7500 ground loop

I pulled the 7125 from my system last nite and connected the 7500.Turned the system on and before the amp even turned on there was a hum threw my speakers.The problem was my cable line into the modem,disconnected the coaxial into the box and it was gone.The 7125 doesn't have a ground on the plug so it never had this problem.Fixed the problem tonite with a inline coaxial ground loop isolator($14.95) at local audio dealer.I did call the cable company first thing today and have them coming out 2morrow,will have to call them back and canceal~~~IT'S FIXED!!!!..

Excellent! Glad to hear you got it fixed so quickly.

What effect does the filter have on the picture and sound quality of the cable system?

A filter should not degrade the signal, assuming the cable company is providing you with a signal that is up to snuff. I've run into trouble with the cable company not being able to maintain a strong enough signal to my house to satisfy digital cable boxes and the cable modem, but a service call or four has led to them putting a signal booster in. In that case, the presense or absence of a isolator was irrelevent, but if I had been using one it would probably have compounded the problem. Bottom line: if an isolator negatively effects your signal, I would recommend getting the cable company out to fix your wiring - either by properly grounding the system to eliminate the need for the isolator, or by fixing whatever is giving you a weak signal to start with.

I havn't noticed any negative effects from the isolator.The high def. looked and sounded fine so we're dailed in for now!

Well I recieved my 7700 and had a terrible ground loop. The in line filter caused some of the HD channels to start dropping. I had to put a cheater plug on the 7700 to fix the problem at the moment...

I used the Xantech 634-00 ground breaker on my Time Warner Cable HD box.I only get TNT and Discovery channel in HD and they looked good with the Xantech.The cable company's need to get their act together on these ground issues with their equipment!

What about using the Ground Lug on Power Conditioners?

Most power bars designed for HT & component style power conditioners all have a Grounding Lug that gives a common ground for all connected equipment. You just run a cable from your component to the Lug and it's supposed to fix all ground loop problem, you might have to ground all of your equipment I am not sure. Has anyone tried using this? I will be getting the 7700 soon, it will be my first 3-prong plug in my rack and if I hear a hum that is the first thing I am going to try, I have heard bad things about using "cheater plugs" on equipment that was designed with the ground in mind.

Question I have is which bolt to run a wire from on the Amp to the Ground Lug. I really don't like having the cheater on it at the moment either...

I know most are going to say put a filter on the cable system, but that's not the issue. Believe me, I have put time into diagnosing the issue. The issue is either the APC Smart UPS battery backup on a portion of the system (TV, 990, DVD, Cable box, Sat box... it's not on the Amp) or the Amp itself. I'm going to try removing the battery backup as soon as I get back home...

I have all my theater stuff connected to a large APC UPS and have used APC UPS's for many years. Unless it's defective, I think it's extremely unlikely to be the source of a ground loop. Most of the APC units have an LED on the back that can indicate if it detects faulty wiring at the outlet it's plugged into. It's almost certainly a loop introduced by your cable box as that is a frequent culprit.

Cheers,

I think you can use one of the screws on the components case; just loosen it and wrap a wire around the screw and run the other end to the lug on your power conditioner. Components are grounded to their case so I imagine this is all that is necessary.

Ritz, yea, it's not the APC, but it's also not the cable because I removed them completely and not effect.

The buzz is in a high frequency range but goes away if I remove the ground... I'll try running a heavy wire from Pre-Amp-Power Dist center.

i did exacty thAT.last winter,to avoid static.strapped 1050(no ground lug) to amp.

OK, so I ran the following ground wires to the commond ground on the power distribution center:

From 990 to common ground.
From 7700 to common ground.

Result, I can now remove the cheater from the amp. It removed 85% of the noise that I was hearing and I have to jam my ear to the speaker to hear any. Good enough for govenment work in my book.

Thanks for the suggestions!

I wonder what would happen if you grounded ALL of your components to that common ground lug Jester? Maybe a project for a rainy day?

I am glad that you have removed the majority of the hum, I guess those ground lugs do serve a purpose after all!

Jester,

I am curious if you would get the same results just grounding the 990 to the common ground plug on the power distribution center (PDC) and not grounding the 7700 to the PDC. My guess is "yes" as the 7700 has three prongs that connect to the power cable while the 990 only has two. I think you should be able to remove the one from the 7700 and elicit the same results.

Zo, the head scratcher is that it's not a hum in the low end, rather a buzz in the high end. I have Rocket RS1000's and its coming from the very top speaker in the array.

Doug your probably right. Thing is that the 990 is plugged into the power distribution center, and the Amp is not, rather to the wall with a surge block between the outlet and the plug. Since I was at it I figured why the hell not, ya know...

I think ALL components would need to be grounded to the same Lug as a Ground Loop is caused by components using seperate ground paths and the Amp is plugged into it's own wall plug; is this plug on the same circut as the one the rest of your components are plugged into? Here is a little background info on Ground Loops:


Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.

When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment. To prevent ground loops, all signal grounds need to go to one common point and when two grounding points cannot be avoided, one side must isolate the signal and grounds from the other.