How to make a crystal tone generator. Two-tone generator. Characteristics of the SLG46620V chip

E. KUZNETSOV, Moscow
Radio, 2002, No. 5

Tones can be used to check the dynamic performance of meters, autolevellers, and noise canceling devices. A stand with a tone pulse generator will also be useful in the study of amplifying and acoustic equipment.

The linearity of the frequency response and the accuracy of the level meter readings are easy to check using a conventional sound signal generator, but a tone pulse generator (TIP) is required to check their dynamic parameters. Such generators, offered by radio amateurs, often do not comply with the standards, where for testing level meters (DUTs) the frequency of a sinusoidal signal in pulses is taken to be 5 kHz, and the beginning and end of the pulses coincide with the signal zero crossings.

Similar problems arise when adjusting auto-level controls for audio signals. The recovery time 0.3 ... 2 s is easy to see on the oscilloscope screen, but the response time of the limiter (limiter) or compressor can be less than 1 ms. For measuring and observing transients in audio equipment, it is convenient to use a GTI. In this case, it is desirable to change the pulse filling frequency using an external tunable generator. For example, at a filling frequency of 10 kHz, the duration of one period is 0.1 ms, and when observing the actuation process, it is not difficult to determine the actuation time. Sound impulses from the GTI output should have a level difference of 10 dB.

In foreign literature, it is usually suggested to measure the response time with a stepwise increase in the signal level by 6 dB above the normalized value, but real signals have a significantly larger level difference. The use of such a technique is often explained by the "clicking" of imported automatic level regulators. In addition, in almost any sound generator, you can jump in the level by 10 dB, using such a level difference is convenient for observation. Therefore, in domestic practice, it is customary to measure the dynamic parameters of autoregulators when changing levels by 10 dB.

Unfortunately, the signal level switches of many generators give a short-term voltage surge at the moment of switching, and they cannot be used to measure the response time, since the automatic regulator "shuts up". In this case, the GTI can be very helpful.

Most radio amateurs have to carry out such measurements infrequently, and it is advisable to include such a device in a measuring stand with wider capabilities. On its front panel there are switching elements, which are very convenient for connecting measuring instruments and customizable equipment. In fig. 1 shows the approximate arrangement of connectors (terminals or sockets) and switches. The stand diagram (Fig. 2) shows these switching circuits.

Instrument diagram

Click on the image to enlarge (will open in a new window)

Input jacks X1 ("IN.1") and X2 ("IN.2") are designed to connect the inputs of the equipment being configured. Toggle switches SA1 and SA2 allow you to connect the inputs to connectors X2 and XZ or short them to a common wire when measuring the level of integral noise. In comparison with buttons, toggle switches give a more visual representation of the connection of inputs. An audio frequency generator and a voltmeter are connected to the central sockets X2 and X3 to control the input voltage. Connectors X5 and X8 are designed to connect the outputs of the configured equipment. One of the outputs can be connected with a toggle switch SA3 to connectors X6 and X7 for measuring instruments. When setting up audio equipment, it is convenient to use a harmonic distortion meter and an oscilloscope.

Switching circuits do not need any power supplies, so with such switching it is very convenient to test various equipment.

If the double toggle switch SA4 (Fig. 1) is in the "POST" position, the signal with a constant level applied to X2, X3 is supplied, depending on the position of the SA1 or SA2 toggle switches, to connectors X1, X4 to the inputs of the equipment under test. If you move SA4 to the upper position, then the signal from the generator will go to inputs 1 and 2 through the GTI circuits. In this case, the stand must be connected to a 220 V AC network.

The SA5 power switch is located on the rear panel, and only the HL1, HL2 LEDs (indication "+" and "-") are displayed on the front panel, signaling the presence of a bipolar supply voltage of ╠15 V.

An electronic switch DA4 is used to generate tone pulses. At terminals 16 and 4, the signal voltage value changes from a normalized value to zero, and at terminals 6, 9, the level difference during adjustment is set with a variable resistor R15. The mode is selected with the SA9 toggle switch.

