The proposed book discusses the features of circuitry solutions used in the creation of miniature transistor radio transmission devices. The relevant chapters provides information on the principles of action and the peculiarities of the functioning of individual components and cascades, concepts, as well as other information necessary when independent designing simple radio transmitters and radio microphones. A separate chapter is devoted to the consideration of practical constructs of transistor micro-graders for the communication systems of a small radius of action.

The book is intended for novice radio amateurs that are interested in the characteristics of the circuitry solutions of nodes and cascades of miniature transistor radio transmission devices.

In microphone amplifiers, field transistors are widely used in microphone amplifiers. In this case, resistive amplifiers on field transistors ensure the coordination of signal sources having a large internal resistance, with a cascade input with a relatively low input resistance value. Strengthening cascades on field transistors are most often performed according to a circuit with a common source.

Schematic scheme designed to work with an electre microphone of the simplest microphone amplifier made in just one field transistor, shown in Fig. 2.10. Strengthening this design is at least 20 dB.

Fig. 2.10. Schematic diagram of microphone amplifier on field transistor

In the scheme under consideration, the signal was formed by the microphone VM1, the signal through the separation capacitor C1 is supplied to the inlet of the amplifying cascade, made on the field transistor VT1, which is enabled according to the circuit with the overall source.

If a variable voltage of the transistor VT1 is for a small amount of the transistor, then with the negative half-wave of this voltage, flowing through the transistor will decrease, and with a positive half-wave - increase according to the relevant law. As a result, the voltage on the R3 resistor will be changed in a similar way. Form of this aC voltage Repeats the input signal form, but the voltage value on the transistor of the VT1 will be much larger than the signal value at its shutter.

To form a displacement voltage supplied to the shutter of the transistor VT1, in this case uses the so-called scheme with an automatic source displacement. The automatic displacement voltage is formed when the flow of the flow of the transistor VT1 is processed through the R4 resistor. This tension is supplied to the shutter of the transistor through the R2 leak resistor, which also provides the flow of charges accumulating on the gate. The mode of operation of this amplifying cascade is determined by the resistance of the resistor R4.

In the absence of an input signal through the transistor VT1 flows the flow current, called rest current. This current ensures the formation of a certain potential difference on the R4 resistor, that is, on the top according to the scheme, the output of this resistor will be a positive voltage of a small value. Between the gate and the hull bus having a zero potential, the R2 resistor is included, the total resistance of which is incommensurable more resistance of the resistor R4. As a result, the shutter of the transistor VT1 is formed by the potential, which will be more negative compared to the small positive potential of the source. This small negative voltage on the gate provides partial closure of the transistor, while the lower value of the flow current is set. Thus, the value of the reservoir of the transistor VT1 depends on the resistance of the resistor included in its source circuit, that is, in this case, the resistance of the resistor R4. The greater the resistance value of the resistor R4, the greater the negative bias voltage is fed to the shutter of the transistor VT1. Therefore, a change in the resistance of the resistor R4 is selected such a bias voltage, in which the operation of the transistor on the linear section of the characteristic is ensured.

In order for the R4 resistor only a constant component of the collector current, parallel to this resistor in the Emitter circuit of the transistor VT1, an electrolytic C3 condenser is turned on. It does not pass through this capacitor, therefore, the C3 capacitor does not have any influence on the position of the operating point of the transistor. The resistance of this capacitor is small, so the variable component of the source current fluidly passes through the C3 capacitor to the hull bus.

This microphone amplifier was made because the noise and insufficient sensitivity of the shopping set and microphones for the computer were extremely annoying, and the hand was not raised to buy high-quality dollars.
The proposed scheme showed a really high sensitivity, a powerful output signal, a low noise level and a pleasant response.

Scheme of homemade microphone amplifier on OU

The basis of the scheme is the operational amplifier NE5532. Of course you can put the best, but this one meets this requirements for 100%. This scheme uses both halves of the amplifier located in a single case, so that the output signal will be very strong (can even be served on headphones). The device must be connected to the Line-IN input, because the typical microphone input is too sensitive and the record will be with overload.

