Complete preamplifier. High quality preamplifier based on EL2125. Transistor preamplifier

Pre-amplifier circuit with tone control.

Greetings, friends. Below in the article, a pre-amplifier project from Maxim Vasiliev is presented, which is essentially a remake of Sukhov’s preamplifier by transferring the circuit from the 157 series of microcircuits to import. More detailed information You can find it on KOTA and the vegalab forum by searching for “Vasiliev’s Complete Amplifier”. Schematic diagram:

To enlarge the image, click on the picture.

The circuit uses dual operational amplifiers. For example, you can put OPA2134P, TL072 or NE5532, as you like or whichever of these on this moment is at hand. The following figure shows the pinout layout of the microcircuits; the above ones are the same, so no matter which MS you use, you don’t need to make any changes to the board:

We won’t write about which microcircuits sound better; you can find a lot of information about this on amateur radio forums, and there are plenty of them on the Internet.

The power supply is bipolar +/- 12…15 Volts.

Variable resistors of group “A” (imported) are used as volume, balance and tone controls; if you use domestic variables, choose with group “B”

The printed circuit board is made of double-sided fiberglass. Upper layer not etched, it is used as a screen. Board dimensions 70x158 mm.

The appearance of the printed circuit board is shown in the following two figures:

A bipolar voltage stabilizer 2 x 15 Volts on 78L15 and 79L15 chips has been added to the board. The figure below shows the pin layout of the 2N5551 transistor:

The circuit diagram and printed circuit board in LAY format can be downloaded via a direct link from our website. The archive file size for downloading is 0.53 Mb.

From a consumer point of view, buying a preamp is a waste of money. Why is this necessary when there are complete amplifiers with rich sound settings? But if you are looking for “that” sound or are building a system and are standing between the choice of an integrated amplifier and separate units, then here are the pros from the famous independent expert Vladimir Elbaev.

Preamp: The System Saga

"Pre" habitat

I am periodically called upon to write articles about the most mysterious "beast" in the home audio system. As a rule, the media “pulls him by the ears” either to an MP3 player, or to karaoke, or to a professional recording studio. Yes, preamplifier can voice all this and much more, but the range of such wide possibilities is not a reason to dismiss his role. We can expect an immediate effect from any preamplifier or AV processor, unless we have some kind of stereo power amplifier. This effect is nothing less than a love of genuine art instead of the simple habit of consuming music in compressed formats. AV processors and good preamps are expensive. First of all, because their circuits “transform” the frail, flat and squeaky sound from the turntables into a “live” sound, the double bass plucks of which give goosebumps every time. The preamplifier is good for liberating the listener. In a word, this product is intelligent.

When selecting or updating your audio, you will certainly come across an offer to purchase two amplification units. One will be called preliminary (aka “pre”), the other powerful amplifier(it is also called the final amplifier), and if they are combined in a common unit, then it is an integrated, or complete, amplifier. In the expensive category of digital multi-channel systems, there is an AV processor (hereinafter referred to as “percent” for brevity). “Previous” the best investment of money and system upgrade.

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Lexicon MC-12B HD AV Processor combines Lexicon LIVE equalization with LOGIC 7 ® surround sound processing

With a “pre” or “proc” your system will look like this: source + preamp + amplifier + acoustics. Sources can be: disc player, vinyl player, transport, satellite TV tuner, cassette deck. The “pre-amp” can be a pre-amplifier or an AV processor. A power amplifier is just that: a power amplifier. Everything is clear with acoustics too. “Pred” is found in nature more often than one might think.

Arsenal Rimbaud

Blessed are the owners of Sharp block mini-systems from the 80s, in which the “pre” is distinguished not only by a beautiful “professional” frequency spectrum indicator. The block-by-block design gave the engineer the opportunity to optimize the circuit, that is, raise the current (V volts) and lower the resistance (Ohm ohms) to the “limit”. In this form, it became possible to “cut” and “color” the signal, safely keeping the signal-to-noise ratio above 100 dB, and distortion below one whole percent. In practice, this is ensured by special calibration of the power transformer for the “pre” circuit.

