Circuits of audio frequency generators using transistors. Audio frequency generator circuit

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SOUND FREQUENCY GENERATOR GZ-2 (ZG-10)

Rice. 1. Generator GZ-2.

The sound frequency generator GZ-2 (Fig. 1) is intended for use as a source of sinusoidal electrical oscillations of sound (low) frequency.

The device is designed for use in laboratory conditions and repair shops.

MAIN TECHNICAL CHARACTERISTICS

1. 
   Range of generated frequencies from 20 to 20,000 Hz divided into three subranges: 20-200; 200-2000 and 2000-20,000 Hz.
2. 
   Frequency setting error ±2%± 1 Hz.
3. 
   Frequency drift after 30 min preheating for the first hour of operation no more than ±0.4%; over the next seven hours of operation, additional frequency drift is no more than ±0.4%.
4. 
   Normal output power 0.5 Tue.
5. 
   Maximum output power 5 Tue.
6. 
   Maximum output voltage at matched load 150 V.

1. 
   The output voltage changes smoothly, as well as in steps after 1 db from 0 to 110 db using two divisors: the first - after 10 db from 0 to 100 db, second - after 1 db from 0 to 10 db.
2. 
   The output impedance of the generator is designed for matched loads of 50; 200; 600 and 5000 ohm
3. 
   Harmonic distortion factor:

10. Uneven frequency response relative to readings at frequency 400 Hz:

• 
  at maximum output power and at all loads at frequencies from 50 to 10,000 Hz no more than ±1 db, at frequencies from 20 to 20,000 Hz no more than ±3.5 db;
• 
  at normal output power at matched load 600 ohm at frequencies from 50 to 10,000 Hz no more than ±0.5 db, at frequencies from 20 to 20,000 Hz no more than ±1.5 db.

1. 
   Calibration error of the indicator scale at a frequency of 1000 Hz at voltage up to 60 V does not exceed ±5%.
2. 
   Power supply of the device from an alternating current network with a frequency of 50 Hz, software voltage; 127 or 220 s±10%.
3. 
   Power consumption from the network is no more than 150 va.

1. 
   Dimensions: 598x357x293 mm.
2. 
   Device weight no more than 35 kg.

DESCRIPTION OF THE CIRCUIT DIAGRAM

The GZ-2 generator (Fig. 2) consists of the following main elements: a master oscillator, an amplifier, an output voltage indicator, an output device and a power source.

The master oscillator is assembled using a rheostatic-capacitive circuit using lamps L 1 (6Zh8) and L 2 (6P9). An abrupt change in the frequency of the generator is carried out by switching resistances R 1 -R 11 , and smooth - by changing the capacity WITH 1 . To increase the stability of the generator, negative feedback is introduced into its circuit, in the circuit of which a thermistor TP6/2 is connected.

The bass reflex stage of the audio amplifier is made according to an auto-balanced symmetrical circuit on a lamp L 3 (6Н8С). Power amplifier with two tubes L 4 And L 5 (6С4С) operates on a push-pull circuit. The gain of the audio amplifier is about 4.

The output indicator is a diode voltmeter assembled using a full-wave circuit on a lamp L 8 (6Х6С). An M5 magnetoelectric device of class 2.5 IP 1 with a scale of 60 was used as an indicator. V, calibrated in effective voltage values ​​at a load of 600 ohm The output device consists of two attenuators - bridge-type voltage dividers U 1 per 100 db in steps of 10 db And U 2 on 10 db in steps of 1 db and transformer Tr 3 , serving to match the generator output with loads of 50; 200; 600 and 5000 ohm A full-wave rectifier on a lamp is used as a power source L 7 (5TsZS) with a two-section L-shaped filter.

All generator tubes (except for the amplifier output stage tubes) can be replaced with ones of the same type without adjusting the generator. When changing lamps L 4 And L 5 (6C4C) it is necessary to select them so that the background level at the generator output does not exceed 15 mv. When measuring background at frequencies from 4000 to 10,000 Hz handle Reg. exit egR 22 should be set to the extreme left position, the handle Exit resistance B 2 - to position 600, switch Internal load B 4 - to position On

OPERATING THE DEVICE

1. 
   Set the fuse to the position corresponding to the mains voltage.
2. 
   Connect the power cable plug to an alternating current network with a frequency of 50 Hz, turn on the network toggle switch, after which the signal light should light up.
3. 
   The exact frequency setting is made after a 30-minute warm-up.

