Preamplifier for microphone, it is also a pre-amplifier or an amplifier for a microphone - this is a type of amplifier, the purpose of which is to enhance the weak signal to the linear level value (about 0.5-1.5 volts), that is, to an acceptable value at which conventional sound power amplifiers work .

Input source of acoustic signals for pre-amplifier Usually the pickups of vinyl plates, microphones, pickups of various musical instruments. Below is three microphone amplifiers on transistors, as well as an option of a microphone amplifier on the chip 4558. All of them can be easily assembled with their own hands.

Scheme of a simple microphone preamp on one transistor

This microphone preamplifier circuit works both with dynamic and electrical microphones.

Dynamic design microphones are similar to loudspeakers. Acoustic wave has an impact on the membrane and an acoustic coil attached to it. At the time of the oscillation of the membrane, in the coil under the influence of the magnetic field of the permanent magnet, an electric current is formed.

The operation of electrical microphones is based on the possibility of certain types of materials with increased dielectric constant (electrotheys) to change the surface charge under the influence of an acoustic wave. This type of microphones differs from dynamic high input resistance.

When using an electrical microphone, to shift the voltage on the microphone, it is necessary to establish the resistance R1

Microphone amplifier on one transistor

Since this microphone amplifier circuit for a dynamic microphone, then when using an electrodynamic microphone, its resistance must be in the range from 200 to 600 ohms. At the same time, C1 must be put up to 10 μF. If it is electrolytic condenser, Its positive output must be connected towards the transistor.

Power is powered by the Crohn battery or from a stabilized power source. Although it is better from the battery to exclude noise. Can be replaced with domestic. Electrolytic capacitors for 16 volts voltage. To prevent interference, connect the preamp to the source of the signal and to the input of the amplifier is necessary to the shielded wire. If you need a further powerful audio strengthening, you can collect an amplifier on the microcircuit.

Microphone pre-amplifier on 2 transistors

The structure of building any preamp is very effect on its noise characteristics. If you take into account the fact that the qualitative radio components used in the preamplifier scheme still lead to distortions (noise), it is obvious that the only output to obtain a more or less high-quality microphone amplifier is to reduce the number of radio components of the circuit. An example may be the following diagram of a two-stage preliminary.

With this option, the amount of separation capacitors is minimized, since the transistors are included according to a circuit with a common emitter. Also between the cascades there is a direct connection. To stabilize the mode of operation of the circuit, when the external temperature and supply voltage changes, the DCO is added to the diagram.

Preamplifier for an electre microphone on three transistors

This is another option. The feature of this amplifier circuit for the microphone is that the power supply to the preamp scheme is carried out along the same conductor ( phantom nutrition) To which the input signal goes.

This microphone preamp is designed for collaboration with, for example, MKE-3. The supply voltage on the microphone goes through the resistance R1. The audio signal from the microphone exit enters the VT1 database through the C1 capacitor. consisting of resistances R2, R3 creates the required displacement on the VT1 database (approximately 0.6 V). Stressed signal From the resistor R5, acting as a load, goes to the VT2 base which is part of the emitter repeater on VT2 and VT3.

Near the output connector, an additional two elements are installed: the load resistance R6, through which is powered, and the SZ separator condenser separating the output audio signal from the supply voltage.

Pre-microphone amplifier on chip 4558

Operational amplifier 4558 is produced by RoHM. It is characterized as a low-power and low noise amplifier. This microcircuit is used in the microphone amplifier, sound amplifiers, active filters, controlled voltage generators. Microcircuit 4558 has an internal phase compensation, an enlarged threshold input voltage, Great gain and low noise level. Also, this operational amplifier has a short circuit protection.

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Microphone preamp 4558

it a good option To build a microphone preamp on the chip. The diagram of the preamp for the microphone is distinguished by high gain quality, simplicity and does not require large strapping. This microphone amplifier for dynamic microphone also works well with electret microphones.

When an error-free assembly, the scheme does not require configuration and starts to work immediately. The greatest consumption current is 9 mA, and in the state of rest consumed the current in the region of 3 mA.

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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Amplifier on the F4558 chip

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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 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 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:

• Input and 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 extraneous noises 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 C, D, H and G classes that occur with the use of digital technologies. 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:

1. 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.
2. For 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.
3. In concert equipment. The quality and capabilities of professional equipment, higher requirements are reasonable due to the large space of sound signals, as well as high demand in the 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.
4. 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.

Thus, in order to enjoy clean and high-quality sound for a long time, it is advisable to study all the variety of proposals in advance and choose an option of audio equipment that matters as much as possible.

This amplifier was built to achieve two goals:

• An increase in the microphone sensitivity for voice recording;
• Reduce the noise level in the record, due to the higher input signal into the integrated audio card;

When choosing a heart of the amplifier, the eye fell on the chip of a dual low-noise operational amplifier 4558С. This microcircuit is issued by different companies and may have names KA4558., LM4558., NJM4558. and so on. The main thing is that the number 4558 in the name. It is such a chip in the area of \u200b\u200b$ 0.15. It can also be taken from a unipolar power source.

