Pre-amplifier for k157ud2 with printed circuit board. Low frequency amplifier on TDA7384 chip
While sorting through the trash in the closet, I accidentally found my last year (autumn 2013) craft - a dial indicator of the sound level on the K157UD2 microcircuit. For some reason, she didn’t want to work for me then, and I threw her far away. And now I’ve decided to finally figure out what’s the matter? After all, the first copy of the device, made that same summer, still works properly.
An article that describes the amplifier circuit on a microcircuit is located, option 2, “Circuit with unipolar power supply" There you can also see the pinout of the K157UD2 microcircuit. I am attaching a diagram with my denominations, the main part of which is the M68501 indicator and its wiring.
I’ll note right away that it can be connected either to exit sound amplifier and entrance. In the first case, the dial indicator will show the power of the output signal (and, accordingly, when the volume is reduced by the regulator, the arrow will “fall”), and in the second case, the power of the input signal, which is sometimes more useful (for example, visually monitoring the power of the input signal, since if it too much comes in, the signal may begin to distort). In the diagram, some numbers of the pins of the microcircuit are indicated in brackets - this means that you can assemble two identical amplifiers on one chip, and, accordingly, connect two indicators: to the right and left channels (or to the input and output of the amplifier).
It turned out that the cannons did not fire for twenty reasons, and the first of them was that there were no shells. And if we talk about the microcircuit, then with its power supply there were serious problems. I also had to replace both electrolytic capacitor(at that time I had not yet purchased them in buckets, so I installed them pulled out from somewhere), deal with the falling leg of the 22 nF capacitor and connect it correctly. After this, the circuit worked, although I still don’t know where it can be adapted.
Diodes - D311. D18 will be a little worse.
Resistor R5 is trimmer and has an asterisk - this means that not only will it have to be adjusted to the signal level (so that, for example, at normal amplifier volume the needle dangles around 75% of the scale), it is also not a fact that 47 kOhm suitable for all occasions.
If you increase the value of resistor R4 (470 - 910k), you can raise the gain of the microcircuit and make it “feel” weaker signals (this is just useful if the indicator is connected to entrance sound amplifier). For example, to observe the sound output from the player I had to install a 1 MOhm resistor.
Some photos of my circuit: 
And a demonstration of the work when the output of “VEF 216” is monitored:
A special feature of the circuit is its low sensitivity to high-frequency signals (the needle moves with greater pleasure from drums and bass guitars than from voices and guitar solos).
And for the night, I built two blue five-millimeter LEDs into the indicator housing. Normally they light from five volts, if less, then only one works, the second one turned out to be burnt. For compatibility with other supply voltages, the backlight is turned on through a 500 Ohm trimming resistor - you can easily power the entire circuit from 5 to 9 volts, you just need to adjust the voltage.
The described amplifier can be used with any signal sources. The amplifier is designed to work with speakers or dynamic heads with a power of 1 - 1.5 W. It can also be used as a headphone amplifier. The amplifier is assembled using widely available components that can be extracted from faulty Soviet-made household equipment.
First option (K157UD2)
Characteristics:
Sensitivity 600 mV.
THD% at a frequency of 1000 Hz no more than 0.7%
Maximum output power no more than 0.7 - 1 W.
The amplifier is assembled using a K157UD2 microcircuit and eight transistors. Distinctive feature The advantage of this amplifier is the presence of a small number of passive components. Only 4 resistors and 4 capacitors per channel.
Electrical circuit diagram of the amplifier:
Principle of operation:
The signal amplified by the microcircuit goes to the output stage assembled on transistors. Each arm of this cascade amplifies its own half-wave of the signal. At the junction point of the emitters of the transistors, the signal is combined and supplied to the load. A voltage equal to half the voltage of the power supply is set by resistors R2 and R3 (left channel), also R5 and R6 (right channel). In the negative circuit feedback There is a resistor R4 (left channel) and R8 (right channel).
DA1 (k157ud2) can be replaced with any dual operational amplifier
Output transistors can be replaced with:
VT1, VT5 kt315 with any letter index, you can also use kt3102 with any letter index.
VT3, VT7 kt361 with any letter index, you can also use kt3107 with any letter index. It is very important that the gains of transistors VT1 and VT3, as well as VT5 and VT7, are equal.
Power transistors can be replaced with KT814 and KT815 with any letter indices, but with equal gain factors.
Option 2 (K157UD1)
Sensitivity 500 mV.
THD% at a frequency of 1000 Hz no more than 0.8%
Maximum output power is no more than 0.7 - 1.5 W.
