High quality preamplifier "Nataly". My version. High-quality Nataly Ump High Quality Pre-Amplifier Scheme

Most audio delivers are quite categorically and not ready for compromise when choosing equipment, rightly believing that the perceived sound must be clean, strong and impressive. How to achieve this?

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Perhaps the main role in solving this issue will play the choice of the amplifier.
Function
The amplifier is responsible for the quality and power of sound playback. At the same time, when buying it is worth paying attention to the following notation, marking the implementation high technologies In the production of audio equipment:

Hi-Fi. Provides maximum purity and accuracy of sound, freeing it from extraneous noise and distortion.
Hi-End. The choice of perfectionist, ready to pay a lot for the pleasure of distinguishing the smallest nuances of favorite musical compositions. Often, this category includes manual assembly equipment.

Specifications that should be paid attention to:

Entrance I. output power. The nominal output power indicator is crucial, because Edge values \u200b\u200bare often unreliable.
Frequency range. Varies from 20 to 20,000 Hz.
Nonlinear distortion coefficient. Here everything is simple - the smaller the better. Perfect value, according to experts - 0.1%.
Signal ratio and noise. Modern technique suggests the meaning of this indicator over 100 dB, which minimizes foreign Summas When listening.
Dumping factor. Reflects the output resistance of the amplifier in its ratio with the nominal load resistance. In other words, a sufficient index of the dumping factor (more than 100) reduces the occurrence of unnecessary vibrations of equipment, etc.

It should be remembered: making quality amplifiers - time-consuming and high-tech process, respectively, too low price with decent characteristics should alert you.

Classification

To understand all the variety of market proposals, it is necessary to distinguish the product on various criteria. Amplifiers can classify:

By power. Preliminary - a peculiar intermediate between the sound source and the final power amplifier. Power amplifier, in turn, is responsible for the strength and volume of the output signal. Together they form a complete amplifier.

Important: Primary conversion and signal processing occurs in advance amplifiers.

On the element base, the lamp, transistor and integral mind differ. The latter arose to combine advantages and minimize the shortcomings of the first two, for example, the sound quality of the lamp amplifiers and the compactness of transistor.
By mode of operation, amplifiers are divided into classes. Basic classes - A, B, AV. If class A amplifiers use a lot of energy, but give high-quality sound, class B accuracy to the opposite, the AB class seems to be an optimal choice, representing a compromise signal quality ratio and a sufficiently high efficiency. Also distinguish classes C, D, H and G, which occurred using digital technology. Also distinguish between the one-step and two-stroke modes of the output cascade.
By the number of channels, amplifiers may be single, two- and multichannels. The latter are actively used in home theaters for the formation of the volume and realism of the sound. Most often there are two-channel, respectively for the right and left audio system.

Attention: The study of technical components of the purchase, of course, is necessary, but often the decisive factor is the elementary listening of equipment on the principle sounds no sound.

Application

The choice of amplifier is more justified by the goals for which it is purchased. We list the main areas of using sound frequency amplifiers:

As part of home audio complex. Obviously, the best choice is the lamp dual-channel one-bit in class A, also the optimal selection can be a three-channel class AB, where one channel is defined for a subwoofer, with Hi-Fi function.
For an acoustic system in the car. The most popular four-channel AV or D class amplifiers, in accordance with the financial capabilities of the buyer. In cars, the crossover feature is also in demand for smooth frequency adjustment, which allows you to cut frequencies in a high or low range as needed.
In concert equipment. The quality and capabilities of professional equipment, higher requirements are reasonable for the largest distribution space. sound signals, as well as high need for intensity and duration of use. Thus, it is recommended to purchase an amplifier class not lower than D, capable of working at almost the limit of its capacity (70-80% of the claimed), preferably in the housing from high-tech materials protecting against negative weather conditions and mechanical impacts.
In the studio equipment. All of the above is valid for the studio equipment. You can add about the largest range of frequency playback - from 10 Hz to 100 kHz in comparison with such from 20 Hz to 20 kHz in the household amplifier. It is also noteworthy the possibility of separate volume control on different channels.

In the way that for a long time Enjoy clean I. qualitative soundIt is advisable to study all the variety of proposals in advance and choose an audio equipment option that meets your requests as possible.

