Purpose of work: Learn to measure the harmonic coefficient using the nonlinear distortion coefficient meter.
1. Equipment:
1.1 Audio complex TR-0157
1.2 UCH studied
1.3 oscilloscope C1-73 (C 1 -112)
1.4 Connecting cables
1.5 Technical descriptions to devices
Brief theoretical information.
Nonlinear distortion is due to the presence of elements with nonlinear characteristics (lamps, transistors, chips, etc.) in the schemes of radio devices, transistors, microcircuits.) Nonlinear distortions are characterized by a harmonic coefficient (kg) (characterizes the difference of the form of a periodic signal from harmonic), which is defined as the ratio of the active voltage value of all higher harmonics of the stressed voltage, starting with the second, to the current value of the first, i.e. Basic harmonic.
This formula is used in the study of high-quality amplifiers, in which kg is (0.2 ... 2)%. In less quality amplifiers (Kg \u003d 2 ... 7%) Nonlinear distortion meters measured not a harmonic coefficient, but a coefficient close to it by approximate formula
where u k is a variation of the input signal.
If the harmonic coefficient kg<10%, то Кг и К"г практически совпадают, реализация устройств для измерения К"г значительно упрощается.
The simplified structural diagram of the nonlinear distortion meter is shown in Figure 1.
Figure 1. Structural diagram of nonlinear distortion meter
The most common method of measuring the nonlinear distortion coefficient is the method of suppressing the main frequency voltage, i.e. The comparison method of the active value of the highest harmonic voltage with the active value of the test signal.
Principle of operation of the meter of nonlinear distortions, cm, bp Chrome and Yu.G. Moses "Electrogenation", M. Radio and Communication, 1985, pp. 252-255 and in the technical description on the device.
The procedure for carrying out work.
3.1 Collect the harmonic coefficient measurement scheme (Figure 2)
Figure 2. Device Connection Scheme
3.2 Ground the devices.
3.3 Turn on the power.
3.4 Prepare devices to work:
3.4.1 Regulators "HF", "HF" UNUC stand to establish in the middle position;
3.4.2 On the TR-0157 audio complex, press the "Mains" and "~ U" buttons;
3.4.3 Using the "Frequency" knob and the "FREQ" buttons. Range "Block" Audio Generator "complex TR-0157 Set the output frequency of 1250 Hz;
3.4.4 Using the ATTENUATOR DB knob (stepwise, smoothly), set the voltage at the output of the stand 1 V.
Monitoring to carry out a voltmeter of the complex using the "~" scale and considering the limit switch positions (red scale);
3.4.5 Oscilloscope controls to achieve a stable oscillogram without visible signal distortions (there should be no visible limit).
3.5 Make a measurement of kg for 3-5 values \u200b\u200bof the ONLC output voltage specified in Table 1. Voltages set by the "Attenuator DB" knobs (stepwise) of the TR-0157 complex.
Table 1 - Measurement results kg
| U out, in | |||||
| Kg,% |
To measure kg, perform the following:
3.5.1 Press the "DIST." Button Complex TR-0157
3.5.2 Set the handle "Range%" block "DIST. Meter "to the extreme right position (" 100 Cal. ")
3.5.3 Perform the device calibration by level, to do this, press the "125 Hz" and "X100" buttons ("Frequ. Selector") block "DIST. Meter "(In this position, the effect of the filter on the signal test) is eliminated). Pull the handle "Call" block "DIST. Meter "and with it to install the voltmeter arrow of the complex to maximum readings (if necessary, switch the voltmeter measurement limit);
3.5.4 Configure the device to the frequency of the signal, to do this, press the button and "x10" ("Frequ. Selector") block "DIST. Meter. " Regulators "ΔF" and "BALLANCE" block "DIST. Meter "achieve minimal voltmeter readings of the complex. At the same time, it is necessary to gradually reduce the measurement limit with the "Range%" block "DIST block. Meter. "
3.5.6 Repeat measurements for all voltage values \u200b\u200blisted in Table 1. To set the required voltage value to execute PP 3.4.4 and 3.4.5, by pressing the "~ U" button. After that, repeat the calibration of the complex again (PP 3.5.1 - 3.5.6.).
4.1 Name and purpose of work.
4.2 List of equipment used.
4.3 Table of measurement results.
4.4 Conclusion on the compliance of the value of non-linear distortions kg of the Amplifier of the LC requirements.
5. Control questions.
5.1 What are the nonlinear distortions in radioshem?
5.2 Give the definition of the harmonic coefficient.
5.3 Give the structural scheme of the meter of nonlinear distortion, explain the principle of its work.
5.4 How can the nonlinear distortion coefficient be measured using harmonic analyzer?
Laboratory work №11.
