entire scale without reacting to anything. While clarifying the reasons on the forum, we came to the conclusion ( possibly false) that the K161PP2 microcircuit has failed. Finding one, as you understand, is not easy. Easier than a complete indicator.
The world is not without good people (believe in it, do good yourself and the result will not take long) and the indicator, together with the ULF-P of the latest revision, the one on the same chip, was given to me by the broadest-hearted man Vasily (Skif on Vegalab). For which I bow to him and be very grateful!!! True, the functionality of the modules was in question.
In the purchased indicator, we had to replace the trimming resistors, which were covered in nail polish and became unusable. The indication of one channel is working!!! But we have a stereo... I didn’t suffer for a long time, but immediately decided to replace the K157UD2. The operation was a success and that unforgettable green spark appeared in RT’s eyes again.
Further more.
The sound after restoration was mesmerizing with bass. It would seem that 2x 20 W, and such bass that the windows tremble, the plasterboard partition in the kitchen vibrates, and in the evening, while watching a movie at a volume level below average, the neighbor from downstairs called and asked in a sweet, restrained voice to turn down the volume.
But the happiness did not last long. After reading strangers opinions and reviews about how much better the single-chip pre sounds, less distortion, etc., I decided to change my native one. ( For the sake of the authenticity of the article, I will inform you that it was replaced at the stage of work with the indicator. Before this, the ULF-P of the old revision was listened to for a couple of weeks.) And at first I really heard ( or wanted to hear) all these advantages: “high-end detail”, “clearer scene”, “grainy mids”, etc.
But in the depths of the soul there is no peace, there is no pleasure when listening, only self-deception driven into the head by meaningless terms. This was no longer the girl I knew.
A week of listening was enough to understand that it was necessary to return the original ULF-P on three microcircuits. But here’s the problem, I had already started to burn bridges when I removed one K157UD2 (DA 1.* in the diagram) from the dismantled preamplifier, which was used to repair the indicator. I was puzzled by the search for information, understood in more detail the structure and operation of 101. I came to the conclusion that exclusion from the DA 1.* scheme does not lead to negative consequences. (DA 1.* in the preamplifier serves to match the piezoceramic pickup, for me this is not relevant).
The signal from the source after the input selector is supplied to R9 and R10, respectively. Interstage capacitors C23, C24 were replaced out of harm's way with new non-polar ones. First launch after modernization: a lot of worries and one small hope to return the former voice...
From the first notes of familiar compositions, I realized that the goal had been achieved, the bass lived in 101 again! I don’t know how to describe the sound in a sweeping manner, I’ll simply say: you either like it or you don’t. Now I like it! Thus, as a result of related events, the third version of the pre-amplifier RT 101, two-chip, appeared.
The popping sound in the speakers when turned on was the result of a malfunctioning protection. Extraneous sounds when the amplifier is turned off, just like the reaction to turning on/off household appliances in the apartment, it was eliminated by installing a noise-suppressing capacitor with a capacity of 1 μF and a voltage of >280V on the contacts of the power switch.
The volume, balance and tone controls are cleaned of dust by air flow and lubricated (Ciatim 201 lubricant).
In addition to the preamplifier, the following changes were made to the RT 101 design:
The original input switch along with the corrector amplifier has been removed.
Instead of the original one, the input selector for three sources is made on a biscuit, which previously served as a “Copier” switch in the amplifier (SA2 on). The switch has 4 pairs of contacts, so it allows you to break even the ground of incoming signals.
The connectors for connecting sources are standard RCA, two pairs on the rear wall and one for “hot plugging” sources on the front panel (in the places where the “five” connections of tape recorders were previously located). After removing unused switches and connectors, the holes on the front panel are closed with aluminum-look plugs (Dubond material).
IN result The amplifier has lost its value for museums, but is compatible with modern sources and works.
This completes the first part of the work. The second is more complex, since it was decided to refine the body and give it a final “gloss”. I plan to veneer the top cover, make a new bottom, and properly design the back panel with connectors. Which I will definitely tell dear readers about in the second part of the article.
The article is devoted to the modification and restoration of the much-loved amplifier “Radiotekhnika-U-101”, which even now captivates with its attractive appearance.
My old dream came true and this “beautiful girl” appeared in my house.
We must pay tribute to the previous owner - appearance hers is wonderful! The device was found unshoveled, with non-wheezing variable resistors and without any interventions or improvements.
