I tried connecting my mp3 player to the line-in of my computer (with an intel HD audio driver) via a 1/8" trs extension wire. It worked, but could somebody explain my observations in electronic terms? I'm planning on building a sort of guitar preamp for the line-in and the information for the mp3 player's connection might help. I am also a EE student at college, so I do know some basic things.

1. When I increase the 'input monitor' volume on the volume control panel, at some point distortion is introduced and it increases with increasing volume.

2. If I raise the mp3 player's volume, I get a distorted sound at some point which increases with a further increase in volume.

3. So really, I can raise the volume in the controls to get distortion which eliminates if I reduce the volume on the mp3 player afterwards.

So my question is, what is at work here - Is the voltage fed to the computer though an impedance - matched circuit (max power), or is it a circuit which draws max voltage instead? Why is it fed this way and not the other way? And HOW do you know what the circuit is, how and where did you find out from, what were your resources? Because I wouldn't know where to look for answers for these things aside from this forum and a few other places.

And does the input resistance, or impedance, of my line in change as I increase the volume in the volume controls? How and why? How does it affect the sound?

What and why is this distortion? A power dissipation greater than the power rating of the load is my guess, but how and why does this happen?

I had a somewhat similar experience when I used a casette tape adapter to listen to my mp3 player through the car's casette player. I could turn up the volume in the casette player and there would be no distortion, but turning up volume in the mp3 player itself does introduce distortion at some point. Why was this, now?

 

Hello,

I think you are listening to clipping.
The signal is to large to be converted and amplified correctly.
I would be carefull with a to large input signal as it may lead to defects on the sound card.

Bertus

 

Oh yeah, you're right. Clipping it is. But why and how does it happen in an analog circuit?

 

At school play with a sine generator and o'scope.
Select appropriate gain ranges and increase the output of the generator and notice that the sign wave gets clipped at the top and bottom if you can over drive the scope input.

 

Overdrive in guitar effects terms.

Input voltage x gain ends up calling for more output voltage than the circuit can deliver thus the tops and bottoms of the waveform beome cut off, or clipped..