Papers by Albert Jônatas Veras
CHAPTER 1. Circuit Variables P 1.24 [a] v(10 ms) = 400e -1 sin 2 = 133.8 V i(10 ms) = 5e -1 sin 2... more CHAPTER 1. Circuit Variables P 1.24 [a] v(10 ms) = 400e -1 sin 2 = 133.8 V i(10 ms) = 5e -1 sin 2 = 1.67 A p(10 ms) = vi = 223.80 W
Todos os direitos reservados. É proibida a reprodução desta obra usando quaisquer meios, impresso... more Todos os direitos reservados. É proibida a reprodução desta obra usando quaisquer meios, impresso ou digital, sem a expressa permissão do autor. Quando não creditadas, fotos e ilustrações de autoria própria.
The phase linearity and electrical stability of the circuit, with any likely reactive load, shoul... more The phase linearity and electrical stability of the circuit, with any likely reactive load, should be adequate to ensure that there is no significant alteration of the form of a transient or discontinuous waveform such as a fast square or rectangular wave, provided that this would not constitute an output or input overload. There should be no tinging (superimposed spurious oscillation) and, ideally, there should also be no waveform overshoot, under square-wave testing, in which the signal should recover to the undistorted voltage level, +0.5%, within a settling time of 20~ts. 9 The output power delivered by the circuit into a typical load-beating in mind that this may be either higher or lower than the nominal impedance at certain parts of the audio spectrum-must be adequate for the purpose required. 9 If the circuit is driven into overload conditions, it must remain stable, the clipped waveform should be clean and free from instability, and should recover to the normal signal waveform level with the least possible delay-certainly less than 20~ts. In addition to these purely electrical specifications, which would probably be difficult to meet, even in a very high quality solid state design-and most unlikely to be satisfied in any transformer coupled system-there are a number of purely practical considerations, such as that the equipment should be efficient in its use of electrical power, that its heat dissipation should not present problems in housing the equipment, and that the design should be cost-effective, compact and reliable. Since it is improbable that all these performance requirements will be met, in any practical design, it is implicit that the designer will have made certain performance compromises, in which better performance in certain respects has been traded off against a lesser degree of excellence in others. For myself, I think that the total harmonic or intermodulation distortion, which is frequently specified in the makers data sheets, is less important in determining the tonal quality of the system, provided that it is better than 0.05%, than its behaviour under transient conditions, when tested with typical (or accurately simulated) reactive loads, performance in which is seldom or never quoted. Where appropriate, in the following text, I will try to show where various benefits are obtained at the cost of some other potential drawbacks. JLH 1996. This Page Intentionally Left Blank CHAPTER 1 Electronic amplifiers are built up from combinations of active and passive components. The active ones are those, like valves or transistors or integrated circuits, that draw electrical current from suitable voltage supply lines and then use it to generate or modify some electrical signal. The passive components are those, like capacitors, resistors, inductors, potentiometers or switches, which introduce no additional energy into the circuit, but which act upon the input or output voltages and currents of the active devices in order to control the way they operate. Of these, the active components are much more fun, so I will start with these. Although the bulk of modem electronic circuitry is based on 'solid state' components, for very good engineering reasons -one could not, for example, build a compact disc player using valves, and still have room in one's house to sit down and listen to it-all the early audio amplifiers were based on valves, and it is useful to know how these worked, and what the design problems and circuit options were, in order to get a better understanding of the technology. Also, there is still an interest on the part of some 'Hi-Fi' enthusiasts in the construction and use of valve operated audio amplifiers, and additional information on valve based circuitry may be welcomed by them. The term thermionic valve (or valve for short) was given, by its inventor, Sir Ambrose Fleming, to the earliest of these devices, a rectifying diode. Fleming chose the name because of the similarity of its action, in allowing only a one-way flow of current, to that of a one-way air valve on an inflatable tyre, and the way it operated was by controlling the intemal flow of thermally generated electrons, which he called 'thermions', hence the term thermionic valve. In the USA they are called 'vacuum tubes'. These devices consist of a heated cathode, mounted, in vacuum, inside a sealed glass or metal tube. Other electrodes, such as anodes or grids are then arranged around the cathode, so that various different functions can be performed. The descriptive names given to the various types of valve are based on the number of its internal electrodes, so that a valve with two electrodes (a cathode and an anode) will be called a 'diode', one with three electrodes (a cathode, a grid and an anode) will be called a 'triode', one with four (a cathode, two grids and an anode) will be called a 'tetrode', and so on. Williamson gave, though, in the UK, many of the commercial designers judged that 12 watts would be adequate for all normal domestic purposes.
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Papers by Albert Jônatas Veras