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Discussion Starter · #1 ·
I have a problem that hopefully you guys can help me with.


Equipment:


Yamaha RXV-800 receiver

Sony DVD -- S-video to TV, Optical to receiver

Sony 36" TV -- audio outs to receiver

Adelphia Digital cable box -- connected to TV via standard cable connection


Speakers: -- all active speakers connect to pre-outs of the receiver.


Paradigm Active 40's, CC, 20's

Martin Logan Descent subwoofer



Here is the problem. Whenever I have the cable and the subwoofer connected I get a ridiculous loud hum thru the sub and all the speakers regardless of whether the mode (ie. radio, TV, DVD etc)


Here is what I have tried.


1) plug sub into a different power outlet in another room -- Same problem


2) bypass internal house cable wiring and connect a run directly from the outside of the house. -- Same problem


3) remove the sub connection from the receiver -- Problem solved but no sub in system.


4) remove the cable from the receiver -- sub works but no cable thru the speakers.


So it seems that whenver the sub and the cable are in the system together IN ANY WAY (audio or video wise) it induces a very loud hum. It doesn't matter how it is connected if the cable is connected to anything that is also connected to the receiver then the sub hums. All is well when I either remove the sub or the cable.


ANY SUGGESTIONS??????


Thanks.
 

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Hey! I don't have a solution, but I have the same exact problem!!!!!


I too own a Yamaha RXV-800 which I've had for about 6 or 7 years. About two days ago while I was upstairs working on the computer, there was this annoying vibration sound shaking my house, and I thought it was my neighbor sanding their floors (I'm in a townhouse). Later on I venture downstairs and the sound becomes EXTREMELY loud. It turns out that it was my left channel and subwoofer buzzing and humming. It was a real bummer because it was to a large enough extent that I thought it damaged my speakers. I hit every switch possible on my receiver until finally the speaker A/B switch made it stop. The magnitude of the hum was unrelated to the volume setting. I turned on my reciever later and the sound came back after about ten minutes. In between these two incidents, I had checked the integrity of all my RCA connections, and replaced the subwoofer cables. This time the speaker switch didn't help, but the loudness switch did. The third time the sound showed up, nothing short of shutting down the receiver got rid of it. The final time I experienced it, I had to both shut down the reciever, and unhook the subwoofer RCA. I am no longer even trying to power up the receiver!


I'm thinking the receiver may have developed a short of some type in the ground circuit for the left stereo channel and subwoofer out. I'm stumped.


I cannot believe I saw this post on here. It's an unbelievable coincidence: same problem, same receiver.
 

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This sounds like a ground loop from the cable TV connection. Try a ground isolator (maybe available from Radio Shack.) It is a little cylinder with a coax connection on one end (input from cable) and a pigtail piece of coax on the other with a connector (output to your gear).


You can also put two 75/300 ohm transformers back-to-back and do the same thing. Connect the 300 ohm sides of both transformers together and then connect the cable TV to the 75 ohm connector on one transformer and your gear to the 75 ohm connector on the other transformer.
 

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Discussion Starter · #4 ·
Alpha, that is exactly what is sound like .....sanding the floor. Wow, i thought I was the only one with the problem. You are also right...nothing short of either removing the cable connection or the subwoofer (which is how I am running the system no -- no sub) will the problem go away.


I am going to see if I can find the ground isolator or the 75/300 ohm transformers that hjones mentioned and see if that helps.



Thanks for the quick responses. any other suggestions will also be appreciated.


I may also try to borrow a buddies receiver to see if the receiver is the culprit. I just don't want to use my friends receiver and cause any problems to it.


Thanks again and please keep the suggestions coming.
 

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Your cable provider is responsible for fixing this problem. They should install the isolator for you at no cost.


Dsmith
 

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just get a three to two prong adaptor for the sub and plug it in.....problem should go away
 

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Discussion Starter · #7 ·
Hjones, You are the man.


The two 75-300 ohm adapters worked. The sound problem is solved.


Alpha, you should give this a shot and see if it works for you.


I didn't try the cheater plug on the sub. I have a cheater plug that I use to use at my old house because of a slightly audible hum but when I plugged the sub at the new house there was no hum so I did not use it. I didn't even think to put that back in the loop to see if it works to solve the problem.


Thanks guys. This now makes my home theater experience that much better since I can now have my sub in the system along with the cable.
 

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I'm not sure that my hum is due to the cable tv. My coax doesn't run through the receiver. I have a cable ground loop isolator that I tried a couple times a year or two back in an effort to reduce noise in my picture, and it actually made the situation worse. I guess I'll try it to eliminate the hum, but even if it works, I don't see how I'll live with the degraded picture. Also, my hum is not only in the sub, but in the left and center channel speakers also.
 

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Discussion Starter · #9 ·
alpha, is the hum still there if you remove your subwoofer from the equation? what about with just the receiver and the main speakers?


I guess you will have to first find out what component is causing the hum and then go from there. I hope you get it fixed.
 

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I haven't had time to troubleshoot today, but will hopefully get to it tomorrow. Thanks for your concern - I'll keep you posted.
 

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Well, I did some experimenting today, and found that the hum is indeed still there without the subwoofer in the system. It is also still present I unplug the coax from the wall. It fades in and out, but seems to get stronger over time. I guess I will have to try some other components to see if they are the culprit. I suppose unplugging each component one-by-one will do it? What if it's actually the receiver itself... then how can I test for that?
 

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Discussion Starter · #13 ·
Congrats on finding the hum. You can now fully enjoy your system. Good luck on the speaker calibrations. I will be working on mine tonight.
 
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