Design Project: Audio Power Amplifier

Discrete Semiconductor Devices and Circuits

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  • Question 1

    Explain how the microphone in your amplifier works. How, exactly, does it convert waves of air pressure (sound) into electrical signals?

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  • Question 2

    Your amplifier design will almost certainly require more than one stage of transistors to properly match the impedance of the microphone to that of the loudspeaker. Identify the topology of each transistor stage (common-emitter, common-collector, common-base, etc.), and explain what the primary form of gain for each stage is (voltage gain, or current gain).

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  • Question 3

    While Class A amplifier circuits are simpler to design and build, they are rarely used for high-power applications. Why is this? Why are Class B amplifier designs much more popular for high-power applications? Would it be practical for you to build a microphone amplifier such as this using nothing but Class A circuitry?

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  • Question 4

    Explain how you plan to test for and eliminate (if necessary) any crossover distortion from your amplifier circuit. Do you suspect crossover distortion will be more noticeable at low volume levels or high volume levels? Explain why.

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  • Question 5

    Sound pressure is often measured in units of dBA. You should be familiar with decibels as a unit of amplifier gain, but what does “dbA” actually mean? How is 0 dBA objectively defined?

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