Telephone Line Tap
I am just copying the circuit given at Circuit Zoo
Below schematic shows the design of a simple Telephone Recording Adapter Circuit Diagram by Philips. The circuit is designed to be connected in parallel with normal telephone.
Tip: Once connecting with sound card of PC, you would use two such circuits, with common sleeve connection. Keep leg after F1 as common sleeve; F2 for both the circuits should be connected with Tip and Ring respectively.
Below schematic shows the design of a simple Telephone Recording Adapter Circuit Diagram by Philips. The circuit is designed to be connected in parallel with normal telephone.
Tip: Once connecting with sound card of PC, you would use two such circuits, with common sleeve connection. Keep leg after F1 as common sleeve; F2 for both the circuits should be connected with Tip and Ring respectively.
T1 is the audio isolation transformer, which seems to have properties quite similar to typical 600:600 ohm telecom isolation transformer. The components F1 and F2 are 50mA fuses. The signal output level is suitable for microphoneinput because the resistors attenuate the voice signals form telephone line around 40 dB (some telephone equipment regulations in Finland needed this).
For few other types of telephone taps, visit: http://www.aaroncake.net/circuits/phonetap.asp
For few other types of telephone taps, visit: http://www.aaroncake.net/circuits/phonetap.asp
Tip: Since this circuit uses an audio transformer for audion coupling, it would be prone to interference. Once combining these circuits for multi-line recorder, have some shielding around each circuit. Keep it away (at least 10 meter) from PC, to avoide interference.