The pulse filling tone comes from the generator to the electronic switch through the DA1.1 buffer op-amp. The second op-amp DA1.2 is used as a comparator, giving out a pulse start synchronization signal when the fill signal crosses "zero". Pulses from the comparator are fed to the clock input of the D-flip-flop DD2. At the input D (pin 9) comes a pulse from a one-shot, collected on the second flip-flop DD2.

The pulse duration is changed using the SA8.2 switch, which changes the resistance in the C15 charging circuit connected to the R input (pin 4) of the one-shot. A conventional oscilloscope is sufficient to set the pulse width. The monovibrator is started by signals coming from a square-wave generator on inverters DD1.1 ≈ DD1.3, or in manual mode by pressing the SA6 "START" button. If the SA7 toggle switch is moved to the "AVT." Position, the duty cycle (period) of the pulses is set using the variable resistor R11 "SCR."

It is very difficult to observe transients on an oscilloscope screen with a tone pulse duration of 3 ms and a high duty cycle. The task is simplified for oscilloscopes that have an external trigger on a standby sweep. To synchronize them, the X9 "SYNCHR." Socket is located on the rear panel of the stand. The trigger pulse is applied to the electronic switch with a certain delay relative to the synchronizing one, determined by the choice of parameters R13, C13.

A high level, at which the DA4 electronic switch passes the tone signal, appears with a positive voltage drop from the comparator after the appearance of a pulse from the one-shot and ends after the end of this pulse (at the next drop in the signal from the comparator). This achieves the coincidence of the beginning of the tone pulse with the transition of the fill signal through "zero" and the requirement to generate an integer number of periods is satisfied. With the SA8 switch position "U Out", the voltage at the DA4 control input is zero and you can set the generator output voltage corresponding to the nominal input level. In the position of the switch SA8 "TACT." the DA4 microcircuit is controlled by a voltage supplied directly from the clock generator. Its switching frequency is set by the variable resistor R11.

After the electronic switch through the DA1.3 repeater and the SA1 and SA2 toggle switches, the tone pulses are fed to the inputs of the tuned equipment. The device also has an inverter DA1.4 and a switch SA10, which can be used to change the phase of the signal at one of the inputs in relation to the other. Such an inverter is needed, for example, when checking the inphase of signals in stereophonic systems, in an AC, but, perhaps, instead of it, it is more useful to assemble a built-in tone signal generator on this op-amp according to the diagram shown in Fig. 3. In such a generator, it is easy to obtain Kg less than 0.2% and for many tests it is possible to do without the use of a generator external to the stand.

To test the level meters, connect the inputs of the two channels (for stereo meters) to the corresponding input connectors. Then, in the "U Out" position of the SA8 switch, set the normalized value of the signal level with F = 5 kHz at the generator output and check the readings of both meter channels. For example, in a level meter, the LEDs corresponding to the "O dB" value should light up simultaneously, and the scale error here should not exceed 0.3 dB. The SA9 toggle switch is set to the "-80 dB" position. Then the switch SA8 is transferred alternately to the positions "10 ms", "5 ms" and "3 ms" and the compliance of the DUT readings with the standards is checked. The SA8 "200ms" position is used when checking average level meters, which, unfortunately, prevail in consumer electronics.

To accurately control the return time, the variable resistor R11 ("SCR.") Sets the frequency of the square-wave generator signals, at which the next pulse would follow immediately after extinguishing the LED corresponding to the -20 dB value on the DUT scale. It is not difficult to determine then the period of the signals using an oscilloscope. The extinguishing of the LEDs in both channels must be synchronous.

When checking the dynamic parameters of the automatic signal level controllers, use the "-10 dB" position of the SA9 switch. The inputs and outputs are connected to the appropriate connectors. The channel outputs are monitored alternately, although with a two-channel oscilloscope, nothing prevents you from simultaneously monitoring both outputs. At the output of the audio frequency generator, when the "U Ex" switch SA8 is positioned, a signal is set with a level 10 dB higher than the normalized value. Then SA8 is transferred to pulses of any duration, and the SA7 switch is set to the "MANUAL" position. The key remains off and allows you to check the voltage at the connectors X1 and X2, which should correspond to the standardized value. Then, using the SA7 switch, the GTI is switched to the automatic mode of operation and, having chosen the required pulse duration and duty cycle, the transients at the output of the autoregulator are observed. When the oscilloscope is in trigger-triggered standby mode, it is easy to determine the trigger time and the presence of trigger noise or overshoot.