Frequency setting

1. 
   Frequencies of the first subband 20-200 Hz Factor is in position ×1. The frequency in hertz corresponds to the scale reading.
2. 
   Frequencies of the second subband 200-2000 Hz are set by turning the scale, while the switch Factor is in position ×10, the scale reading is multiplied by 10.
3. 
   Frequencies of the third subband 2000-20,000 Hz are set by turning the scale, while the switch Factor is in position ×100, the scale reading is multiplied by 100.

Setting amplitude, output voltage
1. The amplitude of the output voltage is adjusted smoothly by the handle Reg. exit eg and steps through 1 db from 0 to 110 db- handles Attenuation db.

The pointer device directly measures the output voltage at a load of 600 ohm and output attenuators (switch Exit resistance at position 600 ohm).

1. 
   When the generator operates at a load of 50; 200 and 5000 ohm switch Exit resistance must be placed in a position corresponding to the load value, the readings of the dial gauge are multiplied by 0.289; 0.576 and 2.89 respectively. In this case, the toggle switch is in position Off If the load differs from the above, then it is impossible to count on the device scale.
2. 
   When operating a generator on a device with a high input resistance, it is necessary to turn on the toggle switch and the switch Exit resistance put in any of four positions depending on the required voltage. In this case, the indicator scale readings are multiplied by the corresponding coefficients.

Two transistors - field-effect VT1 and bipolar VT2 - are connected according to a compound repeater circuit, which has a small gain and repeats the phase of the input signal at the output. Deep negative feedback (NFE) through resistors R7, R8 stabilizes both the gain and the mode of the transistors.

But for generation to occur, positive feedback from the amplifier output to its input is also needed. It is carried out through the so-called Wien bridge - a chain of resistors and capacitors R1...R4, C1...C6. The Wien bridge weakens both low (due to the increasing capacitance of capacitors C4...C6) and high (due to the shunting effect of capacitors C1...S3). At the central setting frequency, approximately equal to 1/271RC, its transmission coefficient is maximum, and the phase shift is zero. It is at this frequency that generation occurs.

By changing the resistance of the resistors and the capacitance of the bridge capacitors, the generation frequency can be changed within a wide range. For ease of use, a tenfold range of frequency changes has been selected using dual variable resistors R2, R4, and the frequency ranges are switched (Sla, Sib) by capacitors C1...C6.

To cover all sound frequencies from 25 Hz to 25 kHz Three ranges are enough, but if desired, you can add a fourth, up to 250 kHz (this is what the author did). By choosing slightly larger capacitors or resistor values, you can shift the frequency range down, making it, for example, from 20 Hz to 200 kHz.

The next important point in designing a sound generator is stabilizing the amplitude of the output voltage. For simplicity, the most ancient and reliable method of stabilization is used here - using an incandescent lamp. The fact is that the resistance of the lamp filament increases almost 10 times when the temperature changes from a cold state to full heat! A small-sized indicator lamp VL1 with a cold resistance of about 100 Ohms is included in the OOS circuit. It shunts resistor R6, while the OOS is small, the POS predominates and generation occurs. As the oscillation amplitude increases, the lamp filament heats up, its resistance increases, and the OOS increases, compensating for the POS and thereby limiting the increase in amplitude.

A step divider is switched on at the generator output voltage on resistors R10...R15, allowing you to obtain a calibrated signal with an amplitude from 1 mV to 1 V. The divider resistors are soldered directly to the pins of a standard five-pin connector from audio equipment. The generator receives power from any source (rectifier, battery, battery), often from the same one from which the device under test is powered. The supply voltage on the generator transistors is stabilized by the R11, VD1 chain. It makes sense to replace resistor R11 with the same incandescent lamp as VL1 (telephone indicator, in a “pencil” version) - this will expand the limits of possible supply voltages. Current consumption - no more 15...20 mA.

Parts of almost any type can be used in the generator, but special attention should be paid to the quality of the dual variable resistor R2, R4. The author used a fairly large precision resistor from some outdated equipment, but dual resistors from volume or tone controls on stereo amplifiers will also work. Zener diode VD1 - any low-power one, for stabilization voltage 6.8...9 V.

