Noisy laptop power supply

Richard Stringer

Sophomore
Jan 13, 2011
124
0
16
Boston, Lincolnshire, UK
Hey ya guys, i've got a laptop and when I have the power supply connected it introduces a lot of noise to the audio signal, but when I disconnect the power supply the noise dissapears totally. Is there any way of getting this noise gone because my laptop needs the power supply in to last the night of the event. Thanks.
 
Re: Noisy laptop power supply

In my experience, sometimes using a passive DI (with ground lift) between the laptop and console can help, but other times it's noise induced in the audio path inside the laptop and there's no way to remove it. The latter is the situation I currently have with a Dell Precision M4500. I can often just get by if I run the app volume and laptop output close to as loud as possible - the noise doesn't seem to scale with audio level.
 
Re: Noisy laptop power supply

I've had great luck with the Whirlwind pcDI: pcDI® - Catalog - Whirlwind . However, the better solution is to use a decent outboard audio interface which also tend to have less noise in general outside of PSU coupled noise. I'm still using my old M-Audio MobilePre USB to go from laptops to mixers locally.

Greg
 
Re: Noisy laptop power supply

I'm using Traktor Scratch Duo 2 software to dj with files on the laptop, and that uses an external usb Native Instruments audio interface. What's the Kensington things, are they power supplies you say?
 
Re: Noisy laptop power supply

Input and poutput because you connect your vinyl turntables into the audio interface and then it also has outputs which go into your dj mixer's line inputs. You have two time coded vinyl which enables you to control .mp3 and .wav files on your computer as if they were real vinyl on the turntables.
 
Re: Noisy laptop power supply

It's a Sony VGN-NW26M. I was looking at the Behringer MicroHD HD400, how good are they exactly? Would I connect the main TRS Jack outputs of my dj mixer to it, and then out the Behringer into my loudspeaker management system or amplifier?
 
Re: Noisy laptop power supply

My friend used to have one of those Radioshack ones and it degraded the sound quality of his system, supposedly the Behringer doesn't degrade the sound, from what I hear.

My experience is that the RS unit makes very little difference to the sound quality. Since you're pulling from the headphone jack on your laptop, you're already dealing with a limited quality output anyway. The behringer unit is ring to be on par with the quality of the components inside, so the difference should be minimal.
 
Re: Noisy laptop power supply

I SMAARTed at Rat Shack isolator a while back and it took quite a bit of level to cause any noticeable saturation and roll-off of the low frequencies. More level than what an iPod or built-in laptop audio card could produce. That said, I have run into an instance where it didn't' fix the noise coupling problem 100% which leads me to believe it doesn't have 100% isolation compared to a good quality passive DI.

Greg
 
Re: Noisy laptop power supply

It may be the noise was in the signal before it hit the output jack. I have run into laptops that had internal noise problems that sounded just like ground problems but were unrelated to grounding (still exist just on battery).
 
Re: Noisy laptop power supply

Agreed. All the more reason to use an external audio interface and avoid using the internal sound card.
 
Re: Noisy laptop power supply

Grab a Kensington or other ungrounded power supply. I wouldn't recommend to anyone to AC ground-lift their "Grounded" laptop PSU, but not connecting the ground on the PSU will fix the problem.

Gee, that's EXACTLY what I recommend with a laptop. Laptop power supplies are notoriously noisy. A ground lift adapter works everytime. Laptops and their usual line wart power supplies are already fully enclosed in plastic (there's your personnel safety).

Mike McNany
 
Re: Noisy laptop power supply

Gee, that's EXACTLY what I recommend with a laptop. Laptop power supplies are notoriously noisy. A ground lift adapter works everytime. Laptops and their usual line wart power supplies are already fully enclosed in plastic (there's your personnel safety).

Mike McNany

Nope. Those 2-3 prong adapters are *not* ground lifts. They are intended to allow you to use grounded equipment with older non-grounded wiring, and it is expected that the adapter be grounded to the metal box. That's what the green tab is for.

Laptop power supplies and other DC power supplies that are in a plastic shell but have a 3-wire cable have that cable for a reason. Usually because either the plastic enclosure does not have sufficient insulating or flame-resistant properties and there's a metal enclosure inside the plastic enclosure that needs to be grounded, or because the earth ground is needed as a drain for the noise filters in the SMPS. Assuming the latter case, lifting the earth ground means that your SMPS is now radiating much more RF than it should, instead of conducting it away to ground.

A "ground lift" in the context of audio or signal wiring in general should only ever lift signal common (shield), which isn't really a ground anyway.