Amplifier Essay Example

Amplifier Essay Example Amplifier Essay Amplifier Essay Class A amplifiers amplify over the whole of the input cycle such that the output signal is an exact scaled-up replica of the input with no clipping. Class A amplifiers are the usual means of implementing small-signal amplifiers. They are not very efficient - a theoretical maximum of 50% is obtainable, but for small signals, this waste of power is still extremely small, and can be easily tolerated. Only when we need to create output powers with appreciable levels of voltage and current does Class A become problematic. In a Class A circuit, the amplifying element is biased such that the device is always conducting to some extent, and is operated over the most linear portion of its characteristic curve (known as its transfer characteristic or transconductance curve). Because the device is always conducting, even if there is no input at all, power is wasted. This is the reason for its inefficiency If high output powers are needed from a Class A circuit, the power wastage will become significant. For every watt delivered to the load, the amplifier itself will, at best, waste another watt. For large powers this will call for a large power supply and large heat sink to carry away the waste heat. Class A designs have largely been superseded for audio power amplifiers, though some audiophiles believe that Class A gives the best sound quality, due to it being operated in as linear a manner as possible. In addition, some aficionados prefer thermionic valve (or tube) designs over transistors, for a number of reasons: Tubes are more commonly used in class A designs, which have an asymmetrical transfer function. This means that distortion of a sine wave creates both odd- and even-numbered harmonics. They claim that this sounds more musical than the purely odd harmonics produced by a symmetrical push-pull amplifier. Though good amplifier design can avoid inducing any harmonic patterns in a sound reproduction system, the differences in harmonic content are essential to the sound of intentional electric guitar distortion. Another is that valves use many more electrons at once than a transistor, and so statistical effects lead to a smoother approximation of the true waveform - see shot noise for more on this. Field-effect transistors have similar characteristics to valves, so these are found more often in high quality amplifiers than bipolar transistors. Historically, valve amplifiers often used a Class A power amplifier simply because valves are large and expensive; Many Class A design uses only a single device. Transistors are much cheaper,

Definition of Boycott

Definition of Boycott The word boycott entered the English language because of a dispute between a man named Boycott and the Irish Land League in 1880. Where Boycott Got Its Name Captain Charles Boycott was a British Army veteran who worked as a landlords agent, a man whose job was to collect rents from tenant farmers on an estate in northwest Ireland. At the time, landlords, many of whom were British, were exploiting Irish tenant farmers. As part of a protest, the farmers on the estate where Boycott worked demanded a reduction in their rents. Boycott refused their demands and evicted some tenants. The Irish Land League advocated that people in the area not attack Boycott, but rather use a new tactic: refuse to do business with him at all. This new form of protest was effective, as Boycott wasnt able to get workers to harvest crops. By the end of 1880 newspapers in Britain began using the word. A front-page article in the New York Times on December 6, 1880, referred to the affair of Capt. Boycott and used the term boycottism to describe tactics of the Irish Land League. Research in American newspapers indicates that the word crossed the ocean during the 1880s. In the late 1880s boycotts in America were being referred to in the pages of the New York Times. The word was generally used to denote labor actions against businesses. For example, the Pullman Strike of 1894 became a national crisis when a boycott of railroads brought the nations rail system to a halt. Captain Boycott died in 1897, and an article in the New York Times on June 22, 1897, noted how his name had become a common word: Capt. Boycott became famous through the application of his name to the relentless social and business ostracism first practiced by the Irish peasantry against the detested representatives of landlordism in Ireland. Although a descendant of an old Essex County family in England, Capt. Boycott was an Irishman by birth. He made his appearance in County Mayo in 1863 and according to James Redpath, he had not lived there five years before he won the reputation of being the worst land agent in that section of the country. The 1897 newspaper article also provided an account of the tactic that would take his name. It described how Charles Stewart Parnell  proposed  a plan to ostracize land agents during a speech in Ennis, Ireland, in 1880. And it described in detail how the tactic was utilized against Captain Boycott: When the Captain sent for the tenantry on the estates for which he was agent to cut the oats, the whole neighborhood combined in a refusal to work for him. Boycotts herdsmen and drivers were sought out and persuaded to strike, his female servants were induced to leave him, and his wife and children were obliged to do all of the house and farm work themselves. Meanwhile his oats and corn remained standing, and his stock would have been unfed had he not exerted himself night and day to attend to their wants. Next the village butcher and grocer declined to sell provisions to Capt. Boycott or his family, and when he sent to neighboring towns for supplies he found it absolutely impossible to get anything. There was no fuel in the house, and nobody would cut turf or carry coal for the Captains family. He had to tear up floors for firewood. Boycotting Today The tactic of boycotting was adapted to other social movements in the 20th century. One of the most significant protest movements in American history, the Montgomery Bus Boycott, demonstrated the power of the tactic. To protest segregation on city buses, African American residents of Montgomery, Alabama, refused to patronize the buses for more than 300 days from late 1955 to late 1956. The bus boycott inspired the Civil Rights Movement of the 1960s and changed the course of American history. Over time the word has become quite common, and its connection to Ireland and the land agitation of the late 19th century has been generally forgotten.