The first time I connected her to the network and tried to hear her voice made a depressing impression on me! THIS could not be called sound. Instead of low frequencies- wheezing, plus a 50 Hz background in the speakers, in general - horror. Conclusion: urgent repairs and modernization!
Several days on the Internet to search for the necessary information. We draw up a work plan on paper. Let me make a reservation right away: we will restore it to its original factory version.
Turn on the soldering iron. Go!
First of all, we change ALL electrolytic capacitors. The device is quite old, released on May 25, 1984. Instead of the above capacitors, there were only objects left in it that looked very similar to electrolytic capacitors, but now with completely different functions. Some went into the class of resistors with some resistance, and the other part went into resistors with infinite resistance!
We also remove “red clay flags”!
1. Power supply
Replace the power supply filter capacitors. For the ±26V power supply, I set 10,000 and 4700 uF and for the ±31V power supply, 4700 uF per arm. We also replace the diodes with KD 213. (These and further in the article, the ratings of the parts are not recommendations, since they were used those that were at hand, i.e. at home). At the same time, we change the wires coming from the transformer to the power supply board to wires with a larger cross-section. Considering the power of the amplifier, I limited myself to a cross section of 0.75 mm 2.We bridge it with film. We remove the thin jumper on the power transformer (pin 6-6*) onto two separate wires from each coil to the common point of the power supply board.
Next, we hang the capacitor parallel to the primary winding of the mains power supply 0.047 µF x 630 V. Thus, we get rid of interference from the mains a little.
Now we have a normal power supply. And this is almost half the road to success.
2. Power supply for input board chips
On the input board U2 we amputate the voltage multiplier (variable 16 V to DC 38 V). We don't need him. We have our own +31 V in the power supply. Remove C7, VD1, VD2. The +31 V voltage is immediately supplied to C10 through the existing fuse.
3. Power supply for pre-amplifier chips
In the U5 ULF-P preamplifier, the supply voltage of the K157UD2 microcircuits sagged when playing sound from 13 V to 9 V! And this is not good! We replace C37, C38 with fresh ones, hang 15 V zener diodes parallel to them, and shunt them with film. Current-limiting resistors R47 and R48 are replaced with 1.1 kOhm resistors with a power of 1 W. Now there is order here too!
4. Output connectors
We change the output connectors. Let's do a little work with a drill and file. Remove the input power connector and install the power fuse holder. As a result we get this:
5. Fight the background
Got it! No forces! We replace the capacitors in the phono stage with fresh ones.
This didn’t give us much, but it won’t hurt for prevention.
During the work being carried out, it was noticed that the background increases when you bring your hand to the cable connecting the input board to preamplifier. Yeah! Got a handsome guy!
We unsolder the wires from the preliminary input and... silence!!! Exactly him! Only mass screening will help!
It would have been possible to run it with separate shielded wires, but I did it differently.
We remove the chip from the cable.
We find a piece of shielded cable, remove the braid from it, shape it, solder the end so that it does not come apart.
Now we carefully insert our train into it. Again we form along the train. We put the chip back. The result is a snake like this.
We insulate the screen braid. It’s better to put a heat-shrink tube on top and shrink it. The connection to the common wire is made only on one side - from the signal receiver side.
We put the train in place. Turn it on. Fon committed suicide! There is a bit of a sting, barely audible when you turn the volume knob to maximum, but it’s nothing compared to the noise that was there!
6. Final amplifier
During the work, the performance of the amplifier was checked after each change. But it's not the same. I wasn't happy with the sound. Somewhat lethargic. And there is no bass. Just some kind of fart. We measure quiescent currents per channel: 26 mA and 30 mA.Then it dawned on me. That's who won't let me in! In the end of the Balts, current equalizing current sensors R32, R33, R38, R39 = 1 Ohm 0.5 W were soldered in!!!
For my speakers, which have a resistance of 4 ohms, an additional two ohms is clearly excessive! White bricks from our yellow-faced brothers will help us here! Change to 0.22 Ohm 5 W.
Turn it on. Here it is - dynamics! Here they are - low! The device was kept in place by protection on transistors VT11, VT12.
Finally the “girl” started singing!!! She started singing!
Along the way, I replaced the P308 wooden transistors (VT7, VT10), which were clearly not thriving in their characteristics (especially the current - 30 mA), with what I had at home - 2N5551, selected in pairs for each channel. The conclusions, however, had to be bent - the base and the collector had to be swapped.