Specifically, the old “Sharps” were striking in their high-quality, dramatically expressive multi-band equalizer. The highest achievement of JVC engineers “pre” JP-S7 for a stereo system, equipped with a device of the same caliber. In both cases, equalizer engines only affect “their own” frequency and do not “capture” neighboring ones. But “pre” or Hi-End AV processors may not have tone controls at all and still produce no less detailed, expressive, dynamic and rich sound.

“Own” power allows you to work out the second switching important function"preda". The JVC preamp features custom input impedance and capacitance (pF) adjustments for turntable input, plus variable output sensitivity (V). Both plus a built-in equalizer diversify the user's capabilities. However, this was not enough for the engineers, and they equipped the “pre” with a function to completely turn off the “bells and whistles”. This is the shortest way to obtain an “uncolored” audio signal. Finally, two pre-out jacks can be effectively used to connect a power speaker with stereo speakers and an active subwoofer. In general, when the arsenal is large, like the movie character Rimbaud in an army warehouse, then you can choose any “weapon” and get an additional thrill from it.

"Preliminary" tips

If the reader thinks that I am pushing the topic, then here it is: there is a generation of integrated amplifiers and even AV receivers with a colossal range of sound adjustments and without tedious distortion. But they and their settings are like roulette. “Interesting” sound is the law and property of any simple “pred”, whose “trance” is not “burdened” with other functions. That is why decks and vinyl have taken root in the stereo format, and in digital systems - transports with “raw” data transfer to “percent”. The more such “decouplings”, the better for the sound of the system, and the decoupling of “pred” from “power” is the last and best in this series.

As a result, such an “arsenal” allows the owner of a “pre” and a serious audio system to neutralize the shortcomings of recording and duplicating discs, as well as frequency resonances inherent in any room. To avoid getting bogged down in the physical aspects, here are some key tips:

1. On the “pre” equalizer, it is better to adjust the central frequency in the low and high frequencies as close as possible to 1 kHz, and “drop” the midrange by half a decibel.

2. Disable all digital effects and reverberations of the AV processor, and in setting the non-disabled Pro Logic modes and other volumes, set the rear and center channels to be equal to the front ones in terms of volume and timbre. This is clearly audible on the test tone and gives the sound in any mode its natural reverberation.

3. The sound function control (sensitivity or load) always obeys the rule: movement from left to right increases the “ringing” and weakens the “bass”. In relation to a power amplifier, it is better to output the “pre” output at the maximum level, and the “power” input, respectively, at the minimum level.

4. The lower the output impedance of the “pre” and the higher the input impedance of the “power”, the better and more dynamic the sound will be. However, practical mistakes This doesn't happen - there are conflicting and confusing specifications. Excellent compatibility is always achieved by the classic combination of a tube-based stereo preamplifier and a MOSFET transistor power supply (MOSFET = metall-oxyde-semiconductor field effect transistor = transistor manufacturing technology).

5. The author is not aware of any good tube AV processors; combining a “processor” with a tube multi-channel power amplifier is problematic, but using a multi-channel analog post-DAC output, the signal from a DVD player can be sent to a tube “pre”, then to a power amplifier.

6. You can connect directly active speakers to the “pre”, but achieve good sound only possible from studio models. Disadvantage: time-consuming configuration setup.

"Orchestral" brass

Not all Hi-End class “pres” are equal, since some companies are not artistic enough, others are not able to overcome their own ideological limitations, and still others are better at power amplifiers.

The price is high, but the specific “color” of Marantz captivates. Just as Frank Sinatra once founded a record company based on the sound of big band and swing, the new “stereo pred” Marantz SC-7S2 impresses with the shining brass of the orchestra, effectively shaded by the double bass and drums. It is not for nothing that the model goes back to a prototype of the same era, produced in 1958. The company has saved on a number of functions today, since in fact valuable materials and high-precision production have become more expensive since then. Thank you, at least they left the sound quality. This is the second modification of the “legend”, equipped to meet the requirements of the current generation of digital media.