Since the microcircuit is a dual amplifier, then the second part was decided to use as a power amplifier for roving the headphones connected to the UNG. The ability to hear your voice through the microphone makes the voice recording much more convenient and easier ...

Nutrition UNH is made from four finger batteries, in order not to have a supply from the network.

The total resistance of the resistors R1 and P1 sets the level of amplification of the cascade of the microphone amplifier. The more resistance the higher the strengthening level.

The ratio of resistors R3 and R10 sets the level of strengthening of the IULC headphone cascade. In this embodiment 22k / 10k \u003d 2.2, i.e., the gain at this cascade will be 2.2 times.

For the possibility of work of computer microphones (Skype headset), there is the possibility of inclusion of phantom nutrition.

It is also worth noting that the output signal of the ONCH is so high that it is not recommended to connect it to the micron input of the audio card, since there is a possibility of the outcome of the latter. UNG must be connected to a linear input.

The author of this scheme engineering is a good friend. Maestro.who has developed a diagram a few years ago and published in one of the rooms of the radio log. The initial version of the scheme showed good parameters and high stability of work, so in a couple of years, the scheme was improved by the joint forces of radio amateurs.

Stabilization on the varicap was added, and also replaced several components of the frequency-waving chain, added a circuit capacitor for convenience of setting up to the desired range. A high-quality microphone amplifier has been added. He became interested in this scheme seriously 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 manually using manicure and toothpicks.

Elemental base

The BA4558 microcircuit meets with different labeling, pay attention only to the inscription 4558. A chip is produced in 8-pin housings. Resistors and capacitors were dropped from motherboards Computer and digital receivers. There are no labels with SMD capacitors, therefore it is desirable to use a capacitors tank meter or a digital multimeter with such a meter. In the extreme case, conventional capacitors can be used.

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

In the transmitter it is not desirable to use domestic transistors, experience has shown that with a similar CT368 reception agency worse.
The contour - wiped with a wire of 0.6-0.8 mm (the optimal version of 0.7 mm) on the 4mm rim and contains 8 turns with a tap from the middle. To begin with, 8 turns are filled with frames, then you read 4 turns and remove the varnish. In the spot purified from varnish, we sear a piece of single-core wire of the same diameter as the coil (the wire is preferably bare)

The process of assembling and setting the scheme does not take away a lot of time, only after assembling the initial version of the scheme complemented the design stabilization and UHF. On all its versions used the same microphone amplifier built on the BA4558 microcircuit. Microphone is the most ordinary - capsule from chinese receiver And even with him the sensitivity of about 5-6 meters, while the transmission of sound is clear, even if we talk near the microphone. Such bug parameters make it possible to use devices as a remote microphone for karaoke, which is why it made a pair of such devices for the conference.

Frequency slope slightness: at a distance of 10-100 meters from the receiver, the frequency floats only 0.1 MHz!

Several assembly tips

It is advisable to do on SMD to SMD, so sharply decreases the size of the radio microphone, several versions were collected, including with ordinary components, with the RMD, no expansion and noise in the reception was observed.

The antenna is better made from the stranded wire in the insulation, the diameter of the wire is 0.5-0.7mm.

Varicap was removed from antenna bloc A domestic TV, but can be used almost any similar varicap, in my case the KV121A is used.

The finished beetle is placed in a metal case, which will simultaneously play the role of the screen, minus bug to sole on the body.
The microphone is desirable to take exactly such as me, they can easily buy on the radio market, with microphones from cell phones and headset, the sound is not bulky, more resembles a narrow-directional microphone and some fragments of speech are difficult to disassemble. Instead microphone OT. mobile phone It is perfect in the event that you are going to use a device as a karaoke microphone.

High stabilization of the scheme allows you to take a device in hand, while in the transmitted distortion signal will not be, if you do not touch the antennas. In order to reduce the length of the antenna, you can take a paste from the helium handle 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 and evenly, the turn to the turn is wound along the length of the entire frame (paste from the handle). After the winding, the paste can be removed, and the spiral antenna is placed in the plastic tube of a suitable diameter.

First start

When the scheme is fully assembled, we connect it to the power source. To begin with, it is desirable to use the usual 9 volt crown. In the plus break, we connect a milliammeter or a digital multimeter in the current meter mode. Properly assembled bug consumes about 10-13mA, in some cases up to 15 mA. Then, with the help of the RF detector, check the radiation.

To do this, approach the detector antenna to the beetle antenna, so that between them was 0.5-1 cm. The arrow of the detector must deviate if this does not occur, then connect the detector antenna with the collector of the transistor transistor - the arrow must deviate if the bug works.

Before assembly, check all active ingredients for performance, even if the latter were bought from the store, i.e. New.
If there is radiation, it's time to turn on the radio. The beetle with such elements in the frequency-waving chain is usually caught in the frequencies of 94-98 MHz, in my case 4 copies were collected, everyone was caught at 96-98 MHz frequencies.

