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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 capacitor will greatly attenuate -- if not exactly isolate -- the phone line ringing voltage, which can be ~90 volts AC.

--
St. John
Arithmetic is being able to count up to twenty without taking off your
shoes.
                -Mickey Mouse
Reply to
St. John Smythe

Why connect a phoneline to a soundcard, what's wrong with a voice modem?

you're almost guaranteed to zap the input with that setup. typically phone lines are -48V to ground, and it gets worse when they ring.

The microrecorder probably isn't grounded.

Bye. Jasen

Reply to
Jasen Betts

Chekc the circuit plans at

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Those should (at least mot of them) work pretty universally all over the world when connected to right wires on the telephone connector your country happens to use.

Using an adapter without isolation can easily kill the soundcard line input and cause lots of mains frequency noise to the line. At worst case some part of that noise can also affect other users on the same telephone cable.

And in worst case if yout housue is hit by a big power surge, short circuit inside computer or wring wiring on computer outlet, a telephone line adapter without proper isolation can cause dangerous voltages entering the telephone cable. Those are potentially dangerous to telephone installation people (at worst case can kill somebody). At worst case can fry the line card on the telephone central (this will be expensice).

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/
Reply to
Tomi Holger Engdahl

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

On Thu, 09 Feb 2006 07:06:28 -0000, Jasen Betts sprachen:

I agree. My voice-modem shows up in Windows as an additional sound card. I can choose to play or record sound to / from it, as an alternative to my normal sound card.

The advantage is, they cost, what, about 10UKP, probly less than 20 AUS. Nice and reliable and already tested safe by somebody else.

I think it'd be easier, more reliable, and probly cheaper.

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Reply to
greenaum

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