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Design Project: Audio Power Amplifier
5 questions By Tony R. Kuphaldt
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Question 1 of 5
Explain how the microphone in your amplifier works. How, exactly, does it convert waves of air pressure (sound) into electrical signals?
Reveal answerThe answer to this question depends on what type of microphone you use:
- Condenser: variable capacitance
- Dynamic: electromagnetic induction
- Crystal: piezoelectricity
Notes:Microphones are important devices in the world of electronics, and students are likely to appreciate their function more when building a project that uses one.
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Question 2 of 5
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).
Reveal answerThe answer to this question, of course, will vary with your particular design of circuit.
Notes:A project such as this really brings to life the concepts of gain, and why different transistor amplifier configurations are necessary to achieve different types of gains.
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Question 3 of 5
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?
Reveal answerClass A amplifiers are much less efficient than Class B amplifiers: a great deal more of the electrical power energizing the circuit gets wasted in the form of heat.
Notes:Discuss with your students the practicality of a Class A audio power amplifier for the scope of this project. Just because I made Class B circuitry a requirement of this project does not mean a Class A amplifier design would be completely impractical. One of my goals in writing this design project was to get students experienced with Class B push-pull circuits, which are more challenging to design and build than Class A.
