Subwoofer Ground Loop Isolator - AVS Forum | Home Theater Discussions And Reviews
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Old 12-30-2012, 04:50 AM - Thread Starter
joeren's Avatar
Join Date: Jan 2005
Location: Upstate, NY near Albany
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A few years ago I purchased a ground loop isolator, ISO-MAX, to solve a hum problem I had when connecting my Sunfire subwoofer, a common problem. Prior to the ISO-MAX I was using an LF audio transformer, which worked well until the levels got a little higher and then would saturate the core producing a horrible sound from the sub. I thought about the saturation problem and wondered if it could still happen. It turns out that I could saturate the ISO-MAX at voltage levels of about 1.5V at frequencies near 20Hz. (Generally not a problem since most preamps’ maximum output is usually below this level. I just couldn’t let it rest though and finally ended up designing an isolation circuit based on Texas Instruments’ ISO124 IC. ( click on the Datasheet window) This circuit completely isolates the ground loop, good up to about 3kVDC of isolation, has a frequency response from DC to 50 kHz. (manufacturers rating but realistically 2kHz) and can’t be saturated, The isolated supply rails go to +/- 15V so there is no way to overdrive it. The down side of course is that it requires a 5VDC supply to function. I designed the circuit board and purchased the parts and constructed a prototype. The circuit works great and can be tailored to match any input/output impedance and will work with single ended and differential inputs.The total cost was about $140.00 Here are a few pictures.
To get a decent price I had several circuit boards fabricated and would like to offer them for sale (Gold plated bare circuit board only, $10.00 ea + shipping) to anyone that wants to try this little project, along with the circuit schematic, bill of Materials and any support information that I can lend via email. The circuit board is 1.5"x2.5". This was a fun project that works great. I would recommend that you have some soldering skills and a basic understanding of electronics to complete this. If interested please email me at

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