# Noise heard through Sub when laptop plugged in...



## JRace (Aug 24, 2006)

When I have my laptop plugged i I can hear a quiet noise coming from the subwoofer. This happens with both a Cerwin Vega powered sub and with my passive shiva/butkicker BK1000 setup.

The sound was not audible at all through a Paradigm Ultracube 10 powered sub.
As well the sound is louder if I increase the subwoofers level control.

When I disconnect the laptop powers supply the sound goes away.
The sound occurs when the laptop is working hard or accessing the HD.
I have tried connecting both power supplies through a power bar, both directly into the same outlet, and both on different oultes (same fuse though).
I have fixed the cable tv induced ground loop hum, and this is stll present.

Any ideas on where to start?


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## brucek (Apr 11, 2006)

Does the noise go away when you use a 'cheater adapter' on the laptop power supply?

If so, it's a simple groundloop..........

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

brucek can probably speak to this better than I can, but I’d suspect the computer’s power supply. In general, they aren’t known for clean power. There may be some residual AC artifacts not being adequately filtered or rectified.

Worse case, using an outboard USB sound card should solve the problem.

Regards,
Wayne


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## JRace (Aug 24, 2006)

I havnt located a cheater plug yet.
If it is a groundloop, and ideas on how to fix?


Wayne: I am running the audio through a Soundblaster external USB and coax.
No diff between that and the onboard audio.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Perhaps we should back the boat up and start from scratch. 

A good place to start would be to give us a description of the system you’re talking about. In your first post you mentioned “plugging in” the laptop, but didn’t tell us what you were plugging it into. You also mentioned “HD” and “cable TV.” So I’m really confused about what we’re dealing with here. I’m not sure if you have some kind of home theater PC rig, or if you’re merely trying to connect a laptop to a regular HT system.

Regards,
Wayne


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## JRace (Aug 24, 2006)

It is a laptop running an external usb (digital coax) to a Marantz reciever.
Video is sent thru the VGA out into a Projector.
The only device going into the laptop is an external USB harddrive.
The subwoofer is conected via the reciever's sub/LFE ouput.
We have internet only through the CATV - no televison.
I eliminated the ground loop hum created by the CATV a year ago, no hum heard through any speakers.

When I refered to "plugging in" the laptop I meant the power supply. The sound heard through the sub goes away when I am on battery power. 

I meant Hard Drive - not High Def!! I can see the confusion now ... 
When the laptop is idle (no cpu draw and not accessing the hard drive) the sound goes away. If I move the mouse the sound returns.

The sound heard is not a HUM - more of a click/clack/tick/tock...if taht makes any sense!

Thanks for the help, I may have a cheater plug by the end of the day.


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## Otto (May 18, 2006)

So it's related to the drive? I believe that the drive could go into some type of power saving mode when you are on battery, and may only be used when it's needed -- it will probably be idle when it's not actively doing something. However, when plugged in with full power, the drive may take liberties to search around for problem areas or in other ways "take care of itself." That's normal drive behavior for 2.5" drive. 

I doubt that a cheater plug will help you in this case, but it may. Does your laptop have a ground pin on its AC plug? I know neither of mine do.


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## Wayne A. Pflughaupt (Apr 13, 2006)

I doubt a cheater plug will help either, although it can’t hurt to try. At least it would verify if its a ground loop problem. (Never been able to figure out why laptop power supplies have grounded plugs anyway...) 

Since it all starts when the power supply is plugged in, I’m still suspicious of it. 

Anyway you can change out the coaxial digital cable to the Marantz with an optical?

Regards,
Wayne


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## JRace (Aug 24, 2006)

Problem still happens with optical...no change.
(The soundblaster external USB does both optical and coax).

The laptop has a three pronged power cord and I have no cheater plug to try at the moment.


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## Guest (Jun 21, 2007)

I am having the same problem !!!!
I bought this ampli with 2 speakers ... and I also bought the creative xmod device (sound going through the usb port) ... I can hear noise through the speakers ...
even with the external usb device !!!
so I bought better cables, a power bar that has filtering. 
and im still having the problem ...
naturally when i unplug the laptop's power the noise goes away ... any help ???


