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Class D transistor amplifiers

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Category: Radioamator i Krótkofalowiec
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Class D transistor amplifiers

Radio amateur and short wave amateur 1971/03
Wojciech Czerwiński

Jerzy Kwaśniewski

Pulse circuits with transistors switched from cut-off to saturation have found wide application in digital and automatic control technology, among others due to their high efficiency. The search for a way to increase the efficiency of transistor acoustic amplifiers has led to an application for amplifying low frequency signals switching amplifiers working in class D. Such amplifiers show efficiency of 90%, unattainable in conventional systems of class A, B or C.

Principle of operation

Let us briefly consider the principle of amplifying harmonic signals in pulse amplifiers. Class D work is a type of amplifying element operation in which the element in the working cycle is only in two states: complete blocking when no current flows through it, or complete unblocking when the voltage drop on it is close to zero. If a current flows through the resistor in the form of rectangular pulses shown in Figure 1, then the average value of the current Io marked with a dashed line may be equal to zero (Figure 1a), greater than zero (Figure 1b) or less than zero (Figure 1c) . The ratio of the pulse duration to the repetition period is called the duty cycle γ.

For the waveforms in Figure 1, the γ factor is respectively: γ = 0.5, γ> 0.5 and γ <0.5. If the change of γ from the maximum to the minimum value is carried out according to the function e.g. sin (ωt), then in such a series of pulses the average value of the pulses will be the low frequency harmonic component sin (ωt).


Fig. 1. Rectangular waveforms with different fill factors.

Otherwise, the stage operating in the impulse system can amplify the low frequency vibrations, if we apply a pulse train in which the positive half-period of the low frequency signal is the pulses with the value of γ> 0.5 correspond to the negative half-period, and the pulses with the value of γ <0.5 correspond to the negative half-period (Fig. 2). We are dealing here with pulse width modulation. It goes without saying that the pulse repetition frequency should be much greater than the highest frequency of the amplified low frequency waveform.

 
Fig. 2. Pulse width modulation with a sine wave>
a - modulating waveform, b - impulse modulated waveform.

Pulse width modulation can be implemented by various methods. The simplest way is shown in Fig. 3. The triangular voltage is compared with the sinusoidal voltage representing the low frequency signal. Square-shaped pulses appear at the modulator output, the length of which depends on the amplitude of the amplified signal. The triangle waveform can be obtained from square pulses using a Miller integrator.

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Radioelektronik (Radioelectronics) 1990/12

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Category: Radioelektronik
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Radioelectronics, December 1990, volume XLI (139)

FROM THE COUNTRY AND FROM THE WORLD (cover page 2)

  • PHILIPS FSB260 and FSB290 hi-fi sets.
    These new, uniform-looking audio sets (photo shown on cover) are intended for a wide range of middle-income buyers. Both types of sets are equipped with remote control systems, have identical turntables and CDs, but some differences exist in other parts of the sets.
  • Handy, amateur mixer - tape recorder.
    The Japanese company Fostex offers a new mixer - X-15-II cassette deck. The device has external dimensions of 75 x 290 x 195 mm (with a plug-in battery: 75 x 290 x 195 mm) and a weight of 2.9 kg (with battery). A standard C-60 or C-90 cassette is used to make a 4-track recording from the four inputs of the device.
  • The easiest installation of optical fibers.
    Early in the development of fiber optics, installing fiber optics was something of a "higher school of gas cooking" - potentially simple, but required special tools and staff preparation. Today, when installing fiber optics in the home and in the car, it had to be kept to a minimum. This is the purpose of the twisted fiber optic connector.

  • Telephones for the cellular network.
    The cellular telephone network in developed countries has been a reality for several years, there is also hope that as a result of giving up the state monopoly, it will appear in our country, at least in the largest urban agglomerations.
  • Cooperation in microprocessors.
    Two European "greats" - Siemens and SGS-Thomson - cooperate in the development, production and sale of 8 and 16 - bit microprocessors. The family of 16-bit microprocessors developed by Siemens is already beginning to appear on the market (the first commercial chip is the 80C116) and, as it turned out, it surpasses everything that was previously available in this class of chips..

ANNOUNCEMENTS (1)

ELECTROACOUSTICS - "Duetto-Stereolith" SPEAKER SYSTEM (2)

The company REVOX, known for its high quality products, offers a stereo loudspeaker system operating in accordance with a new concept. As it is easy to reproduce and gives interesting sound effects, it is worth getting to know it better.
The classic way of stereo reproduction requires the use of two loudspeakers separated by a distance, the so-called base. The optimal stereo listening position is in front of the loudspeakers, symmetrically to them. It has long been noticed that when using loudspeakers with a wide angle of sound or omnidirectional radiating units, the position of the listener in relation to the loudspeakers is less critical, but the stereo image of the sound becomes less accurate, especially in terms of the location of the apparent sound sources.


The Swiss acoustician - Walter Schupbach - proposed a solution consisting in placing the speakers of both channels in one housing in such a way that they radiate in opposite directions, i.e. to the left and to the right of the listener. It turned out that the best results are achieved by a housing with a triangular cross-section (see the drawing), divided by a wall into two parts. This solution can be compared to the radiation of sounds by one source, in principle omnidirectional, but the sounds radiated to the left and right and their reflections differ due to the fact that they correspond to different stereo channels.

