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Telephone Headset Amplifier
All materials and content contained on this page are the exclusive intellectual property of Andrew R. Morris and
may not be copied, reproduced, distributed or displayed without his express written permission.

This circuit goes between a telephone and a headset.  The project has a headset cord and plug (cut from a cheap cell phone headset) on the input and a suitable jack on the output.  The speaker signal passes through this circuit, but the microphone signal is passed straight from the plug to the jack.

This circuit is specifically designed for ultra-low battery consumption.  It uses a special control circuit (Q3, Q4 and !5) to regulate the power amplifier's quiescent current.  Also, effort was spent to design an auto-on circuit (Q10 through Q14) that draws only 1.5 uA, yet has 15mV sensitivity.

More:  Audio Accessories;   Audio Amplifiers;   Headphone Circuits;   Telephone Circuits 

 

Click on Schematic to view PDF

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