In the photo, the top layer is a print with a double-sided sticky ribbon. The microphone is electret, typical. If you need to use dynamic -. The microcircuit was in the covers and the only thing that had to buy -. But even if you buy absolutely everything - the total cost will be close with funny 1 dollar.

All electronics were built into the finished plastic case (although the metal is also welcome). The board is glued to the base of the thermoclaim. The microphone is glued to the body with the same glue as the 9V battery connector (so that the battery does not hang).

The gluing microphone to the case is actually not a very good idea, it is better to do something similar through a soft gum - it will filter vibrations.

After the assembly, the board was covered with a transparent varnish to protect copper from corrosion. The microphone usually works in a suspended position on the stand. A cable for a microphone is 5 meters, naturally this is a shielded cable of good quality.

Microphone tests and conclusions

The microphone is used to record audiobook and voice translated films. If necessary, it can be used as a karaoke-microphone or even a small amplifier - the output signal is so strong that can control 32 Ohm headphones.

Lower nutrition will not go - it is so the limit for this chip, which runs from 9 to 30 V by datashet.

Noise parameter can be further improved using a special low-noise operational amplifier (type OPA).

Perhaps for someone, the microphone will seem not too light and comfortable. But you can do in your own way, reducing the size of the board and the case. The battery works for a very long time, recently recorded audiobook for 10 hours and no problems.

Details created 10/21/2014 07:27

The fundamental component without which there was not a single modern electronic device - transistor. To understand how this semiconductor device works, we collect the simplest amplifier On one transistor.

Since the purpose was familiar with the operation of the transistor, and not the assembly of the final device for use in everyday life, I did not choose and specifically buy some particular transistor, and I took the one that was at hand - p307v. I downloaded the so-called datasheet from the Internet for P307 from which I learned that this type The transistor has a N-P-N structure, low-frequency, low-power and suitable for use in amplifiers.

As is known from the school program of physics, the transistor is, figuratively expressing, a puff pie consisting of three layers of semiconductor material. Semiconductor is such a material that is characterized by a strong dependence of its conductivity from the concentration of impurities and other factors. The most common semiconductor is silicon.

Depending on the impurity administered to the semiconductor, it becomes p-type or n-type. Transistors may have N-P-N or P-N-P structure. The central layer of the semiconductor is called the base, and the two extreme - emitter and collector. In the schemes, they are referred to as follows:

The principle of operation of the transistor is reduced to the fact that small currents supplied to the database can be controlled by large currents occurring between the emitter and the collector.

N-P-N type transistors are controlled (activated) with positive voltage, which is applied to the transistor base relative to the emitter.

Transistors p-N-P type A negative voltage is controlled on the basis of the emitter.

Electricists have one winged phrase: "No one dies so quietly and imperceptibly like a transistor." If the conclusted conclusions are too long, it will immediately fail. Permissible currents for different transistors can be found in the datasheet, for low-power usually not more than 20mA.

You can check the transistor using a conventional multimeter. We turn on the multimeter to the measurement mode in the diapassone of thousands, connect the red probe to the database, and the total is black probe, alternately, to the issuer, then to the collector, the device should show the resistance, in my case about 300 ohms. Next, connect the total probe to the database, and the red probe alternately to the issuer, then to the collector, the device should not show the resistance, as if it is a dielectric. If still shows the resistance in both directions, then p-N Transition pierce. That is, from the base to the issuer and from the base to the collector, the current should pass only in one direction. Transitions base - emitter and base - collector when checking the transistor can be compared with two diodes connected by each other. Transistors p-N-P structure Checked similarly, but the direction of conductivity will be opposite.

In addition to the transistor, you need a microphone, speaker, variable resistor and power supply.

speaker I was at hand, but you can take any, even ordinary headphones-droplets

a variable resistor on 20k, permanent resistors on 10k and 300

power supply - two 3.7V batteries, connected in series, which gives in the amount of 7.4V

All manipulations with electronic components are very convenient to do on a batch card that does not require soldering. To turn on the part in the scheme you just need to stick it into the openings of the board. Makeletuit Cheaper than only to order on Aliexpress, I bought this dead fee complete with a USB power adapter and a jumper set.

