Telephone PC Interface

[Jay]

I am trying to find a way to record telephone conversations to my PC,
(legal, for training purposes only). I have an interface that plugs
into a cassette recorder and that works fine on the cassette. I have
tried this same interface plugged into my computer, either line-in or
the microphone jack, but when I record I get a loud hum noise and I
can faintly hear myself in the background, though I have to talk or
whistle loudly to do so. Apparantly I need a different interface. I
have found them for sale for around $50, but I would prefer to make my
on, usually these interfaces use fairly simply filter circuits. Any
suggestions?

Thanks

 

[Stan]

[email protected] (Jay) wrote:

}I am trying to find a way to record telephone conversations to my PC,
}(legal, for training purposes only). I have an interface that plugs
}into a cassette recorder and that works fine on the cassette. I have
}tried this same interface plugged into my computer, either line-in or
}the microphone jack, but when I record I get a loud hum noise and I
}can faintly hear myself in the background, though I have to talk or
}whistle loudly to do so. Apparantly I need a different interface. I
}have found them for sale for around $50, but I would prefer to make my
}on, usually these interfaces use fairly simply filter circuits. Any
}suggestions?

Yes...google.

Try: phone computer record interface circuit

Stan.

 

[Dana Raymond]

I am trying to find a way to record telephone conversations to my PC,
(legal, for training purposes only). I have an interface that plugs
into a cassette recorder and that works fine on the cassette. I have
tried this same interface plugged into my computer, either line-in or
the microphone jack, but when I record I get a loud hum noise and I
can faintly hear myself in the background, though I have to talk or
whistle loudly to do so. Apparantly I need a different interface. I
have found them for sale for around $50, but I would prefer to make my
on, usually these interfaces use fairly simply filter circuits. Any
suggestions?

Thanks

I suspect the problem is a grounding one. If you plug into the microphone
input of your cassette recorder and all works well and then move the plug
over to your computer mic input and all you get is hum, then check to see if
your 'interface' is powered. If it is, use an isolation transformer or
temporarily run it by battery. If it then works, you can sole the problem
permanently.

 

[George Jetson]

I suspect the problem is a grounding one. If you plug into the microphone
input of your cassette recorder and all works well and then move the plug
over to your computer mic input and all you get is hum, then check to see
if your 'interface' is powered. If it is, use an isolation transformer or
temporarily run it by battery. If it then works, you can sole the problem
permanently.

If your in a real hurry take apart an old modem, lots o filter coupling
parts, and hey they work with phones. Try running the phone line to a
modem(no power to it) and pick the signal off the matching/isolation
transformer output use the soundcard line in.

With a little post processing to even up levels and some VOX software to
conserve disk space I had 100's of hours of conversations.

No, I didn't learn much of the subtleties of phone interface circuits but it
took only minutes and cost me some old hardware from the junk box.

 

[Michael A. Covington]

Soundcards don't take the same kind of microphones as tape recorders. A
tape recorder or PA system takes a microphone that outputs about 1 mV. A
soundcard supplies power through a resistor to a transistor inside the
microphone, amplifying the sound level to about 30 mV.

A few years ago I published an article and circuit in QST (the ham radio
magazine) about how to use a traditional microphone with a soundcard. It's
a 1-transistor amplifier. I don't have the circuit or the exact reference
handy.

 

[Carl Wedekind]

I am trying to find a way to record telephone conversations to my PC,
(legal, for training purposes only). I have an interface that plugs
into a cassette recorder and that works fine on the cassette. I have
tried this same interface plugged into my computer, either line-in or
the microphone jack, but when I record I get a loud hum noise and I
can faintly hear myself in the background, though I have to talk or
whistle loudly to do so. Apparantly I need a different interface. I
have found them for sale for around $50, but I would prefer to make my
on, usually these interfaces use fairly simply filter circuits. Any
suggestions?

Thanks

How about this?

http://www.modemspy.com/en/index.php

 

[Ross Herbert]

On Wed, 15 Sep 2004 22:20:02 GMT, "Carl Wedekind"

|
||>I am trying to find a way to record telephone conversations to my PC,
|> (legal, for training purposes only). I have an interface that plugs
|> into a cassette recorder and that works fine on the cassette. I have
|> tried this same interface plugged into my computer, either line-in or
|> the microphone jack, but when I record I get a loud hum noise and I
|> can faintly hear myself in the background, though I have to talk or
|> whistle loudly to do so. Apparantly I need a different interface. I
|> have found them for sale for around $50, but I would prefer to make my
|> on, usually these interfaces use fairly simply filter circuits. Any
|> suggestions?
|>
|> Thanks
|
|
|How about this?
|
|http://www.modemspy.com/en/index.php


That appears to be software only. You still need a physical hardware
interface.

You might start some reading here

http://www.solorb.com/elect/phone/tap/
http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html
http://www.qsl.net/yo5ofh/hobby circuits/telephone_circuits.htm

there's heaps more but mostly similar to these.

 

[Jay]

Soundcards don't take the same kind of microphones as tape recorders. A
tape recorder or PA system takes a microphone that outputs about 1 mV. A
soundcard supplies power through a resistor to a transistor inside the
microphone, amplifying the sound level to about 30 mV.

A few years ago I published an article and circuit in QST (the ham radio
magazine) about how to use a traditional microphone with a soundcard. It's
a 1-transistor amplifier. I don't have the circuit or the exact reference
handy.

Okay, thanks for the advice. Apparently the mike jack isn't
compatible with a telephone/cassette interface. What about the line
in jack on the back of the computer? Would this be compatible with
this type of interface?

 

[Dbowey]

Ischultz posted:

<< I am trying to find a way to record telephone conversations to my PC,
(legal, for training purposes only). I have an interface that plugs
into a cassette recorder and that works fine on the cassette. I have
tried this same interface plugged into my computer, either line-in or
the microphone jack, but when I record I get a loud hum noise and I
can faintly hear myself in the background, though I have to talk or
whistle loudly to do so. Apparantly I need a different interface. I
have found them for sale for around $50, but I would prefer to make my
on, usually these interfaces use fairly simply filter circuits. Any
suggestions?
The simple answer is that you must use a transformer.

Your telephone line is a "balanced" line. Your sound card has an "unbalanced"
input. When you connect between the telephone and the PC's line input using
your interface (device) you are essentially placing a ground on one side of the
telephone line, unbalancing it and causing it to be a great noise and hum
receptor.

The interface (device) you now have works with the cassette recorder because
the interconnecting cable is short and the cassette recorder is not grounded.
If it *were* grounded, it would cause noise and hummmmm too.

You cannot fix this by using more capacitors anywhere. You must use a
transformer.

Tell us more about your interface device and we can help with specific details
of the transformer you need.

Don

 

[Aidan Grey]

I am trying to find a way to record telephone conversations to my PC,
(legal, for training purposes only). I have an interface that plugs
into a cassette recorder and that works fine on the cassette. I have
tried this same interface plugged into my computer, either line-in or
the microphone jack, but when I record I get a loud hum noise and I
can faintly hear myself in the background, though I have to talk or
whistle loudly to do so. Apparantly I need a different interface. I
have found them for sale for around $50, but I would prefer to make my
on, usually these interfaces use fairly simply filter circuits. Any
suggestions?

Thanks

I think some "voicemodems" allowed voice recordings to be played
on a telephone line. There may be a model that will do exactly
what you want.


Aidan Grey

 

[jakdedert]

I think some "voicemodems" allowed voice recordings to be played
on a telephone line. There may be a model that will do exactly
what you want.

Actually that's all under software (ATAPI standard) control. IOW, with the
proper program, *all* voice modems....

jak