Answer 2—The common-base configuration provides unity-current gain in addition to a large amount of voltage gain. Because the speaker is a low-impedance source, it operates at relatively high currents and low voltages. This arrangement of the transistor acts to impose the AC current of the speaker across the much larger load resistor connected to the collector, providing voltage gain equal to the ratio of the impedances.

Contributor: David Tweed

Published October 2003