Next, I set “zero” at the output of the terminals. Before the replacement of P308 it was 77 mV and 110 mV, after the replacement it became 60 mV and 60 mV, respectively. After the replacement, I adjusted R5 (3k9). I installed a resistor with a nominal value of 4k52 (there were such ones) and the outputs became slightly less than 30 mV. On this I calmed down. I could have tinkered with it some more, but I didn’t. I decided that enough was enough.
Now the quiescent current! It was not possible to set the quiescent current normally due to dusty and aged trimming resistors. Here my favorite multi-spinners SP5-2 helped me. They had to lengthen the legs from MLT-1 resistors of a rarely used value that had served their time.
So I decided to try to write an article about altering the amplifier. Well, I’ll probably start with its history, namely why I decided to completely remake it. Firstly, everything is old and does not correspond to modern times. And secondly, he worked very hard before he fell into my hands, so he broke down more than once. The final stage was repaired 6 times, the tone block was repaired 2 times, there was something incomprehensible with the input selector, and besides, once they burned the indicator by connecting it incorrectly, but they installed another one from another amplifier, but I managed to burn it too when I picked his mustache. In general, let’s say, they passed this thing on to me as an inheritance. I decided to put an end to these glitches by redoing it completely.
Before the modification it looked like this:
Final amplifier. I wanted to insert something more interesting there, not some 7294, but something more serious. After googling for a week, I found what I needed.
The amplifier is an AB class amplifier, it suited me perfectly both in terms of characteristics and cost.
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 (0.5v rms)
Feedback: 57dB
Phase margin: > 90°
Supply voltage: +/- 36v
Biasing: 55ma, 12.1mv across a single 0.22 ohm
Frequency response: 3.2hz to 145khz (-1db) using 4.7uf input cap
Phaseshift at 10khz:<3°
Aren't they beautiful characteristics? Without hesitation, I assembled 1 channel, and then completed 2. The sound quality is wonderful!
A huge minus is that there was no printed circuit board for it in lay format, and I don’t know how to use it in other programs, so I had to overlay the drawing and convert the board to light. Now other people who want to build this amplifier will be able to replicate it without any problems. See appendices for fees.
And the main thing is that the power is about 100W per 4 Ohm load with a power supply of +-33V. This is what you need! Although I was going to redo it, I decided to leave the transformer the same. When straightening to constant, there was a suitable voltage.Another plus, 2 of these amplifiers can work on the original radiator from the u101, without overload, tested! The heating of the radiator at full output power did not exceed 70 degrees for an hour, and I like to listen to music very loudly
A small guide to assembling and configuring the final amplifier.
Transistors output pair 2SC5200/2SA1943, but in the original circuit there were MJL3281A/MJL1302A, and MJE15030/MJE15031 have been 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, it works the same. But there may be problems with the MPSA18; if you don’t find them, you can easily replace it with the BC550, but when soldering it to the board, it needs to be rotated 180 degrees, because it has a MIRROR PIN, unlike the MPSA18.
The trimming resistor VR1 can be a vertical type 3296 multi-turn, or it can be a regular single-turn, I would advise taking a 3296, it’s easier to adjust the amplifier, when you first turn on the amplifier this resistor should have a MAXIMUM resistance.
Resistors R24 R25 0.22 Ohm for 5W cement. Resistors R22 R23 1.2 Ohm, 1 W each. Resistor R26 4.7 ohm for 1-2 W. 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 reserve, mine is 50V with a power supply of +-33V.
Capacitor C3 470uF from 16V. The capacitor at the input of amplifier C1 needs a film capacitor, from 4.7 uF at 63 V, you can use yellow polypropylene, place it vertically, it will be ideal. It is very advisable to use film, but if you can’t find it, then we turn on 2 capacitors of 10 μF per volt with 50 minuses, and solder the extreme positives into the board, and it is advisable to add a film capacitor in parallel to the collecting capacitor, at least 1 μF.
C15 47nF 63V film cap, it is also advisable to put film in the power supply C9 C11 C16 C17.
The rest of the capacitors are ceramic, preferably NPO, but if you can’t find them, 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.
Transistors must be installed on the radiator through insulating gaskets, and under no circumstances should they be short-circuited!
A properly assembled amplifier turns on immediately and can be listened to. It is better to do the first switching on 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 parts will not burn out.
If you are fearless, you are confident in yourself and nothing interferes with you, then well, good luck, turn it on without a lamp, if something is phoning, humming or burning, immediately turn it off and look for errors. But it’s still better to compile without errors, google carefully for each plug, because if you make a mistake, the mistake can be costly.
