Telephone volume amplifier circuit

This circuit is designed for the deaf. JP1 is plugged into the socket of the telephone handle, and the original telephone handle is plugged into the socket of JP2. Switch K1 is a normal/deaf conversion switch. The position in the figure is the normal use state. The receiving signal is sent directly from JP1 to JP2 to the headset without passing through the amplifier, and the electrical appliances are also cut off. When the deaf use it, turn K1, 6V power is added to the amplifier, and the telephone receiving signal is coupled to LM358 through transformer T for pre-amplification. The output signal is adjusted to an appropriate volume by the potentiometer and sent to U2 for amplification. After the output, it is sent to the headset through JP2. When the deaf use it, adjust W to an appropriate volume.

When making, the transformer T can be the output coupling transformer of the ringing circuit in the telephone or the output coupling transformer in the radio. In this circuit, the primary and secondary must be used in reverse. The handset wiring in the sockets JP1 and JP2 should be consistent with the wiring of the selected telephone.