What I have on this moment:

1. Amplifier itself:

2. Naturally, the terminal power supply unit:

When configuring the mind, I use the device that provides safe connection Transformer Mind to the network (via lamp). It is made in a separate box with its cord and a socket and, if necessary, connects to any device. The scheme is shown below in the figure. For this device, a relay with a 220 AC winding is required and with two groups of contacts for closure, one button without fixing (S2), one button with fixation or switch (S1). When the S1 is closed, the transformer connects to the network via the lamp if all the MOD modes are normal, when you press the S2 button, the relay via one contact group closes the lamp and connects the transformer directly to the network, and the second contact group, duplicating the S2 button constantly connects the relay to the network. In this state, the device is up to the moment of opening S1, or the voltage decreases less voltage to hold the relay contacts (including KZ). The next time you turn on S1, the transformer is again connected to the network through the lamp, and so on ...

Noise immunity different ways Screening of signal wires

3. We also have assembled AC protection from constant voltage:

The defense is implemented:
AC connection delay
Protecting against output, from KZ
Control of blowing and disconnecting the AU when overheating radiators

Establishment:
Suppose everything is collected from serviceable and tester tester transistors and diodes. Initially, put the engines in the following provisions: R6 - in the middle, R12, R13 - to the top according to the scheme.
Stabilitron VD7 at first do not seserve. At PP protection, the COBEL circuits needed for the stability of the amplifier, if they are already available on the digestion boards, it is not necessary to solder them, and the coils can be replaced with jumpers. Otherwise, the coils are dumped on a mandrel with a diameter of 10 mm, for example, the tail of the drill - with a wire with a diameter of 1 mm. The length of the resulting winding should be such that the coil is inserted into the holes allotted for it. After winding, I recommend to impregnate the wire with a varnish or glue, for example, epoxy or BF - for rigidity.
Wires coming from protection to the output of the amplifier, while connecting with a shared wire, disconnecting from its outputs, of course. It is necessary to connect with the "Mecca" of the urzch earth protection polygon, designated on PP marked "Main GND", otherwise the protection will not work correctly. Well, of course, GND sites next to the coils.
Turning on the protection with the connected speakers, begin to reduce the resistance R6 before clicking the relay. By reloading another one or two revolutions of the trim, turn off the network protection, turn on two speakers in parallel to any of the channels and check whether the relays will work. If you do not work, then everything works as conceived, when 2 Ohm, the amplifiers will not be connected to it, to avoid damage.
Next, we turn off the wires "from the umzch lk" and "from the UMBC of PC" from the ground, we turn on everything and check whether the protection will work if these wires are submitted constant pressure About two or three volts. The relay must disconnect the speakers - there will be a click.
You can enter an indication "Protection", if connecting the chain from the Red LED LED and the resistor in 10 kΩ between the Earth and the VT6 collector. This LED will show a malfunction.
Next, configure the thermocontrol. The thermistors are dressed in a waterproof tube (attention! They should not get wet during the test!).
It often happens that the radio amateur does not have thermistors specified in the scheme. Two are suitable for the same of the existing, resistance from 4.7 com, but in this case the resistance R15 should be equal to the double resistance of sequentially included thermistors. The thermistors must have a negative resistance coefficient (reduce it with heating), the posistors work on the contrary, and here they are not a place. Capture a glass of water. I give him 10-15 minutes to fit into relax air and lower the thermistors into it. Curtain R13 until the "Overheat" LED has matured - overheat, which was to burn initially.
When the water cools down the degrees to 50 (this can be accelerated, as it is - a big secret) - twist R12 so that the "blowing" LED or Fan ON.
Separate the VD7 stabilitron in place.
If the glitches are not detected from the sealing of this stabitron, then everything is fine, but it was that without it the transistor part works flawlessly, and it does not want to connect the relay in any way. In this case, we change it to any stabilization voltage from 3.3 V to 10V. The reason is the leakage of Stabilon.
When heating the thermistors to 90 * C should light up the Overheat LED - overheating and the relay will turn off the speakers from the amplifier. With some cooler of the radiators, everything connects back, but such a mode of operation of the device should at least alert the owner. With a good fan and not clogged with dust of the thermal triggering tunnel should not be observed at all.
If everything is fine, we solder the wires on the output of the amplifier and enjoy.
By blowing (its intensity) is configured by the selection of resistors R24 and R25. The first determines the productivity of the cooler when the envelope is enabled (maximum), the second - when the radiators are just a slight warm. R25 can be excluded at all, but then the fan will operate in ON-OFF mode.
If the relays have a 24V winding, then they must be connected in parallel, but if 12 is sequentially.
Replacement details. As an OU, you can apply almost any dual cheap OU into the SOIC8 (from 4558 to the ORA2132, though, I hope it will not reach the latter), for example, TL072, NE5532, NJM4580, etc.
Transistors - 2N5551 are changing at SV546-SP548, or on our CT3102. BD139 will be replaced by 2SC4793, 2SC2383, or on a similar current and voltage, it is possible to put even kT815.
The chewfather changes to the similar applied, the choice is huge. The radiator for the bevel is not required.
1N4148 diodes are changed to 1N4004 - 1N4007 or on KD522. In the rectifier, you can put 1N4004 - 1N4007 or use diode bridge with a current of 1 A.
If the control of blowing and protection against overheating umzch is not needed, then the right part of the scheme is not seated - OU, thermistors, feller, etc., except the diode bridge and filtering capacitor. If you already have a power supply of 22..25V in an amplifier, you can also use it, not forgetting about the current consumption current of about 0.35a when inclusion of blowing.

