Laptop sound noise

On any of my Dell laptops I have to use a ground lift while charging and playing back through a mixer. See if that helps
Since you mentioned charging I assume you mean lifting the safety ground and not the audio signal ground. Did you read any of the previous posts in this thread? You know, the ones discussing how this was a code violation and potentially dangerous.

I use my Dell laptop, and have seen many others using Dell laptops, for system alignment and tuning where noise would be a real problem. We simply use a good quality external audio interface and after looking at the response of some internal sound cards, that is the way I would typically approach anything other than a temporary setup, in which case I might use a DI or input transformers. A safety ground lift may help assess a problem but it is not a solution in any situation.
 
The problem is due to the switch mode power supply. Most modern laptops now have switched mode power supplies. These are generally the sole cause of audio system hum when using laptops. When you remove the switch mode power supply from your laptop the hum should be gone. There are a couple of alternatives to this. See if you can source a regular (non switch-mode) power supply for your laptop. This is probably the least favourable solution. The other solutions are to use an audio isolating transformer. This may remove some or all of the hum. But by far the best solution is to use a DI box, or other audio interface via firewire or usb.
 
Ok, I will try using my M-Audio interface. I do not, however, understand why this would eliminate the hum. Could someone enlighten me?

Oh, and it's not exactly a hum. It's more of an oscillating, periodic buzz. It sounds kind of muted, also. Like the upper harmonics are missing.
 
Ok, I will try using my M-Audio interface. I do not, however, understand why this would eliminate the hum. Could someone enlighten me?

Oh, and it's not exactly a hum. It's more of an oscillating, periodic buzz. It sounds kind of muted, also. Like the upper harmonics are missing.

2 main reasons;
1- it gets the analog audio away from the EMI wandering around the motherboard on the laptop, and from the hard drive etc.
2- external interfaces are less worried about an extra 3 bucks in component cost and so generally have far better designed products...
 
Ok - so it's basically the sound being corrupted in the sound card of the laptop, not before it gets there?

I was just wondering why the external interface would help because the audio (signal, at least) will still be originating in the laptop, just travelling through a USB cable before being output through a TRS plug.
 
With an external (USB) sound interface, the USB is carrying the audio as digital, not analogue. The (unwanted) noise is often introduced in the analogue stage, and since an external interface is often better designed, it doesn't suffer from the same problem.
 
Hi guys,

My first post here. I found this thread while searching the Net for possible solutions to laptop computer power supply noise problems. I decided to join up, partly because I am a musician and recording/sound tech professionally, and partly so that I could tell you my experiences on this problem (and what I found to be the solution).

I had been going 'round and 'round with this laptop noise problem for a few years- ever since I purchased a Sager (Clevo) M570-TU laptop for audio work in Aug. 2009. I typically use my M-Audio ProFire 2626 audio interface for recording work, along with various other audio gear- Mackie 1402-VLZ3 mixer, PreSonus HP4 headphone amp, etc.. When using the system with my Sager laptop, I kept getting an intermittent noise in my audio, consisting of a low-level, but very annoying, hashy, dirty hum (not primarily 60 Hz, but higher), mouse zipper noise, and other noises related to computer activity. For example, the frequency of the noise changed when I used a different audio buffer setting on the 2626. I tried a couple Radio Shack "Ground Loop Isolator" stereo cable assemblies between the ProFire 2626 and my mixer, which sometimes lessened the noise. But I would still get the noise in other equipment in the room, such as a bass guitar amp.

I found that if I disconnected the laptop power supply and ran the computer on its internal battery, the noise went away completely. This pretty much narrowed the problem down to the power brick, but I was at a loss about how to eliminate this problem, short of getting an expensive linear power supply for the laptop- I know that 13.8 VDC power supplies are common, but an 18 VDC supply capable of 6 Amps of current is probably harder to find, and more expensive. I lived with the problem for way too long. When I heard some of this noise getting onto a vocal track I was recording for a client, I said, ENOUGH.