Scheme of the second option (1 channel is shown, the second is assembled according to a similar scheme).
Due to the use of more powerful chip K157UD1, there is no need to use transistors VT1, VT3, VT5, VT7, as in the first option. During operation, the output of the microcircuit contains a signal of sufficient amplitude and power to be applied to the bases of powerful transistors.
Parts used and possible replacement:
Instead of the DA1 chip (k157ud1), you can use any single operational amplifier of the Kr574, K140, K153 series. But in terms of saving components, the first amplifier option is preferable.
Instead of output transistors KT814V and KT815V, you can use transistors of a similar type with any letter indices, but (a prerequisite) with equal gain factors.
The video shows the operation of the first version of the amplifier; I assembled the second version but did not shoot a video with it.
The printed circuit board can be downloaded
The industry produces microcircuits that contain two operational amplifiers in one package, in particular K157UD2. Although the chip is designed for low-frequency devices, it works well in radio receivers direct gain on NE and DV and, what is very important, at a low supply voltage of 2...3 V. This allows you to build a miniature radio receiver that does not require preliminary prototyping. The diagram of such a receiver is shown in Fig. 19.12. For simplicity, the receiver is fixedly tuned to one radio station that is best heard in a given area. You can, of course, introduce smooth tuning to the radio station, install a variable capacitor, as in the previous receiver design, but then the dimensions of the receiver will increase. The current consumed by the receiver is about 3 mA.
Rice. 19.12. Schematic diagram radio receiver on the K157UD2 chip
The receiver contains: input circuits, a radio frequency amplifier, a diode detector, and an audio frequency amplifier. The receiver input circuits consist of a magnetic antenna WA1 and a coupling coil with a radio frequency amplifier on an operational amplifier DA1.1. The signal from the radio station, isolated by the input circuit L1, C1, is fed through the coupling coil and capacitor C2 to the input of the op amp DA1.1 (URF). After amplification, the signal from pin 13 is fed to a detector assembled on diodes VD1, VD2, connected according to the output voltage doubling circuit. The detector's DC load is the reverse resistance of its diodes. From the output of the detector, the audio frequency signal is fed through the isolation capacitor C6 to the input of the audio amplifier assembled at the DA1.2 op amp. From the ultrasonic output, the signal is fed through capacitor C8 to headphones BF1.
Details
The parts used in the receiver are small-sized. Resistors MLT-0.125, capacitor C8 K50-6, the rest KM-5. A ferrite rod with a length of 55mm and 08mm is used for the magnetic antenna. Coil L1 contains 80 turns of LESHO 10x0.07 wire, communication coil L2 has 15 turns of PELSHO 0.12 wire. To power the receiver, two D-0.06 batteries connected in series are used. The power switch can be of any type, small-sized.
Most of the parts of the radio receiver are mounted on a printed circuit board made of foil fiberglass laminate 1 mm thick. The type of printed circuit board and the placement of parts on it is shown in Fig. 19.13.
Rice. 19.13. Printed circuit board and placement of radio receiver parts on it on the K157UD2 chip
A correctly assembled receiver, when using serviceable radio components, does not require adjustment and starts working immediately after turning on the power. You only need to change the capacitance of capacitor C1 to tune in to the desired radio station. The receiver does not have a volume control. To change the sound volume, you need to rotate the receiver body.
Literature: V.M. Pestrikov. Encyclopedia of amateur radio.
Hello, dear readers of the site. Needed microphone amplifier for recording songs with a guitar from two microphones, so that you can adjust the voice and the guitar separately.
After searching on the Internet, I chose the domestic K157UD2 microcircuit, which was in stock. The microcircuit is a low-noise two-channel operational amplifier, which is used in a variety of stereophonic equipment. The operational amplifier K157UD2 operates in a wide range of input differential voltages and is protected against short circuits at the exit.
The microphone amplifier uses a typical connection of the K157UD2 microcircuit. The numbering of pins for the implementation of the 2nd channel is indicated in brackets.
After several tests, I became convinced that there was not enough mixer to adjust the gain of both channels. I also found a transistor mixer circuit on the Internet. And when I assembled the amplifier on a breadboard, its sensitivity and quiet operation exceeded all my expectations.
And after drawing the board in LAY, the diagram of this device was born.
Both amplifier outputs are fed to the mixer input through variable resistors. The output from the mixer to the computer is mono, since it’s more convenient for me to make settings and process the recorded material. To eliminate possible interference and interference, the microphones are connected to the amplifier via a shielded wire, and the microphones themselves were purchased on the Aliexpress website. All transistors in the mixer were replaced with KT315G. The circuit is powered by a KRONA battery.
