Do-it-yourself three-band tone block. Powerful and high-quality homemade sound amplifier

Part 1. How to make the IC “sound”.

For a long time I had an amplifier based on a not-everyone-loved, but very popular microcircuit. TDA 7294 in “Datashit” inclusion, coupled with a tone block on L.M. 1036. This tandem replaced the KT808 terminals in the Romantika-222S amplifier and the K174UN10/K174UN12 tone/volume controls, the sound of which, well... you know what it is. At that time, the new version completely satisfied me with the sound, but... Somehow I caught my eye on an article by Audiokiller about an amplifier on TDA 7294 with adjustable output impedance according to the ITUN circuit. Without hesitation, I mocked up a similar inclusion for my terminals. I was convinced that, indeed, the high ones are “sparkling”, and the low ones, well, they just “don’t need it anymore” :). The sound in such a scheme was clearly more interesting than in the “Datashit” one. I don’t remember in what ways, but I finally got to the website of Nikolai Lishmanov, who Lincor . And there is an article about the amplifier on TDA 7294 with “crazy feedback” - M.F. 1 is called... Since then (for about a year and a half now) in “Romance” I have been working with a finalist according to this exact scheme. There is a certain “zest” in its sound... More like, even a bag of raisins :). Read about M.F. 1 can be found here: http://lincor-lib.narod.ru/Amps2.htm. And here is the circuit itself in my “implementation”:

Fig. 1 - Power amplifier circuit.

The amplifier is powered according to the standard circuit:

Fig. 2 - Power supply diagram for a power amplifier.

Part 2. About the fact that a good tone block “can’t spoil the porridge.”

A good tone block should have a good opamp. It is he who will determine the “character” of the sound.As follows from the reviews of the projects Prostor and Tale 3 U , a high-quality tone block “makes” such seemingly familiar terminals on microcircuits sound in a new way. I decided to go for an experiment and “sweeten” M.F. 1 tone block from Tale 3U , which you can look at here: http://yooree.narod.ru/tale3u.html. The diagram of this miracle looks like this:

Fig. 3-Tone block diagram.

Op amp can be used as LT 1356 and LT 1362. The latter, to my ears, sounds even a little more interesting, but I could be wrong. The main thing here is to take into account the rather noticeable heating of the microcircuit LT 1362, which may be a consequence of self-excitation. Therefore, it is advisable to make sure that there is no generation. All elements located on the diagram below the pointsa, b, csoldered directly to the terminals of the variable resistors of the tone block.

It can be powered either by the “budget” version using two stabilizers of the 7812-7912 series, or by the “original” one for Tale 3U PSU, powering it from the power amplifier PSU. The diagram of a “budget” version of the stabilizer may look like this:

Fig. 3 - Diagram of the power supply for the tone control unit.

Epilogue

In this project, I tried to combine two circuits that have already earned recognition from DIYers due to their recognizable and “cute” sound. This amplifier has a very “moving” and “live” sound, if such a thing can be said about the sound. The bass is “monumentally reinforced concrete” and elaborate, midrange and high frequencies are light and detailed. The vocals are very expressive and transparent. The speakers “play” as if “in space”, and not “in themselves”. The seemingly familiar music seemed to have received a new sound. So my next thanks to Yuri, Audiokiller and Linkor for their invisible but very effective participation in the creation of this amplifier :)

Below are schematic diagrams and articles on the topic “timbre block” on the radio electronics website and radio hobby website.

What is a “timbre block” and where is it used, schematic diagrams of homemade devices that relate to the term “timbre block”.

Hello dear radio amateurs! Now I’m assembling 4.1 acoustics on TDA7650 and TDA1562, automotive microcircuits, for home, of course, I could have chosen better, but we’re not talking about them, but about a preamplifier with a tone block. I always wanted to customize the sound “to suit 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 diagram by which we will assemble the tone block on the TDA1524A is shown in the figure:

First, we cut off the required piece of PCB, sand it with scratch paper, and degrease it with acetone.

He carefully wrapped it and began to mercilessly fry the paint so that it would transfer from the paper to the PCB.

After ironing, give the board time to cool. Next, things move to the bathroom. Place the board in water to allow the paper to soften. At this time, you can drink tea or coffee - whoever prefers what.

It turned out to be a beautiful photo, didn’t it? Let's move on, after we have refreshed ourselves, we can move on to what, in my opinion, is the most painstaking task - wiping the paper off the PCB. We carefully tear off the paper so as not to tear it off along with our tracks.

All that remains, without fanaticism, we rub off with our fingertips.

Then we move on to the important matter - etching. I usually poison in ferric chloride, since it is faster than etching in copper sulfate (at first I poisoned with it, but was disappointed, because the wait reached 2 days). Carefully place the board in the solution so as not to splash it.