At first, I assumed that the power supply was generating this noise. But it seems more likely to me that the power supply is acting as a path for noise generated in the laptop to travel back up through the DC cable, the power brick, and onto the AC power circuit via the ground pin. I don't have the test equipment to prove this, but that's my impression. If it was just the power brick generating the noise, why would this noise be affected by activity on the computer? And, when I disconnect the DC cable from the laptop, the noise goes away, even though the power brick is still plugged into the AC outlet. What's interesting to me also, is that the laptop noise is apparently NOT transmitted through the firewire cable to my audio interface- in that case, I would hear the noise in my audio even when running the laptop on the battery, no?

The solution? Lift the ground pin of the laptop's power supply with a 50-cent 3-wire to 2-wire AC adapter, like the one G15 pointed to above. I have not experienced any of the annoying "power supply" noise since.

Now, I can understand the safety concerns about lifting the ground on an AC adapter, but practically speaking, we're not talking about a hazard of high-voltage AC on the laptop side here. We're not using a power tool with a metal casing. Any failure of the power brick on the AC side would be confined to the power supply, right? And besides, as some of you have observed above, many laptop power bricks come with 2-prong AC plugs. What, safety is a concern for some laptop power supplies and not others? I think the hazard is minimal at best. And, AT LAST, I have NO noise related to the laptop's power supply, in my audio system. I have gone over to the dark side, the ground-lifted side, the QUIET side. ;)
 
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The solution? Lift the ground pin of the laptop's power supply with a 50-cent 3-wire to 2-wire AC adapter, like the one G15 pointed to above. I have not experienced any of the annoying "power supply" noise since.

Now, I can understand the safety concerns about lifting the ground on an AC adapter, but practically speaking, we're not talking about a hazard of high-voltage AC on the laptop side here. We're not using a power tool with a metal casing. Any failure of the power brick on the AC side would be confined to the power supply, right? And besides, as some of you have observed above, many laptop power bricks come with 2-prong AC plugs. What, safety is a concern for some laptop power supplies and not others? I think the hazard is minimal at best. And, AT LAST, I have NO noise related to the laptop's power supply, in my audio system. I have gone over to the dark side, the ground-lifted side, the QUIET side. ;)
Apparently you did not read the entire thread or the manual for your laptop that states "The power adapter may have either a 2-prong or a 3-prong grounded plug. The third prong is an important safety feature; do not defeat its purpose."

You appear to have some common misunderstandings. For one, there are no three wire to two wire adapters as those would create a code violation and an unsafe condition. What you are using is almost certainly an adapter intended to adapt the safety ground on a modern three wire plug to an older two prong electrical system that used a method other than a dedicated ground wire to the receptacle in order to provide the ground path, usually through a metal plate and/or box along with either a dedicated ground wire or metallic conduit from the box. The tab or wire on the adapter is intended to be used to create a continuous safety ground path from the third prong on the power supply to that alternative ground path, exactly the opposite of the ground connection being left disconnected or broken off in order to break the ground path.

For another, devices with two prong plugs are almost always double insulated and UL listed as such, meaning that they are designed so that an internal short cannot potentially make the external chassis 'hot' and tested to verify the effectiveness of the design. However, devices with a three prong plug instead rely on the ground to drain off the voltage and current in case the chassis or device body somehow becomes 'hot'. Don't think that the power supply having plastic body prevents the outside of the supply or the cable to the laptop from potentially becoming 'hot'. Break the safety ground path of your power supply and if the chassis ever does become 'hot' then any other potential ground path including a person touching the power supply could be subject to the full voltage and current of the circuit (which is also what leads to the one exception to the potential problem if using a GFCI circuit).

This is one of those situations where the likelihood of breaking the safety ground path actually becoming a problem is very small, however the potential outcome if that happened could be extreme. So you haven't really gone to the dark side, more to the potentially dark and crispy toasted side.

Instead or risking your or someone else's life, get some good audio isolation transformers, use a FireWire or USB interface or find a replacement two prong, double insulated power supply.
 
Brad is correct. Lifting the AC ground in the manner described is not safe. Ebtech makes a product that opens the ground for low potentials but completes the circuit for hazardous potentials. Yes, it costs a few dollars, but it could prevent a death.