To begin with, I decided to check the operation of the transistor in the key mode. The resistor for protection against excess current on the LED is 200 ohms, although the power supply is not powerful enough to output the LED. Thus, the emitter-collective chain is assembled, but the LED does not shine. In order for the current flow, you need to attach a small positive resistance to the database. For this, I took two conductor, one connected to a plus, and the second to the database, and closed them with my finger, so that they do not touch each other. That is, used the resistance of a small piece of skin of the finger. The finger resistance is quite large and the current has greatly decreased, but even this small current on the basis of the transistor was enough to open the transition of the emitter collector and the LED began to glow.

To make simple electronic key On one transistor to make a microphone amplifier, it is necessary to connect the speaker instead of the LED, and the database is a resistor and microphone.

Here I ran into two difficulties, first, I did not know what resistance on the base will be the right current. It is from this so-called "current offsetting current on the base of the transistor" will depend on the amplification, that is, the volume in the dynamics. Therefore, I decided to take variable resistance. By selection it turned out that the amplifier worked with resistance in the range from 11k to 33k, during these limits, nothing was heard in the dynamics. The greatest volume was achieved at about 14k. This value depends on the input signal, in this case from the microphone used.

This amplifier will work if the speaker is connected to the gap between the emitter and the minus and between the plus and the collector.

Although this amplifier was made only in order to familiarize themselves with the operation of the transistor, it is quite efficient and it can be used. Sounds in front of the microphone are clearly audible in the dynamics.

Simple microphone amplifier for computer with your own hands

This article is devoted to the design of a simple microphone amplifier, which can be used to enhance the signal of an electret or dynamic microphone.

With a minimum number of parts, this amplifier allows you to improve the signal-to-noise ratio and increase the gain of the microphone signal compared to the built-in audio driver amplifier. https: // Site /

Everything is going to record your first video lesson. Already made. But, the first attempt to write a voice stumbled on incredibly high noises and an insufficient gain of the microphone amplifier in the built-in audio card.

The most interesting videos on YouTube

When the "Microphone Boost" mode is disconnected, the noises managed to reduce, but the gain level became so low that it was impossible to write anything.

I have already decided to buy a separate audio card, but it turned out that a good audio card is very expensive, and budget for $ 10, although it has a lower noise level, but also has a microphone amplifier with a not very high gain.

So, I took for the manufacture of a simple microphone amplifier.

The first experiments with microphone amplifier layouts showed that noise levels can be reduced, and enhance increased.

There is only a divide to be given to how the developers of computer iron are managed to produce such "pearls" on the mountain, while only a few spear parts solve the problem of noise and amplification.

Construction and details.

When choosing an amplifier scheme, I focused mainly on ease of operation and the minimum number of parts taken to build. The task to make a super-duper Amplifier with record indicators was not put.

After making several schemes on the Sovdeopian chips, I stopped on the K538UN3A chip (KR538UN3A). https: // Site /

The reasons are as follows:

Why DL123A (CR-P2)? Due to the toxic filling, the housing of these elements is made of stainless steel and carefully seal, which eliminates the destruction of the case and damage to the amplifier circuit. The latter often happens when using salt and alkaline (alkaline) elements. (GP alkaine elements damaged my favorite Maglite).

Technical parameters K538UN3A.

Below is the public technical data taken from the paper directory on analog microcircuits, since the network did not find detailed information about this microcircuit.

The microcircuit is an ultra-slip broadband signal amplifier by frequency to 3 MHz. The noise characteristics of the amplifier are optimized to work with low-level signal generators. The gain is fixed with the inner divider, but it is possible to external adjustment. The amplifier is intended for use as a pre-amplifier of playback in the highest class equipment, as well as as an amplifier for low-level sensors. Case 2101.8-1 (DIP8) or 301.8-2.

Electrical parameters.

Rated voltage Power - + 6V.

Current consumption at UP \u003d 6B, T \u003d -45 ... + 70c, no more than - 5ma.