I use it to record from a microphone. free program AUDACITY, as it has a clear Russian-language interface and a large selection of tools for processing recorded material.
All details microphone amplifier In addition to the battery, variable resistors and microphones are located on two printed circuit boards (amplifier and mixer board), made of single-sided PCB 1 mm thick.
The housing for the amplifier is taken from the power supply of the scanner-printer. The amplifier can also be powered from external source voltage, for this it is necessary to provide a socket on the case and place it, for example, next to the toggle switch or at the end.
At the time of writing, the amplifier had worked for 5 hours in a “combat” situation and no problems with power supply had been observed yet. You can also watch a video that shows the capabilities of this microphone amplifier and explains some aspects of working with it.
Archive with printed circuit boards in lay format can be downloaded from the link.
I wish you success in repeating the design!
See you on the pages of the site!
Anatoly Tikhomirov ( picdiod), Riga
The high-fidelity UMZCH described in the UMZCH was developed for subjective examination of the sound of digital laser CD players (LDCs).
During the examination, powerful high-quality acoustic systems (AS) were connected to the output of the UMZCH, and its input was connected to the output of the PCD in order to ensure minimal phase and nonlinear distortions, as well as reduce the noise level through the simplest resistive voltage divider, which was used as a wire-wound variable resistor SP5 -21-A-2 with a resistance of 15 kOhm.
With this divider you can set the volume to 90-94 von, which is necessary for conducting a subjective examination, since at this volume a normal balance of the spectrum is ensured and there is no need for additional frequency correction. Subsequently, adjustment was carried out only when the type of speaker was changed or the rated output voltage of the tested PCD differed from the standard one (2 V eff).
When using the described UMZCH as the base amplifier of a high-quality sound reproducing complex, it must be supplemented with a finely compensated volume control and a tone control with a sensitivity of 150...200 mV. A description of such a control unit, developed by the author, is given in the article published below.
Main technical characteristics
- Input impedance, kOhm - 150
- Rated input voltage, mV - 150
- Rated output voltage, m V - 800
- Relative noise level: weighted value - 94dBA, unweighted value - 88dB
- Volume control depth, dB - 36
- Tone control depth, dB + 10...—10
- Harmonic coefficient, %, at the nominal level of the OUTPUT signal.<0,001 %
- Overload capacity, dB 4-18.
Schematic diagram and operating principle
The block diagram is shown in Fig. 1. Its first stage is assembled on op-amp DA1.1 (DA2.1) and serves as a stereo balance regulator. Using resistor R21, the gain of each channel can be changed within ±4 dB.
The second stage of the block is assembled on op-amp DA1.2 (DA2.2) and is a modification of the active loud-compensated volume control, described in detail in.
The principle of frequency compensation of this regulator in the low-frequency region is based on changing the time constants of the OOS circuits, covering the op-amps C3R5R7.1 and R7.1R9C6 (C15R26R7.2 and R7.2R30C18), when regulating the volume, as well as changing the frequency response of the frequency-dependent divider R5R6C4 (R26R27C16 ) when moving the volume control slider R7.1 (R7.2).
Frequency compensation in the higher frequency region is provided by circuit C5R8 (C17R28), connected in parallel with part of resistor R7.1 (R7.2). In the extreme left (according to the diagram) position of the engine R7.1 (R7.2), the condition C3R5 = C6(R9+R7.1) (C15R26 = C18(R30+R7.2)) is satisfied.
Schematic diagram of a high-quality volume, balance and treble/bass tone control.
Circuit C4R6 (C16R27) is shunted according to the principle of virtual short circuiting of op-amp inputs, and circuit C5R8 (C17R28) is shunted by the corresponding section of resistor R7.1 (R7.2), so the cascade has a unit and frequency-independent (in the audio range) transmission coefficient.
The frequency responses formed by the cascade in the extreme and middle positions of the volume control R7 are shown in Fig. 2 and differ little over the entire control range from the ideal loudness compensation curves constructed on the basis of the Fletcher-Munson equal loudness curves.
The peculiarity of the described volume control is the close to exponential dependence of the transmission coefficient at medium frequencies with a linear functional dependence of the resistance on the angle of rotation of the axis of resistor R7.
This ensures maximum smoothness of control, since turning the axis by the same angle corresponds to equal volume increments. Electronic switches using VT1.1 transistors. and VT1.2 (VT1.3 and VT1.4) allow you to disable loudness compensation.