Ebtech - Audio Solutions

Often there are better approaches to stopping hum and noise problems, like dropping shields on balanced lines, and/or using good quality audio transformers with Faraday shields. In this case, the Ebtech might be a nice solution.
 
Brad is correct. Lifting the AC ground in the manner described is not safe. Ebtech makes a product that opens the ground for low potentials but completes the circuit for hazardous potentials. Yes, it costs a few dollars, but it could prevent a death.

Ebtech - Audio Solutions

Often there are better approaches to stopping hum and noise problems, like dropping shields on balanced lines, and/or using good quality audio transformers with Faraday shields. In this case, the Ebtech might be a nice solution.
The HumX is definitely a step up from completely breaking the ground path but I personally avoid them. Apparently the HumX uses a pair of parallel diodes, one in each direction, which effectively breaks the safety ground path until the diodes see sufficient voltage to start passing current. However, the HumX is only rated for 6A, the current capacity could be increased but the device would probably need to be physically larger and more expensive. This not only means the current capacity of the HumX is less than that of the receptacle or circuit into which it would be plugged, but it also results in having a 6A rated device with a 15A rated receptacle and plug and no fuse or other overcurrent protection, which may be one reason why the HumX is not UL listed. But my biggest concern is that I have had multiple people who know much more about the details than I do and whose expertise on the topic I highly respect state that full circuit current or a surge could cause the 6A diodes to burn out, leaving you with no ground path right when you most need it.

For the price of an Ebtech HumX you might be able to find a compatible double insulated power supply which should address any ground loop issues and also allow your current power supply to serve as a backup or spare.
 
The long term current rating of the diode does not tell the story. Without lab testing, we don't know if the Hum-X can handle the total short of a 20 Amp branch circuit long enough to trip a circuit breaker. I'd bet that it would do that, but it probably sacrifices itself in the process, which is why they put the indicator light on it. If they didn't design it that way, the lawsuits would be the end the company. We also don't know if there is a one-time fuse built into it to limit it to the 6 amp rating. The "fuse" could be as simple as a printed trace of specific dimensions.

Having said that, using the Hum-X would not be my first choice in solving a noise problem. The design is a bit shady as you point out.

As for UL ratings, they aren't worth much. I once encountered a bunch of new computer monitors that had 90V of leakage to the VGA cable shield. They had a UL listing, so I called UL to report it and they could not care less. All they want is the money to test one example of the product. If the production release of it kills someone, they have no liability.
 
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So much for everybody welcoming me to the forum on my first posting here. :) I post a lengthy message detailing my observations and experiences, and I get ripped a new one for something I said in it. Thanks! And btw Brad, I did read every post in the thread prior to my post.

Granted that lifting the ground on an AC plug is not the recommended solution. But it does work in my case, and the risks I take in doing so are my own. Living life is a calculated risk. And some people have a higher risk tolerance than others. In my opinion, the risk in this case is vanishingly low- lower than the possibility of getting struck by lightning while walking to the store, or being T-boned by a drunk pickup truck driver at an intersection. We should take a survey- how many cases has anybody seen of laptop power supplies failing catastrophically and resulting in injury or death to a nearby person?

As FMEng points out, a UL rating on a product does not automatically make it safe under all conditions. There are caveats in using any product, following the usage and safety recommendations or not, and if you like to juggle running chain saws, and have that ability, more power to you.

Now, can anybody address any of the other points in my post, such as thoughts about the possibility of filtering AC components out of the DC side of switching power supplies, so that we can stop the noise nearest to the source, and not have to apply "band-aid" solutions to our audio equipment?

--db
 
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Laptop power supplies are notorious for creating a lot of noise. The sound card or integrated sound commonly picks up that noise and puts it through to the output. There it is amplified by the gain stage of the sound console and amplifiers.

Chances are lifting the ground won't make a bit of difference because the noise is part of the signal and not a ground bias issue. You're best bet is using an external audio interface over Firewire or USB, a good unit will filter the bus power and eliminate the noise. They also are capable of multi channel out and proper +4dBu levels.