IN The history of sound reproduction developed from attempts to bring the illusion to the original. And although the path passed huge, until the complete approach to living sound is still very and very far away. Differences on numerous parameters can be measured, but not enough of them remains out of sight of the instrument developers. One of the main characteristics to which the consumer with any preparation always draws attention is nonlinear distortion coefficient (books) .
And what value of this coefficient is sufficiently objectively indicative of the quality of the device? Impatiently can immediately find an attempt to answer this question at the end. For the rest, we will continue.
This coefficient, which is also called the common harmonic distortion coefficient, is a pronounced ratio of the effective amplitude of harmonic components at the output of the device (amplifier, tape recorder, etc.) to the effective amplitude of the main frequency signal when exposed to the input of the sinusoidal signal of this frequency. Thus, it allows you to quantify the nonlinearity of the gear ratio, which manifests itself in the appearance of spectral components in the output signal (harmonics), missing in the input signal. In other words, there is a qualitative change in the spectrum of the musical signal.
In addition to objective harmonic distortions present in the audible sound signal, there is a problem of distortion that are missing in real sound, but are felt due to the subjective harmonics arising in the middle ear snail at large sound pressure values. The auditory apparatus of a person is a nonlinear system. The nonlinearity of the hearing manifests itself in the fact that when exposed to a sinusoidal sound with a frequency of F in a hearing aid, harmonics of this sound with frequencies 2F, 3F, etc. are born. Since in the primary acting tone of these harmonics, they received the name of the subjective harmonics.
Naturally, it even more complicates the idea of \u200b\u200bthe maximum permissible level of the harmonic of the sound tract. With an increase in the intensity of the primary tone, the value of the subjective, the harmonic increases sharply and can even exceed the intensity of the main tone. This circumstance gives grounds for assumption that the sounds with a frequency of less than 100 Hz are not felt by themselves, and due to the subjective harmonics created by them, over 100 Hz, i.e. Due to the nonlinearity of hearing. The physical reasons for emerging hardware distortions in various devices have different nature, and the contribution of each into the general distortions of the entire path of unequal.
The distortions of modern CD players have very low values \u200b\u200band practically imperceptible against the background of distortion of other blocks. For acoustic systems, low-frequency distortions caused by the bass head are the most significant, and the requirements are stipulated only for the second and third harmonics in the frequency range up to 250 Hz. And for a very well sound acoustic system, they can be within 1% or even a bit more. In analog tape recorders, the main problem associated with the physical framework of the magnetic tape recording is the third harmonic, the values \u200b\u200bof which are usually given in the instructions for information. But the maximum value at which, for example, noise level measurements are always produced, it is 3% for frequency of 333 Hz. The distortion of the electronic part of the tape recorders is significantly lower.
Both in the case of acoustics and for analogue tape recorders, due to the fact that the distortions are mostly low-frequency, subjective substitution of them is much dropped due to the disguise effect (which is that more high-frequency heard from two simultaneously sound signals).
So the main source of distortion in your path will be the power amplifier in which, in turn, the nonlinearity of the transfer characteristics of the active elements: transistors and electronic lamps, and nonlinear distortion of the transformer associated with the non-linearity of the magnetization curve is also added in transformer amplifiers. It is obvious that on the one side of the distortion depend on the form of nonlinearity of the transfer characteristic, but also on the nature of the input signal.
For example, the transfer characteristic of an amplifier with a smooth restriction for large amplitudes will not cause any distortion for sinusoidal signals, smaller levels of restrictions, and with an increase in the signal above this level of distortion appear and will increase. This nature of the restriction is inherent in mainly lamp amplifiers, which to some extent can serve as one of the reasons for the preference of such listeners enhancers. And this feature was used by NAD in a series of their sensational amplifiers with a "soft restriction", produced from the beginning of the 80s: the possibility of incorporating the regime with imitation of a lamp restriction created a numerous army of fans of transistor amplifiers of this company.
In contrast, the characteristic of the central cut-off amplifier (distortion of the type "step"), which is characteristic of transistor models, causes distortion of musical and small sinusoidal signals, and with increasing the level of distortion signal will decrease. Thus, the distortion depends not only on the shape of the transfer characteristic, but also from the statistical distribution of the input levels, which is close to the noise signal for music programs. Therefore, besides measuring the Sinusoidal Signal, it is possible a method for measuring nonlinear distortion of amplifying devices using the sum of three sinusoidal or noise signals that give the above more objective picture of distortion in the light.
Thanks to trading networks and online stores, the diversity of audio equipment proposed for sale is overwhelming for all reasonable limits. How to choose a device that satisfies your quality needs, not significantly overpaying?
