This stereo preamplifier is built around the popular NE5532 op-amp and several discrete components. The pre-amplifier is suitable for working with any signal source, such as an mp3 player or a computer, and in addition to a final power amplifier, it will allow you to get good sound at home.
The preamplifier has a tone block that allows you to adjust the bass and treble, as well as adjust the volume using three paired rotary potentiometers. Placing the potentiometers at the edge of the board eliminates the need for wires connecting the potentiometers to the board, which in turn improves the noise performance of the amplifier.
The preamplifier is powered by a bipolar power supply with a voltage of +/-18 to +/-30 volts.
The circuit diagram of the preamplifier is shown in the figure below: 
The amplifier consists of two identical channels. We will study the work of the preamplifier on one of them. The input signal is fed into the GP1 connector and goes directly to the high-pass filter, consisting of a capacitor C1 (1 uF) and a resistor R1 (100k) with a cutoff frequency of about 1.5 Hz, this effectively cuts the DC component and the lowest frequencies.
Further, the signal is fed to the non-inverting amplifier U1 (NE5532) and resistors R3 (10k) and R7 (4.7 k), which provides a signal amplification by 1.5 times. A small capacitor C3 (10 pF) prevents excitation, while C5 (1 uF) separates the circuits on amplifiers U1 and U2 (NE5532).
The frequency regulator is built on the U2 amplifier, and the frequency control itself is built in the classical way. The elements that change the characteristics are in the negative feedback loop of the amplifier U2. When both knobs are in the center position, the resistance X1 (obtained from the elements: R9 (10k), C9 (33 nF), C7 (4.7 nF), and also: P1 (100k), P2 (100k), R11 (10k ) and R12 (3.3 k) - “in the middle position”) between the input signal and the inverting input of the amplifier U2 is equal to the resistance X2 (obtained from the elements: R15 (10k), C11 (33 nF), C13 (4.7 nF) and in the middle also: P1, P2, R11 and R12 - "in the middle position") between the output of the amplifier U2 and the inverting input. Gain A, is expressed by the following relationship:
It is equal to 1 for the entire operating frequency range of the amplifier.
P1 is responsible for adjusting the low frequencies. For high frequencies, capacitors C9 and C11 are short-circuited, so adjustment with a potentiometer has no effect at these frequencies. The potentiometer is responsible for adjusting the high frequencies, and due to the elimination of capacitors C7 and C13, the adjustment has no effect on low frequencies.
The signal from the output of the frequency controller goes through the resistor R17 (4.7 k) to the volume control potentiometer P3 (100k) and then to the next gain circuit, namely U5 (NE5532). Elements R19 (15k) and R21 (33k) configure U5 to work as an inverting amplifier with a gain of about 2. From the output of U5, the signal through the filter R23 (100P), C21 (1 uF) and R25 (100k) enters the output of the preamplifier GP3 .
The supply voltage for the operational amplifiers is obtained using regulators U3 (78L15) and U4 (79L15), and filtered using capacitors C15-C16 and C17-C18. In addition, the power supply for each of the four op-amps is smoothed by capacitors C19-C20 and C23-C26 (100nF).
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Portable USB oscilloscope, 2 channels, 40 MHz....
Hello dear radio amateurs! Now I am assembling 4.1 acoustics on the TDA7650 and TDA1562, automotive microcircuits, for the home, of course, it could have been better to choose, but this is not about them, but about a preamplifier with a tone block. I've always wanted to customize the sound for myself. And so I decided to assemble such a tone block. The choice fell on the TDA1524A chip. And now we will talk about assembling this miracle from scratch, using LUT technology for the manufacture of a printed circuit board. The standard scheme, according to which we will assemble the tone block on the TDA1524A, is shown in the figure:
To begin with, we cut off the desired piece of textolite, skin it with zero, degrease it with acetone.
He carefully wrapped it, and began to ruthlessly fry the paint so that it would transfer from paper to textolite.
After ironing, give the board time to cool. Next, the case is transferred to the bathroom. We put the board in water in order to let the paper soften. At this time, you can drink tea or coffee - who prefers what.
