Hall Technologies GLI-RCA
Stereo Audio Ground-Loop Isolator & Filter with RCA Connectors
The Hall Research GLI-RCA is a Stereo Audio Ground-Loop Isolator & Filter with RCA connectors. Eliminates ground loop noise between any audio source such as DVD player, MP3 player, or 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. Do you hear hum or noise in your audio setup with certain inputs? Most people would answer yes, and that's because in most installations the audio signals 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 and what it is connected to is automatically ignored. On the other hand unbalanced signals, such as the one coming out of consumer equipment, have no reference other than building/AC ground. 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 unit 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 male RCA connectors on the molded cable are used as input and the female RCA connectors on the box are outputs. The input side incorporates DC blocking capacitors.
Some audio source equipment may have a certain DC bias voltage on their audio output connectors. In order to isolate this Bias level from the transformer coils, DC blocking capacitors are employed by the GLI-RCA. The isolated output is automatically AC coupled and has no bias. 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 male RCA 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.