The reason you don't get noise on battery power is because it's a stable DC source.
 
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I want to put in an official CB safety statement here. Regardless of what some people in this thread believe, it is never a good idea to remove proper grounding. When you remove grounding, regardless of which piece of equipment you are talking about, you open yourself up to a new world of potential danger to both your equipment and yourself. Electricity can and does kill people. Removing the ground is the electrical equivalent of rigging with Chinese made shackles or hanging lighting instruments without a safety cable. Yeah you might be okay for a while, but you are flirting with serious danger. Don't do it.
 
I want to put in an official CB safety statement here. Regardless of what some people in this thread believe, it is never a good idea to remove proper grounding. When you remove grounding, regardless of which piece of equipment you are talking about, you open yourself up to a new world of potential danger to both your equipment and yourself. Electricity can and does kill people. Removing the ground is the electrical equivalent of rigging with Chinese made shackles or hanging lighting instruments without a safety cable. Yeah you might be okay for a while, but you are flirting with serious danger. Don't do it.

Let me just add to the controversy:

The basic issue is that the notebook power supply combination that exhibits this noise issue is incorrectly designed/implemented. I have had this issue with some Dell units, and finally got dell to give me another power supply. I have not found this on any of the more recent models.

SO here is the problem as I see it:
If you lift the ac ground, and the notebook/power supply has a problem, you have a dangerous situation
BUT if you leave the ground connected and elsewhere in the ac system you are connected to has a problem, then you have a dangerous situation as well since you basically have a connection between ground and the power system in a improperly insulated device. (two prong devices are supposed to be doubly insulated) This is why for instance a lot of hand power tools only have a two prong ac connector.
Sharyn
 
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So much for everybody welcoming me to the forum on my first posting here. :) I post a lengthy message detailing my observations and experiences, and I get ripped a new one for something I said in it. Thanks! And btw Brad, I did read every post in the thread prior to my post.

Sorry you did not feel too welcomed, but safety is a primary concern here on this forum. We have to make sure that point is hammered in no matter how long members are on the forum.

Granted that lifting the ground on an AC plug is not the recommended solution. But it does work in my case, and the risks I take in doing so are my own. Living life is a calculated risk. And some people have a higher risk tolerance than others. In my opinion, the risk in this case is vanishingly low- lower than the possibility of getting struck by lightning while walking to the store, or being T-boned by a drunk pickup truck driver at an intersection. We should take a survey- how many cases has anybody seen of laptop power supplies failing catastrophically and resulting in injury or death to a nearby person?

When you share essentially recommend defeating a safety feature, you remove that calculated risk to yourself and spread it to others: "The solution? Lift the ground pin of the laptop's power supply with a 50-cent 3-wire to 2-wire AC adapter, like the one G15 pointed to above." You even bolded this text. This emphasis makes it sound as if you do not care about the safety of others. How many have died from it? I guess we could research this for you. However, the general consumer or IT manager is not likely to defeat this safety feature. I have only known people in the entertainment industry to do so.

As FMEng points out, a UL rating on a product does not automatically make it safe under all conditions. There are caveats in using any product, following the usage and safety recommendations or not, and if you like to juggle running chain saws, and have that ability, more power to you.

No, but the UL listing is going to help you for insurance purposes, defeating it will not. Also, if there is a workplace industry caused by knowingly defeating a safety device, you risk heavy fines from OSHA.

Now, can anybody address any of the other points in my post, such as thoughts about the possibility of filtering AC components out of the DC side of switching power supplies, so that we can stop the noise nearest to the source, and not have to apply "band-aid" solutions to our audio equipment?

--db

This is the real issue. Since this is not the intended purpose of laptops, this is not the main concern of the engineers. Should we become a main source of income for the laptop industry (never going to happen), then I am positive that the manufacturers would spend their efforts on solving this problem. In the mean time, we should only use safe alternatives. Several alternatives have been suggested, and I would suggest that the replacement of your power supply would likely be the best option for you.
 

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