The first version of the circuit without UHF pierced 130 meters to the receiver of the usual mobile telegon, this is with meals from the crown, the latter was filming (7.8 volts)

The second version of the UHF on the low-power S9018 consumes 20-27mA, pierces clean 300 meters - verified personally, received a signal to the same receiver from a mobile phone.
At the expense of the third version - he checked with an imported transistor for 300 MHz, consumed the 68mA scheme, punches 500 meters, but this is not the limit for the third version, with the transistor specified in the circuit can easily break through 1km.

As a case, I used the iron crook from the Chinese electronic transformer by 30-50 watts.

A portion of the transmitter for resistance is poured by paraffin.

Without an amplifier, the RF bug freely breaks through 100-130 meters and it 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 tried many schemes of radio fairs of medium and high complexity, good schemes with quartz stabilization are not available to many, and simple schemes not stable, and the range of 10-50 meters, the same scheme Despite the simplicity of the relatively high quality of the transmitted signal, stability and range, so that there was no doubt that there was no doubt decided to shoot one of the first of its kind trial tests bug .

List of radio elements

Designation	A type	Nominal	number	Note	Score	My notebook
IC1	Operational amplifier	BA4558.	1			In notebook
VT1	Bipolar transistor	SS9018.	1	S9018; C9018; 9018.		In notebook
CD1.	Varicap	KV121A.	1			In notebook
C1.	Capacitor	100 NF.	1			In notebook
C5, C6.	Capacitor	5 PF	2			In notebook
C7	Capacitor	2.2 PF	1			In notebook
C8-C10	Capacitor	0.1 MKF.	3			In notebook
	Variable condenser	1-10 PF	1			In notebook
R2.	Resistor	100 Oh.	1			In notebook
R3	Variable resistor	1 com	1			In notebook
R4, R11	Resistor	100 com	2			In notebook
R5, R7, R9, R10	Resistor	10 com	4			In notebook
R8.	Resistor	470 com	1			In notebook
L1.	Inductor		1			In notebook
	Microphone		1	Capsule		In notebook
	Vercia with UFF
IC1	Operational amplifier	BA4558.	1			In notebook
VT1, VT2.	Bipolar transistor	SS9018.	2			In notebook
CD1.	Varicap	KV121A.	1			In notebook
C1.	Capacitor	100 NF.	1			In notebook
C3, C5, C6	Capacitor	5 PF	3			In notebook
C7	Capacitor	2.2 PF	1			In notebook
C8, C9, C10	Capacitor	0.1 MKF.	3			In notebook
	Variable condenser	1-10 PF	1			In notebook
R1, R5, R7, R9, R10	Resistor	10 com	5			In notebook
R2.	Resistor	100 Oh.	1			In notebook
R3	Variable resistor	1 com	1			In notebook
R4, R11	Resistor	100 com	2			In notebook
R8.	Resistor	470 com	1			In notebook
L1.	Inductor		1	Wire 0.7 mm; Rim 4 mm; 8 vitkov		In notebook
L2.	Inductor	2.2 μH	1			In notebook
	microphone		1	Capsule		In notebook
IC1	Operational amplifier	BA4558.	1			In notebook
VT1, VT2.	Bipolar transistor	SS9018.	2			In notebook
VT3.	Bipolar transistor	KT610A.	1			In notebook
CD1.	Varicap	KV121A.	1			In notebook
C1.	Capacitor	100 NF.	1

The scheme of the self-made pre-amplifier (preampa) with the hammercycle is made on the LM4558 chip. An important part of the audio is a preliminary amplifier. It is desirable that it can not only enhance the signal, but also to regulate its response.

The figure right shows the scheme of an uncomplicated pre-stereoxylter with adjustableness separately in each channel and a common, medium and high frequency adjustment channels in both channels.

Schematic scheme

The diagram is made on a dual operating amplifier of the LM4558 type. And is intended primarily to work with the automotive simple amplifiers Built on chips - integrated bridge UMPs. Therefore, the supply voltage "Automotive" -Oppolar 12V.

But this does not limit the scope of this scheme only by automotive equipment.

Fig. one. Schematic scheme A homemade pre-amplifier with a rampage on LM4558.

The supply voltage can be up to 30V. And you can even go to bubolar nutrition. To do this, remove the divider on the resistors R1, R2 and C2. And conclusions 3 and 5 microcircuits to connect with a total minus power. At the same time, the output 4 disconnect from the minus of the power, and to submit a negative supply voltage on it.

Volume adjustment is carried out by variable resistors R7 and R15, as already mentioned, separately in each channel. On operational amplifiers, A1 microcircuits were made by two active tone regulators, in which it occurs both amplification of the audio signal and the frequency correction using three-band tone regulators.

Adjustment circuits are included in the OCC chain of operational amplifiers. Adjusting the volume at high frequencies - dual variable resistor R8, average frequencies - R9, by low frequencies - R10.

Details

LM4558 chip can replace any ISS - two OU general Or make a diagram on two ICs one by one OU in each.