The op amp DA3.1 (DA3.2) has an active tone control for lower R13.1 (R13.2) and higher R14.1 (R14.2) frequencies. In Fig. Figure 3 shows the frequency response generated by this cascade in different positions of the regulators. As can be seen from the figure, the maximum correction depth is 10 dB, which is quite sufficient for a high-fidelity sound reproduction complex.
At the same time, limiting the correction depth made it possible to reduce the mismatch in the frequency response and phase response of the right and left channels to levels of no more than 0.2 dB and 3 degrees, respectively, in the frequency range 20...20,000 Hz in any position of the regulators (the same applies to to the volume control), which is important for maintaining a constant position of apparent sound sources with natural stereo sound.
The use of active volume and tone controls made it possible to provide the required dynamic range of the device as a whole using fairly simple means.
To measure harmonic distortion, the first harmonic suppression technique described in . In Fig. Figure 4 shows spectrograms of the signal at the output of the volume and tone control unit when a signal from the generator is applied to its input, the spectrum of which is shown in Fig. 5 (the first harmonic with a frequency of 1 kHz in both spectrograms is suppressed by 60 dB).
The relative level of the largest second harmonic is -108 dB, which corresponds to a nonlinear distortion coefficient for the second harmonic of 0.0004%, and taking into account higher harmonics, the total harmonic distortion coefficient does not exceed 0.001%.
Due to the drop in the loop gain of the op-amp at higher audio frequencies, the level of intermodulation distortion of the device is slightly higher. In Fig. Figure 6 shows spectrograms of the output signal when the sum of two sinusoidal voltages with a frequency of 19 and 20 kHz is applied to the input of the device.
In the spectrogram, the levels of useful components (19 and 20 kHz) are suppressed by 45 dB, the relative level of the intermodulation component of the difference frequency (1 kHz) is equal to -92 dB, which corresponds to an intermodulation distortion coefficient of 0.0025%.
Construction and details
The control unit is powered by voltage stabilizers made on transistors VT2, VTZ and zener diodes VD2, VD3 and connected directly to the buses of the unstabilized power supply UMZCH.
The device uses fixed resistors MJ1T-0.125, dual variable precision wire resistors SP5-21A-2 (R7, R13, R14) and SP5-21B (R21). With slightly worse results, you can use SPZ-30g (R7, R13, R14) and SPZ-30a (R21). In this case, the imbalance between volume and frequency response will not exceed 2 dB. K50-16 are used as oxide capacitors, the others are KM-4, KM-5, KM-6, K73-11.
The values of all permanent resistors and capacitors SZ-C6, C9, C15-C18, C21 should not differ from those indicated on the circuit diagram by more than 5%, capacitors C8, C10, C20, C23 - by more than 10%, the rest - by 20 ...80%.
Replacing the K157UD2 op-amp with others is undesirable due to their good noise properties and high linearity, as well as the ability to operate with a relatively low-impedance load.
Both channels of the device are assembled on a printed circuit board made of fiberglass. The pattern of printed tracks is shown in Fig. 7, a, and the location of the parts is in Fig. 7, 6.
With reduced requirements for the volume imbalance of the frequency response and phase response, the limits of volume and timbre control can be expanded.
So, in order to increase the depth of volume control to 60 dB, you should change the values of four resistors (R6 = R27 = 470 Ohm, R9-R30 = 1 kOhm) and two capacitors (C4 = C16 = 1 μF), and to increase the tone control limits to ±16 dB, you need to reduce the resistance of eight resistors (R15 = R16 = R33 = R34 = 300 Ohm, R12-R17 = R32 = R36 = 2.7 kOhm).
Printed circuit board for high quality volume, balance and tone control.
Setting up
A properly assembled volume and tone control unit does not require adjustment. Printed circuit boards for the tone block are supplied by the Mayak cooperative (see Radio 1990, No. 7, p. 80).
N. SUKHOV. Kyiv, Ukraine.
Literature:
- Sukhov N. UMZCH of high fidelity. - Radio, 1989, No. 6, p. 55—57.
- Sukhov N., Bat S., Kolosov V., Chupakov A. High-quality sound reproduction technology. - Kyiv: Tekhnika, 1985, p. 27, fig. 2.8. 6.
- Newcomb A., Young R. Practical loudness: an active circuit design approach.— Journal of the Audio Engineering Society, 1976, Vol. 24, N I, pp. 32—35, fig. 1.
- Sukhov N., Bvt S., Kolosov V., Chupakov A. High-quality sound reproduction technology. - Kyiv: Tekhnika, 1985, p. 35, fig. 2.17.
- Sukhov N. UMZCH of high fidelity. - Radio, 1989, No. 7, p. 59, fig. 7.