While talking to a distant subscriber on
telephone, quite often we feel frustrated when the voice of the distant subscriber is so
faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive
amplifier is presented here. It can be assembled and tested easily. There is no extra
power source needed to power up the circuit, as it draws power from the telephone line
itself. The amplifier will provide fairly good volume for the telephone conversation to be
properly heard in a living room. A volume control is included to adjust the volume as
There is no need of a separate power switch as the
circuit energises (via the normally open contacts of the cradle switch) when one lifts the
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analogkid 2011-12-05 18:25:29
Bad design. The schematic has several problems.
1. D6 and D7 should be connected in parallel, not in series.
2. Output speaker current flows through the audio transformer primary. Feedback will cause oscillations or severe distortion.
3. Loop DC current through the transformer. Extreme distortion.
4. Zener and transformer are in series with phone. Extra voltage drop probably will cause the Central Office to drop the call.
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