It's a beautiful photo, isn't it? Let's go further, after we have refreshed ourselves, we can move on to the most, in my opinion, painstaking task - rubbing paper from the textolite. Carefully tear off the paper so as not to tear it off along with our tracks.
All that remains, without fanaticism, rubbed with fingertips.
Then we move on to the important thing - etching. I usually pickle in ferric chloride, as it is faster than pickling in blue vitriol (at first I poisoned them, but was disappointed, because the wait was up to 2 days). Gently place the board in the solution so as not to splatter.
Now you can go for a walk, or do something else. An hour has passed, you can get our payment. Usually it is etched faster, but I found textolite in the store only 2-sided, and the solution is not the first freshness. We take out the board and see our tracks.
The tracks are now under the toner, it needs to be cleaned off. Many people do this with acetone, or another solvent. I do it with the same fine skin.
That's all, the stage of preparing the board for the tone block circuit has been completed. Further it will be more interesting - we drill holes for parts.
There is nothing more to drill than with a drill, it is extremely inconvenient, especially since her cartridge is staggering. So don't scold too much for crooked holes :)
We produce soldering parts of the tone block. We start doing this with a socket (connector) for the TDA1524A chip.
Now we solder all the jumpers and small parts. We insert the microcircuit last, since during soldering it can overheat and fail, which is very sad.
Well, that's basically it! Below is a photo of my tone block.
After soldering, we check the absence of a short circuit, snot between the tracks, if nothing like this is noticed, then you can safely turn it on. Video demonstration of the device:
I always carry out the first start with a serial connection of a 12-volt car light bulb (for current limiting in the event of a short circuit). Tembroblok assembled - everything works fine. The article was written by: Eugene (ZhekaN96).
The tone block is used to equalize the Amplitude-Frequency Characteristic (AFC) of low-frequency amplifiers. Since many ULFs have a non-linear characteristic in different frequency ranges: in the low and high frequency range, the gain is much worse than in the mid-frequency range. Therefore, for high-quality sound reproduction, it makes sense to use special modules - "tone blocks", with which you can adjust the audio signal over the entire spectrum of the range.
At their core, these are mid-range filters that control the cutoff depth in a given frequency range without touching the low and high frequencies, and therefore the frequency response of the amplifier is leveled, but the amplitude of the input signal is slightly reduced, and additional amplification may be required. Thus, tone control modules can be divided into two classes: passive (only frequency response adjustment) and active (frequency response adjustment + amplifier stage for compensation)
This design of the tone block attenuates the signal in the midrange by about 10 times, and therefore it is placed between two amplifiers - preliminary and final.
The selection of radio components depends on the resistance of the signal source Rc and the load Rн (input impedance of the next amplifying stage). Let's calculate the ratings of radio elements: Variable resistors always take the same with the condition:
Rc The remaining components are calculated using simplified formulas: R1= R4= 0.1R; R3=0.01R; C3=0.1/R; C1= 22C3; C2=220C3; C4= 15C3 The transistor in the device is used to compensate for signal loss. There are no special requirements for it, you can even take the obsolete KT315. I want to say right away that this tone control can easily compete with those used in modern audio equipment, its circuit was copied from some amateur radio magazine, but now I don’t remember which one. One thing I can say for sure with this design of the tone block is happy as an elephant The appearance of the amateur radio design and the placement of components on the printed circuit board, see the figure at the top of the page Here are the passive tone diagrams of world-famous guitar electronics brands such as Fender, Marshall, and VOX. From the simplest with one control to the more complex three-way. Such a simple design allows only a blockage of high frequencies. It is used in the simplest lamp combos. With the help of the Fender Princeton tone block circuit, you can produce both a boost and a blockage of high frequencies. With this tone block, you can adjust the rise in the low and high frequencies. This tone controls both high and low frequencies. Below are some well-known schemes of timbre blocks - two-poles: Fender "BrownFace" Bandmaster 6G7, Ampeg SVT, Marshall JMC800 Mod.2001 Of this trinity of timbres, each is individual and good in its own way. On which one to stop and make the final choice, there is no definite answer. At this point, experiment yourself, the circuits are not complicated and are easily repeated by surface mounting