Re: Converting phone handset audio to PC soundcard line-in audio

From: Rich Grise (null_at_example.net)
Date: 07/17/04


Date: Sat, 17 Jul 2004 11:20:25 GMT

on Friday 16 July 2004 12:28 pm, Isaac Grover wrote:

> Hi everyone,
>
> I have been recording weekly conference calls since January, and I'm
> looking to upgrade the quality of my recordings. Currently, I'm
> connecting my cordless phone to the line-in jack on my PC's soundcard
> with a 6' audio cable.
>
> I would like to take the audio from a landline telephone, so I tore
> apart the handset on my wired phone to see which wires connected the
> handset's speaker to the base. I saw that it was pins 2 and 3 (top
> left and bottom right), so I connected pin 2 (green) on the handset
> jack to ground on a spliced audio cable, and connected pin 3 (red) on
> the handset jack to tip on the audio cable.
>
> I can hear the audio from the phone line, but not without problems.
> There is an intrusive hum that almost drowns the phone line audio, and
> whenever pin 2 (green) is connected to ground on the audio cable, my
> wired phone's base takes the line off-hook, even if the handset is
> still on the cradle.
>
> So can someone tell me how to eradicate the hum, and how to keep the
> line on-hook if I am not using my "high-tech" conversion device?

Use two capacitors. Measure all your polarities, and use about
100-220 uF caps at at least 250V. These will be electrolytics, which
is why you need to know the polarities. This will isolate them, unload
the phone line, and not ground the telco's system.

-- 
Cheers!
Rich


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