Amplifier settings
Already collected? Wow! Congratulations. Now there's just a little bit left to do.
It is necessary to set the quiescent current within 50-70mA. I set it to 70mA.
For successful setup, the amplifier needs to be warmed up, just turn it on and listen to music for about 30 minutes, the fact is that until we set it up, it works in mode B, so it itself will not heat up.
How's the sound? Excellent of course. Now we need a multimeter. We set the measurement mode to millivolts, and connect the probes between the EMMITTERS of the first and second transistors, and set the desired quiescent current by slowly turning resistor VR1. For 70mA this is 30.8mV (U=I*R, U=70mA*(2*0.22 Ohm)=30.8mV).
That's all, congratulations! We do similar things with the second channel.
Slightly modified diagram:
We unsolder the variable resistors from the tone 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 RC4580IP, it was obtained from audio equipment.
All capacitors in the audio path are film! But in the power supply, electrolytes are 470 μF at 25 V. Resistors in the power supply are 1kOhm, 0.5W each. The remaining resistors are 0.25W each. I used 1N4743 zener diodes; unfortunately, there were no other less powerful ones.
No setup required, it works right away.
Attention! The board has an SMD jumper, or a 0 Ohm resistor on the track side. Don't forget to put it!
The payment in *.lay is in the applications.
Here you can choose what you prefer. I preferred caps of 22000 μF, but here it is advisable to parallel several capacitors so that the total is about 20000 μF; the total ESR of the capacitors will be less than that of a large one, therefore, at the peak it can deliver more current. A soft start turned out to be unnecessary here. I have KD2997 diodes. Film capacitors 1-4.7uF at 63V.
See the appendices for the power supply board.
How to connect a transformer?
We connect pins 2 and 2 together. And connect 220 to pins 1 and 1.
Now... We connect pins 7 and 7, and connect pins 8 and 8 to the indicator.
Although you can leave the original one, I still decided to replace it. I used the Slap Mikruham, ready from the amplifier, by Ilya S. (Nem0). Protects from overload and from constant output, and from constant both from plus and minus relative to the ground.
Scheme:
All resistors are 0.25W. Transistor BD135 can also be replaced with BD139; it must be installed on a small radiator. Zener diodes for 12V and 13V, assembled, it turns out to be 25V. 24V relay.
Capacitors C1 C2 C3 C4 for 25V. C5 at 50V.
The payment is also in the applications. One board already has protection for two channels.
I would have left the original indicator here, but since I burned it when it was connected incorrectly, the fact is that they put another indicator there, I couldn’t find a circuit for it anywhere, presumably it was a radio constructor.
I assembled it on two LM3915.
All resistors are 0.25W. The outer LEDs “100W” are red, the rest are green. It is configured as follows: connect to the output of the amplifier and turn the tuning resistor, at maximum volume, so that the entire display scale is shown, 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 speaker connection terminals. Like this, I cut it out of PCB.
The die is painted and the terminals are screwed in.
I did the same for attaching the audio input sockets. I screwed everything up and screwed it down. Final look:
We connect everything with wires.
First, food. We connect the power supply of the amplifiers to the rectifier block, we also connect the tone block board to the rectifier board, and we connect the protection board to the rectifier board in the +33V arm and ground, it won’t work otherwise! But we take the indicator’s power from terminals 8 from the transformer, through a diode bridge.
We connect the output from the amplifiers to the protection board, and connect the protection board with wires to the terminals for connecting speakers.
We connect the transformer to the switch on the front panel, and from it to the 220V power connector. All! You can turn it on! :)
This is what I got from the inside:
What it looks like when fully assembled and working:
I express my deep gratitude to Lyokha () for her help in the assembly! Good luck to all!