The GTI uses four microcircuits, and the current consumption is very low. This allows you to use simple parametric voltage stabilizers on zener diodes instead of integral stabilizers. On the other hand, by installing more powerful integrated stabilizers DA2, DA3 of the DA7815 and DA7915 series, they can be used to power the breadboards of tuned devices by placing an additional connector on the rear panel (not shown in the diagram). The microcircuits provide protection against short circuits, which are not uncommon during experiments.

The front panel of the stand has dimensions 195x65 mm. The stand body is made of steel.

To connect the tested equipment, ZMP-type sockets are convenient. In addition to them, depending on the tested equipment, it is possible to install connectors of the appropriate design on the stand panel, for example, jacks "tulip", "jack", ONTs-VG or others.

Double toggle switch SA4 ≈ PT8-7, P2T-1-1 or similar. Switch SA2 ≈ wafer type PG2-8-6P2NTK. Button SA6 "START" can be of any type without latching, for example, KM1-1.

The DA2 K590KN7 microcircuit can be replaced with a similar one in terms of functionality. As DA1, you can use a microcircuit with four op-amp types LF444, TL084, TL074 or K1401UD4.

Mounting the device board ≈ printed or hinged on the breadboard.

The GTI stand can be used to test compander noise suppression systems, dynamic filters and other sound engineering equipment.

LITERATURE
1. Kuznetsov E. Measuring the level of sound signals. - Radio, 2001, No. 2, p. 16, 17.
2. Microcircuits for household radio equipment. Directory. - M .: Radio and communication, 1989.
3. Turuta J. Operational amplifiers. Directory. - M .: Patriot, 1996.

This article describes a simple audio frequency generator, in other words, a buzzer. The circuit is simple and consists of only 5 elements, excluding the battery and the button.

Description of the scheme:
R1 sets the offset to VT1 base. And with the help of C1, feedback is carried out. The speaker is a VT2 load.

Assembly:
So, we need:
1) A complementary pair of 2 transistors, that is, one NPN and one PNP. Almost any low-power will do, for example KT315 and KT361. I used what was at hand - BC33740 and BC32740.
2) Capacitor 10-100nF, I used 47nF (marking 473).
3) Trimmer resistor about 100-200 kOhm
4) Any low-power speaker. Headphones can be used.
5) Battery. Almost anything is possible. Finger, or crown, the difference will be only in the frequency of generation and power.
6) A small piece of foil-clad fiberglass, if you plan to do everything on the board.
7) Button or toggle switch. I used a button from a Chinese laser pointer.

So. All parts are collected. Let's start making the board. I made a simple surface mount board mechanically (that is, with a cutter).

So, everything is ready for assembly.

First, we mount the main components.

Then we solder the power wires, a battery with a button and a speaker.

The video shows the operation of the circuit from a 1.5V battery. A trimmer resistor changes the oscillation frequency

List of radioelements

Figure 1 shows a diagram of a simple generator, designed mainly for testing low-frequency equipment and identifying faults in it.

The generator has one fixed frequency 1000Hz, the value of which is set by the resistor R1. The output signal level is determined by the position of the slider of the resistor R13. The circuit has a system for supporting the output signal at a certain level, consisting of the elements VT1, VD2, R10, R11, C6. The level of operation of the automatic output voltage maintenance system is set using the resistor R11. The harmonic coefficient of this generator is relatively large, so that it could be used to measure the harmonic distortion of low-frequency equipment. Therefore, at the output of this generator, you need to install a low-pass filter - LPF. Such a filter. Complete with a low-pass filter, this generator has a very clean tone signal with a THD level in thousandths of a percent. The generator must be powered from a stabilized DC source with a voltage of 5 ... 12V. The schematic and drawing of the printed circuit board can be downloaded here.