Abstract: An interface circuit is provided for a telephone answering machine which does not require a transformer and which provides the proper direct current and alternating current terminating impedance for the telephone line. The direct current terminating impedance is provided by connecting a resistor of a selected resistance value across the telephone line, and the alternating current terminating impedance is achieved by multiplying the effective impedance of the resistor for alternating current audio signals by providing an amplifier for the outgoing audio signals with positive feedback of amounts sufficient to provide the desired impedance multiplication effect but which is insufficient to sustain oscillation.

Abstract: A system for a telephone answering machine for recording new announcements on the announcement tape, for dictating notes or other material on the message tape, and for reproducing messages recorded on the message tape, all by means of a single transducer, so that the need for a separate microphone for dictation purposes and for recording new announcements on the announcement tape is obviated.

Abstract: A telephone ring detector system which finds particular utility in a telephone answering unit, since it responds only to ring signals on the telephone line to activate the system, and it is unresponsive to dialing pulses which would otherwise cause a spurious activation of the telephone answering unit. The system of the invention differentiates the ring signals from dialing pulses by detecting whether or not the telephone line to which the telephone answering unit is connected is in an "on-hook" or "off-hook" hook condition, and by providing an output in response to an incoming signal only when the telephone is in the "on-hook" condition. This assures that the signal detected on the telephone line is not a series of dialing pulses, since the dialing pulses occur only when the telephone line is in the "off-hook" condition.