An integrated telephone speech circuit including a line fed loudspeaker amplifier

Abstract

A new electronic speech circuit is described which replaces carbon microphone, hybrid transducer, sidetone network and click suppressor of the conventional telephone set. A low cost dynamic transducer is used instead of microphone and earphone. A low cost loudspeaker may also be used. The circuit is fed from DC line current by a special current source and contains a loudspeaker amplifier, other necessary amplifiers, a circuit for compensating line attenuation dependent on DC line current, and a stabilized DC voltage source, from which almost the whole DC line current may be drawn for other circuits too. Tone quality has been considerably improved in comparison with conventional telephone sets.