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Home › Magazines › 2006 › March › Telephone Eavesdropper

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Telephone Eavesdropper

An advanced amplifier with line output

Published in issue 352, March 2006

Telephone Eavesdropper
Galvanic isolation is a special feature of this telephone amplifier, which includes a line output connection for a hi-fi system.
Although in some countries, including the UK and Germany, analogue telephone connections are something of a dying breed, most residential customers use analogue apparatus, even in cases where the underlying connection is over ISDN.

Components

Resistors:

R1,R3 = 10kΩ

R2 = 8kΩ2

R4 = 100kΩ

R5,R6,R11 = 1kΩ

R7 = 220Ω

R8,R12 = 3kΩ3

R9 = 2Ω2

R10 = 2kΩ2

P1 = 250kΩ  preset H

P2 = 10kΩ logarithmic potentiometer, mono

Capacitors:

C1 = 2µF2 63 radial

C2 = 15nF 400V

C3 = 1nF 400V

C4 = 68pF

C5,C16,C18 = 10µF 63V radial

C6,C10,C15,C17 = 100nF

C7 = 220µF 16V radial (max. diameter 8mm)

C8 = 1nF ceramic (5mm lead pitch)

C9 = 330nF

C11,C12,C13 = 470µF 16V radial (max. diameter 8mm)

C14 = 3nF3 (5mm lead pitch)

Semiconductors:

D1,D2 = BAT85

D3 = LED, low current

D4 = 1N4002

IC1 = LF356

IC2,IC3 = 6N138 (Farnell # 325-831)

IC4 = TDA7052

IC5 = NMV0512SA, C&D Technologies/Newport Components (Farnell # 589-822)

IC6 = 7806

Miscellaneous:

K1,K2 = RJ45 socket

LS1 = 8 Ω / 1W miniature loudspeaker

Solder pins

PCB, order code 030379-1

Click below to download a PDF copy of this article from Elektor magazine.

 

Downloads 
PDF Article (U060362.pdf)
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PCB layout (030379-PCB.pdf)
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Order from Elektor 
PCB 030379-1
030379-1 (USD 16.30)
Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.

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