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Old 04-15-2008, 10:45 PM - Thread Starter
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Hi,

I recently got a new subwoofer and now all my speakers buzz/hum. After some research and experimenting I think it's a ground loop from my hd cable box. I unplug the cable from the box and it goes away. I think I have 2 options

1) put a isolator on the cable line, costs around $50.00 and I'm concerned it could it degrade the picture quality.

2) put a isolator on the subwoofer cable, costs 17.00 from ratshack. It's made for stereo cables, red and white plugs. Will this work ok as a sub cable?
This is the RS one http://radioshack.com/product/in...entPage=family

Thanks,

Jason
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Old 04-16-2008, 05:07 AM
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or you could call the cable company and have them properly ground the cable line to the main first for free. see if that cures the problem and then decide if need to get an isolator. i've had that radioshack one before and it didn't do enough for me to notice the difference.
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Old 04-16-2008, 02:51 PM - Thread Starter
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The cable is grounded. The comcast guy came out today, no luck fixing it. He swore it wasn't possible for the cable to cause any ground loop, because the cable tv wire only caries RF, no electricity. Oh well.

Any thoughts on that RS isolator.
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Old 04-16-2008, 03:19 PM
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The cheapie ground loop isolator will work just fine. I have one hooked up to my SVS sub and one hooked up at my parents house when I heard hum from both subs. Both worked great, took two seconds to install and were cheap and worked as advertised. Don't get the expensive one. Cheap Rat shack cable will work just fine.
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Old 04-16-2008, 03:45 PM
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Try the Rat Shack one, but if you buy a cheapie ground loop isolator for your cable box, it will be a waste of money. I bought one from Dayton and it wreaked havok on my digital cable. Some HD channels would not come in.....screwed up the online guide.....and my PPV did not work. But it did fix the hummm. If you need to go that route...Jensen makes a good one and this one made by viewsonic, I bought it off ebay and works like a charm...got it for around 28 bananas shipped. hmmm..here is alink if you are interested....
http://cgi.*********/VIEWSONICS-VSIS...QQcmdZViewItem

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Old 04-16-2008, 04:32 PM
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I used the same Radio Shack one you have linked in the past, and it worked great with my Paradigm sub. I no longer have the problem with my F113 sub, so I don't use it. I would say go for it. If it doesn't work, Radio Shack has a great return policy.
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Old 04-16-2008, 05:22 PM
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Quote:
Originally Posted by jason978 View Post

The cable is grounded. The comcast guy came out today, no luck fixing it. He swore it wasn't possible for the cable to cause any ground loop, because the cable tv wire only caries RF, no electricity. Oh well.

That's what the first two cable guys said but I browbeat the third one into trying to co-locate his ground with the house ground. It worked like a charm and he was amazed.

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Old 04-16-2008, 05:31 PM
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That's what the first two cable guys said but I browbeat the third one into trying to co-locate his ground with the house ground. It worked like a charm and he was amazed.

I was going to add that they drove a seperate ground rod in at my fathers
house and it created a hum through his stereo.I came over relocated the
ground at the electrical breaker box problem solved hum stopped.Almost
all buzz and hum issues are when a house has mutiple grounds if all the
grounds were tied at the breaker most of these threads would not exist.
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Old 04-16-2008, 05:38 PM
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I had ground loop issues in speakers and displaying on my LCD TV. A good quality surge protector that EVEYTHING connects to (including cable and CAT-5) is what fixed it.

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Old 04-16-2008, 10:56 PM - Thread Starter
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Hey bobcel,

Did your ppv and ondemand stuff still work with the viewsonics one?

jason
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Old 04-16-2008, 11:07 PM - Thread Starter
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my cable guy told me that I can't use anything on the tv cable line because it will ruin(make it not work) the onDemand stuff and that the cable would not be able to send a signal back.

I got the RS one, but it has 2 male plugs on it and it's not long enough to reach the sub. Argg, back to RS tomorrow to get a female coupler so I can join the isolator with my existing sub cable. I'll let you guys know if it works. Fingers crossed.

Jason
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Old 04-17-2008, 04:02 AM
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It also worked for me with the cheap RS isolator.
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Old 04-17-2008, 05:38 AM
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I would consider getting a good unit similar to the Jensen and put it on your cable line. This is likely the major source of the ground loop current and even though you can eliminate most of it with an isolator on the sub line it would be best to eliminate it from your whole system. Ground loop currents can cause system noise other than 60 Hz hum (harmonics). While it's also possible to reduce these currents by relocating grounds you can never completely eliminate them by any means other than isolation.

http://jensen-transformers.com/iso_vid.html
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Old 04-17-2008, 05:55 AM
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Quote:
Originally Posted by jason978 View Post

my cable guy told me that I can't use anything on the tv cable line because it will ruin(make it not work) the onDemand stuff and that the cable would not be able to send a signal back.