Four Wolfson chips make up a “prosaic” volume control and allow you to extend the frequency range up to 150 kHz, the original HDAM modules of Japanese engineer Ken Ishiwata handle the sound in the output part of the circuit, balanced with feedback the circuit receives pure power from a “strong” ring-shaped transformer (trans).

For fans of the studio mix, software Steinberg Nuendo and simply recording to pre or proc blanks offer added audio processing and configuration flexibility. For example, equalized recording, selection of a higher bitrate, upsampling (improving the sound quality of a CD by using technology to increase the data quantization frequency to 192 kHz). The presence of a DAC and ADC in the “process” allows you to process and dynamically “expand”, say, a signal from archival vinyl or filter the noise of an analog tape in digital form, and then turn it into analog on a DAC. Almost studio remastering of old recordings.

"Mirror" signs

How to spot a cool “pre” at first sight? Typically, this is a balanced design, in which both halves of the stereo circuit appear "mirror-like" and terminated on the rear panel with so-called XLR terminals. If the rest of the system is not equipped with this, you will still have high-caliber sound even from regular RCA jacks. Another sign of class is the presence of an input for vinyl from the MC head, which is twice as weak as the MM in terms of signal and twice as “bohemian” in status. The best “preds” have sections inside the body and a massive chassis with copper bolt heads on the bottom and walls.

Distinctive features in the scheme. Special scheme for HDCD no comments. DSP digital audio effects processor Cirrus CS 49326 chip or equivalent. Further. DAC and ADC: Cirrus, Wolfson chips with upsampling capability. Thanks to the massive transformer and energy capacitors in the circuit, these chips are powered better than their counterparts in the player. Thus, all audio on the “process” acquires a natural extended and smoothly decreasing frequency response. It is also important to have an audiophile “direct” mode with all “extra” circuits turned off, except, perhaps, the DAC. In the “process”, detailed tuning of the subwoofer with the choice of LFE filter frequency and its steepness is very important. A quiet level of music should convey bass lines clearly.

Non-obvious signs. You can start from the schema class. Class A means high current consumption and a simpler and more “direct” signal delivery scheme - the so-called “fast” sound. Class D is characteristic of subwoofer circuits because there are more parts involved where the RF signal is “lost.” The most optimal for “pre” “intermediate” class B or AB. Manufacturers like to boast about strict selection, close component ratings in each channel (no higher than 0.5 dB), high stereo separation (about 100 dB), a high-current (75 amp) transformer in the power circuit and a low-impedance low-impedance load on the power amplifier. This also includes dynamic response(0 100 dB) and frequency response (10 Hz 100 kHz).

Control center

A preamplifier, either a stand-alone stereo or part of a multi-channel AV processor, allows the owner to adjust the volume and taste of the system, and switch sound sources, including vinyl. The "pre" is often called the control center or controller because it prepares the signal for the power amplifier. It should be located in plain sight, while the heating and heavy block The power supply can be extended to the length of the cable and hidden (taking into account ventilation).

The electrical circuit "pre" determines the sound quality of the system more than even the acoustics. The equalizer and channel levels in the processor are capable of creating breathtakingly realistic stereo without resorting to digital effects DSP or to the “direct” audiophile path. The quality and length of wires, accessories are important, but in this case they are not critical.

DIY preamplifier— I recommend to radio amateurs a circuit of simple and at the same time high-quality sound power with a built-in timbre block. The preamp is built on the basis of the well-known two-channel audio operational amplifier LM833.

The working area of ​​the microcircuit is implemented using a non-inverting amplifier circuit with serial negative voltage feedback, and the unused area is assembled using a repeater circuit, that is, it is simply muted. The effective bandwidth of this circuit ranges from 0.6 Hz to 18 kHz. The approximate gain is in the range from 0.9 to 110 based on the set values ​​of the trimming resistor.

