Another ground loop question

tcrossma

I just installed two new outlets for my room, where each outlet is on a dedicated breaker at the panel. I did the new outlets while I was waiting for my new amp to arrive, so this setup was not used prior to now.

On one outlet I have only my amp. On the other outlet I have my Monster 3500 power center (which has most everything else plugged into it -- TV, cable box, DVD, etc).

The first time I powered up my amp I got a ground loop hum through the speakers. I figured it was due to the amp and other equipment (most likely cable box) being on different circuits. The power cord I'm current using for the amp is a PS Audio Prelude which has a removable ground prong, so I removed it and that solved the ground hum.

So at this point all is running well, but I'm wanting to buy a new power cord or two for my system. As it now stands I believe any new cord I introduce to the amp will need a removable prong, which may limit my options. So I was wanting to see if there was an easy fix for the root cause of the ground loop hum, or if I should just ignore it and stick with non-grounded cords?

Thanks.

apphd

Just follow the basic troubleshooting routine for ground loops. Unplug everything except the amp and pre-pro. If your good start plugging things back in until you get the hum. This is assuming you don't have the hum with just the amp and AVR (I'm betting this to be the case) I'm also willing to bet the cause will be the cable box or the power center it self. Did you do the wiring? You can get a simple circuit checker for cheap that will tell you if both outlets polarity are correct and if you have an open ground at the outlet (again unlikely because you have a ground loop). Any idea how the cable is grounded where it enters your house? I would bet the problem will be in the cable ground, or the cable box.

Good luck

tcrossma

apphd wrote: »

Just follow the basic troubleshooting routine for ground loops. Unplug everything except the amp and pre-pro. If your good start plugging things back in until you get the hum. This is assuming you don't have the hum with just the amp and AVR (I'm betting this to be the case) I'm also willing to bet the cause will be the cable box or the power center it self. Did you do the wiring? You can get a simple circuit checker for cheap that will tell you if both outlets polarity are correct and if you have an open ground at the outlet (again unlikely because you have a ground loop). Any idea how the cable is grounded where it enters your house? I would bet the problem will be in the cable ground, or the cable box.

Good luck

I did the wiring. Where the line enters the house it goes to the panel, all grounds and neutrals are all tied together, and there's a ground rod in the basement floor.

I will do the test for unplugging everything at some point soon, and I'm pretty sure I'll be able to isolate *what* is causing the problem. But let's assume it's the cable box for a moment -- what's the solution? Move that one item to the same circuit as the amp?

apphd

Plugging the cable box in on the same outlet as the amp might work but more than likely not. If you find it to be the cable box you can call them and explain the situation and see if they might replace the box.

What were you running (amp wise) before you moved things to the new outlets? Can you try the old amp on the new outlets, or is it gone?
Here are some links that might be helpful.

http://www.epanorama.net/documents/groundloop/

http://www.audioholics.com/tweaks/connecting-your-system/ground-loops-eliminating-system-hum-and-buzz

tcrossma

Well, today I went to tackle the ground loop issue. I put the ground pin back in the PS Audio power cord that's on my amp and plugged it back into the same wall outlet (a newly installed outlet). I then unplugged the Monster Power Center from the other new outlet and put it back in its original outlet. I powered everything up, and no hum.

Ok, so I'm thinking maybe utilizing both of the new outlet, with the amp on one and the rest of the equipment on the other was the cause. So I moved the Monster Power Center back to the new outlet, powered everything up, and NO HUM. Now, this was the same exact configuration I had a few weeks ago when I installed my new amp and was getting the hum.

So... As it now stands I have everything plugged into exactly where I want: the amp on its own dedicated circuit and the rest of my equipment on the other dedicated circuit. Ground pin in place on the power cord, and no hum.

But I'm a bit confused as to why I had a problem a few weeks ago and I don't now. I'll leave it this way for a while and see if the problem returns. Maybe it has something to do with other equipment in my house running or something, I just don't know.

apphd

Cool, your hum free. I don't understand it as it sounds like everything is tied to the same ground. Is the humidity higher or overall soil condition moister?

TECHNOKID

Moving your gear around while testing might have freed some loose connections which was originally causing the problem? Did you have any power cables close to any of the amp audio cabling? For example, I had a microphone problem which was causing a hum in the PA system which was cured simply by moving the microphone XLR cable that was running in parallel with a power cord.

Cheers

apphd

One more thought to toss out here. Were there any power cords in the power center that were not grounded and not polarized? I have an older Dual TT with a plug like that. Just wondering if there were any of these maybe when you reconnected you flipped the plug and now all component power polarity are the same.