Laptop sound noise

Actually your point re this not being the intended purpose of laptops is misleading IMO
What we are seeing here is a design flaw, that again in my experience COULD lead to a dangerous situation of the same level as removing the ground pin. IF there were another fault on a device on the same AC connection the problem outlined shows that it would be possible for this fault to be connected directly to the laptop.

What people are missing is that the noise issue shows that there is an improper connection between the AC ground and the "ground" negative side of the audio circuit.

Sharyn
 
What people are missing is that the noise issue shows that there is an improper connection between the AC ground and the "ground" negative side of the audio circuit.

Sharyn

I agree that the laptop PS are faulty in that way, but I disagree with the above. Tons of pro equipment, the majority, tie the signal ground and the chassis ground together. Most of the good equipment also features a "ground lift" switch or jumper, which floats the signal ground from the chassis. Those switches/jumpers may be misleading as some people think they float the chassis ground (safety ground/earth) which they most certainly do not.
 
I agree that the laptop PS are faulty in that way, but I disagree with the above. Tons of pro equipment, the majority, tie the signal ground and the chassis ground together. Most of the good equipment also features a "ground lift" switch or jumper, which floats the signal ground from the chassis. Those switches/jumpers may be misleading as some people think they float the chassis ground (safety ground/earth) which they most certainly do not.
As you noted, many audio devices have the shields (Pin 1 on an XLR) tied to the audio reference ground when they should be tied to the chassis which is in turn tied to the electrical system ground such that any current on the audio cable shield runs direct to ground and not via the device's audio circuitry reference ground. I think that may be what Sharyn was referencing. Good equipment should be in accordance with AES48 and thus not require a ground lift switch, dropping a conductor at either end or any of the other common 'fixes' in order to avoid ground loops.
 
Yes that is the problem:

Here we have a combination of factors, one is that the headphone output jack on a notebook is not a shielded balanced system, and the power distribution in the notebook has to deal with two sources of power, both battery and external. It is not like the external power simply charges the battery, since in a lot of notebooks you can remove the battery and still run the laptop on the external power supply.

What I have found and others have suggested is simply get your self a external USB or firewire audio system, so that you simply do NOT use the headphone jack, and bypass the entire audio ground issues



Sharyn
 
I did look around for a replacement power supply for my laptop which has no ground pin on the AC plug, but I couldn't find one. I'll continue to look around- maybe someone knows of a laptop power brick supplying 18-24V DC at 6A, with a two-prong AC plug.

I did come up with a temporary solution to the noise problem which seems to work well, however. I have two 8-channel mic preamps: an M-Audio Profire 2626, and a Behringer ADA8000. My laptop is hooked up via firewire to the 2626. In my audio software, I send my outputs from the 2626, via ADAT optical, to the ADA8000. This unit's D/A converter outputs the audio onto its 8 XLR connectors, which I connect to my mixer. The result: super-clean audio, no hum, buzz, or digital noise at all. I think this works because the AC adapter for the Profire 2626 is two-prong. The ground is broken at that point. And, since I'm sending the audio out via ADAT, there is no signal ground either.
 
What I have found and others have suggested is simply get your self a external USB or firewire audio system, so that you simply do NOT use the headphone jack, and bypass the entire audio ground issues

Sharyn

I would like to point out, Sharyn, that many of us ARE using external audio interfaces (myself included) and still get these laptop power supply noises in the audio interface. In my case, I believe that the shield of the firewire cable is carrying these noises into the Profire 2626 audio interface. But if I send the audio from the 2626 out thru ADAT, the noise is not carried with it. Just food for thought, and a possible solution, for those of you who have the extra equipment.

--db
 
Amazing what some galvanic isolation can do...
ADAT being an optical signal can NEVER cause ground loops - but they may sneak in through other copper gremlins.

I think the key to remember here is that it is ultimately the device that does the digital - analog conversion that governs the noise, buzz and other pain in the system.
If it has issues, the system will have issues...
 
In this situation, the ADAT optical interface is very similar to an opto-splitter/isolator used for DMX distribution, etc. There is no physical connection, so those problems are a nonissue and moot.
 
In this situation, the ADAT optical interface is very similar to an opto-splitter/isolator used for DMX distribution, etc. There is no physical connection, so those problems are a nonissue and moot.

Good things opto-isolators, isolation transformers and 1:1 isolation amplifiers.

I do not have much to say other than I've been annoyed enough to ask a relatively well regarded manufacturer of sound gear to send me some schematics in hopes of finding a solution to this problem.

So after reading this thread, looking at schematics and specifications I was wondering what some of the rocket scientists I was fortunate enough to work with in another life would do. Well, they would likely have pointed out that instrumentation op amps across the post power source mains feeding a sensitive differentiation amp could trip ye old crow bar as us old timers used to call electronic circuit breakers.