Recommendations for assembling and configuring UMPS:
Before the start of the assembly pCB There should be relatively simple operations with the board, namely, view on the lumen, there is no shortness of the closures between the tracks in the usual lighting. Factory production does not exclude production defects, unfortunately. The soldering is recommended to carry out the PR-61 solder or similar to the melting point not higher than 200 * C.

First, you should decide on the UA applied. The use of OU from Analog Devices is extremely recommended - in this umzch, their character character is somewhat different from the author's conceived by the author, and overly high speeds can lead to a fatal self-excitation of the amplifier. The replacement of ORA134 is welcomed on Ora132, Ora627, because They have smaller distortions on HF. The same applies to the AU DA1 - it is recommended to use ORA2132, ORA2134 (in order of preference). It is permissible to use ORA604, ORA2604, but the distortions will be somewhat more. Of course, you can experiment with the type of OU, but at your own risk. The umzch will work with the KR544UD1, kr574ud1, but the level of zero offset at the exit will increase and harmonics will increase. The sound is ... I think comments are not needed.

From the very beginning of the installation, it is recommended to pairwise select transistors. This is not a necessary measure, because The amplifier will work and during scattering 20-30%, but if you put the goal to get the maximum quality, then pay attention to this. It should be especially highlighted by the selection of T5, T6 - they are best used with the maximum H21 - it will reduce the load on the OU and improve its output spectrum. T9, T10 should also have as close as possible. For transistors, the selection is optional. Weekend transistors - if they are from one batch, you can not pick up, because The culture of production in the West is somewhat higher than usual and the scatter is laid in 5-10%.

Further, instead of the conclusions of the resistors R30, R31, it is recommended to shift the segments of the wire with a length of a couple of centimeters, since the selection of their resistance is required. The initial value of 82 ohms will give a current of the ON of about 20..25 mA, it was statistically from 75 to 100 ohms, it strongly depends on the specific transistors.
As noted in the topic over the amplifier, the use of transistor optocoules is not worth it. Therefore, it is necessary to navigate on the AOD101A-g. Imported diode optocouplers were not tested due to unavailability, it is temporary. The best results are obtained on the AD101 of one batch for both channels.

In addition to transistors, it is necessary to pick up complementary resistors of UNU. The scatter should not exceed 1%. Particularly thoroughly need to select R36 \u003d R39, R34 \u003d R35, R40 \u003d R41. For a guideline, I note that with a scatter more than 0.5% for the option without an OOS, it is better not to move, because Will grow for easy harmonic. It is the impossibility of getting the exact details at one time stopped the author's experiments at an impending direction. Introducing the same balancing in the current OS chain solves the problem not completely.

Resistors R46, R47 can be searched for 1 com, but if there is a desire to more accurately adjust the current shunt, then it is better to do the same as with R30, R31 - to have wiring for subfield.
As it turned out in the course of the repetition of the scheme, at some coincidence, excitation in the EA tracking circuit is possible. This was manifested in the form of an uncontrolled drift of a rest current, and especially in the form of oscillations with a frequency of about 500 kHz on the collectors T15, T18.
The necessary adjustments were initially laid on this version, but it is still worth checking the oscilloscope.

Diodes VD14, VD15 are put on the radiator for the temperature compensation of the rest current. This can be done by leaking the wires to the conclusions of the diodes and gluing them to the radiator by glue type "moment" or similar.