DISTORTIONS CAUSED BY ELECTROLYTIC CAPACITORS (2)

When designing electronic circuits, capacitors are considered linear elements. This does not correspond to reality, especially in the case of electrolytic capacitors, which under certain conditions may cause nonlinear distortions. This is the subject of this article.
We know that the capacitance of electrolytic capacitors varies significantly with temperature changes (it decreases rapidly at subzero temperatures) depending on the frequency of the alternating current. The capacity of a good, fully functional and formed electrolytic capacitor changes slightly depending on the value of the DC bias voltage, as shown in the figure.

It follows that in the case of electrolytic aluminum capacitors there is an increase in capacitance with an increase in the polarizing voltage, and in the case of tantalum capacitors - on the contrary, there is a decrease in capacitance.

Read more: Radioelektronik (Radioelectronics) 1990/12

Radio engineering time travel - 1930

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Category: Radio USA
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Radio engineering time travel (1930)

I invite you to look at the "pictures" related to radio technology in 1930. They come from various sources. The gallery has its sister version in Polish and Russian. Versions in other languages will be added successively. More detailed descriptions can be found in other language versions (articles are related and can be displayed by clicking on the icons with flags on the left, top of the TRIODA website). Of course, I will complement translations of signatures quite slowly. All descriptions are displayed using the present tense and not the past - this is not a mistake only deliberate action - a reference to the original descriptions from those years. In order not to delay the possibility of viewing the gallery, this site is made available as a "site under construction" - for which I apologize to all guests. At the beginning and end of each set of photographs there are links allowing to change the period - calendar year.

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Radio engineering time travel

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Category: Radio USA
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Radio engineering time travel (to 1921)

I invite you to look at the "pictures" related to radio technology. They come from various sources. The gallery has its sister version in Polish and Russian. Versions in other languages will be added successively. More detailed descriptions can be found in other language versions (articles are related and can be displayed by clicking on the icons with flags on the left, top of the TRIODA website). Of course, I will complement translations of signatures quite slowly. All descriptions are displayed using the present tense and not the past - this is not a mistake only deliberate action - a reference to the original descriptions from those years. In order not to delay the possibility of viewing the gallery, this site is made available as a "site under construction" - for which I apologize to all guests. At the beginning and end of each set of photographs there are links allowing to change the period - calendar year.

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WAVAC MD-300B

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Category: Photo gallery
Hits: 19116


Grzegorz "gsmok" Makarewicz

Very interesting and exclusive design. I must admit that until the amplifier hit in my arms I do not even realize that any copy of it is located in Poland. And suddenly such a pleasant surprise. I invite you to analyze the photographs showing construction details.

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Tube Amplifier Yaqin MC-100B

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Category: Photo gallery
Hits: 18927


Grzegorz "gsmok" Makarewicz, This email address is being protected from spambots. You need JavaScript enabled to view it.

Yaqin MC-100B is a Chinese stereo tube amplifier. It's original name, which is a registered trademark, has some strange symbols and you can not write it using "traditional" alphabet. Willy-nilly, in this relation I am forced to use the Yaquin name. This approach is justified because even in the manual, strange symbol appears on the cover, but in the inside you can find the name Yaqin MC-100B. The amplifier does not has sophisticated look. The distinctive frame constituting the tubes cover reminds me of a container for storing bread  and willingly I would use this amp with a frame permanently dismantled and hidden in some inaccessible place.

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Tube amplifier WS17 LUNA

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Category: Photo gallery
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Description and photos of details by  Andrzej Żółtowski, photos by  Piotr Stanisz Łódź.
[page was updated on April 3, 2005.] 

At the end of the first half of the sixties a small audio amplifier appeared in small electronics stores. It had an avant-garde for those times appearance and shocking pink colored casing.

This was, produced by Warsaw manufacturer called "ELZA", the "WS17 Luna" amplifier designed for ad-hoc sound reproduction in medium-sized rooms: school auditoriums, smaller churches, small clubs etc.

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Tube amplifier WR75-62 "Ampli75"

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Category: Photo gallery
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Photographs of WR75-62 "Ampli75" amplifier ( PZT Warsaw 1964) made and gave to us Mr Piotr Kowalski This email address is being protected from spambots. You need JavaScript enabled to view it..
The happy owner of an amplifier is Maciej Myga.

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Tube amplifier STA25 Renaissance

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Category: Photo gallery
Hits: 12820


Grzegorz "gsmok" Makarewicz,  This email address is being protected from spambots. You need JavaScript enabled to view it.

I would like to present some photos of a very interesting STA25 Renaissance tube amplifier manufactured by Woodside Electronics. It's basically a modernized version of the amplifier produced by Radford. The main difference relates to the regulation of quiescent current of output tubes. The amplifier is characterized by interesting and controversial design line. Like previous Radford products, it raises big emotions - from admiration to total criticism.

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Tube amplifier PRIBOJ

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Category: Photo gallery
Hits: 21629


Grzegorz "gsmok" Makarewicz, This email address is being protected from spambots. You need JavaScript enabled to view it.

Tube amplifier Priboj (original russian name - Прибой or Breaker in english) is one of the few secondary market tube audio amplifiers manufactured by our neighbors across the eastern border. Like most of devices from that region it has a hopeless design line and poor craftsmanship. The counterweight to these defects is a thoughtful schematic diagram and outstanding sonic performance. In short it is a princess dressed in a beggar's rags.

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