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NinjaKitten 15th January 2009 08:06 PM

Noise on laptop charger PSU
My laptop's charger lets through ground loop noise. I bought a ground loop isolator for my audio out (to remove the squeaky buzz noise from my sound) for when I connect it to my speakers, but when I want to use my S-Video output, the video noise is horrendous. So, to combat this, I'd like to build a ground loop isolator (or noise canceller) for my power supply. Specs of my supply are:

Input: 110-240V AC (~1.5A)
Output: 25V DC, 3.25 A

I'm in the UK, so my supply is 230V, 50Hz.

I can get hold of a female socket and male connector that match my power cable (saves me butchering it). I've seen circuits that work as GLIs for audio and digital signals, but not for plain DC.

Would it be easier for me to build a GLI for the 230V AC side?

Elvee 16th January 2009 07:33 AM

I think the simplest and most effective solution to your problem is to build a crude 25V linear supply.
It may not be the cheapest or lightest option, but it will be 100% effective.

wakibaki 16th January 2009 07:47 AM

Your PSU or computer are faulty. I can't hear my laptop, or any one I've ever had.

Running it on battery will tell you which.

Simplest thing is replacement.


winny 16th January 2009 07:52 AM

The problem comes from the fact that the charger is the ground point and not the laptop. All current the laptop draws multiplied with the resistance in the cable from the charger to the laptop will equal the potential between real ground and laptop output ground.

Does the problem persist when you run on battery instead of the charger?
Have you tried degrounding your laptop charger?

wakibaki 16th January 2009 12:48 PM

The presumption that this is a grounding problem is premature, despite the apparent success with the ground loop isolator on the audio.

The symptoms of a ground loop in a home audio or video system include a moderate to loud hum being audible or white banded lines appearing on the video monitor.

The kind of hash you are experiencing does not sound typical of a ground loop, but rather a poorly suppressed supply, or other EMC problem in the laptop.

This is more probably a fault condition rather than poor design although obviously that is not impossible.


NinjaKitten 17th January 2009 01:51 PM

It works perfectly when I'm running from battery. The ground loop isolator for my audio works fine too. The only issue is when I put my S-Video cable from my laptop to my amp (it has an upscaler in it which connects to my TV via HDMI cable) and have my laptop plugged into the supply it causes the image to become noisy (the white banded lines you mentioned). The only explanation I can see is that it's a ground loop issue.

The laptop power cable has a sealed plug on it, and as I mentioned before I don't want to butcher it. I've got an old three-way splitter that I can take apart and remove the ground wire from - reckon that'll do the job as a makeshift degrounder?

theAnonymous1 17th January 2009 02:58 PM

I agree with winny and think the simplest way to solve your problem is to just remove the ground pin from the laptop power supply.

Of course I have to say "DO THIS AT YOUR OWN RISK". Not because I personally think there is any real danger, but because there are people that will suggest doing this will cause all of the children, pets, and plant life around you to instantly vaporize. :rolleyes:

NinjaKitten 17th January 2009 03:25 PM

Haha, loving that. The US gets along well enough without ground pins, I'm sure I can too.

wakibaki 17th January 2009 03:31 PM

OK, try it on battery with the supply plugged in and switched off at the socket. If the noise is present then it's due to ground loop.


NinjaKitten 17th January 2009 04:21 PM

Good idea, never thought of that before.

Turns out it was a grounding issue - the buzz stays even when I turn off the power. I'll mess with the ground on that splitter block later.

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