Before the first inclusion, it is necessary to carefully launder the feet of flux traces, view on the absence of closures of the tracks, make sure that the general wires are connected to the middle point of the power supply capacitor. It is also highly recommended to use the Tsobel chain and the reel at the yget output, they are not shown in the diagram, because The author considers their application for a good tone rule. The denominations of this chain are common - this is a sequentially included resistor 10 Ohm 2 W and a capacitor K73-17 or a similar capacity of 0.1 μF. The coil is wound with a lacquered wire with a diameter of 1 mm on a MLT-2 resistor, the number of turns is 12 ... 15 (before filling). On PP protection, this chain is diluted completely.

All transistors VK and T9, T10 in un - attached on the radiator. Powerful transistors Vc is installed through mica gaskets and to improve thermal contact is used by the KPT-8 type paste. The near-computer pastes are not recommended to apply - high probability of fake, and tests confirm that often the CCT-8 is the best choice, moreover, very inexpensive. In order not to fly to the fake - use the CCT-8 in metal tubes, like a toothpaste. Before that, I haven't reached, fortunately.

For transistors in an isolated case, the use of mica laying is optional and even undesirable, because Detect the conditions of thermal contact.
In consistently with the primary winding of the network transformer, be turned on the light bulb at 100-150W - it will save from many troubles.

Rush the Optron LED outputs D2 (1 and 2) and turn on. If everything is assembled correctly, the current-consumed current must not exceed 40 mA (the output stage will operate in C). The constant bias voltage at the yget output should not exceed 10 mV. Unlock LED. The current consumed by the amplifier should increase to 140 ... 180 mA. If it increases more, then check (it is recommended to do this by an arrow voltmeter) T15, T18 collectors. If everything works correctly, there must be voltages that differ from about 10-20 V. in the case when it is a deviation less than 5 V, and a rest current is too big - try changing the VD14 diodes, VD15 to others, it is very desirable that they There were from one party. Current of resting of the umzch, if it does not fit in the range from 70 to 150 mA, can also be installed by the selection of resistors R57, R58. Possible replacement for diodes VD14, VD15: 1N4148, 1N4001-1N4007, KD522. Either reduce the current flowing through them through the simultaneous increase in R57, R58. In the thoughts there was the possibility of implementing the displacement of such a plan: instead of VD14, VD15 use the transitions of BE transistors from the same parties as T15, T18, but then it will have to significantly increase R57, R58 - to full setting Received current mirrors. At the same time, newly administered transistors should be in thermal contact with the radiator, as well as diodes, instead of which they are set.

Next, you need to set the current of resting Unh. Leave the enabled amplifier and after 20-30 minutes check the voltage drop on the resistors R42, R43. There should be 200 ... 250 mV, which means the rest current of 20-25 mA. If it is greater, then it is necessary to reduce the resistance R30, R31, if less, respectively, increase. It may happen such that the current of resting UA will be asymmetrical - in one shoulder 5-6m, in another 50mA. In this case, drop out transistors from the latch and continue without them. The effect did not find a logical explanation, but disappeared when replacing transistors. In general, there is no point in the latch to use transistors with large H21. Such amplification from 50.

After setting up, it is again checking the TCC current. It should be measured on the voltage drop on the resistors R79, R82. The current 100 mA corresponds to the voltage drop of 33 mV. Of these 100 mA, about 20 mA consumes the precomplete stage and up to 10 mA can go to the control of the optocoupler, therefore, in the case when it drops on these resistors, for example, 33 mV - the rest current will be 70 ... 75m. It is possible to clarify it in measurements of the voltage drop on resistors in the issuers of output transistors and subsequent summation. The rest of the output transistors from 80 to 130 mA can be considered normal, and the declared parameters are fully saved.

According to the results of stress measurements on collectors T15, T18, it can be concluded that the control current is sufficient through the optocoupler. If T15, T18 is almost in saturation (the voltages on their collectors differ from the supply less than 10 V) - then it is necessary to reduce the rates R51, R56 by about one and a half times and re-froze. The situation with tensions should change, and the rest of the rest - remain premature. The optimal is the case when the voltages on the collectors T15, T18 are approximately half of the supply voltages, but quite enough deviation from 10-15V power, it is a reserve that is needed to control the optocoupler on a music signal and a real load. Resistors R51, R56 can heat up to 40-50 * C, it is normal.

