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Discussion Starter · #1 ·
Hello everyone. I just recently acquired a home theater system for myself, after having to learn a great deal about home theater and audio in order to set one up for my family. I am having some difficulties with the Onkyo subwoofer with this new system. I have read this forum for alot of information and advice in the purchase and setup of these two systems, so I thought I would ask here for help.


I am currently running a Pioneer VSX-811S Reciever hooked up to an Onkyo HT-S660 system (Long story as to why I don't have the Onkyo Reciever) with a couple of changes. The front and center speakers are the same, but I obtained two more of the large speakers to use as surrounds. The smaller bookshelf surrounds are used as my two rears, leading to a fairly cheap 7.1 system.


The powered Onkyo subwoofer has been giving me two problems.


1. It seems to emit an unusual low hum at all times, beyond the standard powered subwoofer hum.


2. When I play music, the subwoofer seems to have a slightly more powerful hum mixed into the LFE that dulls the subwoofers regular output. This causes for muffled background noise in addition to the "normal" subwoofer output at medium and high volumes.


Currently the Crossover is set at 100Hz since the Reciever doesn't have 80. No DRC is being used. I am Coax connections from my PC and my Cable Box, and an optical from my Playstation 2. All music listening occurs on my PC, which contains Nvidia Soundstorm, this results in Dolby Digital encoding for any sound that comes from my PC (Similar to the integrated dolby digital encoding on an xbox). I have tested the regular analog connections for the PC sound and the hum is still there, so it is not the onboard dolby digital encoding that is causing that problem.


Is there anything with the reciever, or the actual subwoofer connection that could be causing both of these hums, or any settings I may have missed? I am relatively sure that I am not getting magnetic interference, and have tried another powered sub with similar difficulties. Also, could the louder hum in problem number 2 be directly related to the minor hum in problem number 1? These hums are especially bad as this is not truly an HTS, but more of a multifunction personal theater system in a smaller room then most home theater setups.


Thanks in advance

-Dave
 

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Sounds like a ground loop problem. Do a search for "ground loop" here in the forums and you'll find many threads.


Is the sub hooked into the same circuit as the rest of your setup? Do you have cable TV? Cable TV is a big culpret of ground loops. Try disconnecting the cable tv wire from the wall and check to see if the hum is still present..


Hope this helps,


Sorny
 

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Discussion Starter · #4 ·
Bingo, it is a ground loop, resolving it now! Thanks for the help, I didn't know cable itself could interfere, i just thought TVs/Monitors were the major culprits.
 

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Discussion Starter · #5 ·
Ok I'm trying to stomp this ground loop before I buy the isolation transformer. The second I unplug my cable wire from either end, the hum goes away so it is definitely the cable. I have tried switching AC outlets for all of my components, but that does not take care of the loop. Even with no power to any devices but the reciever/sub, the hum is still there. Anything I can do without the isolator?
 

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Since you'll need a surge protector/power center anyway, get one with F-terminal pass-thru for a coax cable. This "bonds" the coax ground plane with the house ground thru the electrical ckt the SP is plugged into.


It may not reduce the sub hum 100 percent, but there's no harm done here in upgrading surge suppression.


In the end -- and physical location may make it difficult in the case of pole-drop cable -- the cabletv coax should have a ground connection to the same earth stake used for the house ground, below the service entrance box.


bill
 

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In all probability you are using a powered Sub and it is plugged into an electrical outlet that is on a different phase then your receiver. The result is the ground loop. And other typical culprit is the CATV system. Cable companies use l20 v amplifers to amplify their RF signals and although they are supposed to install voltage blocks at their distribution taps they ether fail to do so or the blocks fail to work. This also yields a ground loop. You could use CATV isolation transformer for this problem. Look at the URL I posted above at seek out the BB-FF model.


Alan
 

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Discussion Starter · #8 ·
Unfortunately I have digital cable, and the F-connector in my surge protector does not carry greater then 900mhz signals, therefore it does not work. I am probably going to purchase the Jensen Cable isolator because it has the frequency support for Sattellite/Digital Cable. After unhooking my cable, I noticed some other minor performance boosts in the speakers themselves, so hopefully the isolator will take care of those too. I figure the reason for all of this is that the cable in my room is a patch job, and was done after all the other cable in the house was installed. The isolator should work to support the lack of grounding caused by the junky patchwork cable setup.
 

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Discussion Starter · #9 ·
PS: Thanks for the quick response, everyone was very helpful. Was able to immediately tell what was causing the problem, and had a number of suggestions to try and fix it. I have a very complicated setup in my room because of the number of devices involved. In fact, I think the culprit of the phase loop isn't the Reciever/CATV, I believe it is my PC going through my Reciever to the CATV. Breaking the PC or Breaking the CATV connections both fix the problem immediately.
 
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