Microphone preamplifier. Microphone amplifier on a chip (017) Preamplifiers on chips 4558

stereo amplifier on TDA2003 + JRC4558.

We present to your attention a schematic diagram of a complete stereo amplifier built on TDA2003 microcircuits. According to the datasheet the TDA2003 will deliver 6 watts of power into a 4 ohm load. The power supply of the amplifier is unipolar 12 Volts, so it can be used as a car audio system. If you are interested in the parameters of the amplifier in more detail, you can find the full description (datasheet) in the archive with the materials of this article. This amplifier also contains a preamplifier and three tone controls, which is implemented on the JRC4558 MC. Schematic diagrams are shown below:

Power amplifier circuit on TDA2003:

JRC4558 preamp circuit with 3-band tone control:

In the preamplifier, the JRC4558 chip can be replaced, for example, with the TL072.

All elements of the amplifier, together with the regulators, are placed on one board. The PCB sources are shown below:

Using these images, we drew a printed circuit board in the program Sprint layout, below is a view of the LAY6 format amplifier board:

The photo view of the LAY6 format is as follows:

Foil fiberglass one-sided, size 71 x 126 mm.

TDA2003 microcircuits are installed on one common radiator, so do not forget about thermal paste and insulating gaskets with insulating sleeves.

The convenience of the board lies in the fact that regulators are installed directly on it, so the use of wires for external connections is significantly reduced. All variable resistors are paired 2 x 20 kOhm with a linear characteristic, that is, if imported, then with the “B” index, if domestic - with the “A” index.

The appearance of the amplifier board assembly is shown below:

When power is applied to the amplifier, the red LED next to the input jack lights up. In its circuit there is a current-limiting resistor with a nominal value of 2.2 kOhm.

After the elements are soldered, rinse the board thoroughly, for example, with solvent 646, remove excess rosin and make sure there are no “snot” (tin jumpers between the tracks). Check again if the elements are soldered correctly (4558 chip, electrolyte polarity, etc.)
Amplifier assembled without errors and from serviceable parts in advanced settings does not need. Happy repetition.

List of amplifier elements with preamplifier and tone control:

Microcircuits:

● TDA2003 - 2 pcs.
● JRC4558 - 1 pc.

Resistors 1/4W:

● 47R - 2 pcs.
● 2R2 - 2 pcs.
● 220R - 2 pcs.
● 1R/0.5W – 2 pcs.
● 1K - 4 pcs.
● 10K - 2 pcs.
● 2k7 - 4 pcs.
● 100K - 2 pcs.
● 220K - 2 pcs.
● 2k2 - 1 pc.

Capacitors for voltage not less than 16V:

● 1000mF electrolyte - 2 pcs.
● 470mF electrolyte - 2 pcs.
● 100mF electrolyte - 2 pcs.
● 1mF electrolyte - 6 pcs.
● 10mF electrolyte - 1 pc.
● 0.047mF (473) film - 2 pcs.
● 0.1mF (104) film - 4 pcs.
● 0.1mF (104) ceramic – 1 pc.
● 0.0047mF (472) film - 2 pcs.
● 470pF (471) ceramic - 4 pcs.

Rest:

● Twin variable resistor 20k + 20k - 4 pcs.
● 2 Pin 5 mm bolt-on connector for board mounting – 3 pcs.
● 3 Pin 2.54 mm bolt-on connector for board mounting – 1 pc.
● LED – LED 5 mm red – 1 pc.
● 8 Pin socket for JRC4558 – 1 pc.
● Aluminum radiator for TDA2003 – 1 pc.
● Double RCA connector - 1 pc.
● Acoustic connection terminal – 1 pc.

You can download the amplifier circuit for TDA2003 & JRC4558, the LAY6 format PCB and datasheet_TDA2003 via a direct link from our website, which will appear after clicking on any line of the ad block below, except for the “Paid advertising” line. File size - 0.93 Mb.

Most audio enthusiasts are quite categorical and not ready for compromises when choosing equipment, rightly believing that the perceived sound must be clear, strong and impressive. How to achieve this?

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Perhaps the main role in resolving this issue will be played by the choice of amplifier.
Function
The amplifier is responsible for the quality and power of sound reproduction. At the same time, when buying, you should pay attention to the following designations, which mark the introduction of 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 a perfectionist who is ready to pay a lot for the pleasure of distinguishing the smallest nuances of his favorite musical compositions. Often hand-assembled equipment falls into this category.