Well, looks like some clever countries are using such devices called RCDs "A two-pole residual current device" and the wiki page has a nice picture that looks just like the one on ebay for about $10 and probably another $10 for shipping. There is some good science behind the device (crowbars before arrhythmia can kick in) but like all things (GFIs) they can be defeated if we are clever or work hard enough at it or Murphy's Law kicks in.

(I wonder how it handles the voltage drop across the device from heat, amplification, etc., would seem to need a sample and store characteristic curves in the comparator).

My laptop uses 20V @ 5A max and working hot in a lab with 20V DC is, well, wimpy compared to 110v AC which can definitely be lethal. If I were to conduct a FMEA (safety analysis) the only thing in a recording studio to treat with **LOTS** of respect would be Tube devices which are all the rage now (leaving dinosaurs like me scratching our heads).

Theaters in general could be very dangerous w.r.t. Lighting if not given respect. Standard Operating Procedures generally should be followed and Multiply redundant Safety Systems implemented whenever possible (like the insulation on two prong devices mentioned here one would suppose).

Batteries are generally safe but even a 12v car battery will be very unforgiving across a dead short and since we earthlings have a lot of salinity (electrolyte - conducts electricity really, really well) prudent behavior is a very good idea.

So for now I'm running the laptop on battery power and eventually may replace the old tower power supply with one from Antec (reported to be stone cold quiet w.r.t. EMI/RF).

I tried out a tube pre-amp recently but the idea of running 400V to bias the valves (what they call tubes now) is not for me at this time (the heat it put off rang some alarm bells).

Oh, and those nice rugs on stages for performers using mic stands, not just for sound deadening but also provides another layer of insulation. Not a problem though with highly mobile RF mics.

I've also made the assumption that high shielded (properly terminated) cables are being used for microphones and instruments.

So....
(1) If you can walk around with it two prongs are probably o.k. just be careful (Stun guns are two prongs, fit in a pocket, but what a wallop that arc carries).

(2) If you cannot carry it three prongs are needed (and lots of respect).
 
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So....
(1) If you can walk around with it two prongs are probably o.k. just be careful (Stun guns are two prongs, fit in a pocket, but what a wallop that arc carries).

(2) If you cannot carry it three prongs are needed (and lots of respect).
As we live in a country where someone sued the mower manufacturer for not telling them to not use the mower in such a manner after being injured while trying to use their lawnmower to trim hedges, regardless of whether you can carry a device or even if it carries itself around on its own, I think the only appropriate assumption is that if the power plug on the device has three prongs then the ground pin is there for a reason and that defeating it increases your risk.
 
I think part of this is the manufacturers do not pay huge attention to these types of issues, they get parts from various suppliers and pack them based on the cheapest price. I have 2 power supplies that came packed in 2 new Dell D630 laptops back then they were new. Here are the specs:
Family: PA-12
Input: 100-240V~1.5A 50/60Hz
Output: 19.5V DC 3.34A
Differences one is listed as Model FA65NS0-00
the other as Model AA22850

One if 2 prong, the other is 3 prong. One when used the audio makes noise, the other does not.
Its not a grounding noise, it is noise from the power supply. Dell's answer use a external USB audio board.

Go figure..
 
As we live in a country where someone sued the mower manufacturer for not telling them to not use the mower in such a manner after being injured while trying to use their lawnmower to trim hedges, regardless of whether you can carry a device or even if it carries itself around on its own, I think the only appropriate assumption is that if the power plug on the device has three prongs then the ground pin is there for a reason and that defeating it increases your risk.

Sounds Good to Me (No pun intended). But on the flip side Electrical Engineers and Electronic Device Designers see amps, laptops, lighting, power generators, mains, sub-stations, etc. as big white boxes and (being qualified to do so) tend to discriminate between signal ground and power ground.

Obviously things that fly (airplanes and satellites) are out of scope here but they do tend to work without a real earth ground. Aerospace circuitry (Moog comes to mind) can find its way into the theater. But what Engineers and Scientists do in the lab is not what we are talking about.

Hence, I'm including a few references that have taught me a number of things and recommend them as required reading for anyone (including Scientists and Engineers) in the Industry:


References
**************
BBC WORKPLACE - 'EGN3 Electrical Guidance Note 3';
5 Special case - Performing Band electrical and musical equipment
bbc.co.uk/safety/pdf/safety-egn_3_rcds_v2-2_f.pdf

Electrical Guidance Note 4 : Mains isolating transformers (ENG4) Covers Three Phase and other Extreme Industrial Hazards.
bbc.co.uk/safety/pdf/safety-egn-4.pdf

"Electrical safety at places of entertainment" Health and Safety Executive
bigtopmania.co.uk/pdf_downloads/electrical_guidance_documents/Hse_electrical_safety_at_places_of_entertainment.pdf

WORKSAFE WESTERN AUSTRALIA COMMISSION --
ELECTRICITY: RESIDUAL CURRENT DEVICES
OSHA Guidance -- Protection against earth leakage current when portable equipment in use
rigsafegear.com/docs/resource/Worksafe Codes/Electricity.pdf

THE Magazine For Mobile DJs -- Residual Current Devices
PRO MOBILE, THE magazine for Mobile DJs
promobile.org.uk/viewarticle.php?id=78&PHPSESSID=94830daed79ea35a6a081ce88e46a0bb

DISCLAIMER
*********
Obviously not a complete list, please append as you fit.

