Variable gain amplifier for telephone handset - contains microphone and earpiece assembly with fastening strap for universal attachment to telephone handset

摘要

A case (1) has housings for batteries (2) and an amplifier (3) and has the microphone (6) mounted on its front face. The earpiece (7) is located on the rear face and the case is closed at the front by a disc (8) which is rotated to switch the unit on or off. The disc also provides access to the batteries to enable them to be changed. A rubber strap (9) on the front face enables the unit to be maintained in contact with a telephone handset. A flexible gasket (10) prevents external noise from entering the microphone when it is fastened to the earpiece of the handset. The amplifier contains a section for use as a microphone amplifier and a power amplifier section to drive the earpiece. A potentiometer (4) provides manual gain control. The amplifier may be carried by hard-of-hearing persons to facilitate use of any telephone.