Complete Wireless Design
If you want to climb the learning curve with grace, and start designing what you need immediately, this easy-to-understand guide will help you design an entire radio system from the ground up.
TABLE OF CONTENTS Complete Wireless Design
3.7: Audio Amplifiers
3.7 Audio Amplifiers
3.7.1 Introduction
Many nonpower audio amplifier stages need not be matched to their source nor to their load. Since matching is used to maximize power transfer between stages and to reduce standing waves, audio amplifiers are much more concerned with reducing distortions and isolating each stage from the effects of the next. However, matching with low-frequency transformers is quite common with discrete audio power stages in order to obtain high efficiencies, while RC matching is also employed in audio voltage amplifiers. An acceptable single-stage audio voltage amplifier can be designed by using the low frequency bias design formulas as presented in Sec. 3.3, Amplifier Biasing.
Operational amplifiers are far more common for voice-frequency amplification for both low-level voltage signals and high-level power signals. They can be acquired from many manufacturers, and are obtainable in an optimized single-voltage supply package for ease of biasing.
3.7.2 Design of an IC audio amplifier
The National LM386 is a low-voltage audio amplifier that is perfect for low-frequency amplification. In voiceband radios this IC can amplify the audio signal all the way from the detector stage to the 8-ohm speaker or headphones. The National device has very low quiescent current drain (4 mA), accepts a wide range of V cc (4 to 12 V), has adjustable voltage gain (20 to 200), decent distortion levels [<10 percent total harmonic distortion (THD)], and has an output driving power of 700 mW with a 9-V supply into 8 ohms.
To design an audio...
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