Why can't I record or amplify audio coming out of a 3.5mm stereo audio jack?

rodion15

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Sep 11, 2011
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I've connected my computer to an audio output but instead of getting the actual audio, I only get a buzz. I'm connecting to the LINE IN jack on the desktop computer using a 3.5mm plug to plug stereo cable and the audio output is on a landline telephone adapter (this adapter has typical landline telephone RJ11 connector on one side and two 3.5mm stereo female connectors on the other, one for mic and the other for headphones).
When I connect headphones to this same audio output I get good audio, although the volume is too low, that's why I need to amplify it.

Also, when I connect to a mobile phone audio output or the PC audio output, I catch that sound OK. So I don't understand why I only get a buzz when I connect to the audio output on this phone adapter. I've tried regulating the audio level using the Sound icon on the system tray in Windows but to no avail. The result is the same if I connect to the Mic input on the computer.

Thank you ;)
 

VincentP

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What is the actual audio source with this RJ11 output connector?
Typical headphone impedance is 25 to 75 ohms.
A line level output is designed to drive a load impedance of 10000 ohms.
Headphone outputs and line level outputs are not necessarily compatible.
 

rodion15

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Thanks for your answer: I also suspected the impedance difference, but if a headphone works fine, why shouldn't the mic jack on the computer capture the audio? Aren't they the same impedance?
 
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