If you are not an audiophile and the selection of equipment is not the meaning of life for you, the easiest way is to confidently navigate the technical characteristics of the sound inspection equipment and learn how to extract useful information between lines of passports and instructions, critically related to generous promises. If you do not feel the difference between DB and DBM, nominal power Do not distinguish from PMPO and you wish to finally find out what THD is, you can also find interesting under the cut.
Summary Article
Gain. Why do we need logarithms and what is Decybel?
Sound volume. What is the difference between DB from DBM?
Separate and conquer - lay out the signal to the spectrum.
Linear distortion and bandwidth.
Nonlinear distortion. St., KGI, TDH.
Amplitude characteristic. Very briefly about noise and interference.
Standards of output power UHC and acoustics.
Practice is the best criterion of truth. Disassembly with audio center.
Kettle Funning in Möday Bank.
I hope that the materials of this article will be useful for understanding the next one, which has a much more complex topic - "Crossing distortions and feedback, as one of their sources."
Gain. Why do we need logarithms and what is Decybel?
One of the main parameters of the amplifier is the gain coefficient - the ratio of the output parameter of the amplifier to the input. Depending on the functional purpose of the amplifier, the gain coefficients for voltage, current or power are distinguished:
Voltage gain coefficient
Current gain
Power amplification coefficient
The gain of UNG can be very large, even greater values \u200b\u200bare expressed to strengthen operational amplifiers and radio sides of various equipment. The numbers with a large number of zeros are not too convenient to operate, even more difficult to display on the graph of various kinds of dependence having values \u200b\u200bthat differ in one thousand or more times. Convenient way out - view of magnifies in a logarithmic scale. In acoustics it is doubly convenient because the ear has a sensitivity close to the logarithmic.
Therefore, the gain coefficient is often expressed in logarithmic units - decibels (Russian designation: dB; international: DB)
Initially, dB was used to estimate the ratio of capacity, so the value expressed in dB implies the logarithm of the relations of two capacities, and the gain in power is calculated by the formula:
A little different ways with "non-energy" values. For example, we take the current and express power through it, using the Ohm's law:
then the value expressed in decibels through the current will be equal to the following expression:
Similarly for voltage. As a result, we obtain the following formulas to calculate the gain coefficients:
Current gain in dB:
Voltage gain in dB:
Sound volume. What is the difference between DB from DBM?
In the acoustics "intensity level" or just the volume of sound L. Also measured in decibels, while this parameter is not absolute, but relative! All because the comparison is carried out with the minimum threshold of hearing the human ear of the sound of harmonic oscillation - the amplitude of the sound pressure of 20 MCPA. Since the intensity of sound is proportional to the square of the sound pressure, you can write:
where it is not a current, but the intensity of sound pressure of sound with a frequency of 1 kHz, which approximately corresponds to the threshold of audio audibility by man.
Thus, when they say that the sound volume is 20 dB, which means that the intensity of the sound wave is 100 times higher than the threshold of audio hearing the sound.
In addition, the absolute value of power measurement is extremely common in radio engineering dBM. (Russian dBm), which is measured relative to the power of 1 MW. Power is determined on the rated load (for professional equipment - usually 10 kΩ for frequencies less than 10 MHz, for radio frequency equipment - 50 ohms or 75 ohms). For example, "the output power of an amplifying cascade is 13 dBm" (i.e. the power released on the load nominal for this reinforcement cascade is approximately 20 MW).
Separate and conquer - lay out the signal to the spectrum.
It is time to move to a more complex topic - an evaluation of signal distortion. First you have to make a little accession and talk about the spectra. The fact is that in sound engineering and not only it is customary to operate with sinusoidal signals. They are often found in the surrounding world, since a huge number of sounds create oscillations of certain objects. In addition, the structure of the human auditory system is well adapted to perceive sinusoidal oscillations.
Any sinusoidal oscillation can be described by the formula:
where the length of the vector, the amplitude of the oscillations is the initial angle (phase) of the vector in the zero moment of time, the angular speed, which is equal to:
It is important that with the amount of sinusoidal signals with different amplitudes, frequency and phase, you can describe periodically repeated signals of any form. Signals whose frequencies differ from the main integer times are called harmonics of the original frequency. For a signal with a basic frequency F, signals with frequencies
will be aware of harmonics, and signals
odd harmonics
Let's see a graph of a sawtooth signal.
To accurately present it through harmonics, an infinite number of members will be required.
In practice, a limited number of harmonics with the greatest amplitude is used to analyze signals. It is possible to clearly see the process of constructing a sawtooth signal from harmonics in the figure below.
But how Meander is formed, with an accuracy of fifty harmonics ...
You can read more about harmonics in the wonderful article of Habrahabr.ru/post/219337 user Dlinyj, and it's time to turn to distortion.
The simplest method of evaluating signal distortions is to feed on the input of the amplifier of one or the sum of several harmonic signals and the analysis of the observed harmonic signals at the output.
If there are signals of the same harmonics at the output of the amplifier as the input, distortions are considered linear, because they are reduced to the change in the amplitude and phase of the input signal.
Nonlinear distortion is added to the signal new harmonics, which leads to distortion of the input signals.
Linear distortion and bandwidth.
Gain TO The ideal amplifier does not depend on the frequency, but in real life it is not so. The dependence of amplitude from frequency is called amplitude-frequency characteristic - Ahh And they are often depicted in the form of a graph where the voltage gain coefficient is deposited by vertical, and the frequency horizontally. Pictures on the chart of achm of a typical amplifier.
ACH is removed, consistently feeding the signals of different frequencies of a particular level to the amplifier input and measuring the signal level at the output.
Frequency range Δf., within which the power of the amplifier decreases no more than twice the maximum value, called strip bandwidth.
However, the graph of the voltage gain is usually placed on the chart, and not by power. If you designate the maximum voltage gain as, then within the bandwidth, the coefficient should not fall lower than:
The frequency and signal level values \u200b\u200bwith which the UUCH works may vary very significantly, so the frequency response is usually built in the logarithmic coordinates, sometimes it is called lach.
The gain of the amplifier is expressed in decibels, and on the abscissa axis, the frequencies are deposited through decada(The frequency interval of different among themselves is ten times). Is it not possible to look like a schedule not only prettier, but also informative?
The amplifier not only unevenly enhances the signals of different frequencies, but also shifts the signal phase to different values, depending on its frequency. This dependence reflects the phase-frequency characteristic of the amplifier.
When the oscillations enhance only one frequency, it seems to be not scary, but for more complex signals leads to essential form distortions, although it does not generate new harmonics. In the bottom of the bottom it is shown how the two-frequency signal is distorted.
Nonlinear distortion. St., KGI, TDH.
Nonlinear distortion is added to the signal not previously existing harmonics and, as a result, change the initial form of the signal. Perhaps the most visual example of such distortions can serve as a limitation of a sinusoidal signal over the amplitude shown below.
On the left graph shows distortions caused by the presence of additional signal harmonics - limiting the amplitude of one of the half-filled signal. The source sinusoidal signal has number 1, the oscillation of the second harmonic 2, and the resulting distort signal 3. The result of the third harmonic action is shown on the right figure - the signal "Cropped" from two sides.
In the time of the USSR, nonlinear distortion of the amplifier was taken to express with the help of the harmonic distortion of the CGI. It was determined as follows - the signal of a certain frequency was fed to the amplifier input, usually 1000 Hz. Then the level of all the harmonics of the signal at the output was calculated. For the KGA, the ratio of the mean square voltage of the sum of higher harmonics of the signal, except for the first, to the voltage of the first harmonic - the very frequency of which is equal to the frequency of the input sinusoidal signal.
A similar foreign parameter is referred to as - Total Harmonic Distortion for Fundamental Frequency.
Coefficient of harmonic distortion (KGI or)
This technique will only work if the input signal is ideal and contain only the main harmonic. This condition is not always possible, therefore, in modern international practice, another parameter of estimating the degree of nonlinear distortions - books was much more distribution.
Foreign analog - Total Harmonic Distortion for Root Mean Square.
Nonlinear distortion coefficient (book or)
The KNY is the value of the ratio equal to the ratio of the mean square sum of the spectral component of the output signal, missing in the input spectrum, to the mean-square sum of all spectral components of the input signal.
Both books and kgs are relative values \u200b\u200bthat are measured as a percentage.
The values \u200b\u200bof these parameters are associated with the relation:
For the signals of a simple form, the magnitude of the distortion can be calculated analytically. Below are the values \u200b\u200bof the books for the most common signals in the audio engineering (the value of the KGI is indicated in brackets).
0% (0%) - the signal form is an ideal sinusoid.
3% (3%) - the signal form is excellent from sinusoidal, but distortion is invisible to the eye.
5% (5%) is the deviation of the signal shape from the sinusoidal noticeable eye on the oscillogram.
10% (10%) - a standard level of distortion, in which the real power (RMS) is considered, noticeable for hearing.
12% (12%) is an ideal symmetric triangular signal.
21% (22%) - "Typical" signal of the trapezoidal or stepped form. 43% (48%) is an ideal symmetric rectangular signal (meander).
63% (80%) is an ideal sawdow signal.
Another twenty years ago, complex expensive devices were used to measure harmonic distortions of the low-frequency path. One of them SC6-13 is shown in the figure below. 
Today, the external computer audio card with a set of specialized software is much better coped with this task, which is not exceeding 500USD.
Signal spectrum at the audio card input when testing a low frequency amplifier.
Amplitude characteristic. Very briefly about noise and interference.
The dependence of the output voltage of the amplifier from its input, at a fixed frequency of the signal (usually 1000 Hz), is called an amplitude characteristic.
Amplitude characteristic The ideal amplifier is direct, passing through the origin, since its gain is a constant value at any input voltages.
On the amplitude characteristic of the real amplifier, there are at least three different sections. At the bottom, it does not reach zero, since the amplifier has its own noises that become at low volume levels commensurate with the amplitude of the useful signal.
In the middle part (A), the amplitude characteristic is close to linear. This work plot, within its limits, the distortion of the signal form will be minimal.
At the top of the graph, the amplitude characteristic also has a bend, which is due to the restriction at the output power of the amplifier.
If the amplitude of the input signal is such that the operation of the amplifier goes on curved areas, non-linear distortions appear in the output signal. The larger the nonlinearity, the stronger the sinusoidal signal voltage is distorted, i.e. At the outlet of the amplifier, new fluctuations appear (higher harmonics).
Noises in amplifiers are different types and are caused by different reasons.
White noise.
White noise is a signal with a uniform spectral density at all frequencies. Within the operating range of the frequency of low frequency amplifiers, an example of such noise can be considered thermal, caused by the chaotic movement of electrons. The spectrum of this noise is uniform in a very wide frequency range.
Pink noise.
Pink noise is also known as flickering (flicker noise). The spectral power density of pink noise is proportional to the ratio of 1 / f (the density is inversely proportional to the frequency), that is, it is evenly decreasing in the logarithmic scale of frequencies. Pink noise is generated as passive and active electronic components, scientists still argue about the nature of its origin.
Background from external sources.
One of the main causes of noise is a background in addition from foreign sources, for example, from an AC network of 50 Hz. It has a major harmonic in 50 Hz and multiple to her.
Self-excitation.
Self-excitation of individual cascades of the amplifier can generate noise, as a rule of a certain frequency.
ONLC and acoustics output power standards
Rated power
Western analog RMS (Root Mean Squared is a standard value) in the USSR was determined by GOST 23262-88 as averaged value of the linked electrical power of a sinusoidal signal with a frequency of 1000 Hz, which causes nonlinear signal distortions that do not exceed the specified value of the book (THD). It is indicated by both AC and amplifiers. Typically, the specified power was adjusted for the requirements of GOST to the class of complexity of execution, with the best combination of measured characteristics. For different classes of KOD devices can vary very significantly, from 1 to 10 percent. It may turn out that the system is declared in 20 watts to the channel, but the measurements were carried out at 10% of the book. As a result, listening to acoustics at this power is impossible. Acoustic systems are capable of playing a signal on RMS power for a long time.
Passport noise power
Sometimes they are also called sinusoidal. Nearest Western Analogue DIN. - Electrical power limited exclusively thermal and mechanical damage (for example: sliding the turns of the sound coil from overheating, burning off the conductors in the locations of the inflection or spike, breaking the flexible wires, etc.) when taking pink noise through the adjusting chain for 100 hours. Usually DIN is 2-3 times higher than RMS.
Maximum short-term power
Western analog Pmpo. (PEAK MUSIC POWER OUTPUT - peak output musical power). - Electrical power that speakers of speakers are withstanding without damage (checked according to the absence of rattling) for a short period of time. A pink noise is used as a test signal. The signal is fed to the AC for 2 sec. Tests are carried out 60 times with an interval of 1 minute. This type of power makes it possible to judge short-term overloads, which can withstand the speaker of the AC in situations arising during operation. Usually 10-20 times higher than DIN. What is the benefit of whether a person recognizes that his system may have a short, less second, low frequency sinus with high power? However, manufacturers really love to bring this parameter on the packages and stickers of their products ... The huge numbers of this parameter are often based exclusively on the turbulent fantasy of the marketing department of manufacturers, and then the Chinese are undoubtedly ahead of the planet all.
Maximum long-term power
This is an electrical power that the speakers of the AU are withstanding without damage for 1 min. Tests are repeated 10 times with an interval of 2 minutes. Test signal is the same.
The maximum long-term power is determined by the violation of the thermal strength of the speakers of the AU (sliding the turns of the sound coil, etc.).
Practice is the best criterion of truth. Disassembly with audio center
Let's try to apply our knowledge in practice. Look at one very well-known online store and find a product there is an even more well-known company from the rising sun.
Yeah - this is a music center of futuristic design for sale in just 10,000 rubles. For the next promotion.:
From the description, learn that the device is equipped not only with powerful columns, but also a subwoofer.
"It provides excellent sound cleanliness when choosing any volume level. In addition, such a configuration helps make sound saturated and volumetric. "
Satisfying, perhaps you should look at the parameters. "The center contains two front speakers, each power of 235 watts, and an active subwoofer with a power of 230 watts." At the same time the sizes of the first total 31 * 23 * 21 cm
Yes, it is some kind of nightingale a robber, and the voting strength and size. In a distant 96, I would have stopped my research on this, and later, looking at my S90 and listening to the homemade Ageevsky amplifier, it would be rapidly discussed with friends as far from the Japanese our Soviet industry - for 50 years or all the same forever. But today with the availability of Japanese technology, the situation is much better and has collapsed many myths with it related, so before buying we will try to find more objective data on the quality of sound. On the site about it there is a word. Who would doubt that! But there is an instruction manual in PDF format. Cook and continue searching. Among the extremely valuable information about the fact that the "sound coding technology license was obtained from the Thompson" and how much to insert batteries with difficulty, but it is possible to find something resembling technical parameters. Extremely scarce information is picked up in the depths of the document, closer to the end.
I bring it literally, in the form of a screenshot, since, starting from now on, I began to have serious questions, as in the given numbers, in spite of the fact that they are confirmed by a certificate of conformity and their interpretation.
The fact is that just below it was written that the power consumption of the first system is 90 watts, and the second is generally 75. Hmm.
Invented the Eternal Engine of the Third Rod? Or maybe in the body of the musical center hide batteries? Yes, it does not look like - the claimed weight of the apparatus without acoustics is only three kilos. Then how consuming 90 watts from the network, you can get at the output of 700 mysterious watts (for references) or at least miserable, but quite tangible 120 nominal. After all, the amplifier must have an efficiency of about 150 percent, even with a disabled subwoofer! But in practice, this parameter rarely exceeds the bar in 75.
Let's try to apply the information received from the article in practice.
The stated power for reference 235 + 235 + 230 \u003d 700 is clearly PMPO. With rated clarity a lot less. Judging by definition it rated powerBut it cannot be 60 + 60 only for two main channels, excluding a subwoofer, at the rated power of consumption in 90 watts. It is more and more reminds no longer a marketing trick, but a frank lie. Judging by the dimensions and the unlawful rule, the ratio of RMS and PMPO, the real rated power of this center should be 12-15 watts per channel, and the general one does not exceed 45. A natural question arises - how can you trust the passport data of Taiwanese and Chinese manufacturers, when even famous Japanese Is this a firm?
Buy such a device or not - the solution depends on you. If in order to put in the morning on the ears of neighbors in the country - yes. Otherwise, without prior listening to several musical compositions in different genres, I would not recommend.
Kettle Funning in Möday Bank.
It would seem that we have an almost exhaustive list of the parameters required to estimate the power and quality of sound. But, with closer attention, it turns out to be far from a number of reasons:
- Many parameters are more suitable not so much for objective reflection of the signal quality, as for the convenience of measurement. Most are conducted at a frequency of 1000 Hz, which is very convenient for the best numerical results. It is located far from the frequency of the electrical network of 50 Hz and in the most linear portion of the frequency range of the amplifier.
- Manufacturers often sin with a frank fit of the characteristics of the amplifier under tests. For example, even during the times of the Soviet Union, UNG was often developed in such a way as to ensure the best indicator of the KGI, with a maximum output passport power. At the same time, at a half level of power in two-stroke amplifiers, the type of step is often manifested, because of which the harmonic distortion coefficient with an average position of the volume handle could be used for 10%!
- In passports and operating instructions, non-standard fake, absolutely useless characteristics of the PMPO type are often given. At the same time, it is not always possible to find such basic parameters as a frequency range or nominal power. About Ahh and FFH and nothing to say!
- The measurement of the parameters is often produced by consciously distorted, methods.
It is not surprising that many buyers fall in such conditions in subjectivism and oriented when buying, at best, exclusively on the results of a short listening, at worst price.
It's time to spin, the article and so it turned out excessively long!
The conversation on the quality assessment and the causes of the distortion of low frequency amplifiers we will continue in the next article. Armed with the minimum luggage of knowledge, you can move to such interesting topics as intermodulation distortions and their connection with the depth of feedback!
In conclusion, I would like to express my sincere thanks to Roman Parpalak Parpalak for his online editor's project with Lateech and Marcdaun. Without this tool, and so difficult work on the introduction of mathematical formulas in the text would be in the truth of hell.
The coefficient of harmonic distortion (THD).
The beep consists of a plurality of frequencies and halftone. Harmonica is a halftone of the initial note (main frequency), which is responsible for the nature of the sound of notes. A beep can be represented as a complex combination of oscillations of precisely interconnected sinusoidal waves (harmonics).
During the amplification process, passing through various amplifier blocks, the beep is distorted, "fines" by unnecessary harmonics. The increased number of harmonics in the enhanced signal, expressed as a percentage, and there is a harmonic distortion coefficient (Total Harmonic Distorsion). The amplifier specification indicates several harmonics coefficients for different frequency ranges, output power levels and load resistance. The smaller this coefficient, the higher the quality of the amplifier.
The TD TD value for Hi-Fi amplifier is 0.1%. However, already noted, the amplifier with THD 0.001% may be worse than the sound than the other, with THD 0.1%. The fact is that with such small values \u200b\u200bof this parameter, the distortion is difficult to trace in the form of an output signal or feel hearing. Therefore, the difference between 0.1% and 0.001% will not hear.
The coefficient of nonlinear distortion (books) or Total Harmonic distorsions (THD) is an indicator that characterizes the difference in the form of a signal from sinusoidal, one can also say this is the value for a quantitative estimate of nonlinear distortions of the periodic signal.
The Russian term "distortion coefficient" is equivalent to a foreign term "distorted power factor". It can also be expressed through THD as shown below:
2) Nonlinear Distortion Coefficient (KOB) - The value for a quantitative estimate of nonlinear distortions equal to the ratio of the mean square sum of all higher spectral components of the signal, to the mean-square sum of the spectral components of the entire signal (except for the constant component), is sometimes used non-standard synonym - a clearing (limits. With it.). The book is a dimensionless value, it is usually expressed in percent.
The harmonic coefficient (kg) is as well as the books express in percent. The harmonic coefficient (KG) is associated with KOB (KN) by the ratio:
 |
Important note:
It should be recognized that this terminology has long been "correct" for Russian-speaking, German-speaking literature, as well as these definitions continue to be used in some network analyzers, but in connection with the predominance of reverse terminology in most modern equipment (network analyzers, UPS, stabilizers, proofreaders Power factor, etc.) It is recommended that the terms of the terms presented at the very beginning are recommended.
This terminology cannot be recognized incorrect, but the data and technical specifications of the N-POWER equipment are indicated in accordance with European and international terminology, therefore, the use of terms given at the very beginning.
Russian standard. Nonlinear distortion coefficient (books) and quality of network power supply (GOST 13109-97)
Below are shutters from GOST 13109-97:
Calculate the value of the coefficient of distortion of the sinusoidality of the voltage curve of the CT in percent as the result of the I-th observation by the formula:
Note:
The relative error of determining the QUI using formula (B.16) instead of formula (B.15) is numerically equal to the value of the voltage deviation U (1) I from the UAn.
The formula given in this GUTE first (B.15) corresponds to the international definition of the term of the book / THD (see the beginning of the article, see the EN 62040-3 standard).
European Network Power Quality Standard (EN 62040-3), and Nonlinear Current Distortion Coefficient
The coefficient of non-linear distortion in the current in% is identical to the basic definition of the KNS, defined in the EN 62040-3 standard and is calculated as the percentage of the average mean values \u200b\u200bof higher harmonics to the base (first) harmonic. See the attached formula.
F.E. Evdokimov. Theoretical foundations of electrical engineering M., Academy 2004 PR. 262.
G.I. Atabekov. Basics of chains theory p.176, p. 434
Fluke 435 Network Analyzer. User Manual
Directory for radio-electronic devices. In 2 tons. Ed. D. P. Linde - M.: Energy, 1978
Gorokhov P. K. Explanatory dictionary on electronics. The main terms - M: Rus. Yaz., 1993
Nonlinear distortion coefficient: http://ru.wikipedia.org/
Total Harmonic Distortion: http://en.wikipedia.org/wiki/total_harmonic_distortion
Total Harmonic Distortion: http://de.wikipedia.org/wiki/THDI http://de.wikipedia.org/wiki/total_harmonic_distortion
P.Shpriceite. Reference guide on sound circuit engineering 3.1.1. Moscow World 1991.
Metage analyzer DMK62 Lovato. User's manual:
GOST 8.331-99 GSI. Garmonic coefficient meters. Methods and means of calibration and calibration.
Hioki3197 network analyzer. User's manual
Modern international designations of the book (THD)
The following terms repeat the definitions presented above.
I.
Supplement1
Note: There are other definitions of books (THD) for example, they are not used in power electrical engineering:
I THD
II THD + N
THD + N denotes common distortion plus noise.
Supplement2.
Attention!
In order to avoid confusion, the terms previously used in Russian-language textbooks on radio / electrical engineering are shown below.
These terms can be used now in radio engineering, but in power electrical engineering in order to avoid confusion, the use of international terms above is recommended.
In Russian-language literature, the designations and terms were previously adopted:
I.
Nonlinear distortion coefficient (books)
or distortion coefficient (s)
or harmonic signal distortion coefficient
it is equal to the ratio of the current value of the main (first) harmonic to the current value of the entire signal (the entire function).
d \u003d book \u003d book \u003d a1 / a \u003d i1 / i
For sinusoids D \u003d 1, for a triangular signal D ~ \u003d 0.99, for straight. Signal d \u003d 0.9.
Additional Information:
II.
The coefficient of nonlinear distortion (books) is the value for a quantitative estimate of nonlinear distortions equal to the ratio of the mean square sum of all higher spectral components of the signal, to the mean square sum of the spectral components of the entire signal (except for the constant component), sometimes non-standard synonym is used - a cleaner (limits. With it.) . The book is a dimensionless value, it is usually expressed in percent.
The harmonic distortion coefficient is a value that expresses the degree of nonlinear distortion of the device (amplifier, etc.) equal to the ratio of the standard voltage of the sum of higher harmonics of the signal to the voltage of the first harmonic when exposed to the input of the sinusoidal signal.
The harmonic coefficient as well as the book is expressed as a percentage. The harmonic coefficient (KG) is associated with KOB (KN) by the ratio:
Note 1: It should be recognized that this terminology has been "correct" for Russian-speaking, German-language literature for a long time, as well as these definitions continue to be used in some network analyzers, but due to the predominance of reverse terminology in most modern equipment (network analyzers, UPS, stabilizers , Coeffer Correctors. Power, etc.) It is recommended to use terms of the terms at the very beginning.
This terminology cannot be recognized incorrect, but the data and technical specifications of the N-POWER equipment are indicated in accordance with European and international terminology, therefore it is recommended to use terms of the above.
Of the definitions given in GOST, it is clear that the second formula corresponds to the definition of the books (despite the fact that the term of the company is absent).
F.E. Evdokimov Theoretical foundations of electrical engineering M., Academy 2004 C.262.
G.I. Atabekov Basics of chains theory C.176, 434С.
Network Analyzer Fluke 435 User Manual
Radio electronic devices handbook: in 2 tons; Ed. D. P. Linde - M.: Energy, 1978
Gorokhov P. K. Explanatory dictionary on electronics. The main terms - M: Rus. Yaz., 1993
http://ru.wikipedia.org/ Nonlinear Distortion Coefficient
http://en.wikipedia.org/wiki/Total_harmonic_Distorion.
http://de.wikipedia.org/wiki/THDI http://de.wikipedia.org/wiki/total_harmonic_distortion
P.Shprittek Reference Guide for Soundless Engineering 3.1.1, Moscow World 1991
Metage Analyzer DMK62 Lovato User Guide.
http://www.lovatoeelectric.com/ricerca/italiano/03_istruzioni/i104igbfe04_08.pdf.
GOST 8.331-99 GSI. Garmonic coefficient meters. Methods and means of calibration and calibration
GOST 8.110-97 GSI. State calibration scheme for means of measuring the harmonic coefficient
GOST 13109-97
Hioki3197 Network Analyzer User Manual
With comments on the content of this section, please contact :.
Alexander.
Siel has configured that everything is right with THD
You can entirely text in the article to include + this standard too.
Daniel A.
________________________________________
From: Mazza Angelo
Sent: Wednesday, December 21, 2011 7:33 pm
To: Daniil A.
CC: "Oleg Sergeev"; Matoshi Gladiola; Pensini Glauco.
Subject: R: Safepower EVO INPUT THD // L2
Dear Mr. Daniil,
tHE VALUE THDI%, INDICATED IN THE MANUAL, IS THE DISTORTION OF TOTAL HARMONIC DISTORTION AND EXACTLY EQUAL TO THE DISTORTION AND EXACTLY EQUAL TO THE DISTORITION EXPRESSED by UPS Statement of EN 62040-3, Which Defines It As The Percentage Ratio of the RMS Value of the Harmonic Content and The RMS Value of The Fundamental Component (First Harmonic) Which Expressed by The Following Relationship:
The Values \u200b\u200bi1, i2, i3, ect ... .are RMS Values.