The voltage gain coefficient with internal feedback at UP \u003d 6B, F \u003d 1 MHz, URH. \u003d 1MV, RN \u003d 10KOM, T \u003d + 25С:

not less than 200,

no more than 300

typical value - 250.

Voltage enhancement coefficient without internal feedback At the UP \u003d 6B, F \u003d 1MHz, UVH \u003d 1MV, RN \u003d 10K, T \u003d + 25C, type value - 3000.

The normalized voltage of its own noise at UP \u003d 6B, F \u003d 1MHz, UVH \u003d 1MV, Rg \u003d 500Ω, RN. \u003d 10kom, t \u003d + 25c, no more - 5 NV / √Hz, typical value - 2,1 NV / √Hz.

Maximum output voltage UP \u003d 6B, RN \u003d 2K, kg \u003d ≤ 10%, T \u003d -45c, not less than 0.5V, typical value - 1B.

The upper frequency of the cut at UP \u003d 6B, RN \u003d 2k, KW \u003d 100, T \u003d + 25c, the standard value is 3 MHz.

Input resistance - 10k.

Limit operational data.

Maximum supply voltage - 7.5V.

Maximum input voltage - 200mv.

Minimum load resistance (short-term) - 0 Ohm.

Environmental temperature, long-term exposure: -45 ... + 70c, short-term impact: -60 ... + 125С.

Appointment of the conclusions of the K538UN3A microcircuit.

Case 2101.8-1.

1. Food.
2. Not used.
3. Correction.
4. Entrance.
5. The output of the gain factor adjustment.
6. Connecting a DC OS filter.
7. Common.
8. Output.

Case 301.8-2.

Several obsolete version of the microcircuit.

Typical circuit on the microcircuit.

1. C2 - Power filter.
2. C5 - dividing.
3. C6 - adjusting.
4. C8 - DC OS filter.
5. R4 - Adjusting OS by variable current.

The presented microphone amplifier circuit can enhance the signal, both an electre and dynamic microphone.

The size of the resistor R4 determines the gain of the DA1 chip.

The maximum gain coefficient is achieved at R4 \u003d 0.

For prompt adjustment and restrictions on the input signal level, the R3 potentiometer is used.

The R2 resistor, the VD2 diode and the HL1 LED are a voltage divider on which 2,2B is formed to power the electrical microphone. Resistor R1 is the load of an electre microphone. The HL1 LED also performs the power indicator function.

The scheme can be considerably simplified if you calculate only on the use of a dynamic microphone. We only need to keep in mind that when using a passive dynamic microphone with a small sensitivity, you may need to increase the gain coefficient, which will lead to a certain increase in the noise level of the microphone amplifier.

Printed circuit boards.

On the images of printed circuit boards, a view from the elements is presented. The tracks are shouted through the fee.

In the picture, an example of the wiring of the printed circuit board of the universal microphone amplifier.

1. Entrance.
2. Upper scheme end of the R3 potentiometer.
3. R3 potentiometer engine.
4. Anode LED HL1.
5. Case.
6. Power + 6V.
7. Output.
8. Case.

An example of the wiring of the printed circuit board of the amplifier of the dynamic microphone.

1. Entrance.
2. Case.
3. Power + 6V.
4. Output.
5. Case.

I myself made a printed circuit on the basis of the size of the controls and enclosures available in my disposal.

Case.

To place the design, it would be nice to choose a metal case. If a plastic case is used, then it is desirable to put the entire design to the screen. The screen can be made from tin cans from condensed milk. These banks are still covered with tin, and they are perfectly soldered (they do not even need to brow). And delicious and useful ... for the self-dealer. The signal controller housing must be connected to the entire amplifier screen.

In the picture, the housing from duralumin and the printed circuit board assembly. On the board, two independent amplifiers with separate power control. To write a stereo signal using two arbitrary microphones, the amplifier of each channel is equipped with a separate input manner.

Controls are installed directly on pCB. Adjusting the gain is carried out once by selecting permanent resistors when adjusting the amplifier.

