We know from your earlier posts that the plasma has a three-wire power plug. The fact that the other two sets do not have hum PROVES that the hum is a ground loop problem with the plasma. Read Bill Whitlock's paper on eliminating noise and actually go through the steps, one at a time, at least mentally, to determine where the problem is.

Isolating the cable ground helped part of the problem, and it seems to me that breaking the dish ground by using the window cable thingie (technical term), since it will break the dish ground to this part of the system, should fix the rest of it. You can test that by disconnecting the dish feed while your satellite has its menu image up, and seeing if the hum disappears. If it works, go with it!



Be careful here with your concepts, because they might lead you away from solving the problem -- trying to find a problem with a troublesome samsung receiver will take an AWFUL long time if the trouble is simply your grounds, and not the receiver. PROVE that the receiver is troublesome before you call it that...which also means you can only call it troublesome after you have solved the problem.


We have told you to break the ground to solve the problem, but we have also told you to add a ground to solve the problem. These sound opposite because we have not told you the actual goal: we want you to do something that will make ground current NOT flow wherever the heck it is causing the problem. That can be done either by interrrupting the flow, using the glass thingie, or by adding another ground, so that the current flow that is causing the problem goes through a different ground path and not through the ground path that results in visible hum.

So where do you ground the multiswitch? In the basement? Try grounding the "troublesome" satellite receiver. Try grounding the dish (groan -- a separate ground wire run down from the roof). Try grounding to a water pipe, or to a piece of metal driven into moist ground right outside where the receiver is. Grounding to a power ground at an outlet will most likely not solve the problem.

In the realm of KISS troubleshooting, I also like to make sure that the electrical outlets are wired correctly. You can purchase a simple and cheap electrical plug/outlet tester at Home Depot ...etc. This simple device will let you know if you have an open grd, hot neutral, hot/grd reverse ...etc.

[Link: awsperry.com]

Make sure that all of your outlets are wired correctly before you start to chase ground loops in the AV gear. I've seen some incorrectly wired outlets by qualified electricians.

Cheers

You say I can't use the same outlet because the plasma is on the other side of the room. What if you use an extesion cord on a temporary basis to plug all the equipment into the same outlet?

Could your problem be with the multiswitch power supply?

Did you try a different sat receiver?

phil,
we have not heard from glaro that he has tried all of the other things presented. Actually, I thought the problem was solved with Michael's idea of using a glass-link to break the satellite ground (loop).

Hey, glaro, how's it humming?

without being on site it's going to be a hard one to give advice on but I'll give it a long winded try. The multiswitch should definately be bonded to the main electrical service ground. Idealy you need to bring in your coax from the dish at the same point of entrance as the electrical service and ground the coax at that point, before it enters the house. By just grounding the multiswitch you are providing some protection but if this thing gets blasted by lighting it will travel the whole way through the house before hitting a ground point. NOT a good thing. I know we have all done it at some point or another but you may want to take a second look at the install. Once that is done I would eliminate other possible ground loops by connecting the plasma directly to the SAT receiver and plugging the plasma in to the same outlet as the SAT receiver. This really is critical. I think I would move the SAT receiver to the plasma rather than running an extension cord for the plasma. While you are at it disconnect the other two sat feeds from the LNB just to make sure there are no other ground loops involved. I would also do this without ANY monster cable, panamax or any other MOV based surge protection in place. It is possible for a device like that to create havoc by constantly feeding voltage onto the ground wire. You should not have any noise at this point. If you do then something is designed very poorly and I'd start by trying a different receiver, even if it isn't HD, just to see if something changes. If you have no noise then put the receiver back in the rack and use an extension cord to plug the plasma into the same outlet as the SAT receiver. If you have noise at that point then either the plasma or the SAT receiver is very sensitve to ground loop voltage and your going to have to break the loop. It seems that the glass link or maybe a Jensen transformer are the best options. I'll call Jensen myself and talk to them about it if you get to that point. Also use one of those $3 testers to make sure the AC outlets are wired corectly. Is the multiswitch powered or passive? and is it mounted to a rafter or in a metal can? If it's mounted in a metal can, is the can bonded to the main service ground? --- I wrote this BEFORE reading the second page so some of it has allready been said...----

This message was edited by Ted Wetzel on 07/27/03 17:26.

