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Discussion Starter #1
I recently purchased the Logitech Z-5500 Digital surround sound system for my living room. It's wickedly awesome for the price, only missing some inputs.


Anyway, the subwoofer produces a low buzz/hum when powered on. When I mute the system, it goes away, as it does when powered off.


I do not have cable/sat in my home. I have a Phillips DVP-642 connected via optical and a MediaMVP connected via the supplied cables with a game adapter to RCA, if that makes any sense.


The noise is more obvious when nothing is playing while on the MediaMVP than the DVP-642. A JVC 36" CRT is my display and that's all the audio/video equipment I have in the room. No standard receiver or FM radio or anything, yet on occasion I can discern a local FM Radio station (105.9FM) coming through the sub.


NO buzz/hum is heard through the satellite speakers. At first I thought the muffled voices were coming from outside, but upon closer listening, it's my sub. Weird.


The noise is quite annoying, at night, or soft passages, it is most definitely noticeable. I plugged in the power to my PC's APC BackUPS 500VA and unplugged the UPS from the wall and the noise got WORSE! I went to Radio Shack and bought a single surge suppressor/noise filter and the noise remains the same.


I am beginning to suspect it's Radio Frequency Interference and not a ground loop. Obviously I am not certain or I wouldn't not be asking for assistance here. Please help me with this, it's starting to make me insane.
 

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I plugged all my gear into a Monster Power HTS3500 Mk II but forgot to plug in my subwoofer. I leaned over the sub and plugged it into a wall outlet and noticed a slight hum. I only heard it if everything else was silent and if I was within a few feet of the sub.


I went through the hassle of crawling behind my audio cabinet and fishing it into the Monster line conditioner and the hum went away. A cheapie UPS or surge protector isn't going to solve the problem. You can try a decent line conditioner that isolates the different devices from each other and see if that solves the problem. Belkin and Pure AV are other names besides Monster. The only reason I got the 3500 MkII is because it was $127 after rebate. Otherwise, Monster is overpriced.
 

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Is the sub quiet (no hum or radio station) when powered on and the audio input line is disconnected?


If so, a simple isolation transformer in the audio line may be the answer.
 

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Discussion Starter #4
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Originally Posted by NightHawk
Is the sub quiet (no hum or radio station) when powered on and the audio input line is disconnected?


If so, a simple isolation transformer in the audio line may be the answer.


The sub is only quiet when on Mute or powered off.


I took the sub and control box all over my house and it makes the buzz/hum in each location. It doesn't matter what is connected to it, or what is not connected, it makes the noise.


I have an old ground loop isolator (With RCA input/output) I used in my car stereo for unwanted noises, tried connecting a DVD player to the GL isolator to a RCA to headphonejack adapter, to the input on the Z-5500 and still the noise. I'm sure it makes no sense because the sub makes the buzz/hum anywhere in my home regardless, but I thought it was worth a shot.
 

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Discussion Starter #6
It is possible.


However, when I take the sub+control pod to another location per the Hum FAQ and I hear no buzz/hum at all, that would indicate it is NOT a defective unit and the trouble lies within my home.


Hypothetically, if that were to happen, i.e. I take it next door to my neighbor's or 2 doors down to another neighbor's house and at each location the noise is not audible, what would be the next step to troubleshoot my problem?
 

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If the problem is isolated to your house current it sounds like you could possibly have a miswired outlet somewhere with a netural-ground swap. It wouldn't even need to be the one your using for the surround sound to be causing noise problems in your setup. It will also require an electrican to locate unless your handy in that area.
 

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Discussion Starter #8
Ok, so if I have a miswired outlet in one of the many outlets in my home..could I take a surge protector or a battery back ups to each outlet and see if the "Wiring Fault" LED lights up? I have three APC devices 2 UPS and one super power strip that have a red LED indicator for wiring fault and green for "all good".


I recently moved in(almost 7 months ago really) and I am continually in re-model mode. So after carpet+tile was laid, I switched the outlet receptacles with newer ones. Well to make a long story short, I crossed some wires in one of the bedrooms and went to turn the breaker back on and it sparked and fried the breaker. Had to call an electrician to track down the troubled outlet and pay a hefty fee for his services and the cost of a new breaker.


So I would love to find an alternative method of detecting bad ground(s) in my home with minimal effort and minimal cost to me. Something from Radio Shack I can purchase cheaply to aid me in finding bad outlets?


Thanks for you help NightHawk!
 

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A fault detector might be able to find the problem but there is no guarantee. They cannont detect every type of miswire condition. I'm not an electrican and I'm not sure how you could determine for certain yourself if this is the problem.
 

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Do you receive OTA television? If so, unplug your antenna and see if the hum goes away. I dont have sat/cable either, and had a loud sub hum. I discovered it was due to my new outdoor antenna.
 

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Discussion Starter #11
I guess one way is to take the sub and control pod over to a different house, and if there is no noise, it's definitely something in my home causing the noise. If there is, then it's the "noise floor" or a faulty component. I'll do that when I get home.


In the Hum FAQ it says "NOTE: optical interconnects are immune to ground loops and EMI/RFI."


Does that mean when a DVD player is connected to a receiver, and there is a presence of EMI/RFI Ground Loop problems, you can not tell because the optical cable is plastic and immune to such interference? When I have my DVP-642 connected via Radio Shack 12' Optical Cable, and turn the volume all the way down on the Z-5500 I still hear the Hum. What does that indicate?


The FAQ also says EMI/RFI has a hiss quality rather than a deep hum. I don't really know the difference unless he means EMI/RFI sounds like pink noise and GL problems sound like huge power lines humming.



Now that leaves me with two paths(I think) either it's my AC power or RFI. Since the hum is there no matter if devices are attached or not, that eliminates EMI correct?


Does that sound right?


How do I test for RFI? In the Hum FAQ it does not mention RFI test procedures, just EMI and jumps right to power problems.
 

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Discussion Starter #12
Quote:
Originally Posted by kwill
Do you receive OTA television? If so, unplug your antenna and see if the hum goes away. I dont have sat/cable either, and had a loud sub hum. I discovered it was due to my new outdoor antenna.
Nope, I have no coax cable running to my Home Theatre. The only coax in my house goes to my cable modem, and it's one straight piece of cable from the pole to the wall plate. There's no cable running through my walls, nor telephone wires. Ripped it all out when I moved in.
 

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There are reasons optical cables are immune to certain types of interference. Because they don't conduct electrical current they cannont provide a path for ground-loop currents. Typically ground-loops are multiples of 60 Hz and result in a low-frequency hum. That's not saying however that just by having an optical cable in your system you will prevent a ground loop. Ground loop currents can often be sneaky and find other paths. The optical cable will simply reduce the chance.


RFI and EMI are less common than ground loop problems and less well defined. They can result from anything from appliances to automobile ignitions to radio stations or even stellar noise. Again being plastic means an optical cable canont be an antenna. RFI and EMI typically enter a system via an unintentional antenna. Just because you have an optical cable however dosen't mean RFI will not enter your system somewhere else.


The sound of RFI/EMI is dependent on the source and be heard as buzzing, ticking, pops, whines or simply excessive hiss. The best tests for RFI/EMI is it is typically both time and location dependent. A ground-loop or power issue, which I suspect is really your problem, is constant for any given set of AC power outlet/grounding conditions.
 
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