When setting up, you need to pay attention to the smoothness of generation at approximately the middle position of the trimmer resistor R8 slider. If its resistance is too low, generation may stop in some positions of the frequency setting knob, and if its resistance is too high, distortion of the sinusoidal signal shape may be observed - limitation. You should also measure the voltage at the collector of transistor VT2; it should be equal to approximately half the voltage of the stabilized supply. If necessary, select resistor R6 and, as a last resort, the type and type of transistor YT1. In some cases, it helps to connect in series with an incandescent lamp VL1 an electrolytic capacitor with a capacity of at least 100 µF(“plus” to the source of the transistor). Finally, resistor R10 sets the signal amplitude at the output 1 V and calibrate the frequency scale using a digital frequency meter. It is common for all ranges.

The peculiarity of this sound generator circuit is that everything is built on an ATtiny861 microcontroller and an SD memory card. The Tiny861 microcontroller consists of two PWM generators and, thanks to this, is capable of generating high-quality sound, and is also capable of controlling the generator with external signals. This audio frequency generator can be used to test the sound of high-quality speakers or in simple amateur radio projects such as an electronic bell.

The audio frequency generator is built on the popular KP1006VI1 timer microcircuit (almost according to a standard scheme. The output signal frequency is about 1000 Hz. It can be adjusted over a wide range by adjusting the ratings of radio components C2 and R2. The output frequency in this design is calculated by the formula:

F = 1.44/(R 1 +2×R 2)×C 2

The output of the microcircuit is not capable of providing high power, so a power amplifier is made using a field-effect transistor.

Oxide capacitor C1 is designed to smooth out power supply ripples. The SZ capacitance connected to the fifth output of the timer is used to protect the control voltage output from interference.

Any stabilized one with an output voltage from 9 to 15 volts and a current of 10 A will do.

Such a device will be very useful when testing audio circuits of amplifiers of receivers, televisions and other industrial and home-made equipment. The generator circuit is based on the book by V. G. Borisov “Young Radio Amateur” (from 145-146 in the 8th edition), with minor changes.

AF generator circuit

The generator is assembled on a K155LA3 microcircuit (you can use K555LA3), which consists of 4 2I-NOT elements. The generator itself is formed by series-connected logic elements DD1.1, DD1.2, DD1.3, connected by inverters. Capacitor C1, with a capacity of 0.47 μF, creates positive feedback between the output of DD1.2 and the input of DD1.1. In principle, the signal can be taken from the output of DD1.3; the DD1.4 element simply inverts them. The pulse frequency can be changed using a variable resistor R1. Resistor R2 serves as a regulator of the output signal level. Resistor resistance R1 680 Ohm, R2 10 kOhm, variable resistors can be of any type. With the parameters of radio components indicated in the diagram, the pulse frequency can be changed within 500 - 5000 Hz. Diode VD1 serves to protect against power supply of incorrect polarity; any low-power diode, for example D220, is suitable for it. The circuit is mounted on a small breadboard. But thanks to the small number of parts, the circuit can be mounted using a wall-mounted design.

Generator assembly

The standard supply voltage of the K155 and K555 microcircuits is 5 V, but the generator is operational when powering the circuit from a “square” battery with a voltage of 4.5 V (battery type 3336 according to the old nomenclature), the voltage drop across the VD1 diode does not affect the operation of the device. The device can be used for audio frequency.

What is a sound generator and what is it used for? So, let's first define the meaning of the word “generator”. Generator – from lat. generator- manufacturer. That is, to explain in everyday language, a generator is a device that produces something. Well, what is sound? Sound- these are vibrations that our ear can discern. Someone farted, someone hiccupped, someone sent someone - all these are sound waves that our ears hear. A normal person can hear vibrations in the frequency range from 16 Hz to 20 Kilohertz. Sound up to 16 Hertz is called infrasound, and the sound is more than 20,000 Hertz - ultrasound.

From all of the above, we can conclude that a sound generator is a device that emits some kind of sound. Everything is elementary and simple;-) Why don’t we assemble it? Scheme to the studio!

As we can see, my circuit consists of:

– capacitor with a capacity of 47 nanoFarads

– resistor 20 Kilohm

– transistors KT315G and KT361G, maybe with other letters or even some other low-power ones

– small dynamic head

- a button, but you can do it without it.

On the breadboard it all looks something like this:

And here are the transistors:

On the left is KT361G, on the right is KT315G. For KT361 the letter is located in the middle of the case, and for 315 it is on the left.

