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ccdoggy 13th January 2008 06:51 AM

Electrical Saftey and a ground loop
Hello, I have a wanna be theater in my room (college student) and I have a big problem with ground loops and my sub amp. I have a Behringer EP2500 for my sub, an Arcam AVR300 for a receiver, a denon dvd player and a computer hooked up.

The ground loop isent a quiet one, its pretty loud and can be heard over music for sure. Only in my Sub. All components on the same leg of power, amp and arcam on same outlet, computer across the room. connected via Digital coax. Good cables all around.

My solution so far has been to connect the chassis of my computer (from what i hear causes allot of problems) to the chassis of the amp thus allowing that little bit of current to go through that instead of eventually traveling out the sub out on the receiver causing the hum. That did not get rid of all the hum though, so i started testing different locations for attaching another chassis ground on the amp to see if i could improve more. I found that attaching it to the ground on another Digital input on the Arcam greatly reduces it.

Is this safe? I tried a ground loop eliminator but made the bass sound like crap. Can i just cut off a rca cable and connect the ground on it to my ground wire and be safe?

Thanks for the help!

peufeu 13th January 2008 08:04 AM

Since you're using SPDIF you can either use optical connection or insert a pulse transformer in the SPDIF line which will isolate the computer from the rest of the system.

You can use a 100 Mbps ethernet thansformer, salvaged from an old network card or you can get a Pulse HX1198 which should work (not tested).

This will add a little jitter to your system but it will definitely be a huge improvement compared to loud mains hum ;)

audio1st 13th January 2008 12:58 PM

Has your Arcam got a "ground lift" switch on the back near the power socket? My AVR 200 has one..May help..

ccdoggy 13th January 2008 05:49 PM

I dont have optical, it would make things so much easier.

Im not so good with intricate electronics, i wish i was but i just dont feel confident.

Yes the ground switch is there and i have it set on the quieter setting. It removed the hum from the mains but it is still present in the sub.

Thanks for the suggestions.

ccdoggy 13th January 2008 09:44 PM

So what i have ended up doing is placing the ground loop isolator on my spdif connection from the computer and i has helped allot.

But it has jumpy sound, as in every like 15 or so seconds it stops transmitting sound for asplit second. so there is a gap in the audio.

Is this because its a crappy radioshack isolator, or is it just inherent to isolators on digital connections?

ccdoggy 15th January 2008 06:51 PM

Turns out that my receiver was looking for a reference ground signal so confirm signal and the isolator was creating problems for it. So i ended up placing a 100 ohm resistor across the ground bypassing the isolator and now all is working great.

peufeu 20th January 2008 07:55 PM

Well, your radio shack isolator is a transformer, and apparently it has enough bandwidth to pass SPDIF. I wouldn't have thought that ;) Lucky for ya.

ccdoggy 21st January 2008 06:43 AM

Yea i know, it surprised me too.

Although it is weird, some times it cuts out for like 2 seconds, but only within the first 5 min of turning my receiver on. after that its fine.

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