Specifications to pay attention to:

• Input and output power. The nominal value of the output power is decisive, since edge values ​​are often unreliable.
• Frequency range. Varies from 20 to 20000 Hz.
• The coefficient of non-linear distortion. It's simple - the smaller the better. The ideal value, according to experts, is 0.1%.
• Signal-to-noise ratio. Modern technology assumes a value of this indicator above 100 dB, which minimizes extraneous noise when listening.
• dumping factor. Reflects the output impedance of the amplifier in relation to the nominal load impedance. In other words, a sufficient damping factor (more than 100) reduces the occurrence of unnecessary vibrations in equipment, etc.

It should be remembered: the manufacture of high-quality amplifiers is a laborious and high-tech process, respectively, too low price with worthy characteristics should alert you.

Classification

To understand all the variety of market offers, it is necessary to distinguish the product according to various criteria. Amplifiers can be classified:

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

Important: the primary conversion and signal processing takes place precisely in the preamplifiers.

• By element base distinguish between tube, transistor and integrated PA. The latter arose in order to combine the advantages and minimize the disadvantages of the first two, for example, the sound quality of tube amplifiers and the compactness of transistor ones.
• According to the mode of operation, amplifiers are divided into classes. The main classes are A, B, AB. If class A amplifiers use a lot of power, but produce high quality sound, class B is the opposite, class AB seems to be the best choice, representing a compromise between signal quality and sufficiently high efficiency. There are also classes C, D, H and G, which have arisen with the use of digital technologies. There are also single-cycle and push-pull modes of operation of the output stage.
• By the number of channels, amplifiers can be one-, two- and multi-channel. The latter are actively used in home theaters to form the volume and realism of the sound. Most often there are two-channel, respectively, for the right and left audio systems.

Attention: the study of the technical components of the purchase, of course, is necessary, but often the decisive factor is the elementary listening to the equipment according to the principle of sounds or does not sound.

Application

The choice of amplifier is more justified by the purposes for which it is purchased. We list the main areas of use of audio frequency amplifiers:

1. As part of a home audio system. It's obvious that the best choice is a two-channel single-cycle tube in class A, also optimal choice can constitute a three-channel class AB, where one channel is defined for a subwoofer, with a Hi-fi function.
2. For speaker system in the car. The most popular four-channel amplifiers are AB or D class, in accordance with the financial capabilities of the buyer. In cars, the crossover function is also in demand for smooth frequency control, which allows you to cut frequencies in the high or low range as needed.
3. in concert equipment. Higher demands are reasonably placed on the quality and capabilities of professional equipment due to the large distribution space. sound signals, as well as a high need for intensity and duration of use. Thus, it is recommended to purchase an amplifier with a class not lower than D, capable of operating almost at the limit of its power (70-80% of the declared one), preferably in a case made of high-tech materials that protects against negative weather conditions and mechanical influences.
4. in studio equipment. All of the above is true for studio equipment. You can add about the largest frequency reproduction range - from 10 Hz to 100 kHz in comparison with that from 20 Hz to 20 kHz in a domestic amplifier. Also noteworthy is the possibility of separate volume control on different channels.

So that you can enjoy pure and high-quality sound, it is advisable to study all the variety of offers in advance and choose the option of audio equipment that best meets your needs.

The author of this circuitry is good friend Maestro, who developed the scheme a few years ago and published it in one of the issues of the radio magazine. The initial version of the circuit showed good parameters and high stability of operation, therefore, in a couple of years, the circuit was improved by the joint efforts of radio amateurs.

Stabilization on the varicap was added, and also replaced several components of the frequency-setting circuit, added a loop capacitor for easy tuning to the desired range. A high quality microphone amplifier has been added. I became seriously interested in this scheme and developed several modifications.

The first version is suitable for signal transmission at a distance of up to 150 meters. Printed circuit board The initial versions of the bugs were drawn by hand, using a manicure and a toothpick.

Element base

The BA4558 microcircuit is found with different markings, pay attention only to the inscription 4558. The microcircuit is produced in 8-pin packages. Resistors and capacitors were soldered from motherboards computer and digital receivers. Unfortunately, there are no markings for SMD capacitors, so it is advisable to use a capacitor capacitance meter or a digital multimeter with such a meter. In extreme cases, you can use ordinary capacitors.

For low-power versions, I advise you to use imported S9018 series RF transistors in the transmitter and UHF. The transistor is sometimes labeled as SS9018, C9018 or 9018.

It is not advisable to use domestic transistors in the transmitter, experience has shown that with a similar KT368, reception is an order of magnitude worse.
The contour is wound with a wire of 0.6-0.8mm (the best option is 0.7mm) on a 4mm frame and contains 8 turns with a tap from the middle. To begin with, 8 turns are wound on the frames, then we read 4 turns and remove the varnish. In a place cleaned of varnish, we solder a piece of single-core wire of the same diameter as the coil (preferably bare wire)

The process of assembling and setting up the circuit does not take much time, only after assembling the initial version of the circuit, I supplemented the design with stabilization and UHF. On all his versions, he used the same microphone amplifier built on the BA4558 chip. The microphone is the most ordinary - a capsule from a Chinese receiver and even with it the sensitivity is about 5-6 meters, while the sound transmission is clear, even if you speak near the microphone. Such parameters of the bug make it possible to use the devices as a remote microphone for karaoke, which is why I made a couple of such devices for the conference.

