Pre-amplifiers on Hi Fi chips. Low frequency preliminary amplifiers from whale master. About location and connection

Pre-amplifier diagram with tone controller.

Greetings, friends. Below in the article presents a preliminary amplifier project from Maxim Vasilyeva, which is essentially alteration of the Sukhika preamply by transferring the scheme with a 157 series of microcircuits to import. For more information, you can find on the Côte and the Vegalab forum on request "full amplifier Vasilyeva". Schematic diagram:

To enlarge the image, click on the picture.

The diagram used dual operational amplifiers. For example, you can put OPA2134P, TL072 or NE5532, who like it or what of this is currently there is at the time. The following figure shows the location of the chip conclusions, it has the same one, therefore, no matter what MS you apply, no changes should be made in the board:

About which chips sound better, we will not write, you will be able to find a lot of information on the radio amateur forums, and there are plenty of them in the network.

Food two-polar +/- 12 ... 15 volts.

A variable resistors of the group "A" (imported) resistors (imported) are applied as the volume of volume, balance and timbres, if you use domestic change - choose with a group "in"

The printed circuit board is made of two-way fiberglass. The top layer does not deteriorate, it is used as a screen. Circuit sizes 70x158 mm.

The appearance of the printed circuit board is shown on the following two drawings:

A two-polar voltage stabilizer 2 x 15 volts on 78L15 and 79L15 chips is added on the board. Below in the figure shows the location of the conclusions from the transistor 2N5551:

The principal scheme and printed circuit board in Lay format can be downloaded for a direct link from our site. File size archive for download - 0.53 MB.

LF filter for subwoofer

The low-frequency acoustic system is usually cumbersome and the road, and taking into account the fact that the human hearing cannot recognize the stereo at low frequencies, it is clear that there is no point in two low-frequency speakers on one for each stereo channel. Especially if the room where the stereo system is not very large.

In this case, you need to sum up the signals of stereokanals, and then from the resulting signal to allocate low-frequency. Figure 1 shows a diagram of an active filter made on two microcircuit reinforcements TL062..

Stereokanal signals come to the X1 connector. Resistors R1 and R2 in conjunction with the inverse input of OU A1.1 create a mixer that shapes a common monosign with a stereo signal, OU A1.1 provides the necessary gain (or loosening) input signal. The signal level is controlled by a variable resistor R3, which is part of the OC A1.1 chain. From the output A1.1, the signal comes to the FNF at A1.2. The frequency can be adjusted by a dual variable resistor consisting of R7 and R8.

The LB signal on the low-frequency UHC or the active low-frequency speaker comes through the X2 connector.
Power - a bipolar, comes through the X3 connector, possibly from ± 5V to ± 15V, the scheme can be assembled on any two general-purpose amplifiers.

Mixer for working with three microphones.
If you need signals from three separate sources, for example, from microphones to submit one input to the recording or reproducing audio device, you need a mixer with which you can combine audio signals from three sources to one, and adjust their ratios from levels as required.

Figure 2 shows a mixer made on a type chip LM348.in which there are four operating amplifiers.
Microphone signals are fed, respectively, on the connectors x1, x2 and x3. Further, on microphone pre-amplifiers on operating amplifiers A1.1, A 1.2 and A1.3. The gain coefficient of each OU depends on the parameters of its OOS circuit. This allows in a wide range to adjust the gain coefficient by changing resistors R4, R10 and R17, respectively. Therefore, if the microphone is not used as one or more of the sources of the signal, and the device with a higher level of output voltage ZCh, it will be possible to determine the coefficient of the corresponding OE to set the selection of the resistance of the corresponding resistor. Moreover, the gain setting the gain is very large - from hundreds and thousands to one.

The reinforced signals from three sources go to variable resistors R5, R11, R19, with which you can quickly adjust the signal ratio in the overall signal, until the signal is completely suppressed from one or more sources.
The actual mixer is made on the OU A1.4. The signals on its inverse entrance come from variables of resistors through resistors R6, R12, R19.
The LF signal on an external recorder or an amplifying device comes through the X5 connector.
Power supply - bipolar, enters through the X4 connector, possibly from + 5V to + 15V.