The LM833 dual operational amplifier was originally designed for use in high-end audio applications. Such, for example; like pre-amplifiers and filters that cannot work without a bipolar power supply. The circuitry of this device is capable of operating with supply voltages in the range from ±6v to ±18v, while the coefficient of nonlinear distortion (THD) is only 0.002%. The peak voltage gain of the LM833 op amp reaches 112dB with a rated current of 6mA.

Pre-amp circuit

Any other two-channel op-amp can be used as an operational amplifier.

Low pass filter for subwoofer

Low-frequency speaker systems are usually bulky and expensive, and given that the human ear cannot detect stereo at low frequencies, it is clear that there is no point in having two low-frequency speakers - one for each stereo channel. Especially if the room where the stereo system will operate is not very large.

In this case, you need to sum the signals of the stereo channels, and then extract the low-frequency signal from the resulting signal. Figure 1 shows the circuit of an active filter made on two operational amplifiers of the microcircuit TL062.

Stereo channel signals are sent to connector X1. Resistors R1 and R2, together with the inverse input of op amp A1.1, create a mixer that forms a common mono signal from a stereo signal; op amp A1.1 provides the necessary amplification (or attenuation) of the input signal. The signal level is regulated by variable resistor R3, which is part of the OOS circuit A1.1. From output A1.1, the signal goes to the low-pass filter at A1.2. The frequency can be adjusted with a dual variable resistor consisting of R7 and R8.

The low-frequency signal to the low-frequency ULF or active low-frequency speaker is supplied through connector X2.
The power supply is bipolar, supplied through connector X3, possibly from ±5V to ±15V. The circuit can be assembled using any two general-purpose operational amplifiers.

Mixer for working with three microphones.
If you need signals from three separate sources, for example, from microphones, to be fed to one input of a recording or playback audio device, you need a mixer that can be used to combine audio signals from three sources into one and adjust their level ratio as required.

Figure 2 shows a mixer made on a chip like LM348, which has four operational amplifiers.
Signals from microphones are supplied, respectively, to connectors X1, X2 and X3. Next, to microphone preamplifiers on operational amplifiers A1.1, A 1.2 and A1.3. The gain of each op-amp depends on the parameters of its OOS circuit. This allows you to widely adjust the gain by changing the resistances of resistors R4, R10 and R17, respectively. Therefore, if not a microphone, but a device with more high level output voltage of the AF, it will be possible to set the gain of the corresponding op-amp by selecting the resistance of the corresponding resistor. Moreover, the range of setting the gain is very large - from hundreds and thousands to unity.

Amplified signals from three sources are supplied to variable resistors R5, R11, R19, with the help of which you can quickly adjust the ratio of signals in the overall signal, up to complete suppression of the signal from one or more sources.
The mixer itself is made using op amp A1.4. Signals to its inverse input come from variable resistors through resistors R6, R12, R19.
The LF signal is supplied to an external recording or amplifier device via connector X5.
Power supply is bipolar, supplied through connector X4, possibly from +5V to +15V.

The circuit can be assembled using any four general-purpose operational amplifiers.

Pre-amplifier with tone control.
Many radio amateurs will build UMZCHs based on integrated circuits UMZCHs, usually intended for car audio equipment. Their main advantage is that a completely high-quality UMZCH is obtained in the shortest possible time and with minimal labor costs. The only drawback is that the ULF is not complete, without a preamplifier with volume and tone controls.

Figure 3 shows a diagram of a simple preamplifier with volume and tone controls, built on the most common element base - transistors of the type KT3102E The amplifier has a high enough input impedance that it can work with almost any signal source, from a PC sound card and digital player, to an archaic turntable with a piezoelectric pickup.

The cascade on transistor VT1 is built according to an emitter follower circuit and serves mainly to increase the input resistance and reduce the influence of the signal source output parameters on tone control.