Instant power in the very hard case - at an output voltage close to zero - does not exceed 125-130 W on the transistor (according to technical conditions, it is allowed to 150W) and it acts almost instantly, which should not behave any consequences.

The triggering of the latch can be determined to be a subjective-sharp reduction in the output power and the characteristic "dirty" sound, simply speaking - there will be a strongly distorted sound.

4. Preliminary amplifier and its BP

Material on high quality PU:

It serves for timbre correction and dedication when adjusting the volume. Perhaps use to connect headphones.

As a temprel, the TB Matyushkina has been used well. It has a 4 accent adjustment of the LC and smooth adjustment of the RF, and its response corresponds to the auditory perception well, in any case, the classic bridge TB, (which can also be applied), the listeners are estimated below. The relay allows, if necessary, turn off all the frequency correction in the path, the output signal level is configured by a rapid resistor by equality of amplification at a frequency of 1000 Hz in TB mode and during bypass.

Calculation characteristics:

Kg in the frequency range from 20 Hz to 20 kHz - less than 0.001% (typical value of about 0.0005%)

Rated input voltage, 0.775

Overload capacity in TB bypass - at least 20 dB.

Minimum load resistance in which the operation of the output stage is guaranteed in mode A - with the maximum swing of the output voltage "from peak to peak" 58V 1.5 com.

When using PU only with SD players, it is permissible to reduce the power supply voltage to + \\ - 15V because the output voltage range of such sources is obviously limited from above, it will not be reflected in the parameters.

A complete set of boards consists of two channels PU, RT Matyushkina (one board on both channels) and a power supply. Printing boards are developed by Vladimir Lepoehin.

Measurement results:

Preamp circuits There are many, and subject to some simple precautionary measures and the use of modern operating amplifiers, they are very easy to develop and provide high performance. I appeal to those who are "under the ban": Please skip this section, but only after reading the following two paragraphs.

Despite the fact that in audible circles, the operating amplifiers are considered to be something bad, it is necessary to remember that the sound from the musician tool to the ears of the listener passes through somewhere from 10 to 100 operating amplifiers - in a mixer (as a rule, more than once ), V. external devices Effects, in the recording device (analog or digital), and finally, in the player of the CD. Many of them are not as good as those used in this design.

This does not mean that a good lamp preamp will not sound better (or, perhaps, just differently), but should not also believe myths about poor "microchipped sound", which are very popular. This is the opinion of those who used both lamp preamps, and preamplifiers on the OO of my design.

Description

The preamprifier has optional timbre and balance regulators that may not be included if desired. The input selector can be extended if it is necessary to provide more sources of signal.

The tone controller is built on passive control elements, but does not include the traditional scheme with feedback Baxandala. It provides adjustment within ± 6 dB at a maximum, which may seem insufficient (most tone regulators are offered from 12 to 20 dB), but in reality, this is usually enough for those adjustments that are usually necessary.

Note: The timbre controller was slightly changed since the original publication of this scheme. In the RF regulator, ideally, 1 NF capacitor should be used (10 NF was used earlier). The diagram provides an adjustment of ± 3 dB at 6 kHz frequencies and 55 Hz in the extreme positions of potentiometers. If the change in the timbre is too insignificant, an increase in the capacitance of capacitors in the low and high frequency adjustment circuits (100 NF and 1 NF, respectively) reduce the frequency, and vice versa. In case of small use acoustic systems In the chain of the regulator low frequencies It is better to use a condenser 47 NF.

The scheme provides an optional entry. It can be excluded if it is not needed. Overly to say, any recording device can be used, and it does not have to be a tape recorder.

Fig. 1. Input selector and circuit switching

There are no any features in the design here, but when installing, care should be taken to ensure that the wires of the left and right channels are separated wherever it is possible to prevent cross-interference. As a selector of the inputs, it is recommended to use a swivel switch with an extended shaft. This will allow you to place all the inputs and switch within the same section and secure them.

Input control regulators for CD and DVD inputs allow you to balance the levels with other sources. Hanging a small amount of Experiments It is necessary to ensure the ability to switch from one input to another while maintaining the volume level.

Fig. 2. Input buffer and tone adjustment

The diagram shows only the left channel. The right channel is identical, and uses the second half of the NE5532. Note how power is connected to the OU:

+ V - PIN 8, -V - PIN 4
With incorrect connection, the operational amplifiers will fail!