The frequency slope is negligible: at a distance of 10-100 meters from the receiver, the frequency floats by only 0.1 MHz!

Some assembly tips

It is desirable to make the circuit on SMD, so the size of the radio microphone is sharply reduced, several versions were assembled, including those with conventional components, with SMD no excitations and noises were observed in the reception.

It is better to make the antenna from a stranded wire in insulation, the wire diameter is 0.5-0.7 mm.

The varicap was removed from antenna unit domestic TV, but you can use almost any similar varicap, in my case I used KV121A.

Place the finished beetle in a metal case, which will simultaneously play the role of a screen, minus the beetle soldered onto the case.
It is advisable to take a microphone exactly like mine, they can be easily bought on the radio market, with microphones from cell phones and headsets, the sound is not voluminous, more like a highly directional microphone and some fragments of speech are difficult to make out. Instead of a microphone mobile phone perfect if you are going to use the device as a microphone for karaoke.

The high stabilization of the circuit allows you to pick up the device, while there will be no distortion in the transmitted signal if you do not touch the antenna. In order to reduce the length of the antenna, you can take the paste from the helium pen and wind the spiral antenna. For this, a single-core wire with a diameter of 0.6-0.8 mm and a length of 40-50 cm is taken and evenly, coil to coil is wound along the length of the entire frame (paste from the handle). After winding, the paste can be removed, and the spiral antenna placed in a plastic tube of a suitable diameter.

First start

When the circuit is fully assembled, we connect it to a power source. To begin with, it is advisable to use a regular 9 volt crown. We connect a milliammeter or a digital multimeter in the current meter mode into the power supply gap. A properly assembled bug consumes about 10-13mA, in some cases up to 15mA. Then, using an RF detector, we check the radiation.

To do this, we bring the detector antenna closer to the beetle's antenna, so that there is a gap of 0.5-1 cm between them. The detector arrow should deviate, if this does not happen, then dock the detector antenna with the collector of the transmitter transistor - the arrow must deviate if the bug is working.

Before assembly, check all active components for operability, even if the latter were purchased from a store, i.e. new.
If there is radiation, then it's time to turn on the radio. A beetle with such elements in the frequency-setting circuit is usually caught at frequencies of 94-98 MHz, in my case 4 specimens were collected, all were caught at frequencies of 96-98 MHz.

The first version of the circuit without UHF penetrated 130 meters to the receiver of an ordinary mobile telegon, this is powered by a crown, the latter was run down (7.8 Volts)

The second version with UHF on a low-power S9018 consumes 20-27mA, breaks clean 300 meters - personally verified, received a signal from a mobile phone to the same receiver.
At the expense of the third version - I checked it with an imported transistor at 300 MHz, the circuit consumed 68mA, it penetrates 500 meters, but this is not the limit for the third version, with the transistor indicated in the circuit it can easily penetrate 1 km.

As a case, I used an iron casing from a Chinese electronic transformer for 30-50 watts.

Part of the transmitter is embedded in paraffin for durability.

Without an RF amplifier, the bug freely penetrates 100-130 meters and this is through concrete walls, so that this bug is quite suitable for wiretapping or passing exams.

In the end, I want to say that I have tried many radio bug circuits of medium and high complexity, good quartz-stabilized circuits are inaccessible to many, and simple circuits not stable, but the range is within 10-50 meters, the same scheme, despite its simplicity, has a relatively high quality of the transmitted signal, stability and range, so that no one had any doubts decided to shoot one of the first tests of its kind for the range of a bug .

List of radio elements

Microphone preamp, it is also a preamplifier or amplifier for a microphone - this is a type of amplifier whose purpose is to amplify a weak signal to a linear level (about 0.5-1.5 volts), that is, to an acceptable value at which conventional sound power amplifiers operate .

The input source of acoustic signals for the preamplifier is usually the pickups of vinyl records, microphones, pickups of various musical instruments. Below are three diagrams of microphone amplifiers on transistors, as well as a variant of a microphone amplifier on a 4558 chip. All of them can be easily assembled with your own hands.

Schematic diagram of a simple microphone preamplifier on a single transistor

This mic preamp circuit works with both dynamic and electret microphones.