As a Safety Officer I'd admonish electricians from working "Hot" and require a true earth ground (in the case of facilities that is a ground penetrating 10-15 foot copper pole with 2" ground straps running to every lab, stage, studio, etc.)...
 
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What kind of meter did you measure that with? A lot of switching power supplies have caps from the ungrounded and grounded conductors to the grounding conductor. A voltage can be measured but no significant current flows.


123.5v Across rails, 60V AC Across Switching Power Supply Pin to Wall Ground (No Load Infinite Resistance).

**** thing visibly Arc'd when I plugged it in. Having tested 20KV connectors for Corona I'm still respectful of even small arcs as the instantaneous voltage across air in that milli- (or micro- second in the high frequency domain) is exponentially higher than what is measured on a DVOM (upwards of a million ohms impedance on the input of a typical Digital Volt Ohm Meter).

Where is that digital storage scope when you need one ?

I just witnessed at least a 1KV instantaneous spike across a (60v ?) Chinese or Mexican cap with a dielectric that will certainly fail (short) after a finite number of spikes (plugging it in with everything "On" a worse case test scenario - but a real one none the less).

For personnel reasons out of scope here I do not fear death. Full load is playing KLOVE (iTunes under Religion) right now just below distortion fed into a balanced three way cross-over. I need the laptop as a DAW and/or backing track or two.

Do not draw any "Safe" conclusions unless a lot of your professional life was spent in "Failure Analysis" of high potential effects.

Evertime a dielectric experiences a voltage spike a microscopic conductive well begins to be formed. Sure, no uamps until that well gets close enough to the rail. Then catastrophic failure, hopefully with no human near the thing. I have not checked recent theory but a nano "plasma" model probably fits.

Oh, when a 20KV Corona Test fails it sounds like a half stick of dynamite going off. At the same worksite (Power Plant OEM) an electrician died outside my window. F---ing working HOT.

Mother nature will and does readily kill those who do not respect her.
 
Anybody try this ???

"Universal notebook power adapter
- Compatible with models from Dell, Toshiba, Acer, HP, Sony, Fujitsu, Compaq, ASUS & more. For a complete list, visit" antec.com/snp90

"And with seven detachable connectors, the SNP90 works with virtually any notebook on the market, including the latest models from Dell, Toshiba, Acer, HP, Sony and more. Lighten your load and charge your notebook with 90 watts of Continuous Power with one notebook power adapter: Antec's SNP90." $60
store.antec.com/Product/notebookadapter/snp90/0-761345-22090-3.aspx
 
$46 on Amazon, reviews favorable except for recent Dell Studio Series which is reportedly chipped to recognize and use OEM chargers only (HP reportedly does this as well). IMHO they have gone overboard with these models, targeted at video editing and multimedia in general. Sort of like tower wanna-bees masquerading as laptops (and Rolex watches to match no doubt).

Professional editing is probably a joke as laptop I/O on the internal buss(es) will never approach that of a well designed tower. But hey, what ever floats your boat.

Worth a try on older laptops unless audio is reportedly trashy which would be uncharacteristic of Antec.

The SNP90 seems to have all sorts of connectors (as opposed to the slightly cheaper NP90 with one connector ?).

I have no monetary or other interest in this (did I really need to say that ?)...
 
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Sounds Good to Me (No pun intended). But on the flip side Electrical Engineers and Electronic Device Designers see amps, laptops, lighting, power generators, mains, sub-stations, etc. as big white boxes and (being qualified to do so) tend to discriminate between signal ground and power ground.
I prefer the terminology signal ground and safety ground, as that is really what they are. The reason we have to worry about ground loops is basically because many Electronic Device Designers have been lazy, cheap or simply ignorant and have not properly addressed the path of the signal ground to the safety ground. If that is properly addressed, for example per AES Standard » AES48-2005 (r2010): AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry, then ground loops would not be such a common issue for audio devices.

As a Safety Officer I'd admonish electricians from working "Hot" and require a true earth ground (in the case of facilities that is a ground penetrating 10-15 foot copper pole with 2" ground straps running to every lab, stage, studio, etc.)...
I believe that the important point is having a reliable, very low impedance path to that single earth ground point for the building. Some facilities may use a single ground electrode rod while others use mulitple bonded rods within a small area. And some critical facilities or those with certain soil conditions may utilize a chemical/electrolytic ground electrode rather than copper rod(s).
 

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