These transistors are complementary pairs to each other.

And here is the video:

The frequency of the sound can be changed by changing the value of the resistor or capacitor. Also, the frequency increases if the supply voltage is increased. At 1.5 Volts the frequency will be lower than at 5 Volts. In my video the voltage is set to 5 Volts.

Do you know what else is funny? Girls have a much greater range of perception of sound waves than boys. For example, guys can hear up to 20 Kilohertz, and girls can even hear up to 22 Kilohertz. This sound is so squeaky that it really gets on your nerves. What do I mean by this?)) Yes, yes, why don’t we choose resistor or capacitor values ​​such that girls hear this sound, but boys don’t? Just imagine, you are sitting in class, turning on your organ and looking at the dissatisfied faces of your classmates. In order to set up the device, we will of course need a girl to help us hear this sound. Not all girls also perceive this high-frequency sound. But the really funny thing is that it’s impossible to find out where the sound is coming from))). Only if anything, I didn’t tell you that).

A generator is a self-oscillating system that generates electric current pulses, in which the transistor plays the role of a switching element. Initially, from the moment of its invention, the transistor was positioned as an amplifying element. The presentation of the first transistor took place in 1947. The presentation of the field-effect transistor occurred a little later - in 1953. In pulse generators it plays the role of a switch and only in alternating current generators does it realize its amplifying properties, while simultaneously participating in the creation of positive feedback to support the oscillatory process.

A visual illustration of frequency range division

Classification

Transistor generators have several classifications:

• by frequency range of the output signal;
• by type of output signal;
• according to the operating principle.

The frequency range is a subjective value, but for standardization the following division of the frequency range is accepted:

• from 30 Hz to 300 kHz – low frequency (LF);
• from 300 kHz to 3 MHz – medium frequency (MF);
• from 3 MHz to 300 MHz – high frequency (HF);
• above 300 MHz – ultra-high frequency (microwave).

This is the division of the frequency range in the field of radio waves. There is an audio frequency range (AF) - from 16 Hz to 22 kHz. Thus, wanting to emphasize the frequency range of the generator, it is called, for example, an HF or LF generator. The frequencies of the sound range, in turn, are also divided into HF, MF and LF.

According to the type of output signal, generators can be:

• sinusoidal – for generating sinusoidal signals;
• functional – for self-oscillation of signals of a special shape. A special case is a rectangular pulse generator;
• noise generators are generators of a wide range of frequencies, in which, in a given frequency range, the signal spectrum is uniform from the lower to the upper section of the frequency response.

According to the operating principle of generators:

• RC generators;
• LC generators;
• Blocking generators are short pulse generators.

Due to fundamental limitations, RC oscillators are usually used in the low-frequency and audio ranges, and LC oscillators in the high-frequency range.

Generator circuitry

RC and LC sinusoidal generators

The most simple way to implement a transistor generator is in a capacitive three-point circuit - the Colpitts generator (Fig. below).

Transistor oscillator circuit (Colpitts oscillator)

In the Colpitts circuit, elements (C1), (C2), (L) are frequency-setting. The remaining elements are standard transistor wiring to ensure the required DC operating mode. A generator assembled according to an inductive three-point circuit—the Hartley generator—has the same simple circuit design (Fig. below).

Three-point inductively coupled generator circuit (Hartley generator)

In this circuit, the generator frequency is determined by a parallel circuit, which includes elements (C), (La), (Lb). The capacitor (C) is necessary to create positive AC feedback.

The practical implementation of such a generator is more difficult, since it requires the presence of an inductance with a tap.

Both self-oscillation generators are primarily used in the mid and high frequency ranges as carrier frequency generators, in frequency-setting local oscillator circuits, and so on. Radio receiver regenerators are also based on oscillator generators. This application requires high frequency stability, so the circuit is almost always supplemented with a quartz oscillation resonator.

The master current generator based on a quartz resonator has self-oscillations with a very high accuracy of setting the frequency value of the RF generator. Billions of a percent are far from the limit. Radio regenerators use only quartz frequency stabilization.

The operation of generators in the region of low-frequency current and audio frequency is associated with difficulties in realizing high inductance values. To be more precise, in the dimensions of the required inductor.

The Pierce generator circuit is a modification of the Colpitts circuit, implemented without the use of inductance (Fig. below).

