Telephone pickup preampliifer

  
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Here is a simple circuit based on IC uA 741 that can be used to pickup voice from telephone lines without even contacting the line. If a high impedance magnetic core is placed near a telephone instrument or near one of the telephone wires, it picks up inductively both sides of the telephonic conversation without any electrical contact. A preamplif
Telephone pickup preampliifer - schematic

ier based on IC uA741 is used to pickup these signals. The circuit is nothing but an inverting amplifier whose gain depends on the feedback resistance R4. The Op-Amp produces the necessary gain to drive the headphone. The circuit can be used as a telephone bug too.



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