Question

Problem 1 Hi-fi audio amplifiers are usually built as discrete difference amplifiers with a rel atively large gain (near 55dB or more) and with built-in feedback that reduces the closed-loop gain to a much smaller value in the range of 30-35dB. Since loudspeakers predominantly act like a resistor (nominal impedance: 42) with an inductor in series, the feedback network can also be used to improve the frequency response in the audio range up to 20 kHz. In this problem, we are primarily con- cerned with gain and frequency response of the amplifier Vour(s) Feedback Speaker Gra(s) Discreto operational V(s) Gra(s) Vals Figure I: Simplified schematic (A) and block diagram representation (B) of a hi-fi ampli- fier output stage with feedback network and loudspeaker impedance. The magnetic force that drives the membrane is proportional to the coil current Is and the coil current is therefore the output variable that we are interested in A. One of the key features of amplifiers with feedback is that the gain is dominated by the extemal feedback nctwork, which allows larger variations of the inter- nal gain g. Presently, the feedback network is a 1:32 resistor divider with the

Answer 1

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