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## Guest (Jun 22, 2007)

I've had the same problem with my laptop. I got this advice from my supplier:
'The cause of this is a ground loop and the ground plug must be lifted.
the ground pin is the middle pin on the power plug. It can be removed or you can use a three to two pin adapter.

http://www.dself.dsl.pipex.com/ampins/groundloops/grndloop.htm'

I haven't tried this out yet but hopefuly it'll work.


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## JRace (Aug 24, 2006)

Hmmm, I have always been advised that the ground plug is there for a reason and removing it form the circut should be only used to test the problem not as a solution.


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## bob1029 (Feb 26, 2007)

I believe that if the problem still occurs with optical then you have a problem with the actual soundcard in your laptop, as the optical cable could not create any electrical loops. I know that the optical outputs "digital", but when you are playing anything non-dvd, be it mp3, cd, game, youtube, etc... all that has to be re-encoded by the soundcard to the digital signal (pcm/dd/dts). It would seem that the problem (if it is infact in the onboard sound) would be centered in the chip before the dacs/amps. I would try playing a dvd or ac3 file with s/pdif passthrough enabled to see if the sound is still there.


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## JRace (Aug 24, 2006)

Thanks for the input....problem is the sound is present even with the computer disconnected from my receiver and when the receiver is turned off.


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## Hakka (Sep 10, 2006)

If your laptop is connected to the projector via VGA and there is a connection between your projector and receiver/dvd player then that would complete the ground loop even though you are using an optical connection between the laptop and receiver. The receiver doesn't need to be turned on to complete the circuit as you can see. 

I get the same noise you are talking about if I have the laptop on mains power while connected to the HT, which isn't a problem for me because I only have it connected to do REW measurements. I don't know if its a ground loop, it certainly doesn't sound like the ones I've heard.

I have an Xbox running XBMC with a network connection to the same laptop to stream DVDs and video and I do not get any noise through the HT.

Hakka.


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## bob1029 (Feb 26, 2007)

You mentioned cable internet... Perhaps the modem is plugged in directly to the laptop via an ethernet cable? In any case I would try unplugging that temporarily to eliminate another possibility.


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## JRace (Aug 24, 2006)

Laptop is connected to the Cable Modem via wireless router.

Video connections are as follows:
Laptop - VGA - Projector
Receiver - Composite - Projector
DVD - DVI/HDMI - Projector
Playstation 2 - Component - Projector

Audio from laptop is through a USB soundcard (Sound Blaster) and the problem is the same via coax or optical.

Next I will try disconecting everything from the laptop and will see if that fixes the problem, if so I will then re-connect until it comes back...
If it persists without anything but AC power connected I will try and plug into an outlet on a different fuse.


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## JRace (Aug 24, 2006)

Well I have narrowed it down to the VGA/Projector connection....everything else can be disconnected and the problem persists.

Any more ideas?


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## MatrixDweller (Jul 24, 2007)

If your TV had a ground loop on it maybe the projector is suffering from it too. Either your projector or the amplifier has introduced a ground loop (probably the latter). You could place an isolation transformer on the subwoofer. Many power conditioners have them built in or you can buy dedicated ones. Here is an example of one: http://www.tripplite.com/products/product.cfm?productID=226

What sort of cables are you using? Try swapping out the VGA/DVI cable with something really thick and possibly with ferrite cores or try a shorter one. The cable does do 2 way communication so maybe there is some sort of feedback being sent back down the cable from the projector (or the problem is the cable).


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## Blackstone (Jun 25, 2009)

OK guys .. i can 100% affirm this problem is solved with a 'cheater plug' (3-prong to 2-prong adapter).

I have been trying to solve this problem since 2007.

I have 2 identical laptops:
Gateway MX7515
AMD 4000+
2GB RAM
Windows XP Pro SP
Hitachi 7200rpm 100GB

I had this problem with two different external "sound cards":
Event EZbus digital mixer over USB
M-Audio Firewire 410 (firewire obviously)

I ran all my power through an ETA PD8L rack mount power conditioner.