The volume control - variable resistor R3, is also the load of the emitter follower on transistor VT1.
Next is a passive bridge tone control for low and high frequencies, made using variable resistors
R6 ( low frequencies) and R10 ( high frequencies). Adjustment range 12dB.

The cascade on transistor VT2 serves to compensate for signal level losses in the passive tone control. The gain of the cascade on VT2 largely depends on the magnitude of the feedback, specifically the resistance of resistor R13 (the lower, the greater the gain). The DC mode is set by resistor R11 for the cascade on VT2 and R1 for the cascade on VT1.

The stereo version should consist of two such amplifiers. Resistors R6 and R10 must be doubled in order to adjust the tone in both channels simultaneously. Volume controls can be made separate for each channel.

The supply voltage is 12V, unipolar, corresponding to the rated supply voltage of most microcircuits - integrated UMZCH, designed for use in automotive applications.

Radio adapter
All stationary audio equipment must have line-out and line-in connectors. The linear input can be supplied with a signal from external source In order to use the main device as an amplifier with speaker systems or for recording, most portable equipment simply does not have a line input. The only "means of communication with outside world"are a microphone and a built-in radio receiver. One of my friends tried to transfer the signal from an MP-3 flash player to a magnetic cassette by putting headphones on the microphone “hole” of an old portable CD recorder. It turned out terrible. Although, it was possible to use the built-in FM receiver, but for this you need at least a simple adapter.

For high-quality stereo signal transmission, you can use a purchased FM modulator designed to wirelessly connect an external audio source to the car radio. It has a stereo modulator, a good transmitter with a frequency synthesizer and, often, a built-in MP-3 player with an external flash drive or memory card. Well, in the simplest case, you can make a primitive single-transistor low-power transmitter, the signal of which the receiver can receive when the transmitter is located close to its antenna.
The adapter circuit is shown in Figure 4.

The circuit is a cascade of an RF generator on transistor VT1, operating at HF ​​according to a circuit with common base, into the base circuit of which a modulating low-frequency signal is supplied.

An audio frequency signal from an external source is supplied to the base VT1 through capacitor C4 and two resistors R1 and R2, which serve as a mixer of stereo channels. Since the circuit is very simple and there are no nodes in it that form a complex stereo signal, the signal will be sent to the receiver input in monophonic form.

LF voltage, arriving at the base of transistor VT1, changes not only its operating point, but also the junction capacitance. The result is mixed amplitude-frequency modulation. Amplitude modulation is effectively suppressed in the receiving path of the radio receiver, and frequency modulation is detected by its frequency detector.

The HF frequency at which the broadcast occurs is set by the L1-C2 circuit. In fact, there is no antenna - the adapter is located in close proximity to the receiver antenna, and the signal comes to it directly from the loop coil.
The L1 contour coil is frameless, its internal diameter is 10-12 mm, wound with PEV 1.06 wire, 10 turns in total. You can adjust the circuit either with a tuning capacitor or by compressing and stretching the turns of the coil.
Power supply - two elements of 1.5V (3V).

Level indicator.
To correctly establish stereo balance and avoid overloading the ULF and speaker systems, it is desirable that the ULF includes an indicator of the signal level entering the ULF input.

From a practical point of view, for self-made, the best indicator is based on an LED scale; it is mechanically much stronger than a pointer and is simpler and cheaper than a scale mnemonic.

Figure 5 shows the indicator diagram for both stereo channels. It is based on a microcircuit TA7666R.
Inside the TA7666R IC there are two amplifiers with detectors at the outputs and two lines of comparators, five comparators for each channel.

The gain of each amplifier can be set individually by selecting the resistance of resistors R1 and R2. With the value indicated in the diagram, the first stage of the LEDs (HL1 and HL6) lights up at input levels of 48 mV, the second stage (HL2, HL7) at 86 mV, the third stage (HL3, HL8) at 152 mV, the fourth stage (HL4, HL9) at 215 mV, fifth (HL5, HL10) at 304 mV. The method of displaying the indication is “bar”, that is, “thermometer column”, in other words, the larger the signal, the longer the line of glowing LEDs.
You can always change the sensitivity by selecting the resistances of resistors R1 and R2.