The scheme can be collected on any four general-purpose operating amplifiers.

Pre-amplifier with rates.
Many radio amateurs will skip the umzch based on the integral umzch microcircuit, usually intended for automotive audio equipment. The main advantage of them is that quite a quality umzch is obtained in the shortest possible time and with minimal labor costs. The disadvantage is only that uncle is not complete, without a preamp with the volume adjustments and timbre.

Figure 3 shows the scheme of a simple preamp with the volume control and the timbre built on the most common element database - type transistors CT3102E.The amplifier has a fairly large input resistance so that it can work almost with any source of the signal, from the PC sound card and the digital player, to the archaic player of the vinyl discs with the piezoelectric head of the pickup.

The cascade on the VT1 transistor is built according to the emitter repeater scheme and serves mainly to increase the input resistance, and reducing the effect of the signal source output parameters to the tone adjustment.

Volume controller - Variable resistor R3, simultaneously is the load of the emitter repeater on the VT1 transistor.
Next - Passive bridge tone controller at low and high frequencies, made on variable resistors
R6 (Low Frequencies) and R10 (High Frequencies). 12DB adjustment range.

The Cascade on the VT2 transistor serves to compensate for the signal level loss in the passive tone regulator. The coefficient of amplification of the cascade on VT2 largely depends on the value of the OC, specifically resistance to the resistor R13 (the smaller, the greater the amplification coefficient). DC mode is displayed by a R11 resistor for a cascade on VT2 and R1 for a cascade on VT1.

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

The supply voltage is 12V, unipolar, corresponds to the nominal supply voltage of most microcircuits -integral umzch, designed to work in the automotive machinery.

Radioadapter
All stationary audio equipment necessarily has a linear output and linear entrance connectors. You can use a signal from an external source to a linear input, which would use the main machine as an amplifier with acoustic systems or for recording, in most portable equipment linear input is simply not. The only "means of communication with the outside world" are a microphone and a built-in radio. One of my friend tried to rewrite a signal from a MP-3-flash player on a magnetic cassette. Sewing headphones on a microphone "hole" of an old portable CD magnet. It turned out terrible. Although it was possible to use the built-in FM receiver, but for this you need at least the simplest adapter.

For high-quality transmission of the stereo signal, you can use the purchase FM modulator designed to wirelessly connect to the automagneto of the external audio source. It has a stereo modulator, a good transmitter with a frequency synthesizer and, often, built-in MP-3 player with an external flash drive or memory card. Well, in the simplest case, you can make a primitive monotransmistant low-power transmitter, the signal of which the receiver will be able to take the transmitter when close to its antenna.
The adapter diagram is shown in Figure 4.

The scheme is a Cascade of the RF generator on the VT1 transistor operating on the RF according to a circuit with a common base, which is supplied to the base circuit of which the modulating LC signal is supplied.

The sound frequency signal from the external source enters the VT1 database through the C4 capacitor and two resistors R1 and R2, serving a mixer of stereokanal. Since the scheme is very simple and there are no nodes forming a complex stereo signal to the receiver input will receive a monaural form.

LF Voltage, entering the VT1 transistor database, changes not only its operating point, but also the transition container. As a result, mixed amplitude-frequency modulation is obtained. Amplitude modulation is effectively suppressed in the receiving path of the radio receiver, and the frequency is detected by its frequency detector.

The frequency of the RF, on which the broadcast occurs, is set by the L1-C2 circuit. In fact, there are no antennas - the adapter is located in close proximity to the receiver antenna, and the signal to it comes directly from the contour coil.
The contour coil L1 is a frameless, its inner diameter is 10-12 mm, wounds with a wire PEV 1.06, only 10 turns. You can customize the contour as a trimmed capacitor and the compression of the coil's turns.
Power - two elements of 1.5V (3V).

Level indicator.
To properly establish sterea balance and preventing the overload of UNG and acoustic systems, it is desirable to ensure that the signal level indicator arrives at the ONLC input.

From a practical point of view, for self-making, the indicator is best based on the LED scale, it is mechanically much stronger than the arrogant and easier and cheaper than the scale mnemometric.