Now you can go for a walk, or do some other activity. An hour has passed, we can take out our board. Usually it is etched faster, but the textolite I found in the store was only 2-sided, and the solution was not the freshest. We take out the board and see our tracks.

The tracks are now under the toner, it needs to be cleaned. Many people do this with acetone or another solvent. I do this with the same fine sandpaper.

That's all, the stage of preparing the board for the tone block circuit is completed. Next it will be more interesting - we drill holes for the parts.

There is nothing else to drill with except a drill; it is extremely inconvenient, especially since its chuck is wobbly. So don't criticize too much for crooked holes :)

We perform soldering of the tone block parts. We start doing this with the 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 all! Below you can see a photo of my tone block.

After soldering, we check for 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). I assembled the tone block - everything works great. The article was written by: Evgeniy (ZhekaN96).

The device presented below has good sound quality and low noise level, and also has a bypass function (direct frequency response), at the same time, the simplicity of the circuit will not scare away novice radio amateurs. The passive part of the circuit is based on a development described by E.J. James back in 1948, and the whole device together looks like the work of Baxandall from 1952 :) It looks like using an amplification stage, in this case an op-amp, which can increase the amplitude "eaten "(the amplitude of this regulator drops five times or -13 dB!) by the 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 didn’t manage to take real frequency response graphs, but we present the result of the simulation in the Tone Stack Calculator program. This circuit is notable for its use of R5-R6, which provide a narrower frequency boost without affecting the midrange. These resistors are not in the design of E.J.James, so the simulation will take place without them :). However, this will not affect the overall impression of the graph, it’s just that the high-frequency rise band will be wider.

But I would like more: an even greater increase in the low frequencies and especially high frequencies, so to speak, with a reserve, 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 tone block in the RRR UP-001 was not at all suitable, since it only raised the upper bass region (200-250 Hz, it’s hard to call it bass, more like a hum). However, on acoustic systems produced by the Riga radio plant 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 adjusted and, if the amplifier is defective, they are carried out with other circuit 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’re not here to correct the flaws of expensive acoustics, are we?

Total +6 dB at the main low frequency, and +5 dB at the high one. It was decided to increase the -3 dB drop in the mid-frequency region by amplification at the op-amp. I admit, it became a little too much. In the circuit, it is difficult to achieve a smooth frequency response by turning the controls (or rather, not at all), so it was decided to add a device that turns off the tone block. This may be useful if you are using a more advanced equalizer with your amplifier. Simply short-circuiting the input and output of the passive part or the entire timbre block (in the first case, capacitor C3 is short-circuited and, as a result, the highs fall off, in the second case, the HF and LF adjustment is preserved, albeit within small limits) is not enough here. Therefore, it is possible to carry out elementary switching using a relay with changeover contacts (type RES-9, RGK-14, etc.).

It is worth separately touching on the well-worn topic of capacitors in the tone block. According to my subjective experience of operating the famous Shmelev preamplifier, in the design of which I unhesitatingly used imported ceramics, widely used in stores, 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 it was deeply imprinted 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, it’s rich :). Capacitors of the BMT-2, BM-2 and MBM series were pulled out from the accumulated reserves.

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 capacitors of the MBM series, 90% had an excess of rated capacity by 40-50%, which is two times more than their tolerance. Measuring capacitance allows you to select capacitors in pairs for 2 channels to ensure symmetrical adjustment. The first inclusion and verdict is definitely preferable to using Chinese ceramics. To my shame, I was unable to find a paper capacitor in the HF circuit, so I used a KTK series capacitor, which was widely used in tube televisions and other equipment. Among other things, this capacitor has good thermal stability. The silver linings did not affect the sound in any way :) (although after expanding my knowledge about this capacitor, the sound gradually began to become more beautiful and... :)). Graphs that were captured:

The controls are turned to maximum:

The controls are turned to minimum:

Diagram of the resulting device:

Characteristics of this tone block:

• Harmonic coefficient, %: no more than 0.02.
• Adjustment range, no less: LF +-16 dB, HF +-17 dB.
• Input signal: ~1V.

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. Op-amps such as NE5532, NJM4558, LM358 will fit perfectly here. You can also experiment with single op-amps (with further modification of the PP) 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 stabilizer is used on two arms + and - without using any amplification elements, since in this circuit the total current consumption is less than the rated current of the zener diodes. To smooth out the residual pulsations caused by the pulsations of the UMZCH power supply, there are two electrolytes in the circuit. Their capacity is small to ensure low inertia. Such a small set gives a low background level when operating the device.

Of course, this is not enough to ensure a minimum background level. Grounding the housings of variable resistors can help reduce hum. Some groups of regulators have a separate output for this (for example SP3-33-23). I had at my disposal widely used B-group resistors (they are not suitable for adjusting the balance), the housing of which, after sanding, I grounded. I brought the earths to one selected point (the housing of the low-frequency regulator), from where I sent them to the earth of the UMZCH power supply. Photo of the device and printed 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 repetition! .