Based on this microcircuit, you can make a kind of light-dynamic device, for example, composed of concentric circles of incandescent lamps or LED lamps, for example, used in automotive optics. In this case, additional powerful output stages will be required.
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High quality preamplifier NATALY

Schematic diagram, description, printed circuit board

This preamplifier is used for timbre correction and loudness compensation when adjusting the volume. Can be used to connect headphones.

For a high-quality path that includes an UMZCH with nonlinear and intermodulation distortions of the order of 0.001%, the remaining stages become important, which should allow the full potential to be realized. Currently, there are many known options for implementing high parameters, including using op-amps. The reasons for developing our own version of the preamplifier were the following factors:

When assembling a preamplifier on an op-amp, the threshold of its output voltage, and therefore the overload capacity, is entirely determined by the supply voltage of the op-amp, and in the case of power supply from +\-15V it cannot be higher than this voltage.
The results of subjective examinations of preamplifiers based on op-amps in their pure form (without output repeaters) and with those, for example, based on a parallel amplifier, show listeners’ preference for the op-amp + repeater circuit, with almost identical parameters “from the point of view of Kg”, this is explained by the narrowing of the spectrum of op-amp distortion when working with a high-resistance load and operating its output stage without entering the AB mode, which produces switching distortions that are practically below the level of sensitivity of the devices (Kg OU ORA134, for example - 0.00008%), but clearly noticeable when listening. This is why, as well as for a number of other reasons, listeners clearly distinguish a preamplifier with a transistor output stage.
The well-known circuit solution containing an integrated repeater based on the BUF634 parallel amplifier is quite expensive (buffer price is at least 500 rubles), although internal circuit buffer can be easily implemented in discrete - for a much more reasonable amount.
Amplifiers in which the op-amp operates in small-signal mode show high performance, but according to the results of the auditions they lose. In addition, they are very critical to set up and require, at a minimum, a square wave generator and a wideband oscilloscope. And all this with clearly worse subjective results.

The lack of output voltage in the PU circuit (op-amp + buffer) can be eliminated by implementing voltage amplification in the buffer, and deep local feedback eliminates distortion. A sufficiently high initial quiescent current in the output transistors of the buffer guarantees its operation without distortions characteristic of push-pull structures in the AV mode. The presence of only a twofold voltage amplification allows one to achieve an increase in overload capacity by 6 dB, and with a threefold amplification, this figure becomes equal to 9 dB. When the buffer operates from a +\-30V power source, its output voltage range is 58 volts peak to peak. If the buffer is powered from +\-45V, then the output voltage from peak to peak can be about 87V. Such a reserve will have a positive effect when listening to vinyl discs that have characteristics in the form of clicks from dust.
The two-stage implementation of the preamplifier is due to the fact that the timbre block introduces attenuation into the signal up to 10...12 dB. Of course, you can compensate for this by increasing the gain of the second stage, but, as practice shows, it is better to apply as much voltage as possible to the tone block - this increases the signal to noise ratio. In addition, it is quite common to find discs recorded with a high crest factor (loud peaks and rather low average volume). This is not a lack of mixing, rather, on the contrary, because sound engineers often abuse the compressor, trying to fit all levels of sound volume into the CD range. But we cannot pretend that such records do not exist. The listener turns up the volume. Thus, the second stage must have no less overload capacity, in addition, it must have low intrinsic noise, high input impedance and the ability to pass the real signal without distortion after the timbre block, in which the extreme frequencies of the audio range go with the greatest rise. An additional requirement is a linear frequency response when the tone control is turned off, an even response when testing with a meander, and subjective invisibility of the control unit in the path.

