Theory: 3H preamplifiers. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Theory: 3H preamplifiers. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

Comments on the article

Preamplifiers are usually voltage amplifiers, and low-power ones, since their output is designed for a load from 600 ohms to several tens of kilo-ohms. As a rule, they work on the high-impedance input of the power amplifier and therefore their output current is very small.

Usually, preamplifiers have several inputs designed to connect various sources: the line output of a tape recorder, an electromagnetic or piezoelectric pickup, a radio receiver, and sometimes (less often) a broadcast line.

Requirements for input parameters - sensitivity (the minimum signal voltage required for normal operation) and input resistance - differ for different inputs. Moreover, correction of the frequency response of the amplifier is often required when working with one or another signal source. A magnetic head, for example, develops an EMF proportional to the rate of change of the magnetic flux, and hence to frequency. But at higher frequencies, the EMF drops due to a decrease in the effective thickness of the tape layer at short recording wavelengths, the finite width of the head gap, and other reasons. Therefore, the corrector amplifier must have a rise in the amplitude-frequency characteristic (AFC) at lower and higher frequencies.

The necessary amplification to raise the signal level from a few millivolts to fractions of a volt in the AF preamplifier is usually obtained using one or two transistor stages. Moreover, to simplify the amplifier, a direct connection between the cascades by direct current is often used. A practical diagram of such an amplifier is shown in fig. 39.

Theory: 3H preamplifiers

The input signal through the decoupling capacitor C1 is fed to the base of the transistor VT1, and from its load (resistor R1) - to the base / T2. The stabilization of the transistor mode occurs as follows: the collector voltage of the transistor VT1 (usually 1 ... 2 V) is "repeated" at the emitter VT2, where the bias resistor R3 is connected. The amplified signal is removed from the load of the transistor VT2 (resistor R4) and is fed through the isolation capacitor C3 to the UMZCH.

Capacitor C2 eliminates AC negative feedback for audio frequencies, thereby increasing the gain, which in this amplifier can reach several thousand. Resistor R2 creates an OOS in the first stage - it reduces the gain, but it increases the input impedance and reduces distortion. Its resistance can be varied over a wide range, when it is reduced to zero, the gain will be maximum.

You can also reduce the gain by turning on a resistor in series with capacitor C2, thus creating an OOS in the second stage. By reducing the capacitance of the capacitor, it will be possible to correct the frequency response. providing a rise in the higher frequencies of the audio spectrum due to the fact that the capacitance decreases with frequency, reducing the feedback at these frequencies. To attenuate the higher frequencies, you need to include a small capacitor between the collector and the base of one of the transistors. As a result, an OOS will appear, operating mainly at these frequencies.

If it is necessary to increase the input and lower the output impedance of the amplifier, emitter followers are turned on at its input and output.

Author: V.Polyakov, Moscow

See other articles Section Beginner radio amateur.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

LG Optimus G Pro 28.07.2013

LG Optimus G Pro is the current flagship of the Korean manufacturer, which is emphasized by its outstanding size and technical characteristics. The dimensions of the monoblock have grown due to the installation of a 5,5-inch display with an IPS matrix and a density of 400 dpi. It supports Full HD resolution, so watching movies on it will not only be comfortable, but very comfortable.

The Qualcomm Snapdragon 600 system-on-chip with a built-in 4-core processor will ensure the smooth launch of high-definition movies. Its frequency is 1,7 GHz. The speed of the smartphone LG Optimus G Pro is also affected by 2 GB of RAM.

The smartphone is equipped with many modern technologies: apart from a powerful SoC and a large display, it also has support for fourth-generation cellular networks and two built-in cameras - one at 13 and the other at 2,1 megapixels. All this iron draws energy for its work from a 3140 mAh battery.

Memory for user data, including applications, media content, and more in LG Optimus G Pro provides exactly 16 GB in the form of a flash module. It is possible to expand this volume by installing a microSDXC card up to 64 GB.

The LG Optimus G Pro smartphone is supplied to the Russian mobile market in black and white cases. The monoblock received dimensions of 150x76x8,5 mm.

Other interesting news:

▪ Compact portable solar-powered refrigerator

▪ Computer without wires and batteries

▪ Shape memory wool fabric

▪ New Debug Platform for DaVinci Processors

▪ Nvidia Parker - new generation single-chip system for the automotive segment

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Indicators, sensors, detectors. Article selection

▪ article Supercomputer. History of invention and production

▪ article Why are lizards that reproduce by parthenogenesis still involved in mating games? Detailed answer

▪ article Working with a drying chamber. Standard instruction on labor protection

▪ article Antison for the viewer. Encyclopedia of radio electronics and electrical engineering

▪ article Gas burner. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews