Thermal distortion in HiFi 2 amplifiers. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Thermal distortion in HiFi amplifiers. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

Comments on the article

When the development of HiFi amplifiers began several decades ago, electronics as a science was still very poorly developed. However, despite this, the results were very good (to date). Over the past 30 ... 40 years, light has been shed on many more or less significant issues, but the results of this development have in no way (or almost nothing) affected HiFi technology.

Readers interested in this area observe with great amazement that there is no progress in HiFi technology, and on the contrary, sometimes retreats are observed (for example, digital, TV with its specific sound quality). Several decades have passed since the first landing on the moon, and sound engineering still remains somewhere in the era of "horse-carriages".

Let's get acquainted with such physical phenomena, which are rarely discussed even in the specialized HiFi literature. And meanwhile, in reality, this is the very "Columbus egg" ...

Preamplifiers, HiFi power amplifiers and other audio devices are known to be double-checked. On the one hand, specialists in electronics and acoustics subject any device to strict control using measuring instruments, both in the process of assembling it and in assembled form. On the other hand, each amplifier is also characterized by people with good hearing - not necessarily specialists (for example, they can be musicians or music lovers). Listening to the sound of music without any devices, they attribute the amplifier to one class or another.

The peculiarity of the emerging situation is that in practice the results of these two checks very often contradict each other. It happens that despite good measurement results, the sound quality does not seem very good to the ear, and vice versa. For example, several decades ago, the author built his first HiFi semiconductor amplifier, which had very good characteristics obtained using the measurement methods that existed at that time. But the amplifier had such a killer "fresh" sound that it was a pity for the time and work spent, and I enjoyed the beautiful sound of the vacuum tube amplifier for a long time afterwards.

Over the past years, more and more electrical testing procedures have been developed by specialists, amplifiers with ever higher electrical characteristics are being born, and the sound quality, as determined by listening, still leaves much to be desired.

Specialists (now even non-professionals) are especially annoyed by the fact that a device classified in terms of electrical characteristics to a high class, when used as an amplifier, gives an unpleasant (sometimes unbearable) sound. Many of my friends who are passionate about electronics and familiar with HiFi, after lively discussions, began feverishly redesigning measuring instruments, developing new ones, inventing ingenious ways of measuring, spending months on it and then getting angry that all this does not lead to truly convincing results. Electrical characteristics and listening scores very rarely correlate with each other.

The fact that somewhere between known things some "muck" might be hidden, the author first noticed when, having modified the method of measuring intermodulation distortion using two signals, he applied (purely by chance) a third one (which turned out to be at hand - a slow signal with a frequency of about 0,1 Hz, approximately triangular in shape). The result, controlled by an oscilloscope, turned out to be very peculiar. Until now, the amplifier, which had passed the "exam" quite well, now at certain points in time began to introduce various gross distortions, undoubtedly associated with the presence of a third signal. And at the same time, the amplifier was undoubtedly in nominal mode during the test, well below the overload limit. The nature of the distortions was rather bizarre and capricious: at some moments of time they looked like an "amplitude cutoff", giving either the second or the third harmonic. Using an oscilloscope to observe the entire "repertoire" was difficult, it was impossible to accurately assess these distortions. and it was not clear what to do with "it". When the frequency of the slow signal in the infrasound range changed, the nature and magnitude of the distortion changed somewhat. An amplifier of another type, which immediately, "in hot pursuit", was "subjected to the same tests, similar distortion was less. Despite fairly good measurement results (spectrum analysis showed less than 6,1% harmonic distortion), both Amplifiers were perceived equally poorly by ear.

The author has long classified amplifiers as devices "dangerous for the nervous system." And the whole series of measurements was taken due to the fact that the standard measured parameters looked stereotyped and annoyingly beautiful, which cannot be said about the listening results. All this seemed illogical and incomprehensible. Since it was not possible to evaluate the detected distortions, the measurements were interrupted, although during the discussion of the problem with acquaintances, some excellent hypotheses were successfully tested. And only a few years later the problem accidentally found its solution.