Matyushkin’s well-proven tone block was used as a tone block. It has a 4-stage low-frequency adjustment and smooth high-frequency adjustment, and its frequency response corresponds well to auditory perception; in any case, the classic bridge TB (which can also be used) is rated lower by listeners. The relay allows, if necessary, to disable any frequency correction in the path; the output signal level is adjusted by a trimming resistor to equalize the gain at a frequency of 1000 Hz in the TB mode and when bypassing.
The balance regulator is built into the OOS of the second stage and has no special features.
The low bias voltage of the OPA134 (in the author’s practice, at the output of the second stage is no more than 1 mV) makes it possible to eliminate transition capacitors in the circuit, leaving only one at the input of the control unit, because the level is unknown DC voltage at the output of the signal source. And, although at the output of the second stage the diagram shows capacitors of 4.7 μF + 2200 pF - with a zero offset level of about a millivolt or less - they can be safely eliminated by short-circuiting them. This will put an end to the debate about the effect of capacitors in the path on sound - the most radical method.

Design characteristics:

Kg in the frequency range from 20 Hz to 20 kHz - less than 0.001% (typical value about 0.0005%)
Rated input voltage, V 0.775
The overload capacity in the tone block bypass mode is at least 20 dB.
The minimum load resistance at which operation of the output stage is guaranteed in mode A is with a maximum peak-to-peak output voltage swing of 58V 1.5 kOhm.

When using a pre-amplifier only with CD players, it is permissible to reduce the buffer supply voltage to +\-15V because the output voltage range of such signal sources is obviously limited from above, this will not affect the parameters.
Setting up a pre-amplifier should begin by checking the DC modes of the output buffer transistors. Based on the voltage drop in the circuits of their emitters, the quiescent current is set - for the first stage it is about 20 mA, for the second - 20..25 mA. When using small heat sinks, which become mandatory at +\-30V, it is possible, depending on the temperature situation, to increase the quiescent current a little more.
It is best to select the quiescent current using resistors in the emitters of the first two buffer transistors. If the current is low, increase the resistance; if the current is high, decrease it. Both resistors need to be changed equally.
With the quiescent current set, we then set the TB regulators to the position corresponding to the flattest frequency response, and, by applying a 1000 Hz signal with a rated voltage of 0.775V to the input, we measure the voltage at the output of the second buffer. Then we turn on the bypass mode and use a trimming resistor to achieve the same amplitude as with the TB.
At the final stage, we connect the stereo balance control and check for the absence different forms instability (the author has not encountered such a problem) and conduct listening. Setting up Matyushkin's TB is well covered in the author's article and is not discussed here.
To power the preamplifier, a stabilized power supply is recommended, with independent windings for control panel and relay switching. Technically, the power requirements are nothing new. The main thing is the low level of mid-range and high-frequency noise, the suppression of which by power supply is known for the op-amp. About the ripple level - it should not exceed 0.5 - 1 mV.

A complete set of boards consists of two PU channels, Matyushkin RT (one board for both channels) and a power supply. Printed circuit boards were designed by Vladimir Lepekhin.

Double Sided Pre-Amplifier PCB:

INCREASE

Printed circuit board for TB Matyushkin with relay switching:

ENLARGE The circuit is stable. There is no noticeable voltage ripple at the output; measurements were taken on an oscilloscope in the 0.01 division/volt mode (for mine this is the minimum limit).

INCREASE

Measurement results:

On OPA134 (only the first link of two), the power supply is single-stage, +\-15V:

Kni(1kHz)........................ -98dB (about 0.0003%)
Kim(50Hz+7kHz)................less than -98dB (about 0.0003%)

On ORA132 (both links), full version, two-stage power supply:

Kni (1kHz)........................ -100dB (about 0.00025%)
Kim (19kHz+20kHz)................... -96dB (about 0.0003%)

In the case of self-excitation of HF cascades, mica correction capacitors with a capacity of 100 to 470 pF should be soldered in parallel with resistors R28, R88 and their complementary ones in another channel. This was discovered when using transistors BC546\BC556 + 2SA1837\2SC4793.

In the attachments you can download all the schematic files and printed circuit boards in SPlan 6.0 and SL 5.0 formats, respectively,