In my(unfortunately) long experience with cable guys, I find they come in two varieties. The vast majority are like CSRs and simply go through their standard tests and standard dialog; they are incapable of responding to your particular situation and cannot (will not) understand what you are saying. A few are willing to listen and respond.

Statements like the one you quote as well as the earlier quote about not being able to do anything about the ground loop because the cable does not handle any power are equally nonsensical but that is what they are trained to say.

I do not know the RS unit but I have used an APC filter for years (for protection, not ground loop cure) and it works fine for all functions.

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Old 04-17-2008, 06:06 AM
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how about the hum-x



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Old 04-17-2008, 06:48 AM
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how about the hum-x



It's difficult to picture how this "magic" box works. If it maintains a soild safety ground connection as advertised how can it eliminate a ground loop? I would be skeptical.
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Old 04-17-2008, 07:18 AM
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It's difficult to picture how this "magic" box works. If it maintains a soild safety ground connection as advertised how can it eliminate a ground loop? I would be skeptical.

I suspect its just a "cheater plug", Hey!! I have one I had an annoying hum in my sub system only because it was on a separate circuit then my AVR.

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Old 04-17-2008, 06:45 PM
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The Hum-X does work... I've used one for a while with two or three separate power amps in my 2-channel setup.
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Old 04-17-2008, 07:32 PM
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Quote:
Originally Posted by jason978 View Post

my cable guy told me that I can't use anything on the tv cable line because it will ruin(make it not work) the onDemand stuff and that the cable would not be able to send a signal back.

I got the RS one, but it has 2 male plugs on it and it's not long enough to reach the sub. Argg, back to RS tomorrow to get a female coupler so I can join the isolator with my existing sub cable. I'll let you guys know if it works. Fingers crossed.

Jason

Try THIS Holland cable isolator for $12.25. I'm using it on my Comcast on-demand HD dvr at this moment and it works fine. It stopped my hum. I've used it for the last 2 years. I've moved from an apartment with a bad ground to a house with a bad ground.
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Old 04-18-2008, 10:46 PM - Thread Starter
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Well the RS isolator did the trick. I ran REW to make sure that nothing funny was going on. The graph was the same, only lower. I had to turn the sub level up 5 dB to get it to match the previous values. Thanks for all your input.

Jason
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Old 04-23-2008, 04:07 PM
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But its possible for the cable tv wire to pick up the a/c hum (60hz) because of broken shielding or bad connectors on the ends that are in the wall, run under the house, etc.

If you could hook up a spectrum analyzer to the cable tv wire at the receiver, it may be interesting to see whats there (if there is any signal in the sub-100hz range).

If your cable wire runs close to and parallel to a/c wiring in a wall somewhere, for example, it could pick up the 60hz hum, especially if there is a weak spot in the shielding/connectors
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Old 05-07-2008, 12:49 PM
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I am in the same boat. I put in a new eD A2-300 sub yesterday and got a constant hum from it (increases at higher gain levels). Before I try out the radioshack isolator I'll try plugging the power cord into its own outlet. Right now it is going into a surge protector that powers all my A/V equipment.

If the hum still exists I'll know that my Comcast HD-DVR is the culprit and I'll get the isolator.

HT: 60" Samsung UN60F7100, Infinity Primus 360 towers/152 rears/PC350 center, Elemental Designs A2-300 12" sub
Music: PSB Image 6 bookshelf pair, Yamaha R-S500 stereo receiver, Def Tech AW5500 outdoor speakers for patio
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Old 05-07-2008, 12:55 PM
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Quote:
Originally Posted by jason978 View Post

Well the RS isolator did the trick. I ran REW to make sure that nothing funny was going on. The graph was the same, only lower. I had to turn the sub level up 5 dB to get it to match the previous values. Thanks for all your input.

Jason

The RS isolator uses a cheap transformer for each channel. In addition to the loss of level, there is also a likely frequency response issue. Most cheap transformers roll off at low frequencies. Not trying to rain on your parade, just letting you know my experience with those things.
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Old 08-13-2008, 03:06 AM
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excuse me all ye with ground loop isolator experience...

but..