But I still got this high pitched noise. It's not recorded but its ever-present whirring at the volume i like to listen to would drive me nuts when in between takes of audio recording.

I tried the suggestion mentioned above .. i dug through my bag of electrical cords and fortunately I had TWO adapters, one for each laptop. I plugged them both in and voila! The noise went away .. at least at 0Db at the mixer .. if the mixer is pushed above 0Db then the noise comes in .. 0Db is going to be perfectly loud enough .. If you're pushing above 0Db then you're doing something wrong (except perhaps in the old days of 2" analog tape)

Laptop A:
Audio from the 1/8" stereo outs to L/R RCA (RCA -> 1/4" phono adapters)

Laptop B:
Audio over USB 2in/2out

DEAD QUIET.

I read somewhere where someone else was having this same problem, another person suggested using a DI (Direct Injection) Box to solve this problem but this didn't make sense to me since the signal chain was over USB .. there was no way you could insert a DI box into the chain. I had one on had but it was just an illogical suggestion.

I don't really understand the whole ground loop thing but these $1 adapters solved the problem!

Thank G0d

:yay:


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## MatrixDweller (Jul 24, 2007)

3 to 2 prong adapters = :scared:

It's just skating around the problem and is a good way to get electrocuted. The ground plug is there for a reason. 99.9% of the time it will be ok however...it's just that 0.1% of the time that you don't know about that will change (or end) your life.


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## driscoz71 (Sep 20, 2008)

I get a lot of interference with my laptop as well, but only when it is plugged in, I'll try some of the things mentioned above.


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## Blackstone (Jun 25, 2009)

Well my system is grounded .. at the amp .. so that should be good enough .. the ground is lifted on all the other gear.


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## MatrixDweller (Jul 24, 2007)

It doesn't matter if your amp is grounded if you have a cheater plug on your cable box, external sound card or hard drive or other gear. The ground won't perpetuate through the AV cables. 

The metal case, knobs and or frame of the component are tied to the ground wire. If there is no ground and a short to case occurs then the case is live and will present a shock or electrocution hazard. 

It may not be you who touches the case. It could be a loved one (your kids, your Mom, etc) or a friend. That then provides a vehicle to get sued for wrongful death and possibly charged with manslaughter. You could possibly do some time in prison, loose your job because of that and face a multi-million dollar lawsuit. It would be your fault if you bypassed a safety mechanism that would have prevented the accident. Even though the chance is slim, the odds are a lot better of getting electrocuted than winning the lottery. People do win the lottery all the time I should remind you. Is it worth the risk?

2 prong cheater plugs also disable the ability for most surge suppressors to work as they bleed excess voltage off to ground through a varistor (or MOV). So then how are you protecting the equipment from surge damage? A lightning strike or large spike could fry the ungrounded/unprotected device and other devices connected to it. I see that lot in computers where the PC has a surge suppressor but a lightning strike came through the phone line and fried things. All points of electrical input need to be protected. 

It can also disable any varistors used inside the component's power supply, which can adversely effect the way it operates.

Also if you ever have a fire that started in your AV cabinet the insurance adjuster would probably negate your claim. They like to take your money but don't like giving it back. So you could loose your home and all its contents.

There are alternatives to using cheater plugs and they should be explored. Using a cheater plug should not even be considered an option.


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## Blackstone (Jun 25, 2009)

I guess I'm not understanding the situation .. I have gear that ONLY has 2 prongs to begin with .. how is lifting the ground out of 3-prong any different than a CE manufacturer only including a 2-prong figure-8 connector to a standard 2-prong US at the other end?

My understanding is that if they are all on the same 'bus' and one is grounded then they are all grounded. If there is a short .. it goes to the one grounded machine???

Really .. all I want is silence from my system.

Geez the whole manslaughter .. killing people thing .. don't you think that's a bit much?

[edited by management]


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## Blackstone (Jun 25, 2009)

And if it's me that touches the ungrounded box .. then so be it .. who cares.


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## MatrixDweller (Jul 24, 2007)

I guess that is the question then...do you really care.