You need to proceed from the fact that most electrical methods of measurement and listening differ from each other in one seemingly insignificant, but very important point. How are measurements taken? We first apply signals from some generator to the input of the amplifier and only then control the output signal. The whole measurement method itself is a stationary process: the signal has been in the amplifier for quite some time before being subjected to Fine Analysis. The measurement process is quite long (for example, it takes several seconds or even minutes), and its results refer to the steady state and characterize the continuous presence of a standard, well-defined measuring signal at the input.

What happens when listening, and what is the difference here? The musical input produced, for example, by a violinist chaotically plucking a bow across the strings of a violin, or a guitarist plucking the strings of a guitar ferociously, or a drummer pounding a drum frantically, or an inspired singer singing, can be anything but standard. signal at 1 kHz. It (the input signal) varies pseudo-randomly in amplitude, frequency, spectral composition and stereo characteristics. And the ears and the brain perfectly analyze the acoustic quality of such a signal and infallibly evaluate the impressions of additional sound signals that appeared in addition to (instead of) the original sound melody. which, although somehow connected with this music, has nothing to do with it.

All sound transmission systems introduce certain distortions. And this applies not only to any "noisy" music with its wide range, but also to narrow-band speech, for example, to any lecture, in a "wooden" language. The main question is how to measure these distortions and how to classify amplifiers. The experience of past years shows that the control carried out so far was not correct enough and did not provide a reliable foothold for such a classification.

In industrial electronics (measuring technology, automatic regulation and control technology, instrumentation), professionals have accumulated a huge number of observations, developed and widely used measurement methods that (due to their high cost and highly specialized nature) can be mastered and used only by a small group of specialists . If it were possible to invest the same amount of money and intellectual energy in the development of HiFi technology, then, without a doubt, we would not be where we are now.

What has not yet been sufficiently controlled by specialists in acoustics and electronics is the rather rapid thermal changes in regimes and the sometimes very significant transient distortions caused by them. These distortions are not detected by any of the currently existing measurement methods, since, in essence, they are all stationary. These distortions could only be captured with a dynamic test signal and a fast distortion meter (spectrum analyzer).

Most readers, of course, know that when the external temperature and the temperature of the semiconductor crystal change, the entire set of parameters of the semiconductor changes: Therefore, it is hardly possible to obtain an improvement in sound engineering parameters without taking into account thermal processes. And all this is so simple that, probably, that is why it has been overlooked until now.

Author: S.GYULA; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Transistor power amplifiers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

Topological insulators - the basis of lasers 15.02.2018

Researchers from Israel and the United States have worked out the concept of a laser, which includes analogues of topological insulators. These materials conduct electrons in only one direction, which makes transmission through them resistant to interference. For lasers, it was proposed to use similar structures that conduct photons. Calculations show that the energy efficiency of lasers with topological insulators will be several times higher than that of lasers based on "old" principles.

The surface of topological insulators is a very thin layer of highly conductive materials, and their core is made of dielectrics. They are two-dimensional and three-dimensional. For the laser model proposed by the authors of the articles under discussion, two-dimensional insulators were used, each of which consisted of a network of interlaced rings. Only the outer rings are conductive. If one or more of these rings fails, the flow of particles in the desired direction will not stop, and interference will not appear. Thanks to this, additional energy losses for conducting the beam can be avoided. And this means that less energy is required to supply beams of the same power to a laser based on topological insulators.

Another feature of lasers using the principle of topological insulators is that they do not need electromagnetic fields to work. This removes a number of restrictions on the use of such devices. And experiments with a prototype of a new type of laser confirmed the theoretical assumptions. The energy pumped into the outer row of rings of the topological insulator passed unidirectionally in the form of photons around the entire perimeter of this insulator and exited from another point in the form of a light beam.

The described lasers can be used in optics, as well as quantum networks. In addition, with their help, it is likely that it will be possible to create faster and more reliable electronics.

Other interesting news:

▪ Ultra high speed liquid crystals

▪ Nanowires three atoms in diameter

▪ The distance of ultrashort flashes of light is calculated

▪ Helicopter to search for submarines

▪ rice gel

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site House, household plots, hobbies. Article selection

▪ article Theory of chemical structure. History and essence of scientific discovery

▪ article When did man start domesticating animals? Detailed answer

▪ article Peanut. Legends, cultivation, methods of application