I have been suffering a bit of a bad hum in my sub... so today I purchased an isolator from jaycar electronics in Australia. It's labelled as a car audio model, but I can't see how there would be any difference.. it has the RCA stereo ins, and outs.

Anyways.. it removed about 98% of my hum.... BUT... also reduced the volume of my sub by about 14dB!!! a HUGE drop in volume..

I have had to dial my RXV3800's sub output up to +10, and also crank the actual volume on my sub amp.

HELP!?!? Is this meant to happen?!?!

Scott
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Old 08-13-2008, 06:51 AM
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Quote:
Originally Posted by scott_richardson View Post

excuse me all ye with ground loop isolator experience...

but..

I have been suffering a bit of a bad hum in my sub... so today I purchased an isolator from jaycar electronics in Australia. It's labelled as a car audio model, but I can't see how there would be any difference.. it has the RCA stereo ins, and outs.

Anyways.. it removed about 98% of my hum.... BUT... also reduced the volume of my sub by about 14dB!!! a HUGE drop in volume..

I have had to dial my RXV3800's sub output up to +10, and also crank the actual volume on my sub amp.

HELP!?!? Is this meant to happen?!?!

Scott

I would look at your electrical closer or maybe call a electrician as for the
piece you bought it sounds like all its doing is attenuating the signal.
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Old 08-13-2008, 05:28 PM
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My father in law is an electrician... and it just dawned on me what may be causing SOME of the issues

my sub is at the back of the room.

amp at the front

to get the signal to the sub, I run an RCA from the amp to an RCA wall plate. The cable that runs up the wall, along the roof, and down the back wall, is actually speaker cable, and not RCA cable. Then I run another RCA cable from the wall plate at the back of the room to the sub.

Could it be that my speaker cable in the roof, which is acting as an RCA cable, is allowing more hum and noise through?

I tried connecting a LONG RCA cable from the amp to the sub directly, and the hum was still there, but only about half as loud. Still too loud though.

Anyways.... for now I have a solution. Please let me know if this is okay:

1. Turn my sub volume knob down until the hum is pretty much inaudible. My sub volume knob is just over a quarter..
2. Turn the sub output on my receiver up to about +5dB.

Tell me, is this a fairly okay solution? There's no real issue running the receiver's sub output so high is there? I mean it's all relative right? The final output volume of the sub seems to be the same as before (volume knob on half, sub output on -3dB on receiver)

??
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Old 08-13-2008, 05:50 PM
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Quote:
Originally Posted by scott_richardson View Post

to get the signal to the sub, I run an RCA from the amp to an RCA wall plate. The cable that runs up the wall, along the roof, and down the back wall, is actually speaker cable, and not RCA cable. Then I run another RCA cable from the wall plate at the back of the room to the sub.

Could it be that my speaker cable in the roof, which is acting as an RCA cable, is allowing more hum and noise through?

I tried connecting a LONG RCA cable from the amp to the sub directly, and the hum was still there, but only about half as loud. Still too loud though.

Passing a line-level signal with speaker wire is problematic due to the possibility of interference with a line-level signal. It shouldn't really be done. But, as you point out, it is probably not the only source of your hum


Quote:
Originally Posted by scott_richardson View Post

Anyways.... for now I have a solution. Please let me know if this is okay:

1. Turn my sub volume knob down until the hum is pretty much inaudible. My sub volume knob is just over a quarter..
2. Turn the sub output on my receiver up to about +5dB.

Tell me, is this a fairly okay solution? There's no real issue running the receiver's sub output so high is there? I mean it's all relative right? The final output volume of the sub seems to be the same as before (volume knob on half, sub output on -3dB on receiver).

Yes, it is all relative. And +5dB is not really that much.

"All men are frauds. The only difference between them is that some admit it. I myself deny it."
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Old 08-13-2008, 06:09 PM
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thanks sivadselim.

I will try, when my father in law is back up, to get him to rewire the roof cabling with some proper coax/RCA.

Scott
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Old 08-13-2008, 07:01 PM

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Behringer makes a compact 2 channel hum destroyer.

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Old 01-07-2009, 12:56 PM
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Behringer makes a compact 2 channel hum destroyer.


Thx for the info, I have ground loop in my IB sub, so I'm spending $30 @ PartsExpress:
(I'm using cheater plugs now for amp and BFD, they are on a dedicated isolated ground recept different from the HT AV which is also on a dedicated isolated ground recept, still hummmmmmm)
Behringer HD400 Ultra-Compact 2-Ch Hum Destroyer
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