Telephone interfaces for sound cards come in two varieties
- Connects to the telephone handset plug. Only records calls when that particular telephone handset is lifted.
- Connects to main telephone line. Can record all calls made by any extension on that telephone line.
The handset plug interface is useful for recording from office phones connected to a PBX with weird non-standard telephone wiring, since the handset wiring will usually still be a standard interface.
Here are some places to find a telephone/sound card interface for recording calls. We haven’t tried all these ourselves, and have no connection to these companies:
Can a telephone tape At the suggestion of one customer, we tried the 43-228A Telephone Recording Control from RadioShack. This seems to work rather well. Perhaps we might wish for a little higher sound volume, but for the most part this particular gadget works adequately, and we can recommend you try it.
At the request of another customer, we tried and analyzed the Radio Shack Multi-Phone Recording Control (43-1236). This device is designed to work with cassette tape recorders, but we wanted to know if it could be made to work with sound devices. We discovered that this gadget does not have an isolation transformer in the signal path, which is fine for battery-operated devices such as tape recorders, but allows too much noise due to ground loops when used with a line-operated device such as a sound card. Conclusion: Some telephone taping devices might work for sound cards, but others will not.
Prior to discovering this device, we built the following circuit, which seems to work adequately (for USA type telephone lines) (soon to be a gif file for better readability, but until then make sure your browser window is wide enough so the lines don’t wrap around):
Phone ||C1 R1 T1 R2 sound card Tip-----||------/\/\/--+ +-----/\/\/----+-------+------mike-input || | | | D1 | D2 tip ) || ( ----- ---- ) || ( /\ \ / ) || ( / \ \/ ) || ( ---- ----- Phone ||C2 | | | | sound card Ring----||-------------+ +--------------+-------+------mike-input || outer ring
(RS means Radio Shack nearest-equivalent part number)
R1,R2 10kohm,1/2watt (RS271-1126)
C1,C2 Â .1uF, >200V (RS272-1053)
T1 600ohm 1:1 telephone audio transformer (RS273-1374)
D1,D2 generic signal diodes (RS276-1653)
Telephone tip and ring are the two center conductors of a four-conductor modular telephone connector, and for this circuit it doesn’t matter if they are reversed. (RS279-391)
Sound card microphone-input connector is a 1/8″ 3-conductor audio male plug.(RS274-284C)
Theory of Operation: C1 and C2 block DC current path, so this device does not bring the phone line to off-hook state, but the capacitors pass AC voice signals. The device Â D1 and D2 limit ringing voltage that can reach microphone. T1 provides isolation between telephone line and sound card.
The “near side” of the conversation may be significantly louder than the”far side” when recording to the sound card with this type of circuit, but with proper adjustment both sides of the conversation should be intelligible.
This does not constitute legal advice: Recording of telephone conversations may be subject to federal (or national) and state laws. In the USA, for instra-state calls, some states require one-party consent, others require two-party consent, with numerous exceptions and special cases. Some countries have major restrictions on devices that may be attached to telephone lines.
For further information on telephone interfacing circuits, try www.epanorama.net/documents/telecom/teleinterface.html.
If you need further help, or have suggestions or comments, please send e-mail.