Discuss the article TEMBRAL BLOCK

set NK022

Any high-quality amplifier must not only have the ability to adjust the gain of the input signal, but also provide correction of the amplitude-frequency response for each channel in at least two frequency regions: upper and lower. Electronic devices called tone blocks successfully cope with this task.

Circuit design options for building tone blocks are based on the use of RC circuits. When they are included in the audio signal circuit, the effect of filtering a single frequency region in the frequency band 20...20000 Hz is obtained. This is because the capacitance of RC circuits depends on frequency. High- and low-pass filters, as well as band-pass filters widely used in graphic equalizers, are built on RC circuits.

Some filters allow you to change the amplitude-frequency response of the amplifier quite effectively. During the correction process, they are capable of introducing not only attenuation, but also amplification of the signal. Such filters are called active, since RC circuits are included in the feedback circuits of active radio elements, for example, transistors or operational amplifiers. Their disadvantages include distortion of the input signal caused by the nonlinearity of the characteristics of active radio elements.

Another class of filters are passive filters. They consist only of capacitors and resistors. But passive filters have a rather low transmission coefficient. For example, at medium frequencies (800... 1200 Hz) they reduce the signal level by 10... 12 times! Therefore, when using them, it is necessary to use additional signal amplification stages. In addition, the limits of regulation of low and high frequencies by a timbre block built on passive filters are wider, the lower the output impedance of the signal source and the higher the input impedance of the subsequent stage. However, compared to active filters, the nonlinear distortion of passive filters is minimal.

The NK022 tone block is built using passive low-frequency (LF) and high-frequency (HF) filters. It is intended for use in high quality stereo low frequency power amplifiers. The timbre block allows you to adjust the amplitude-frequency response of the amplifier simultaneously on two channels in accordance with the individual desires of the listener, the characteristics of acoustic systems and room features, as well as separately adjust the HF, LF and volume tones of each of the two channels. The device supply voltage is 9… 18 V.

Description of the electrical circuit of the tone block

The appearance of the tone block board with elements installed on it and the electrical circuit of the tone block are shown in Rice. 1 And Rice. 2.

Rice. 1. External view tone block

The device has two separate channels for adjusting the amplitude-frequency characteristics. Let's look at the operation of the block using the upper channel as an example. The input signal is fed to an amplifier made on transistor VT1. Amplification is necessary because passive filters, as mentioned above, significantly attenuate the input signal. The amplified signal is fed to filters for low-pass (P1) and high-pass (P2) adjustment.

It is known that the capacitance for low frequency alternating current is a fairly high reactance, and for high frequency currents it is low. Therefore, the capacitive chain C5-C6 “short-circuits” the HF component of the input signal to the common wire, and at the common connection point of resistors R7 and P1 only the LF component is present. At the connection point of resistors P1 and R8 LF-co-

Rice. 2. Electrical circuit of a stereophonic tone block

The value is significantly weakened by this resistive divider. This means that moving the slider of the variable resistor P1 from the top position in the diagram to the bottom will lead to a smooth decrease in the spectrum of the low-frequency component at the output of the timbre block.

A similar situation occurs with a tunable high-pass filter. At the point of connection between C9 and P2 there will be a maximum of the HF component, and at the point of connection between P2 and SJ there will be a minimum. By moving the slider of resistor P2 from top to bottom, we obtain a smooth decrease in the level of the RF component in the spectrum of the output signal.

Variable resistor P4 forms an adjustable voltage divider relative to the common wire of the circuit, that is, it changes the output voltage of the tone control unit. It is designed for frequency-independent changes in the sound volume of one of the power amplifier channels.

The second channel of the tone block works similarly to the first channel.

Assembling the tone block

Before assembling the stereo tone unit, carefully read the recommendations for installing electronic circuits given at the beginning of this book. This will help avoid damage to the printed circuit board and individual circuit elements. The list of set elements is given in Table 1.

The locations of the elements on the tone block board and the board with installed elements are shown in Rice. 3. On Rice. Behind The connection lines of the assembled device are also shown.

Rice. 3. Arrangement of elements on the printed circuit board of the tone block: a - locations of elements on the board; b - board with installed elements

Form the element leads, install the elements on the board and solder their leads; At the same time, install small-sized ones first, then all other elements. After assembly, check the correct installation, especially carefully check the correct installation of electrolytic capacitors. A correctly assembled tone block does not need adjustment.

Table 1. List of elements of the NK022 set

If you, dear reader, intend to assemble a power amplifier for a home audio center, you will find everything you need for this in the MASTER KIT catalog, given in the appendix to this book. This includes a stabilized power supply, a power amplifier, and even a suitable housing. Assembling a high-quality low-frequency amplifier is a very real task!

A set for a stereophonic tone block, as well as other sets that may be needed when assembling an amplifier, can be purchased at radio parts stores or at radio markets.