Microphone amplifier assembly. The microphone amplifier is connected to the computer shielded cable, at the end of which the jack connector is 3.5mm (Jack 3,5mm).

Comparative tests.

With a comparative test, the regulators were set in such a position that would provide the same level of the recorded signal, both using the microphone amplifier and without it.

Green - noise level.

Raspberry - noise view.

On the graph of the noise level of the microphone amplifier in the built-in audio card in the MICROPhone Boost mode.

Recording level - 1.0.

Noise level is about -80db.

In order to get the minimum noise level, I set the maximum signal level R3 resistor. This made it possible to use the linear entry amplifier audio card with a low level of amplification.

On this schedule, the noise level of the self-made microphone amplifier.

Recording level 0.05.

Noise level near -110db.

The audio frame drivers usually do not allow the recording level with such high accuracy.

You can set the recording level with an accuracy of the percentage of a percentage using a free portable audio unit Audacity, a link to which in "additional materials".

The record itself or sound broadcast can be performed using any other programs.

How to connect a dynamic microphone to the cable.

Having a stereo microphone from an old coil tape recorder, I wanted to record stereo sound. But it was not there…

The sensitivity of dynamic microphones is inferior to the sensitivity of electra, which places the first increased requirements for the shielding from interference and press. However, these requirements are often ignored by the manufacturer. That was the situation with my microphones. They were connected to the cable in different ways, but each is wrong in its own way.

1. Case.
2. Conclusion of the coil.
3. Conclusion of the coil.

The figure shows that the left microphone was generally not connected to the housing, but at the right, one of the conclusions of the coil was connected to the housing. Both of these connections are incorrect, especially if we consider that a cable with shielded twisted pair was applied.

The picture shows how to properly connect the dynamic microphone to the microphone amplifier with an asymmetric input.

And this is a microphone connection to the microphone amplifier with a symmetric input.

The cheapest dynamic microphones are connected using a single-wire shielded cable. Figure a diagram of such a connection.

If you hear the flooring in the form of a background with a frequency of 50 Hz, then the microphone is better to connect using the shielded twisted pair.

The dotted line in the diagrams shows the microphone metal case, which should be connected to the shielding cable. The conclusions of the coil must be combined with a twisted pair. Not all budget dynamic microphones allow it to make it painlessly. Often one of the coil wires is already connected to the microphone metallic housing.

Do not try to overpass the coil wire to another contact. The coil is wrapped with a wire of 0.05mm and thinner. For comparison, the thickness of the human hair is 0.03-0.04mm. Any careless touch of the conclusions of the coil will inevitably lead to a cliff. In addition, the conclusions of the coil are additionally covered with glue, which also complicates the task.

Hooray! Earned!

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Five-second stereo record made using two dynamic microphones and self-made microphone amplifier. (You need to click on the picture).

The size of the resistor in the feedback circuit R4 \u003d 50 Ohms.

Microphone amplifier signal level - maximum.

Recording level by linear audio card input \u003d 0.2.

To build a sensitive microphone scheme, we will need:

1. TRANSISTOR BC547 or CT3102, you can try KT315.
2. Resistors R1 and R2 with a nominal 1 com. To increase the sensitivity R1 under the capsulus, a par value from 0.5 - 10 com.
4. Disk ceramic condenser with a par 100-300 PF. It can not be turned on if initially no "spikes" or excitations will not be.
5. Electrolytic condenser 5-100 μF (6.3 -16 V).

First of all, we define the polarity of the connection of the microphone-capsule. This simple is done: minus is always connected to the case. Then we collect the scheme, at least mounted installation, at least on the mini board. All sensitivity of the pre-amplifier will depend on the gain of the transistor and the selected resistor R1. Usually the amplifier is going and works at once, its sensitivity should be enough with a margin.

The recording is made on the caps without the pre-amplifier scheme.

The recording is made on the capsule from the pre-amplifier scheme.

The difference is visible not armed with an eye. Now the microphone does not necessarily hang on the neck and shout into it. You can completely put it on the table and speak without extra effort. Well, if the sensitivity turns out to be too big, it can always be reduced to the settings in the operating system without any problems.