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anonymous 4 January 2009

I have tried all different types of connections and I get horrible noise when the laptop is plugged in. I have tried plugging up stuff all over the studio, putting them on power grids, and what not. Is there anyway to get around this problem. I figure the converter is creating some crazy feedback.

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pr0gr4m Tue, 01/06/2009 - 10:05

The cheap and dangerous solution is to use a ground lift. It's a little plug adapter that converts a 3 pronger into a 2 pronger.

It's cheap cuz those things are like 98 cents. It's potentially dangerous because you are removing the ground which could cause your equipment to fry if there was a power surge.

I've used them before without any problems.

anonymous Tue, 01/06/2009 - 17:18

Link555 wrote: Sorry Program, I would never consider that as a option. Its a fire hazard at the very least, it could lead to death. The grounds are there for a reason, they shunt any dangerous spike to earth with a lower impedance path than your body does.

DO NOT REMOVE THE GROUND

I agree.

DO NOT REMOVE THE GROUND

Boswell Thu, 01/08/2009 - 05:51

This has very little to do with the quality of the ground and much to do with the quality of the laptop power supply. Isolating a noisy supply using a transformer doesn't make it any less noisy. Get a better mains power supply, or run the laptop off a 12V car adaptor fed from a 12V d.c. linear mains supply.

anonymous Thu, 01/08/2009 - 06:24

Don't remove the ground pin on your AC outlet.

I've been able to eliminate the power supply noise by using a DI with the ground lifted.

Also try plugging the laptop and the mixer into the same outlet. In residential electrical wiring half of the outlets are out of phase with the other half. This makes the power company happy, but audio engineer ... bald.

Using a USB sound card that has a transformer isolated output can also work.

anonymous Thu, 01/15/2009 - 14:52

What is a DI?

I have been thinking about getting a cheap desktop (i.e. - http://cgi.ebay.com…)

Would the humming likely stop with a desktop?

Would this computer be good enough to run everything?

My laptop is top of the line however.

Where can you buy mains power supplies?

I didn't understand what you was saying about the power inverter thing. Could you elaborate more?

I have a deep cycle 12v battery that I could hook an inverter up to to run the laptop. Would that work?

anonymous Thu, 01/15/2009 - 15:22

1. DI = Direct Inject. This is probably your cheapest option if the free ones didn't work. Search your favorite online gear dealer for "DI" or "DI box" or "Direct Box"

2. Desktops do not have this problem
3. The computer you have selected should be fine for home recording, but it depends on the load that your plug-ins have. Simulated synthesizers and cabinet cims and other resource hogs will kill it for you.

Or just use a power conditioner or UPS (uninterrupted power supply) if that is really the problem. Make sure to get one powerful enough for ALL your audio gear.

anonymous Thu, 01/15/2009 - 16:51

Yes, that is a DI. The variable pad is overkill for the application. Any passive DI will be easy to use. If you get a 2 channel DI (or two DIs) you can run stereo. Or get one with a linked input and connect the left and right to the two linked inputs. Or get two cheep passive DIs.

Computer -> DI -> Mixer

dvdhawk Thu, 01/15/2009 - 19:03

This is what I use on my installs if connecting the 1/8" stereo mini from a computer to a sound system.

http://www.markertek.com/Product.asp?cat=AUDIOEQUIP&subcat=&prodclass=AUDCONV&baseitem=LTI%2D100&search=0&off=0&showreturn=1&utm_source=&utm_medium=&utm_term=&utm_content=&utm_campaign=

I agree with Link555 you would hard pressed to build one for much less. What you would save would hardly be worth the bother, burns, and band-aids.

anonymous Wed, 01/28/2009 - 06:09

qwerty11 wrote: Any help??

The very first thing you should do is prove that the AC transformer (for the laptop) is causing the noise....before you go buy anything.

This can be done by simply running the laptop on the internal battery. If the noise remains, then it may very well be related to a DI situation or other equipment/AC problems.

However, if the noise goes away, it is indeed the noisy laptop transformer (and is very very common on laptops). I went through this problem for the first time about 8 years ago and and solved it by using the cheap little "ground lift" (3 prong to 2 prong power adapter).

A lot of people will scream "don't remove the ground" and rightfully so in MOST cases, but not necessarily this one.
In fact, you'll notice that Dell removed the grond to their transformes on a recent line of Lattitudes. Also note that the power actually being supplied to you laptop (the end that plugs in to your laptop) is DC, being made from an AC transformer....which (except in top of the line electronics) is an inherently noisy porcess ( on a silly scope) in and of itself.

Anyway, I hope this can help you determine what your problem is and gives you a course of action in the event you have a (typically) noisy laptop transformer.

As a side note and again, don't do this "ground lift" method on anything but the laptop power supply for now.

anonymous Wed, 01/28/2009 - 07:39

I'm with Greener and Link on this one.

If your power supply malfunctions, and you have 120 VAC connected to the ground or 12VDC line on your lap top, then you are going to get not going to be happy. Either dead because you were touching something that got bumped up to 120v, or have a fried lap top. The ground pin on a three prong is to take the bulk of the current if this happens and spread it to earth ground until your breaker trips.

Power supplies that are designed with 2 prongs have other fault protection built in to keep you from getting fried. It's not just a 3 prong power supply with the ground pin removed.

Link555 Wed, 01/28/2009 - 07:51

Just to beat a dead a horse:

http://www.allaboutcircuits.com/vol_1/chpt_3/8.html

This is somewhat over simplified. Remember unless your standing very close to the panels earth connection is still a resistance between your ground and the earth ground.
Ohms Law Voltage= Current * Resistance.
This should a very small value however….should be…

How well do you know your panels wiring?

These little things seem to add up…

anonymous Wed, 01/28/2009 - 08:29

Greener wrote: What are your intentions?

:oops:

Fair enough: My intentions in this case are only to help figure out what the problem is caused by. And if it's the laptop transformer, to provide an easy method of dealing with it.
I'd never recomend doing this with a metal cased object such as an oven, but in the laptop ? not as much of a major concern in my opinion.
The transformer itself is sealed (in plastic) against outside elements (including your fingers) which would provide against accidental "hot" situations such as shown in one of the diagrams provided in the circuit link.
Aside from that, the DC power to your laptop is also shielded by the plastic (in most cases) laptop itself.
Yes, I agree that it does not take much of a current draw to cause human damage or death its just that the other elements making up Ohm's law have to be there too and in this case they're likely not.
(the first diagram and explaination ?)

Your car battery is a good example for DC power, it is capable of providing upwards of 500 amps yet it doesn't kill you when you touch the terminals....figure out why ?

Seriously, I don't claim to be an expert or know it all and we all have acess to the net to help figure these things out.
It's just that I've seen, experienced and helped with this particular problem (if it IS the problem) so much that I do feel confident about the temporrary solution. the very nature of a laptop is temporrary.

My apologies if I offended anyone, I'm just your average dufus who enjoy's the heck out of recording and stummbled across this site last night :D

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