Pierce generator circuit without the use of inductance

In the Pierce circuit, the inductance is replaced by a quartz resonator, which eliminates the time-consuming and bulky inductor and, at the same time, limits the upper range of oscillations.

The capacitor (C3) does not allow the DC component of the base bias of the transistor to pass to the quartz resonator. Such a generator can generate oscillations up to 25 MHz, including audio frequency.

The operation of all of the above generators is based on the resonant properties of an oscillatory system composed of capacitance and inductance. Accordingly, the oscillation frequency is determined by the ratings of these elements.

RC current generators use the principle of phase shift in a resistive-capacitive circuit. The most commonly used circuit is a phase-shifting chain (Fig. below).

RC generator circuit with phase-shifting chain

Elements (R1), (R2), (C1), (C2), (C3) perform a phase shift to obtain the positive feedback necessary for the occurrence of self-oscillations. Generation occurs at frequencies for which the phase shift is optimal (180 degrees). The phase-shifting circuit introduces a strong attenuation of the signal, so such a circuit has increased requirements for the gain of the transistor. A circuit with a Wien bridge is less demanding on transistor parameters (Fig. below).

RC generator circuit with Wien bridge

The double T-shaped Wien bridge consists of elements (C1), (C2), (R3) and (R1), (R2), (C3) and is a narrow-band notch filter tuned to the oscillation frequency. For all other frequencies, the transistor is covered by a deep negative connection.

Functional current generators

Functional generators are designed to generate a sequence of pulses of a certain shape (the shape is described by a certain function - hence the name). The most common generators are rectangular (if the ratio of the pulse duration to the oscillation period is ½, then this sequence is called a “meander”), triangular and sawtooth pulses. The simplest rectangular pulse generator is a multivibrator, which is presented as the first circuit for beginner radio amateurs to assemble with their own hands (Fig. below).

Multivibrator circuit - rectangular pulse generator

A special feature of the multivibrator is that it can use almost any transistors. The duration of the pulses and pauses between them is determined by the values ​​of the capacitors and resistors in the base circuits of transistors (Rb1), Cb1) and (Rb2), (Cb2).

The frequency of self-oscillation of the current can vary from units of hertz to tens of kilohertz. HF self-oscillations cannot be realized on a multivibrator.

Generators of triangular (sawtooth) pulses, as a rule, are built on the basis of generators of rectangular pulses (master oscillator) by adding a correction chain (Fig. below).

Triangular pulse generator circuit

The shape of the pulses, close to triangular, is determined by the charge-discharge voltage on the plates of capacitor C.

Blocking generator

The purpose of blocking generators is to generate powerful current pulses with steep edges and low duty cycle. The duration of pauses between pulses is much longer than the duration of the pulses themselves. Blocking generators are used in pulse shapers and comparing devices, but the main area of ​​application is the master horizontal scan oscillator in information display devices based on cathode ray tubes. Blocking generators are also successfully used in power conversion devices.

Generators based on field-effect transistors

A feature of field-effect transistors is a very high input resistance, the order of which is comparable to the resistance of electronic tubes. The circuit solutions listed above are universal, they are simply adapted for the use of various types of active elements. Colpitts, Hartley and other generators, made on a field-effect transistor, differ only in the nominal values ​​of the elements.

Frequency-setting circuits have the same relationships. To generate HF oscillations, a simple generator made on a field-effect transistor using an inductive three-point circuit is somewhat preferable. The fact is that the field-effect transistor, having a high input resistance, has practically no shunting effect on the inductance, and, therefore, the high-frequency generator will operate more stable.

Noise generators

A feature of noise generators is the uniformity of the frequency response in a certain range, that is, the amplitude of oscillations of all frequencies included in a given range is the same. Noise generators are used in measuring equipment to evaluate the frequency characteristics of the path being tested. Audio noise generators are often supplemented with a frequency response corrector to adapt to subjective loudness for human hearing. This noise is called “gray”.

Video

There are still several areas in which the use of transistors is difficult. These are powerful microwave generators in radar applications, and where particularly powerful high-frequency pulses are required. Powerful microwave transistors have not yet been developed. In all other areas, the vast majority of oscillators are made entirely with transistors. There are several reasons for this. Firstly, the dimensions. Secondly, power consumption. Thirdly, reliability. On top of that, transistors, due to the nature of their structure, are very easy to miniaturize.