Stereo Audio Isolator
Stereo Audio Isolator
(C) G. Forrest Cook 2004
Introduction
This circuit is useful for removing ground loop hum on a remote line level audio
signal line. It can be used to to connect a computer sound card to a stereo
amplifier's line input. Other uses include tapping into a line level
signal for powering a remote amplifier, and removing common mode ground
interference on 12 Volt audio equipment such as a car stereo.
The circuit can be used in mono applications by simply
ignoring the second channel.
Specifications
Connections: L and R RCA Jacks, stereo 3.5mm jacks
Operating voltage: 1V P-P nominal (line level audio)
Input Impedance: 10K ohms
Output Impedance: 10K ohms
Frequency response: untested
L-R Channel isolation: untested
Theory
The audio signal is passed through the transformer from one side to the
other. Ground loop noise that would otherwise travel from the ground
on one side of the isolator to the other side is blocked.
Construction
A custom PC board was made for this circuit, it could easily be built with
perforated circuit board, or free-wired with the connectors mounted
in a small metal box. Multiple connector types as shown in the photo
are optional. If the circuit is put inside of a metal box, ground the box
to the transformer cases.
Use
Connect this circuit between an audio source and an and audio destination.
Turn on the signal source, listen for the audio signal on the destination.
Parts
4x PC mount RCA jacks
2x PC mount 3.5mm stereo jacks, Mouser 161-3501
2x 10K - 10K audio transformer, Mouser 42TM018
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