GLI-3.5mm Stereo Audio Ground-Loop Isolator & Filter with 3.5mm connectors. Eliminates ground loop noise between any audio source such as a notebook PC and audio equipment. Perfect frequency response of +.03 db from 20 to 20,000Hz. Uses proprietary audio transformers and filters for total elimination of any spurious buzz and hum in the audio.

Have you ever connected a PC or notebook to an audio amp or a TV and gotten all kinds of ugly noise? Most people would answer yes, and that's because the audio output from these devices are not balanced. Professional equipment have balanced audio which uses a + and a - signal for each L/R side and therefore does not rely on ground. Any noise in the ground between the source of the Audio signal and the amplifier is automatically ignored. On the other hand unbalanced signals, such as the one coming out of your notebook, have no reference other than building/AC ground. In fact you may have noticed that if you disconnect your notebook power supply and ran on batteries the noise has gone away. This is because, by doing so you inadvertently eliminated the ground loop. Line-level audio is a very tiny low-level signal, so any noise in AC ground, even as little as 0.004v, will be quite audible - yuck!

The GLI-3.5mm is simply inserted in series with the audio and it literally eliminates the ground connection between the two sides, passes all the audio while filtering out any noise using high performance audio transformers.

In most cases the unit can be used in either direction, however it is designed so that the Female 3.5mm mini-stereo connector is to be used as input and the male connector is the output. The input side incorporates DC blocking capacitors. Some audio source equipment may have a DC bias voltage on their audio signal. In order to isolate this Bias level from the transformer coils, DC blocking capacitors are employed in the GLI-35mm.

It uses 1:1 audio transformers therefore it does not change the impedance. So if your load is 5K Ohm, adding the isolator in front of it, the source still sees a 5K Ohm load impedance.

A couple of important things to note:
The input side (the female 3.5mm at end of cable) has DC blocking capacitors, so it is a good idea to make sure to not reverse the input and output. Most audio sources should have these AC coupling caps on their outputs anyway (so their average output voltage is not biased at some DC voltage), but once in a while you have a source that has a DC output offset. If you connect the output with DC offset directly to the coils of the transformer a DC current will flow in the coil that may or may not affect the way the source behaves.