Cable box causing hum. Need to fix? - AVS Forum
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post #1 of 16 Old 12-26-2012, 02:24 PM - Thread Starter
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Hey guys, I finally figured out what was causing my sub, powered by an EP4000, to hum. The moment that I unplugged my cable going into the cable box, the hum stopped. So with this being said, what are my options on fixing this? Is there anything that I can pick up locally, at say....Wal-Mart or Radio Shack, that would eliminate this problem?
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post #2 of 16 Old 12-26-2012, 04:40 PM
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The problem is that cable box (STB) and the cable coming into your house are not connected to the same ground point as your AC power. If the STB has a 3 pin AC cord and some of your audio equipment have 3 pin AC cords plug everything into the same outlet strip. If your have a surge suppressor outlet strip with co-ax cable connectors built-in, loop the cable through the surge suppressor. It may limit the number of cable channels that work. If it solves the hum situation, it's evidence to show the cable tech that they have a problem.

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post #3 of 16 Old 12-26-2012, 05:03 PM
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Originally Posted by Martycool007 View Post

Hey guys, I finally figured out what was causing my sub, powered by an EP4000, to hum. The moment that I unplugged my cable going into the cable box, the hum stopped. So with this being said, what are my options on fixing this? Is there anything that I can pick up locally, at say....Wal-Mart or Radio Shack, that would eliminate this problem?

Not locally that I know of - but one device that has been known to work well is the Jensen Transformers VRD-1FF (PDF file). Unfortunately, it's 50 bucks. Markertek has them here.
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post #4 of 16 Old 12-26-2012, 07:08 PM
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cheapest solution; http://www.amazon.com/dp/B0017I3K9M/ref=pe_175190_21431760_M3T1_SC_dp_1

Several companies sell these and you can find them in male/female configurations.

"I should really see what dB levels I'm pushing. Long as it can't foam my beer during a movie we are ok "
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post #5 of 16 Old 12-26-2012, 07:51 PM
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Originally Posted by Speedskater View Post

The problem is that cable box (STB) and the cable coming into your house are not connected to the same ground point as your AC power.
The problem is that they are, just at the wrong place. All grounds end up back at the service entrance ground. Multiple pathways to that final point of zero resistance to ground potential is what creates the ground loop. According to code the cable must be grounded at the service entrance. That creates at least two ground pathways from there to the AV system, almost guaranteeing a ground loop. AV system noise is not considered by the code.
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cheapest solution; http://www.amazon.com/dp/B0017I3K9M/ref=pe_175190_21431760_M3T1_SC_dp_1
Several companies sell these and you can find them in male/female configurations.
+1. Parts Express has them, Radio Shack might.

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post #6 of 16 Old 12-27-2012, 04:13 AM - Thread Starter
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Thanks guys, I will pick up one of those things that Autox320 linked in his post. Do you think that devise will solve this issue? How do I go about fixing the actual ground problem? I am more than comfortable handling the cable, as far as cutting and splicing go, I am just not sure what to do to fix the ground issue?
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post #7 of 16 Old 12-27-2012, 06:23 AM
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Originally Posted by Martycool007 View Post

Thanks guys, I will pick up one of those things that Autox320 linked in his post. Do you think that devise will solve this issue? How do I go about fixing the actual ground problem? I am more than comfortable handling the cable, as far as cutting and splicing go, I am just not sure what to do to fix the ground issue?
If disconnecting the cable stops the hum then the transformer should fix it. To clarify, there is no ground problem per se. The issue is actually caused by grounding that's electrically correct, it's the inherent deficiencies of using unbalanced audio connections that results in hum. This link explains why. In your case the cable box/cable ground adds one additional ground path to the system that must be isolated. You don't mention how the sub amp is connected to your receiver, the fixes shown in the document may also work.
http://www.rane.com/note110.html

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post #8 of 16 Old 12-27-2012, 07:28 AM
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Originally Posted by Martycool007 View Post

Thanks guys, I will pick up one of those things that Autox320 linked in his post. Do you think that devise will solve this issue? How do I go about fixing the actual ground problem? I am more than comfortable handling the cable, as far as cutting and splicing go, I am just not sure what to do to fix the ground issue?

As mentioned by Bill, if removing the cable fixes the problem, the isolator should fix it as well. You won't need to splice the cable if you use one of these F-type male-to-male adapters. Just put it on the cable box and then you can connect the isolator to it on one end and the cable to the other.