Dynamic microphones are similar in design to loudspeakers. The acoustic wave acts on the membrane and on the acoustic coil attached to it. At the moment the membrane vibrates, an electric current is generated in the coil, which is under the influence of the magnetic field of a permanent magnet.

The operation of electret microphones is based on the ability of certain types of materials with a high dielectric constant (electrets) to change the surface charge under the influence of an acoustic wave. This type microphones differs from dynamic high input impedance.

When using an electret microphone, to bias the voltage on the microphone, you must set the resistance R1

Since this microphone amplifier circuit is for a dynamic microphone, when using an electrodynamic microphone, its resistance should be in the range from 200 to 600 ohms. In this case, C1 must be set to 10 microfarads. If it is an electrolytic capacitor, then its positive terminal must be connected towards the transistor.

Power is supplied from a krone battery or from a stabilized power source. Although it is better from the battery to eliminate noise. can be replaced with a domestic one. Electrolytic capacitors for a voltage of 16 volts. To prevent interference, connect the preamplifier to the signal source and to the amplifier input with a shielded wire. If further powerful sound amplification is needed, then you can assemble an amplifier on a microcircuit.

Microphone preamp with 2 transistors

The construction structure of any preamplifier greatly affects its noise characteristics. If we take into account the fact that high-quality radio components used in the preamplifier circuit still lead to distortion (noise) to one degree or another, then it is obvious that the only way to get a more or less high-quality microphone amplifier is to reduce the number of radio components of the circuit. An example is the following two-stage preliminary circuit.

WITH this option the number of coupling capacitors is reduced to a minimum, since the transistors are connected in a common emitter circuit. There is also a direct connection between the cascades. To stabilize the operating mode of the circuit, when the external temperature and supply voltage change, a direct current feedback was added to the circuit.

Three-transistor electret microphone preamplifier

This is another option. The peculiarity of this amplifier circuit for a microphone is that the power supply to the preamplifier circuit is carried out through the same conductor (phantom power) through which the input signal goes.

This microphone preamplifier is designed to work with, for example, MKE-3. The supply voltage to the microphone goes through the resistance R1. The audio signal from the microphone output is fed to the base VT1 through the capacitor C1. , consisting of resistances R2, R3, the necessary bias is created based on VT1 (approximately 0.6 V). Enhanced signal from the resistor R5, acting as a load, goes to the base VT2 which is part of the emitter follower on VT2 and VT3.

Near the output connector, two additional elements are installed: a load resistance R6, through which power is supplied, and an isolation capacitor C3, which separates the output audio signal from the supply voltage.

Microphone pre-amplifier on a 4558 chip

The 4558 operational amplifier is manufactured by ROHM. It is characterized as a low power and low noise amplifier. This chip is used in a microphone amplifier, audio amplifiers, active filters, voltage controlled generators. 4558 chip has internal phase compensation, increased threshold input voltage, large gain and low noise. This op amp also has short circuit protection.

(140.5 Kb, downloaded: 2 485)

This a good option for building a microphone preamplifier on a microcircuit. The microphone preamplifier circuit is high quality amplification, simple and does not require much wiring. This microphone amplifier for dynamic microphone also works well with electret microphones.

The scheme of a self-made preamplifier (preamp) with a tone block, is made on the LM4558 chip. An important part of an audio amplifier is the preamplifier. It is desirable that he could not only amplify the signal, but also regulate its frequency response.

The figure on the right shows a diagram of a simple stereo pre-amplifier with volume control separately in each channel and a common tone control in both channels for low, medium and high frequencies.

circuit diagram

The circuit is made on a dual operational amplifier type LM4558. And it is designed primarily to work with automotive simple amplifiers built on microcircuits - integrated bridge UMZCH. Therefore, the “automobile” supply voltage is unipolar 12V.

But this does not limit the scope of this scheme only to automotive vehicles.

Rice. one. circuit diagram homemade preamplifier with tone block on LM4558.

The supply voltage can be up to 30V. And you can even switch to bipolar power. To do this, remove the divider on the resistors R1, R2 and C2. And pins 3 and 5 of the microcircuit are connected to a common power minus. In this case, pin 4 is disconnected from the minus supply, and apply a negative supply voltage to it.

Volume control is carried out by variable resistors R7 and R15, as already mentioned, separately in each channel. On the operational amplifiers of the A1 chip, two active tone controls are made, in which both the amplification of the audio signal and frequency correction occur using three-band tone controls.

Adjustment circuits are included in the OOS circuits of operational amplifiers. Volume control at high frequencies - with a double variable resistor R8, at medium frequencies - R9, at low frequencies- R10.

Details

The LM4558 chip can be replaced by any IC - two op amps general use or make a circuit on two ICs, one op-amp in each.