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Telephone Eavesdropper

An advanced amplifier with line output

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.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

R1,R3 = 10k?
R2 = 8k?2
R4 = 100k?
R5,R6,R11 = 1k?
R7 = 220?
R8,R12 = 3k?3
R9 = 2?2
R10 = 2k?2
P1 = 250k? preset H
P2 = 10k? logarithmic potentiometer, mono
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)
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
K1,K2 = RJ45 socket
LS1 = 8 ? / 1W miniature loudspeaker
Solder pins
PCB, order code 030379-1
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