So from now on throw caution to the wind. Drive with out your seat belt on, smoke 3 packs of cigarettes a day, operate heavy machinery while intoxicated and dive in the shallow end.

If a unit does not have a ground prong then it does nothing with grounding. If a cheater plugged device had a short to its chassis it's not going to magically attach itself to another device's ground. The only way would be to attach a wire to each device's chassis and connect them all together so they would share one device's ground prong. In that case I don't know why a cheater plug would even be used. 

The neutral wire will meet ground in the main panel but it's not the same thing. Large current on the ground will trigger a breaker whereas current on the neutral is normal.


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## Blackstone (Jun 25, 2009)

Well I'm still a bit confused by what you're saying Matrix .. by .. "the ground perpetuating through the AV cables."

I know this site is called Home Theater Shack but my situation is a music studio.

Every piece of gear is going through the same power conditioner. The amp .. which theoretically draws the most power is grounded. Some of the gear I have only has two-prongs from the factory so is not ground-able. The remaining 3-prong gear has been lifted with a cheater plug. It's my understanding that I could have plugged the 3-prong gear into a power strip with a Ground Lift feature but that would achieve the effect.

My understanding is because they are all on the same >power< circuit, then a short should be grounded by the amp. I never had any expectation the AV cables would enter into the picture. 

I mean I touch phono connectors all the time and don't get electrocuted. The exception to this would be if I was running 48 Volt phantom power for microphones .. where I am aware there is a risk of electrocution.

Again .. There is tons of gear that comes from the factory with only two-prongs .. how are these manufacturers not putting end users at risk? (Cell phone chargers, routers, USB hubs, 16 channel mixers). And if they are .. how do you remove a ground loop from a collection of gear where two or more items have 3 prongs while at the same time securing even the dumbest user against faulty gear and electric shock?


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## Blackstone (Jun 25, 2009)

btw: Here's a bit of my rig


Wall socket 
-- Rack mount power conditioner/distribution (3-prong)
-- 1400 watt power amp (3-prong) grounded
-- Tape deck (2-prong)
-- Power strip (3-prong)
-- Laptop (cheater plug)
-- Laptop (cheater plug)
-- 24" monitor (cheater plug)
-- 8 channel digital mixer (cheater plug)​
-- Power strip
-- 16 Channel mixer (2-prong)
-- Synthesizer (2-prong)
-- Synthesizer (cheater plug)​
You're saying this is unsafe? If so what do you do about it? What about the factory 2-prong gear?


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## MatrixDweller (Jul 24, 2007)

Anything with a cheater plug will not be grounded. It doesn't matter if they are plugged into a power conditioner. The ground on the device must connect to the mains ground (outlet's ground) somehow.

The laptops are probably safe. The ground wire on it would most likely be for power regulation within their power supplies. The monitor would be the same. Still a short inside either could present a shock hazard if the right part of the case were touched.

The synthesiszer and mixer could present a shock hazard. If the mixer or keyboard were to form a short to ground then touching a metal screw, metal casing, etc could be an electrifying experience. The cases/chassis would be tied into the ground on the circuit boards.

2 prong devices deal with shorts differently and do not bond into the chassis for grounding.

The reason why you are most likely hearing some ground loop hum is that one of the devices is bleeding of a little current to ground or there is some inductance/interference on one of the ground lines caused by thin poorly shielded power cables.

The following has some fairly good advice:
http://www.epanorama.net/documents/groundloop/problem_solving.html

More on 2 prong vs 3 prong: 
http://www.howstuffworks.com/question110.htm


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## Blackstone (Jun 25, 2009)

Hmm ... interesting .. well I guess this is a bit more involved than I thought .. all I really wanna do is make music .. now I have to be an electrician too? .. lol

Well I'll talk to my keyboard tech and see if he can give me a simple way of setting up my studio so it's safe >and< quiet.

Thanks Matrix


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## wglyons (Sep 7, 2009)

I had this problem...I was plugging my laptop into the power strip. Once it was unplugged and on battery power, the noise went away. So, I tried plugging the laptop into the back of the receiver. Not saying its the best scenario, but it completely solved the noise issue...


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