The input cascade has a gain of 2 (6 dB) and performs the role of buffer for the ramp. The buffer cascade at the flow output also has a 2-hook gain to compensate for the loss at the timbre adjustment stage (6 dB). Thus, the overall gain after the tone regulators is 4 (for those frequencies that are reinforced to maximum). Taking into account the standard signal 2 in the RMS from the CD player, the output will be 8 in RMS or amplitude peak 11.3 V (provided that the input level control is maximum).

To prevent the signal from the s), the OU supply voltage should be not lower than ± 15 V. The signal level of other sources will be significantly below 2 in the RMS of the CD player. Therefore, all the probable clipping capabilities are excluded.

Please note that the tone regulators in the central position provide almost even response. Any deviation will be caused, most likely mechanical, and not electrical causes.

When switching S2, all the elements of the collector and the output buffer are excluded from the chain.

Fig. 3. Balance, volume, reinforcement cascade

The output stage provides the main part of the amplification (12.6 dB), and includes volume and balance regulators. Balance control makes a weakening of 2.3 dB in the central position and has a half-term characteristic. Therefore, in the area of \u200b\u200bthe central position of the engine, accurate control is easily provided. When the control is rotated to the extreme position, the opposite channel receives 1 dB of the signal. Using stepped gain adjustment can reduce noise level

If your amplifier has an unusually high sensitivity, it is necessary to increase the R19 value. Strengthening this cascade is determined by the formula:

Ku \u003d 20log ((R18 + R17) / R17) - 2.3 dB (2.3 dB lost in balance control)

The overall gain of the system with all control elements (except the timbre regulators) at a maximum is 18.5 dB, therefore 230 mV will output an amplifier with the sensitivity of the input 2 in full power.

If more gain is required (which is very unlikely), it can be implemented by reducing the R17 nominal in the terminal output cascade (currently 22 com). If, for example, a total gain of 24 dB is needed, the value of R17 must be reduced to 12 kΩ. In this case, its own noise increases in proportion to the increase in the gain.

To work with the power amplifiers of the usual sensitivity (with a gain of 27 dB), the total coefficient of strengthening the preamp of 10 dB is sufficient for most sources. This value can be achieved by increasing R17 to 82 com, so the overall strengthening will be

6 dB + 7 dB - 2.3 dB \u003d 10.7 dB

Optionally, R17 and R18 can be divided into 10 (up to 10 com and 2.2 kΩ, as shown in the diagram). This can reduce the noise due to lower impedances. I did not measure noise levels in both configurations, but they will be very low in any case.

All potentiometers are used with a linear characteristic.

Each OU should be drawn by electrolytic condensers of 10 μF x 25 V from each shoulder of power to the ground and capacitors with a capacity of 100 NF between power outputs (see Fig. 4). The latter should be located as close as possible to the OU power supply conclusions, the location of the electrolytes of 10 μF is not critical. The refusal to shunt leads to the emergence of high-frequency oscillations, which significantly distort the sound of the preamp.

Fig. 4. Shunting scheme OH powered

Specified OS are very common, and they will not be difficult to find. Undoubtedly, there is best devices, but common quality NE5532 used in this design must satisfy the most demanding listeners. These devices have an internal stabilizer, and no external stabilization is required.

Please note that all operational amplifiers (with the exception of tone buffer) work with a strengthening by dC. This leads to the appearance of constant voltage at the OU outputs within a few Millivolt. To eliminate this it would be necessary to use electrolytic capacitors on the way of passing the signal, which I wanted to avoid.

Using the output capacitor with a capacity of 2.2 μF to prevent constant voltage from entering subsequent devices. It is strictly recommended to remove these capacitors, because The constant voltage (even in small quantities) is not allowed to transmit to the amplifier! Parallel inclusion Two 2.2 MKF capacitors provides a signal at -3 dB at a frequency of up to 5 Hz and a load of 10 kΩ. This should be acceptable for most amplifiers.

The 100 Ohm exit resistor is designed to prevent any oscillations of OU when connected to a coaxial cable.

As a suitable power supply, it is advisable to use an external transformer to eliminate any possibility of filing, especially if the phono-director is used.

A suitable power source is presented in the project 05 (see Project 05). In this case, a transformer that provides 16 V alternating voltage is used, and straightening, filtering and stabilization are mounted within the preamp chassis.

If you want to include a transformer in the chassis, use a toroidal type transformer (20 wa more than enough) to reduce magnetic fields to a minimum.