or on a breadboard. For the purity of the article, I will also give diagrams of three-band timbral blocks. IMHO the most popular among all radio amateurs. These branded guitar designs allow you to adjust low, mid and high frequencies. Marshall gives a heavier sound than the Fender tone block. Below are the ratings of radio components in various variations of these schemes. The circuit of the tube tone block for the amplifier is based on the LM1036N, which controls the volume and balance in car radios. An additional control input makes it quite easy to apply volume compensation. All you need to assemble a transistor tone block with your own hands is an LM1036N, 15 capacitors, several fixed resistors and several potentiometers. As a result, you will get a high-quality device for controlling volume and other sound parameters. The circuit I used is shown in the manufacturer's data sheet: link Look at page 6. The circuit works just fine, so if this is your first try, use this one, it will work great as long as you don't screw up the parts. You will need: I spent about 1000 rubles on everything about everything. I started by building the circuit on a breadboard. This is very handy if you are a beginner and are not sure that everything will work right away, but keep in mind that you should not trust simulations too much. When I did the tests, there was quite a lot of noise in the audio signal. You can skip this step and start soldering right away if you are sure that everything will work out for you. I want to note that I used my fingers to check the incoming signal. When you touch the plug with them, a bad sound, similar to noise, should be made. Unscrew the potentiometer, which is responsible for the volume to the maximum, if you do not hear any sound, then you should not connect your phone, as there may be a short circuit in the circuit or simply something is not connected correctly. Note: All electrolytic capacitors must be connected correctly. They have markings on one of the sides (most often on the negative), take a little time to figure it out. After I heard noise on each of the channels, I connected my phone and turned on the music, checked all the buttons and listened to the difference in sound. Another point is the output signal. I used regular headphones. If you use cheap ones, you may not notice much difference in the settings. In the first photo, I have soldered most of the components. Try to install the capacitors as close to the chip as possible, as this will shorten traces and minimize noise. This will also help when choosing a case, it will be smaller and the board will fit better into it. In the second photo you can see the finished circuit with the output cables soldered on the bottom. Yellow and red are channels, black is ground. In the third photo you can see the small input cables. They come from old headphones, which already have a 3.5 mm jack, which means it does not need to be soldered. You will most likely want to mount the potentiometers on one side of the box. I used a plastic case to fit my board. I drilled four holes in the front to fit the potentiometer shafts through them, which are tightened on a small plastic piece inside the case. The device presented below has good sound quality and low noise, and also has a bypass function (direct frequency response), at the same time, the simplicity of the circuit will not scare novice radio amateurs. The passive part of the circuit is based on the development described by E.J. James "back in 1948, and the whole device together looks like the work of Baxandall" a sample of 1952 :) It looks like using an amplifier stage, in this case an op-amp, which can raise the amplitude "eaten " (with this regulator, the amplitude drops five times or -13dB!) with a tone block. Analyzing sources widely known to any radio amateur (in which there is some historical inaccuracy), it was decided to experiment with this little thing: Unfortunately, I did not have time to take real frequency response graphs, however, we will present the simulation result in the Tone Stack Calculator program. This circuit is notable for the use of the R5-R6, which provide a narrower boost without affecting the mids. These resistors are not in the development of E.J. James "a, so the simulation will occur without them :). However, this will not affect the overall impression of the graph, just the high-frequency rise band will be wider. But I would like more: an even greater rise in low frequencies and especially high frequencies, so to speak with a margin, although in your case everything may be completely different. Or rather, not in your case, but in the case of your acoustics :). For example, from the experience of operating the products of the Berdsk radio plant VEGA 50AC-106, adjusting the low frequencies of the timbre block in RRR UP-001 was not at all suitable, since it raised only the upper bass region (200-250 Hz, it’s hard to call it bass, rather a rumble). However, on acoustic systems manufactured by the Riga radio factory Radiotehnika RRR S50b, it was possible to achieve acceptable