telephone to sound card plug

Does anyone have a circuit for an interface suitable to connect an Australian telephone socket to a pc soundcard?

I want to try the VRS software on

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but don't want to spend the US $84 on their recommended device that according to their forum also zaps out line in sockets on some sound cards.

I have been lent an adapter from a friend's micro recorder and all it is is a couple of diodes, caps and resistors. Can't see any line isolation, so worst come to worst I could just copy that one and risk zapping an input.

Cheers

Reply to
Zaphod
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a micro recoder is isolated from ground...

you computer is grounded (unless its a lap top)

so you need to use a transformer (or other balanced to unbalanced system) to provide isolation...

you are not allowed to connect one side of the phone line to ground.

a small audio transformer is probably the best solution... Mark

Reply to
Mark

Check out the circuit at

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Just use the audio path circuitry and dispense with the relay. Connect the transformer output directly into the sound card input. As a precaution, connect a back-to-back series pair of zener diodes rated at about 4.7V across the transformer secondary (parallel with C2).

Cheers!!

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in 
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Reply to
DaveM

Many thanks to those that replied here and in the other groups.

I've taken your coments on board particularly the safety issues, and I'll use some parts from an old modem to make sure.

For those that have followed this thread with a view to making their own as well, here are the links to my preferred circuits that I found after following helpful suggestions.

I'm building this for the Australian telephone system. So if anyone has any comments or further suggestions, I'll be happy to hear them.

Thanks again to all.

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Reply to
Zaphod
[snip]

There's nothing special about the Australian telephone system- it's just standard 48V POTS. (The reference line impedance is slightly different to that in other countries, and some tones are unique, but that's not a big problem.) Specifying "Australian" may have reduced the quantity or quality of the replies you received. Besides, it's always better to design for the global market, even if it's just a hobby thing.

My $0.05.

Regards, Allan

Reply to
Allan Herriman

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