When connecting to the power grid, be careful and observe the precautions, the mains voltage is dangerous for life! In this case, use the standard IEC power connector. To connect to a voltage source 12, I recommend using XLR connectors. They are significantly more reliable than tubular power connectors and never fall out. XLR connections are described on the power source project page.

In the photo: The preamplifier "Natalie" in the housing satellite receiver

In the article, it will be about my assembly. pre-amplifier "Natalie" with a successful solution to the problem of the housing.

This project has become another long-term in my list and broke all the deadlines for implementation. The fact is that the thought of the preamp assembly appeared more than a year ago, and together with the thought in my box for details, almost all the components needed for this scheme were settled.

And, as often happens, all enthusiasm suddenly evaporated somewhere, so I had to minimize everything started at an indefinite time. Although why an indefinite ... very definite - before the onset of autumn cold weather, when all summer affairs, which were very much this year, will be completed and free time for soldering will be completed.

About the scheme and details

The scheme chose a long time, very long! The path to this preliminary amplifier began with the use as a PU with a distributor of specialized chips like LM1036 or TDA1524, but from this sin, local forum users were dissolved. Next was the scheme taken from some foreign site on three OU type TL072 with an adjustment of HF and LF. Even Introiled PP and gathered, and listened for some time this prevolution, but did not lay the soul to him.

Then he drew attention to the scheme of the famous Sunthi preamp, and already during the search for information on Sunzhev, stumbled upon a scheme resembling Solntsevskaya in a bundle with the passive RT Matyushkin. It was . It was just what I need!

A bit of simplifying the scheme of the preamp and, having completed it under him, received this result. The transition to one-storey power and removal of "unnecessary" parts made it possible to somewhat simplify the wiring of the board, make it one-sided and most importantly reduce the sizes of PP. In the scheme, nothing significant changed that the sound quality could worsen, only removed the functions of the timbre, balance sheet and the tone control unit unnecessary to me.

In the timbre regulator circuit did not make her own, but it still needed to breed a board again, because I did not find a ready-made one-sided in the Internet. Switching the temprel modes is made on domestic RES-47 relays.

In order to make the control of the tone regulator and the preamp for me for several days, it was plunged into the theory of the principles of the counters and the triggers of domestic microcircuits. For the preamp, he chosen the housing from the satellite receiver, who taught his own, in which there was a rather large window, and it was necessary to fill in something beautiful and helpful. So, I wanted to make a visual information about the timbre regulator modes, and better if it were not the LEDs, but the figures are familiar and the brain. As a result, such a scheme of three ms was drawn.

K561L5 Specifies the pulses that enter the inputs K174I4 and K561I9A. The meter on Ye9 manages 4 keys switchable relays on RT Matyushkina. At the same time, the meter on Ye4 changes the readings on the aloxy indicator of ALS335B1, indicating, in which mode there is a tone regulator at the moment. The digit "0" corresponds to the mode with the minimum level of low frequencies, the number "3" is maximum. Another simple electronic switch is made on MS K155TM2. One half of the chip controls the rely cheese, switching the signal level indicator modes, the second half is responsible for the input selector relay. Well, and the diagram of the signal level indicator on the MS LM3915 is separately for each channel.

Power Supply Made on the basis of the TP-30 transformer, of course with a rewinding voltage secondary winding.

All stresses stabilized:
+/- 15V - on / lm337 to power the preamp board
+ 9V on 7805 for power relay and control unit
+ 5V again on to power USB sound card

About configuration and possible problems

Despite all the seeming complexity of the scheme and many details, with the correct assembly and the use of knowingly good and recommended components for this scheme, it is possible to exist with a lot of probability from unpleasant surpriseswhich may occur when assembling this PU. The only part of the whole schema that needs setting is the preamp itself itself. You need to set the rest current, check the level of constant non-output, and the signal shape.

The recommended resting current for this is PU 20-22 MA, and it is calculated by the drop in voltage at 15 ohmic resistors R20, R21, R40, R42. For current 20-22 mA, 300-350 mV should fall on these resistors (300: 15 \u003d 20, 350: 15 \u003d 22). The voltage drop, and accordingly, the current can be adjusted in one direction or another to the change in the ratio of the resistors R9, R10, R30, R31 (in the original scheme 51 ohms). Larger resting current corresponds to greater resistance of the resistor and vice versa. In its variant, instead of constant resistors of 51 ohms, I have fallen a multi-turn trimmer with a face value of 100 ohms, which allowed without extra effort And with high accuracy to set the desired reservoir.