Figure 5 shows the indicator circuit on both stereo channels. It is based on chip TA7666R.
Inside IS T7666R, two amplifiers with detectors on the outputs and two line of comparators, five comparators for each channel.

The gain of each of the amplifiers can be installed individually by selecting resistance resistors R1 and R2. With the first stage of the LED (HL1 and HL6) indicated on the diagram, it lights up at levels at the inputs 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 display is "BAG", that is, the "thermometer column", in other words, the greater the signal, the longer the line of luminous LEDs.
Change sensitivity can always be selected with resistor resistors R1 and R2.

Based on this chip, a peculiar light-dynamic device can be made, for example, composed of concentric circles of incandescent lamps or LED lamas, for example used in automotive optics. In this case, additional powerful output cascades will be required.
Other news

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 ), in external effects of 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 Baxandal feedback circuit. 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 the case of using small acoustic systems in the low frequency regulator circuit, 47 NF capacitor is better.

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. After conducting a small number of experiments, it is necessary to provide the ability to switch from one input to the other with the maintenance of 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 are also the best devices, but the overall quality of the 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 constant current gain. 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! The parallel inclusion of two capacitors 2.2 μF provides a signal at -3 dB at a frequency of up to 5 Hz and a load of 10 com. 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 turn on the 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.

Introduction Story about preliminary amplifiers

In Hi-Fi technician pre-amplifiers (Soc., Jargon - preamp, Prev) are installed between the signal source and low frequency power amplifier (UMCH). Sometimes the pre-amplifier is combined in one case with UMCH. Then such an amplifier is called integrated.
The main functions of preamplifiers. In specific designs, only some functions can be implemented:
1. Strengthening the signal to the required level for the subsequent gain amplifier. Some sources (from modern - cell phones, Bluetooth adapters or some audio cards / DAC / DAC) When directly connected to UMCH, do not allow to implement the full power of the amplifier. Using a pre-amplifier, the signal is enhanced to the desired level ("swing")
2. Volume adjustment
3. Switching inputs from various sources
4. Coordination of the signal source and power amplifier. In such cases, buffers are made in the preliminary amplifier - amplifiers with coefficients. Strengthening 1 by voltage. Enhance only current.
5. Changing the signal - from the simplest tone regulators (changing the frequency response to the more "pleasant" for our ears) to complex sound processors.
6. Sometimes different equipment are embedded in preamps. For example, amplifiers for headphones, phonic directorists, mixers, karaoke, signal level indicators and more.

Many modern sources of the signal do not need additional strengthening for "Rashchka" UMCH. There is a temptation to get rid of the excess link in the signal gain circuit - the pre-amplifier. However, in many systems, pre-amplifiers are present to match the chain: "Signal source -\u003e UMCH -\u003e Acoustic system."

In the case of cloning of products of the company Naim, the usual path of the radio amateur such. The clone NAP 140 is going. Sound like it! Further upgrade details - I like the sound! We collect the power stabilizer. The result is positive. There is a temptation to collect a preliminary amplifier - there are only a few details - the mock / Lut, the hour of soldering and before ready. The sound is liked and a pre-amplifier is going to UMCCH. Then they write on the forums - Naim without betrayal is not Naim.

Approximately it came out. Without a consensus, the sound of Umpech "Light" somehow a bit. With the foremost - everything is OK.

Originals from 70s-90s

On the original UMCH Naim, it is possible to connect only NAIM preliminary amplifiers. In order not to connect products from other manufacturers, Naim uses special branded cables and connectors to connect a pre-amplifier to UMCH. In the photo these connectors on the left:


Schemes of preliminary amazes Naim 70s - 90s
The basic scheme of the amplification module (signal amplification of about 10 times):

Buffer:

All polar capacitors (except for power filter) are tantalum.

Full diagram of the pre-amplifier from the 70s. Such: Input connectors -\u003e "Mechanical Signal Selector" -\u003e "Buffer" -\u003e "Volume Controller" -\u003e "Power Module" -\u003e "Unflux connectors".

Different versions of NAIM preliminary amplifiers were produced. In addition to the price, the devices were distinguished by the presence / absence of buffer, various power schemes (from UMCH, from external BP, separate power supply channels of the pre-amplifier, separate power supply and buffer module), service devices in the pre-amplifier housing.