There is no need to mirror printed circuit boards.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Amplifier | |||||||
| Q1, Q2 | Bipolar transistor | MPSA18 | 4 | can be replaced with BC550, mirror pinout | To notepad | ||
| Q3, Q4 | Bipolar transistor | BC546 | 4 | To notepad | |||
| Q5, Q6, Q7 | Bipolar transistor | 2N5401 | 6 | To notepad | |||
| Q8, Q9 | Bipolar transistor | 2N5551 | 4 | To notepad | |||
| Q10 | Bipolar transistor | BD139 | 2 | To notepad | |||
| Q11 | Bipolar transistor | 2SC4793 | 2 | To notepad | |||
| Q12 | Bipolar transistor | 2SA1837 | 2 | To notepad | |||
| Q13 | Bipolar transistor | 2SC5200 | 2 | To notepad | |||
| Q14 | Bipolar transistor | 2SA1943 | 2 | To notepad | |||
| R4, R6 | Resistor | 680 Ohm | 4 | 0.25W | To notepad | ||
| R1 | Resistor | 10 kOhm | 2 | 0.25W | To notepad | ||
| R2 | Resistor | 10 ohm | 2 | 0.25W | To notepad | ||
| R3, R7, R9 | Resistor | 22 kOhm | 6 | 0.25W | To notepad | ||
| R5 | Resistor | 220 Ohm | 2 | 0.25W | To notepad | ||
| R8, R16 | Resistor | 510 Ohm | 4 | 0.25W | To notepad | ||
| R10, R14 | Resistor | 150 Ohm | 4 | 0.25W | To notepad | ||
| R11 | Resistor | 68 ohm | 2 | 0.25W | To notepad | ||
| R12, R13 | Resistor | 47 kOhm | 4 | 0.25W | To notepad | ||
| R15 | Resistor | 2 kOhm | 2 | 0.25W | To notepad | ||
| R17, R18, R19, R20 | Resistor | 22 Ohm | 8 | 0.25W | To notepad | ||
| R21 | Resistor | 33 Ohm | 2 | 0.25W | To notepad | ||
| R22, R23 | Resistor | 1.2 Ohm | 4 | 1W | To notepad | ||
| R24, R25 | Resistor | 0.22 Ohm | 4 | 5W | To notepad | ||
| R26 | Resistor | 4.7 Ohm | 2 | 1W | To notepad | ||
| R27 | Resistor | 10 ohm | 2 | 2W | To notepad | ||
| VR1 | Trimmer resistor | 1 kOhm | 2 | 3296 | To notepad | ||
| C1 | 10 µF 63V | 2 | To notepad | ||||
| C2, C6 | Capacitor | 100 pF | 4 | NPO | To notepad | ||
| C3 | Electrolytic capacitor | 470 µF 50V | 2 | To notepad | |||
| C4, C9, C11, C13, C14, C16, C17 | Capacitor | 100 nF | 14 | NPO | To notepad | ||
| C5 | Capacitor | 22 pF | 2 | NPO | To notepad | ||
| C7, C8 | Capacitor | 330 pF | 4 | NPO | To notepad | ||
| C10, C12 | Electrolytic capacitor | 100uF 50V | 4 | To notepad | |||
| C15 | Capacitor | 47 nF | 2 | NPO | To notepad | ||
| C18, C19 | Electrolytic capacitor | 1000uF 50V | 4 | To notepad | |||
| Operational amplifier | NE5532 | 1 | To notepad | ||||
| C1 C2 | Capacitor | 1 µF | 2 | 63V | To notepad | ||
| C3 C4 | Capacitor | 3.3 nF | 2 | 63V | To notepad | ||
| C5 C6 | Capacitor | 33 nF | 2 | 63V | To notepad | ||
| C7 C8 | Electrolytic capacitor | 470 µF 25V | 2 | To notepad | |||
| Capacitor | 100 nF | 2 | To notepad | ||||
| R1-R4 | Resistor | 4.7 kOhm | 4 | 0.25W | To notepad | ||
| R5-R10 | Resistor | 10 kOhm | 6 | 0.25W | To notepad | ||
| R11, R12 | Resistor | 1 kOhm | 2 | 0.25W | To notepad | ||
| R13 R14 | Resistor | 1 kOhm | 2 | 0.5W | To notepad | ||
| VD1 VD2 | Zener diode | 15V | 2 | 1N4743 | To notepad | ||
| VR1-VR3 | Variable resistor | 100 kOhm | 3 | TEMBER, BASS, BALANCE | To notepad | ||
| VR4 | Variable resistor | 47 kOhm | 1 | VOLUME | To notepad | ||
| LED driver | LM3915 | 2 | To notepad | ||||
| Rectifier diode | 1N4001 | 2 | To notepad | ||||
| Diode | Diode bridge | 1 | Any on 1 | To notepad | |||
| Electrolytic capacitor | 22 µF 16V | 2 | To notepad | ||||
| Capacitor | 100 nF | 2 | To notepad | ||||
| Electrolytic capacitor | 470 µF 16V | 1 | To notepad | ||||
| Variable resistor | 22 kOhm | 2 | To notepad | ||||
| Resistor | 510 Ohm | 2 | 0.25W | To notepad | |||
| Resistor | |||||||
