📄 power_amplifier_60w_class_a_eng.htm
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</big><em><font face="Arial">Power amplifier <a name="60">60</a>W Class A </font></em><big>
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<td width="100%"><font FACE="Verdana" SIZE="2"><p ALIGN="JUSTIFY"><font color="#800000">There
is one amplifier configuration that is universally accepted as the ideal for audio use:
Class A operation . Many early amplifiers operated in Class A, but as output powers rose
above 10W the problems of heat dissipation and power supply design caused most
manufacturers to turn to the simpler, more efficient Class B arrangements and to put up
with the resulting drop in perceived output quality. <u>Why Class A ?</u> Because , when
biased to class A, the transistors are always turned on, always ready to respond
instantaneously to an input signal. Class B and Class AB output stages require a
microsecond or more to turn on. The Class A operation permits cleaner operation under the
high-current slewing conditions that occur when transient audio signal are fed difficult
loads. His amplifier is basically simple, as can be seen from the block diagram </font>[<a
href="#60">Fig.1</a>]. </font></td>
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<td width="100%"><font FACE="Verdana" SIZE="2"><p ALIGN="JUSTIFY"><font color="#800000">The
simplified circuit [<a href="#60">Fig.2</a>] shows that each sub-<a name="amplifier">amplifier</a>
consists of two voltage gain stages. The first stage consists of a complementary
two杝tage common emitter [Q1-7] whose gain is about x2.3. The second stage is a current
mirror stage [Q13-14] which drives the voltage across a load resistor tied to 0V. the gain
of this stage is about x200. Thus the overall open loop voltage gain is of the order of
x460 and so, as the closed loop gain is x26.7, the reduction due to negative feedback is
x17.2 or about 24db. The input amplifiers are powered from <font FACE="Symbol">⌨️ 快捷键说明
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