A New Problem w/ AC Power

JakeJ · « **on:** 31 Jul 2008, 02:02 pm »

Hi All,

Within the past 48 hours a buzz has appeared in my system that is audible from the seated position ~9 feet from the front of the speakers it also comes through the subs. Sounds like typical 60Hz buzz. If I drop the XO point below 60Hz it no longer comes from them (duh) but I have my Quads sitting on the subs and need to XO higher since the Quads are not getting their bass reinforcement from being set on the floor.

I tried several things to try and isolate the source including shutting off everything in the house but the stereo and it persists.

This was not present just two days ago.

Can anyone suggest a way to monitor the incoming AC for noise? It may be a bad pole pig somewhere nearby on my part of the grid.

My thanks for any ideas,
Jake

BradJudy · « **Reply #1 on:** 31 Jul 2008, 02:35 pm »

A 60Hz hum isn't noise on the line, it's a ground loop problem. Troubleshoot by disconnecting components from the system until it goes away rather than turning off other items in the house.

The most common culprit is the cable TV line, but there are many possible origins.

JakeJ · « **Reply #2 on:** 31 Jul 2008, 03:59 pm »

Thanks, BradJudy

Don't have cable (or other TV feed), and I haven't been changing out equipment just re-arranging the Swarm sub modules, but anything is possible so I will try disconnecting things to further isolate the source.

Jake

JakeJ · « **Reply #3 on:** 3 Aug 2008, 07:13 pm »

Send this thread off to the IGWB.

BradJudy was absolutely correct on the ground loop problem. At some point an electrician (or electrician wannabe) lived here. I discovered that one outlet in my listening space is on another circuit breaker, actually its own 15A breaker. I had stuff plugged in on the two breakers and viola! Ground loop.

Thank you,
Jake

markC · « **Reply #4 on:** 4 Aug 2008, 01:43 pm »

So now you have a dedicated line that you didn't know you had.

JakeJ · « **Reply #5 on:** 4 Aug 2008, 03:31 pm »

Yes! It was a bonus....in disguise!

awe-d-o-file · « **Reply #6 on:** 26 Aug 2008, 05:56 pm »

With a passive bi-amp and a regenerator (three ground paths) I had a ground loop that was slightly audible when the system was idle. It was annoying but I couldn't hear it when music was playing even at a low volume. I asked the regenerator manufacturer if I could lift the ground and they said yes. The hum was reduced but there was still some (from the two amps). But the sound improved a lot in quality when the ground was lifted from the regenerator. Then I lifted both amp grounds- holy crap!! It was like a new system. Way better than before. I was stunned! I posted in AA about it and Charles Hansen (Ayre) said his system is ungrounded and speculated that safety grounds might act as an antenna for RFI & EMI. So do it for the hum but enjoy it for the improved sound. People will tell you not to for safety reasons.

ET

JoshK · « **Reply #7 on:** 27 Aug 2008, 02:01 pm »

I've said it before, but it bears repeating. There are safe ways to "cheat" your ground loop problem but cheater plugs aren't one of them. Read this...

http://sound.westhost.com/earthing.htm

refer to "Figure 3 - A High Current Safety Loop Breaker Circuit" for an example of how to safely lift a ground in your amps.

Also, Dan Banquer had an article that he wrote on the subject and copied it a few places. Its in the lab threads somewhere. It more or less explains the same thing in a slightly different angle. When you read the two of them it really helps clarify the issue.

The idea is you let your safety ground connect directly to your circuit ground/neutral in only one component (typically either your source or your preamp) and then you add the safety loop breaker (also called ying/yang diode thing) to the amps and other components. Isolate the RCA and other interconnect plugs so that they don't ground the return cable to the chassis. Viola, no ground loops through earthing.