Idol 001 repair pre-amplifier

REPAIR OF THE ICON AMPLIFIER

Recently, one of my clients, for whom I repaired a lot of equipment, brought his brother - a very respectable and wealthy man (he owns a shoe store). And guess what, he asked me to fix a Soviet amplifier! It was a top-class ULF "KUMIR - 001". As it turns out, the man is a big fan. high-quality sound, for which he has a special room with a computer, a large meter-long screen, AC-90 speakers, a DVD player, an old analog Japanese FM tuner and, of course, a domestic “KUMIR” amplifier. The renovation is interesting, and so are the people, so I took it on with pleasure.

So, the amplifier. It has a three-band tone control, input and output switches, volume and balance controls and a loudness button. A large iron case, on the sides of which there are powerful duralumin radiators with transistors KT818 - KT819. Anyone who wishes can do so in the BOOKS section of the amplifier.

The layout inside is almost a copy of the Amphiton: a tone block in front, channels on the sides, and a transformer with stabilizers in the center. I connect my homemade 50-watt speakers to it, send a signal from the Iriver MP3 player through a simple adapter and start a survey: What are we complaining about? The volume control wheezes, one channel plays noticeably quieter than the other, and the bass is almost completely lost.

Let's start by replacing the variable resistor with the RG. Soviet regulators are noticeably inferior in quality to imported ones, but since ALPS was not at hand, I had to install the same one. The noise when rotating the new regulator immediately disappeared. Already better.

Let's move on, problems with the bass. Naturally, the first thought is the tone block. The second thought is that capacitors are electrolytes. This is one of the diseases of Soviet radio-electronic equipment, and we had to deal with their drying out more than once. I take a new imported 50V capacitor (for guarantee) 20 microfarads and begin to poke it one by one in parallel with the old capacitors installed on the board. Naturally with the music on.

Almost immediately I found a candidate for soldering. The bass rose sharply. I am replacing the capacitor. The same procedure for the other channel. That's it, the problem with the bass is solved. It remains to equalize the power balance of the channels.

Measurements of the quiescent current revealed an almost twofold imbalance in the current consumption of the right and left channels. Either the modes went away over time, or the quiescent current regulator was shaken off a little... In general, by twisting the trimming resistor a little, I achieved the same current and, accordingly, almost the same level of output power for both channels. That's all. We assemble, close and give the amplifier a mandatory one-hour run after repair.

Good day, dear forum users! I ask for your help, because I don’t have enough traction myself. There is an amplifier Kumir 35U-201S. The amplifier was in excellent condition, all capacitors were replaced, the output of the left channel was 0.003 V constant, the right channel -0.002. The quiescent current of both ends is 65mA. It worked perfectly, no noise, several modifications were made - the UM and UP inputs were on separate tulips, the network socket from the computer power supply, the outputs on the clamps, the correction amplifier and the input selector boards were removed, instead of the RP1-57 (the disease of these amplifiers) there is a Tocos A100K.

During the next revision there was a failure. Without going into details, I will say that pin 12 of the indication board (also known as the protection board) was connected to ground or to the socket phase. What we have now: the protection does not turn off, the overload indicators are on, the relays do not work.
During troubleshooting the following was found:
- power supply of all units is normal;
- there is no constant at the output of the terminal;
- transistors V7, V8, V9 of the indication (protection) board are broken. After replacing them, V9 cuts out again.
Voltages:
based on V9 0.6V instead of 1.2V (according to the diagram);
based on V7 0.2V instead of 0V (according to the diagram);
on 4.5 contacts 0V (the constant comes from the PA output here)
on the V9 40V manifold

The principle of operation of the protection of this amplifier:

The relays are switched on by the VT9 KT972A transistor on the indication board. The capacitance of Conder C4 500 μF determines the delay time for switching on the relays.
When the amplifier is operating, the signal from the PA outputs through circuit R15R16С3 goes to the base of transistor VT7, also on the display board. In the normal mode of operation of the amplifier, this transistor is closed, because in the absence of a constant voltage at the outputs of the PA, the voltage on the C3 connector and the base of this transistor does not have time to reach the opening voltage.
If a constant positive voltage appears at the output of any channel of the PA, C3 is charged and VT7 opens. The voltage on its collector and VT9 base drops sharply below the opening threshold, and VT9 closes, turning off the relays.
When a negative DC voltage appears at the outputs of the PA, VT9 closes thanks to VT8.

I have attached the amplifier circuit, the indication (protection) board on last page in the lower right corner.
Amplifier circuit
Schematic reader(djvu reader)

Master's answer:

Many music lovers who truly appreciate the sound quality of music certainly have Soviet sound amplifiers. Most often, these are the “Idol -001” amplifiers, which from time to time fail, just like, in principle, other equipment.

So, if your ULF “Idol” suddenly refused to work, then the reason may be hidden in various details. But first you need to know what this device is. On bulky metal case There are input-output switches, a powerful volume and balance control, and a button for loudness compensation. The sides of the case are “equipped” with duralumin radiators with transistors KT818 and KT819. It would be nice if you had the circuit diagram for your amplifier.

Inside, the device is arranged similarly to the Amphiton circuit: a transformer with several stabilizers is installed in the center, a tone block is in front and channels are on the sides. To find out the cause of the malfunction, connect speakers (50W) to the amplifier and send a signal from any MP3 player using the simplest adapter.

If you hear that the volume control is “wheezing”, and one of the channels sounds much quieter with completely lost bass, start the repair by replacing the damaged variable resistor on the volume control. Soviet-made regulators are quite inferior in quality to imported regulators. But since it is not always possible to find an ALPS device, install a regulator similar to the previous regulator. The disappearance of noise will immediately become noticeable when the new regulator is installed.

Next, we fix the problem with the bass. Leave the tone control unit in the background and focus on capacitors and electrolytes. It is because of their drying out that Soviet radio-electronic equipment so often becomes unusable. Turn on the music and place the “legs” of a new, preferably imported, capacitor (20 µF) one by one against the old capacitors on the board. During such a procedure for connecting capacitors in parallel, you will certainly find a faulty element: it will immediately reveal itself with a sharp increase in bass. Replace the part and perform the same manipulations with the other channel. Thus, the problem with low frequencies will be solved.

Now all you have to do is equalize the power balance of both channels. Measure the quiescent currents. If a 2-fold imbalance is detected in the current consumption of the left and right channels, then the reason may be hidden in a gradual shift of modes, or in the current regulator, which, probably, was previously thoroughly shaken. Adjust the trim resistor slightly so that the output power level on both channels is the same. The mids may “pump up” a little, but you can’t adjust it with a twisted midrange control. And why, the sound will be wonderful anyway.

Assemble the amplifier and run it for at least an hour.

Of course, although the device is Soviet, it works in the highest class: deep soft bass, excellent highs, and a significant power reserve. And all this despite the fact that the ULF has only 2x35 watts of power.