The grounding problem is due to having two earth connections - the one for the main electrical system and the one for the cable system, allowing 60 Hz hum currents to flow between the two grounds. The isolator is a through connection for the cable center conductor and a low-value capacitor for the cable shield (ground). The cap acts as a short circuit to the RF-frequency signal in the shield, allowing that signal to pass, and an open circuit for the 60 Hz hum current in the shield, blocking it. IOW, the isolator is the fix.
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post #9 of 16 Old 12-27-2012, 07:37 AM
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There is also the possibility the cable guys never properly grounded it outside the house. My house and cable use the same ground rod outside and I have never had any hum. Go outside and check that its properly grounded before spending money. Treat the disease, not the symptoms(if possible, of course)smile.gif
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post #10 of 16 Old 12-27-2012, 09:50 AM
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Originally Posted by Fatawan View Post

There is also the possibility the cable guys never properly grounded it outside the house.
That's not what causes a ground loop. Having separate wires from that grounding point to the AV gear, one on the A/C line and another on the cable shield, can. But not always, depending on how the cable box/receiver/sub amp are configured.

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post #11 of 16 Old 12-28-2012, 06:11 AM - Thread Starter
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Would there be any thing to gain by having a dedicated 20amp line ran from my cable box, to the theater, and with this line having its own earth grounding point? I would imagine that having a dedicated 20 amp line would also be better for my audio gear in general, right. Or possible modifing the actual cable that brings in the TV and Internet signals, perhaps like running a higher quality cable that has its own dedicated earth ground? I have absolutely zero knowledge about this stuff, so pardon my ignorence.
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post #12 of 16 Old 12-28-2012, 06:22 AM
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Originally Posted by Martycool007 View Post

Would there be any thing to gain by having a dedicated 20amp line ran from my cable box, to the theater, and with this line having its own earth grounding point?
Not really, since fixing ground loops with transformer isolation is so easy. You don't even need to transformer isolate the cable, you can lift the extra ground by disconnecting the cable shield. Alternately you can lift the extra ground at the sub amp by disconnecting the shield from the RCA connector.

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post #13 of 16 Old 12-28-2012, 06:56 PM
 
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Originally Posted by Fatawan View Post

There is also the possibility the cable guys never properly grounded it outside the house. My house and cable use the same ground rod outside and I have never had any hum. Go outside and check that its properly grounded before spending money. Treat the disease, not the symptoms(if possible, of course)smile.gif

truth be told..
if you ground the AC system and the cable system to the same rod, it doesnt mean the problem goes away.. it means the problem is simply much smaller, to the point of not being noticeable through hum from a speaker.. but still possible to be seen with the measuring equipment.
the reason for that is because the ground signal has two sources of entry.. one from the AC system and one from the cable system.

one would think, if the electrical grid was really networked, then those two systems would use the same exact ground .. and if that were true, then there wouldnt be any ground hum at all to be heard.

and be smart.. every cable connection, as well as every AC system connection all have (or are typically supposed to have) an individual ground connection per house.
and that doesnt say anything about the cable system having any ground connections at the hub boxes that sit outside in the neighborhood.

it is easier to simpy assume there are two individual ground sources using two seperate grids, and those two have come into contact with eachother and the connection must be broken.
what that little filter does is break the connection.

i've got the same problem here, and it got a whole lot worse when i connected the television to the computer .. there was a rolling hum bar on the screen and noise from the speaker.
and comcast didnt care to do anything about it, probably because i disconnected the computer from the television and the hum bar went away.
i told them to listen to the headphones to hear the hum, and they acknowledge it was there.. but they said they wouldnt do anything about fixing it, leaving it up to me to get one of them isolator filters.

truth be told..
it is simply because the cable box doesnt have the filter already installed inside on the circuit board as it should, leaving room for people to go out and get one themselves.
and yes, it is possible to ground both systems to the same rod.. but most houses dont even use a ground rod into the house, they mount a strap to the metal pipe that holds the high voltage electrical wires.
with that said.. most houses need a cable box with the filter inside of it, but it does save money to build the box without the isolator on the circuit.
and more to the point ... if the box already had an isolator inside of it, and the customer put another isolator on the line.. it could actually age the cable hub outside somewhat faster, or cause line distortion that plagues the signal.

and i think hackers would want to use two isolators to try and slow the signal down (or at least put a gap of space in the line) to grab information and inject their data into the line.. known as a sandbox.

if 60hz is what the ground is functioning at .. then the isolator is basically just a transformer that allows all frequencies to pass through the air from the copper to the magnet except for 60hz.
kinda like a parametric equalizer with a very narrow Q (down to one frequency only)
but it is better to view it as electrons flowing from the copper to the magnet.

they say it is just a capacitor.. and that means the capacitor has been engineering using chemistry to specifically block one single frequency and let everything else pass.
the real problem is adding two of those capacitors together.. because 61hz starts to bend in, and 62hz starts to bend in.. and in terms of tiny distortion, those two frequencies bowing in starts to fill up the 60hz area again .. that is known to the world as harmonics.
and if you want to read up about it.. you could take the kindergarden route and view maxxbass bass enhancer, because they claim to give speakers more bass by adding two frequencies together to make it sound like lower bass.
and the principle really works extremely well.
the one frequency gets thrown out from the speaker, and the second frequency is a subtraction at a specific rate .. and the rate is what changes the physical soundwave to become the lower bass frequency.