Two troublesWith which a person who decided to repeat this preamp is to repeat this preamp - this is a remuneration, and standing at the exit. And, as a rule, the first problem generates the second. First you need to make sure that it is not the lack of constant component at the output of each buffer and each OU. A small amount of constant is allowed, but it is small, roughly speaking no more than a few mV.

If there is no constant, I congratulate you! If there is - we are looking for what is the reason, and the reasons are not so much. This is either an error in the installation, or the "not that" item, or somewhere there is a bump. First of all, you need to carefully inspect the fee for an indifferent or vice versa - the merged tracks, to double-check all the details of the desired nominal value you use, and if the third option remains correctly, i.e. Run. You need an oscilloscope for his search.

I myself encountered this problem. In all four buffers there was an outcomes in the amount of 100-150 mV. And the cause of its occurrence was like "not that" item. The fact is that instead of OPA134 operating amplifiers, I had NE5534, which are not quite suitable for use in this scheme. For a long time and unsuccessfully, I fought with this problem, and the problem disappeared by itself after replacing the OPA on OPA134.

About location and connection

Due to the fact that the available case was not very large, it was necessary to draw all the boards to re-in order to make them more compact for a couple of centimeters. Placing boards in the housing turned out very dense, but fortunately everything was fitted. All is the preamp board, the tone controller, the dual board of the control unit and indication, USB sound Map, power supply transformer and rectifier-stabilizers, and two small input selector boards and volume control and HF.

All common wires connected at one point, on the volume of the volume and high frequency controller. It got rid of the frightening problems of the roast and backgrounds, which are possible with incorrectly divorced land.

Again due to the constrained conditions, the control board and the indication had to make a composite consisting of one large and one small fee. They are connected to each other through the pin connector.

All boards fucked to the chassis of the case through these plastic insulating spacers. This allowed to fully isolate the cards from contact, as with metal caseand from each other, in places where it is not necessary.

Comfortable housing

I'll tell you a little and about the body itself. As I mentioned - a housing from a satellite receiver is used as a housing for the preamp. The old man was faithfully served for many years, he was repaired several times and after another trip to the workshop, I was transferred to me with a diagnosis of "corpse".

Good were before the hull, big! It is because of its sizes and a large window, I chose this case. There was nothing superfluous on the front panel. Stayed, of course 3 unused buttons, but it is not scary. Painted the inscriptions of matte paint from the title purchased in the auto shop. Paint interest on 98 coincided with the color with the one that was painted the case initially. The difference can be noticed only if you look very careful.

As a handle for these regulators, installed, which by the way. They are excellent (in my opinion) fit into the overall design of the preamp, which is designed in silvery-black color.

About sound and impressions

And it's time to tell about the most interesting, about what happened in the end. And in the end, it turned out another good toy in my collection of sound-reproducing equipment.

The scheme undoubtedly deserves attention and that it is repeated. The sound of the finished device liked it, it makes some kind of color to music. Despite just 4 steps in the tone regulator, Matyushkin, I can not say that low frequency adjustments are missing. The four positions of the LF regulator are quite enough in order to find the desired level of low frequencies for a particular style of music and its preferences.
Do you like an explosive bass? We switches the collector to the fourth position and let the speakers are rushes! The range of adjustments in high also enough with an excess when the handle is right to the right, the number of high starts to cut the hearing.

Preamplifier do it yourself - I recommend radio amateurs of simple and together with a high-quality sound power with the built-in timbre block. The prepamp is based on a widely known two-channel operating audio amplifier LM833.

The working area of \u200b\u200bthe microcircuit is implemented according to the scheme of an inverting amplifier with a consistent negative feedback on the voltage, and the unused area is assembled according to the repeater scheme, that is, it is muffled. The effective bandwidth of this scheme is ranging from 0.6 Hz to 18 kHz. The approximate gain is in the range from 0.9 to 110, based on the values \u200b\u200bof the trimmed resistor.

Dual operating amplifier LM833 was originally developed for use in high quality sound devices. Such, for example; As before amplifiers and filters that cannot work without a two-polar power supply. The diagram of this unit is capable of working with feeding voltages in the range from ± 6V to ± 18V, while the coefficient of nonlinear distortion (books) is only 0.002%. Peak reinforcement for the voltage LM833 reaches 112DB with a rated current 6mA.