Grounds should only be bonded to the same ground as the electrical service. I only use a cold water pipe if there is a connection to the electrical service ground and the same water pipe in close proximaty to each other. Driving your own ground rod is against code and can KILL people. The only way that this is acceptable is if it is installed by an electrican and properly bonded to the existing ground rod. Cheers.

sorry for no reply--i 've been relaxing in cape cod while my customer continues to hum--- anyway i narrowed it down to the sat feed the day i installed the plasma. i remove the feed and the lines go away....i will order the glass link as the "easiest" solution-if it works. i have not tried plugging the plasma into the same outlet--i will when i return this week..
the problem, i believe, is the power coming into the house, so the elec. company says, therfore i was looking for a simple temporary solution. lipa, the power co., says they need to break the concrete street in order to fix the problem, which could take six to 12 months. there is noise all over the house but this is the only place where i am not able to filter it. if i could fit a monster 5100 behind the plasma it would probably fix the problem, i think. any thank you all for your input as i am planning on starting my own "noise filtering buisness after the experience i've had with this job. Thank god this customer has been very patient

glad to hear it but one word of caution. while I have no idea what the power company could be talking about you can not continue to think of this as filtering noise, you clearly have a ground loop problem. Your installs are affected everyday by ground loops and unless you take the time to understand them you will continue to chase your tail and throw money at the problem until it goes away. Ground loops are always fixable with a simple, straight forward approach and they cause problems in ways that you can not even see. I was on a job a few months ago where a company had done an install that smoked two amplifiers in a row with no clear reason why. It was a ground loop between the FM antenna and the equipment.

Are you connection the Channel 3 output of the sat receiver to your cable system for modulation?

If so, you may want to use a ground breaker at the ch.3 output. You can simulate this by using (2) 300-75 ohm balluns tieing the 300 ohm ends together. This is essential a 1:1 isolation transformer....

i am using component out of the b&k to the plasma..it's a hd setup. comp. out of the samsung to the b&k the comp. to the plasma. i just got the comp. line filter and i ordered the glass link. going to try both for future reference. Ted, sorry about the wording, i've come to understand a ground loop a little better through this experience. am i correct in saying that the ground loop generates noise and i am assuming if i can't break the ground, as in this case then i should focus on the noise? what is the straight foward solution to a ground loop? the power company says it's something with the neutral.

I agree with Ted W. - no matter what the power co does, you will continue to have this problem. Here is why:

When two pieces of equipment are connected via an unbalanced interface, the noise current flows in the shield conductor of the cable. Because the shield has impedance, a small noise voltage drop appears across the length of the cable, according to Ohm's law. Since the cable shield is also part of the signal circuit, the noise voltage will be directly added to the signal at the receive end of the cable, which is the sum of all the voltages in the loop from point A to point C. Because the shield impedance is part of two circuits, noise current and signal current, this mechanism is called common-impedance coupling.

Consider this typical scenario. Two devices are connected by an RCA audio cable. Both devices have 2-prong power cords, and their power-line capacitances cause a 300uA, 60Hz noise curent to flow between them through a typical 25-foot unbalanced cable. The cable has a foil shield and a 26-gauge drain wire, making its resistance, or 60Hz impedance, about 1 ohm. Using Ohm's law, we calculate the resulting voltage drop to be 300 uV. With respect to the nominal consumer signal reference level of 300 mV, this noise level is only 60 dB. And the high-frequency noise may be even worse and more audible as buzz.

The magnitude of the noise current can be much higher if both devices are safety grounded (i.e., having 3-prong power cords). Referring to Figure 1, consider that leakage currents from all devices on a branch circuit cumulatively flow in the safety ground wiring. Since leakage currents for safety-grounded devices are not limited to the 0.5 mA allowed for 2-prong equipment, it is not uncommon to have leakage currents of 100 mA flowing in portions of the safety-ground wiring. Because of the impedance of the safety-ground wiring, this could result in well over 10 mV of noise voltage between the safety ground pins of two different receptacles.

And this can get much higher between two outlets on different branch circuits. For two safety grounded devices, this voltage will be impressed across the length of the signal cable shield and be directly added to the signal. For 10 mV of noise voltage, the noise would be only 30 dB with respect to reference level.

In a standard video interface, reference level is 1 volt peak-to-peak, including sync. The active range from reference black to reference white spans about 600 mV peak-to-peak. Since our previous noise voltage of 10 mV (rms) equals about 30 mV peak-to-peak, our signal-to-60Hz hum ratio would be 26 dB. This would cause a visible hum bar in a video display. Even higher voltage differences can result if one of the devices is connected to an outside ground point such as a separate earth ground or a CATV drop.

The above has been copied from: [Link: svconline.com]
(but I did stay at a Holiday Inn Express last night!)

I had this same problem a few years ago where an 80" Mits RPTV, which was located on the other side of the room from all the other equipment, kicked my a?? with video noise and I never really understood what the heck was going on.
Here is the room - [Link: genelarge.com]
click on Media Center
-yes that is a Bose Lifestyle 30 system which I did not sell them! It was all changed out at a later date-but the video noise stayed. The equipment (DSS, DVD, VCR, A/V Receiver, etc) was in a cabinet in the back left corner of the room.

Sorry for such a long post. This house no longer belongs to the owner of the website above so please do not call.

tried out the iso-max vbh-3rr video ground loop corrector-
the lines are gone!