How modern Naim preliminary amplifiers are arranged - I do not know.

Details with pre-amplifiers Naim can be found on the site. Section "Naim Preamp Mods and Upgrades". There are also printed circuit boards for self-assembly of a pre-amplifier clone.
Chinese clones
On website and online stores for sale various options for pre-amplifiers Naim: printed circuit boards, assembly sets, collected constructors, ready-made pre-amplifiers in the housings.
Differ in detail from which consist and power schemes.
Consider a briefness of the Chinese industry:

Option 1. Two separate fees with independent power on each (search according to Naim Preamp).


The same in the case. Power here is a separate case.


Option 2. The ability to connect several different nutrition - to each part of its:


In the housing:


With the input selector:


Option 3. The simplest scheme: only the amplification module. One diet into two channels:


This module, like the cheapest, I bought on a sample. To understand whether to bother with a preamp or not. Prior to that, collected a pre-amplifier on the layout.

Chinese designer:

More photos

Transistors (such as in the original, you will not find now) replaced with modern 2SC1815 / 2SA1015. The board is compact enough. All polar capacitors (except meal filters) are tantalum. As it should be. The original is so. Branded feature Naim - the use of tantalum capacitors. Volume control (RG) in this designer - 20 kΩ (the potentiometer got more or less without jambs).

Collected scheme:


Power Spa:


Power - one winding on 24V alternating voltage, 0.3a. Channels are separated by resistors.

After assembling the scheme starts to work immediately.

Measurements:


Input signal:


Output signal:


Strengthening about 10 times.

Measurements in RMAA. At the output signal level VPP 3.24V.

My design
After listening to Chinese whale, I decided not to engage in the modernization of the Chinese (there is no independent nutrition for each channel, the ALPs WG does not install, excessive wires, etc.), but to collect in its own way. Took the standard clone diagram of Naim:

Used such details. Stabilizer: instead of LM317 installed LT1085. I liked the sound with them. All polar capacitors - Tantalt Kemet (except C3 capacitor at 47 μF - there was no tantalum of such a capacity in the presence - installed Nichichon for Audio). C2 510 PF is a polypropylene capacitor (on Ebee are searched for PolyPropylene and Styroflex). RG is a variable resistor Alps in 10 com. The RG was standing at the beginning of 50 com - it was sufficiently audible even on the midnight background. Replaced on Alps 10 kΩ - everything was OK. The background is heard only on Max Volume. Two channels are connected together only on the input jacks. Otherwise, two fully independent channels with their power supplies.

R13 resistor affects the magnitude of the increasing scheme. I installed its value in 4.7 com. Strengthening the scheme - 5 times approximately. Standard 10 times - a lot for me with my signal sources. Less than 4 comments of this resistor are better not to choose - there will be distortions. With 4.7 com all ok.

I decided to make two fees. On the first: amplifier with stabilizers. Perhaps later remake this fee. At the plant I will order the seal and saving on it. So far, let it be. The second board as a chassis: there are transformers on it: the first 10VA for power supply (two secondary windings by 22 V -), the second 10VA (two secondary windings 7B - - to power switching and 5 V in the form of a USB connector for connecting external devices) , Stabilizers on 5 V, switching relay and variable resistor WG.

In the power filter two capacitor Nichichon for Audio 3300 μF / 50V per channel. SUMPED SMD-ceramics right on the outputs. Diode bridges on nutrition tires 24 V on Schottky diodes.


The body took on the same eBay - e: It is selected according to "2606A Full Aluminum Preamp Chassis". The hull is made qualitatively. The paint does not register, all accessories are in the presence. In the housing:












Made from the pre-amplifier three entrances. Two on the preamp on the RG and one input directly to the output of the pre-amplifier bypassing the volume control and the gain scheme. This login has done to connect the output of the front channels from the sound processor of the home theater receiver. Switching - on the relay. The relays are controlled by a gallery switch. Implemented the "Direct" mode - connecting the inputs by the pre-amplifier circuit directly to the power amplifier input.

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.

A dual operational 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.

Preliminary amplifier scheme

As an operational amplifier, you can apply any other two channel OU.