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Design Project: Audio Power Amplifier
5 questions By Tony R. Kuphaldt
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Question 4 of 5
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.
Reveal answerCrossover distortion is detected by using an oscilloscope to display the output waveform, and is eliminated through proper biasing of the push-pull transistor pair. This type of distortion is generally more noticeable at low volume levels, but I’ll let you explain exactly why!
Notes:Crossover distortion is the bane of Class B amplifier designs, and may be frustrating for the beginning electronics student to successfully eliminate without causing other problems (such as transistor overheating from excessive Class AB biasing).
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Question 5 of 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?
Reveal answer0 dBA = 1 pW/m2 ≈ “Threshold of human hearing”
Notes:Discuss with your students how decibels are an appropriate way to express sound intensity, due to the very nonlinear sensitivity of human hearing. In fact, the very genesis of the decibel scale was early telephone system design, where engineers had to rate signal loss in terms that were meaningful to human users.