sound quality. Although all this is considered pampering, since it only corrects the listening impression, the frequency response of the speakers is corrected and, if the amplifier is defective, they are carried out by other circuitry research, for example, parametric equalizers with adjustments not only for gain, but also with the ability to move the raised frequency and quality factor. But we are not going to correct the flaws of expensive acoustics here, are we? Total +6 dB at the main low frequency, and +5 dB at the high one. It was decided to raise the -3 dB drop in the mid-range by increasing the gain on the op-amp. I'll admit it got a little too much. In the circuit, by turning the knobs it is difficult to achieve a smooth frequency response (or rather, not at all), so it was decided to add a device that turns off the tone block. This can be useful when using a more "advanced" EQ with your amplifier. A simple short circuit of the input and output of the passive part or the entire timbre block (in the first case, the capacitor C3 closes and, as a result, the tops collapse, in the second, the treble and bass adjustment is preserved, albeit within small limits) is not enough. Therefore, it is possible to carry out elementary switching on relays with changeover contacts (such as RES-9, RGK-14, etc.). It is worth touching separately on the well-worn topic of capacitors in the timbre block. According to my subjective experience of operating the well-known Shmelev preamplifier, in the design of which he used imported ceramics, widely distributed in stores, without hesitation, the output signal was saturated with harmonics, which was felt by ear. Perhaps in a blind test of this tone block with other capacitors, I would not have noticed this, but nevertheless, this was deeply deposited in my memory. In this design, I decided to use exclusively paper-based capacitors. Of course, here I will not describe the experience of using imported capacitors for hundreds of dollars, but as they say, what is rich :). From the accumulated reserves, capacitors of the BMT-2, BM-2 and MBM series were pulled out. So, when using these capacitors, the first thing to do is measure their capacitance and inspect for external damage (especially for BMT-2). Among a dozen samples of MBM series capacitors, 90% had an excess of rated capacity by 40-50%, which is two more than their tolerance. Capacitance measurement allows matching capacitors in pairs for 2 channels to ensure symmetrical adjustment. The first inclusion and the verdict - definitely preferable to using Chinese ceramics. To my shame, I could not find a paper capacitor in the RF circuit, so I used a KTK series capacitor, which was widely used in tube TVs and other equipment. Among other things, this capacitor has good thermal stability. Silver plates did not affect the sound in any way :) (although after replenishing the baggage of knowledge about this capacitor, the sound gradually began to become more beautiful and ... :)). Graphs that were captured: The controls are turned to the maximum: The controls are turned to the minimum: Diagram of the resulting device: Characteristics of this tone block: Indicators for CG, signal / noise depend on the applied op-amp. The choice fell on TL072, (this is a dual op-amp from ST) due to its cheapness and prevalence. Such opamps as NE5532, NJM4558, LM358 will fit perfectly here. You can also experiment with single op-amps (with further modification of the software) TL071, NE5534, KR544UD1.2, K157UD2 (with correction circuits) and so on. With paper capacitors and an op amp in a gold case, why not a rarity? To quickly replace the microcircuit (if you prefer another op-amp), it is recommended to first install the DIP-8 socket in the appropriate place. To power the active part of the device, a parametric voltage regulator is used on two arms + and - without using any amplifying elements, since in this circuit the total current consumption is less than the rated current of the zener diodes. To smooth out the residual ripples caused by the ripples of the UMZCH power supply, two electrolytes are present in the circuit. Their capacitance is small to ensure low inertia. Such a small set gives a low background level during operation of the device. Of course, this is not enough to ensure a minimum background level. Grounding the housings of variable resistors can help reduce the background. Some groups of regulators have a separate output for this (for example, SP3-33-23). At my disposal were the widespread B-group resistors (they are not suitable for adjusting the balance), the case of which, after sanding, I grounded. He brought the earth to one selected point (low-frequency regulator housing), from where he sent them to the earth of the UMZCH power supply. Photo of the device and circuit board: The size of the printed circuit board is 140x60 mm, here you can download the file in the format .lay. I wish you success in your replay! . Discuss the article TEMBROBLOK
Step 1: Basic Information
Step 2: Experimenting
Step 3: Making the Schematic
Step 4: Making the Body