(just saying.. on a forum like this.. that is how you get 20hz from a ported subwoofer box tuned to 32hz)
it works as long as the room isnt a pressure chamber.
(and if there is mild pressure in the room, that simply means the sound processor needs to be adjusted to bring the functionality back up)

be sure to share that information before the moderators come in here claiming i am off topic with my audio advice on an audio|video forum.
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post #14 of 16 Old 12-28-2012, 07:00 PM
 
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Originally Posted by Bill Fitzmaurice View Post

Not really, since fixing ground loops with transformer isolation is so easy. You don't even need to transformer isolate the cable, you can lift the extra ground by disconnecting the cable shield. Alternately you can lift the extra ground at the sub amp by disconnecting the shield from the RCA connector.

you will probably just ruin the cable if you cut the ground shield.. i've tried it myself and the cable signal stopped working.
obviously there is more signal on that shield than ground.
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post #15 of 16 Old 12-29-2012, 05:57 AM
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you will probably just ruin the cable if you cut the ground shield.. i've tried it myself and the cable signal stopped working.
obviously there is more signal on that shield than ground.
There is only a ground. If there is a ground loop present there are two ground paths, that provided by the shield and that provided by the A/C line. You can remove the second ground path on the A/C line with a 'cheater', and risk electrocution or fire in the event of a component failure, or safely remove it by disconnecting the cable shield on one end. If disconnecting the shield kills the signal it means you didn't have a cable sourced ground loop to begin with.

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post #16 of 16 Old 12-29-2012, 07:46 AM
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There is a nice sticky in the Audio forum called .... Hum FAQ .

I had similair problem with my cable causing hum and posted a few years back my solution in that sticky, which helped at all my cable<>AVR points not just 1:
http://www.avsforum.com/t/322698/hum-faq/120#post_17240091
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Originally Posted by mtbdudex View Post

Note:

I posted this response in the "Subwoofers, Bass, and Transducers" forum, http://www.avsforum.com/avs-vb/showt...9#post17154999

but it should be part of this sticky as knowledge base info.
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Originally Posted by NCARalph View Post

I recently redid my AV system to use pretty much all HDMI cables and removed some obsolete components. The result was a very annoying hum.
After some isolation, I determined it was originating in the Comcast cable feed and being distributed by the HDMI cables. Putting in a 3 to 2 prong plug to lift the ground from TV (the only component with a 3 prong plug) helped but didn't fix the problem, plus running completely without a ground worried me.
So I got a Jensen Transformers VRD-1FF on ebay, plugged it in, and POOF! the hum completely went away, even at high volume and no input. This has had no impact on the quality of the cable video including the HD channels. I don't use view on demand or any of the premium channels so I can't comment on those.
Worked for me.
NB - Read and follow the directions that come with it!
I had same problem, the cable people did a crappy job with grounding using cheap clamp, it had I think a bi-metallic corrosion going also as well. (wiggly clamp)

Before showing cable install job:



I took the clamp off, went to HD, bought 6' copper wire, attached to inside home copper pipe, actually next to where the 200A main also had a ground wire attached.

Copper wire going into basement shown:



To make matters a little more complicated, my outside faucets are "isolated" and not really connected to my inside pipes, due to my whole home EcoSmarte system, which uses various plastic/assy stuf for flowmeters, electrodes, etc.

So I connected a jumper wire from my inside pipes to my outside pipes, just to have them on the same ground plane.

This pict shows my whole home H20 system, kinda complicated but great H20 for whole home.


I also made sure the OTA antenna ground plane was same datum.

Here is in construction phase showing the home 2 ground rods.


Here is the OTA antenna being correctly grounded to the red circled one, it is visible just past hot tub cement pad.


Showing OTA copper wire on LH going around the corner under deck, while the antenna lighting rod is grounded next to the elect meters.



So, when solving ground loop issues you have to totally trace/follow your elect system and cable/sat/OTA/etc ground points.

For me, no more ground loop issue.
Maybe $12 max.
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