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 using only one 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.

Here is the printed circuit artwork in PostScript format, it can be printed onto Press-n-peel blue transfer material for making a PC board.

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, Jameco 112475
2x PC mount 3.5mm stereo jacks, Mouser 161-3501
2x 10K - 10K audio transformer, Mouser 42TM018

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