Recording interface from Tekniikan Maailma magazine

The third circuit was shown in an article written by Martti Koskinen 
in Tekniikan Maailma magazine issue 8/1994 pages 94-95. 
The circuit is designed for recording telephone conversations using normal tape recorder. 

The circuit has an option to also play back sound tot the telephone line from reparate connector. 
The transformer T1 is typical 600:600 ohm telephone isolation transformer 
with centre tapped secondary. 

This circuit is also designed to be used in parallel wiht existing telephone. 



The capacitors C1 to C4 are connected in parallel to make about 200 nF capacitance. 
Four separate capacitors can be more easily fitted to 
one case than single 200 nF 250V capacitor which is quite large. 
I don't know the reason of why R1 and R2 are connected in parallel, 
because single 4.7 kohm resistor would do their job as well.