A clean laptop power supply?

jamos · Posted: Mon Dec 05, 2005 11:28 pm Post subject: A clean laptop power supply?

I'm playing with a couple of laptoppers these days. Onne of them is running a Dell laptop; when he plugs in his external power supply there is all sort of noise in his audio output. I've had similar problems with my Dell laptop - different model but a similar power supply - which is one reason I don't use it anymore. Running on batteries, both sound fine.

Does anyone know of a source for _clean_ power supplies for laptops? If not, I think I've just discovered a market niche.

Mohoyoho · Posted: Tue Dec 06, 2005 6:56 am Post subject:

What I've had to do is get a two prong adaptor to lift the ground. Also a better audio out improves performance markedly. I use the Echo card which has made an amazing difference.

Kassen · Posted: Tue Dec 06, 2005 7:41 am Post subject:

jamos · Posted: Tue Dec 06, 2005 8:23 am Post subject:

Thanks - we've actually done both of those things with mixed results.. sometimes we get noise, sometimes not. It's nasty, whatever the cause.

deknow · Posted: Tue Dec 06, 2005 8:38 am Post subject:

jamos, i have written about this a few times on the forum. i install/train speech recognition systems, and this is a common problem. it can happen under any (or all) of the following circumstances:

plugged in and battery is fully charged
plugged in and the battery is charging
running on battery

so there are a few obvious solutions (like if it only happens when the battery is charging, then plug the laptop in with the battery fully charged). you might also try removing the battery and running on ac

if none of this works, you can also try grounding the laptop (probably a good idea to use a multimeter to make sure there isn't a large current first). you can use any of the shields on any connector in the back printer port, etc), or what i've done is cut the end off a usb connector, and soldered a ground wire to the shield only.

deknow

deknow · Posted: Tue Dec 06, 2005 8:40 am Post subject:

btw, i'm not convinced that it's the "power brick" that is at fault, so an aftermarket "clean" one might not help. the power supply (in the laptop) has to decide when to charge the battery, and i expect this is a large part of the problem.

deknow

jamos · Posted: Tue Dec 06, 2005 9:17 am Post subject:

What we've found is that the noise is present any time the block is plugged in, regardless of whether the battery is fully charged or not. I think. We will need to do some experiementation. Thanks for all the suggestions.

I've always associated grounding problems with hum, not the high frequency hash noise that we hear, which I'm pretty sure is a result of the switching power supply.

deknow · Posted: Tue Dec 06, 2005 9:40 am Post subject:

you might want to read the following:
http://www.rme-audio.com/english/techinfo/hdsp_notebase.htm

again, i'd try grounding the laptop, i think you will find this noise will reduce considerably.

deknow

deknow · Posted: Tue Dec 06, 2005 10:22 am Post subject:

...one other suggestion. make sure all of the audio devices (cd, line, mic, wave,) that are not needed are muted in the system's mixer, i've seen these bring in tons of noise.

deknow

Mohoyoho · Posted: Tue Dec 06, 2005 10:23 am Post subject:

Try the Echo Indigo sound card. That really makes a difference. The sound cards that come with laptops are terrible, and there is something about them or the way they are wired that makes them noisey. When I installed my Echo, it was night and day (and that is no exagerration). I use the standard Echo Indigo because the I/O wasn't available at the time.

mosc · Posted: Tue Dec 06, 2005 11:30 am Post subject:

Kassen. Your post about lifting the grounds brought tears of joy to my eyes. You are wise beyond your years...

jksuperstar · Posted: Tue Dec 06, 2005 12:41 pm Post subject:

My laptop gets crazy crap coinciding with what's displayed on the screen...I can actually *hear* my mouse moving! Not using the laptop's sound (an Emu 1616m PCMCIA card) changed everything.

However, once in a blue moon, I can faintly hear the same crap coming through into my speakers. The DAC's on my system are the outboard kind, and the mechanism to communicate between PCMCIA and external box is differential, with no ground. I can only guess it's electro-magnetically transmitted. Odd, even from an LCD.

Lifting the ground on the power supply can definitely help though, or if your laptop supports it, using SPDIF out to an external piece of gear. (I've noticed lots of laptops supporting SPDIF out via the microphone plug & external dongle). (btw- this is my method of getting good audio out of Linux, sending SPDIF into an outboard reverb that has good DACs and SPDIF!).

mosc · Posted: Tue Dec 06, 2005 12:44 pm Post subject:

I would guess that Firewire and even USB (if you cut the ground) would provide the same isolation.

elektro80 · Posted: Tue Dec 06, 2005 12:49 pm Post subject:

Some IBM and Dell laptops will send a high frequency noise out on the audio line out in sync with mouse movements. In some cases this can also be solved by lifting the ground. On the 6 machines I have seen with this "problem" the high freq noise and the hum went away when an echo PC thingie was used instead of the PC audio line outs. Same thing with a Motu 896 firewire thingie.

djfoxyfox · Posted: Tue Dec 06, 2005 3:56 pm Post subject:

Last September at Different Skies, my laptop's power supply was also making noise. But the noise wasn't only in my mixer's audio output. Noise was going THROUGH THE POWER CABLE'S GROUND into someone else's synthesizer. This synthesizer's audio outputs were not going through my mixer but still had noise since its power cord was plugged into my power strip.

LIFT THE GROUND!!!! Smile

sheldonstv · Joined: Nov 26, 2005 Posts: 7 Location: uk

The ground connection on the primary side of your laptop switch mode power supply is a saftey feature,but due to the way the power supply works (due to defective components-it is a fault!!!-but not a dangerouse one...) there can be a large amount of noise due to the earth connection.
UNDER NO CIRCUMSTANCES DO YOU CONNECT THE POWER SUPPLY - CONNECTION TO GROUND(THE SECONDARY SIDE NEGATIVE CONNECTION )!!!-THERE WILL BE A BANG!!
Due to the fact any smps doesnt supply mains isolation(switched mode power supply) any connection to mains earth will instantly kill it...
Have you access to a scope to check if there is any ripple on your power supply outputs?
regards mike

zyld crin · Joined: Jun 13, 2008 Posts: 1 Location: Normal, IL. USA

Mohoyoho you are a life-saver, nay, a genius Idea

- OK you're both!
I have a HP Pavilion that I have been using in my studio and the only way I could do a session is to unplug the brick power supply and run on batteries. The downside Crying or Very sad

is that when the battery gets low I have to end my recording time and plug it back in. What a drag.
Idea

I had determined that I was going to buy (1) 6-Volt and (1) 12-Volt Gel Cell or Zinc-Acid or some other suitable battery compliment, run them in series and operate my computer from them when in record mode. The batteries would probably last days between charges and I would be rid of the hum, but with a new problem: battery maintenance and charging regulation.
Your solution worked wonderfully and at 1/1000th the cost! Very Happy

Well done!

Mohoyoho · Posted: Fri Jun 13, 2008 11:00 pm Post subject:

You're welcome. I learned from experience and pass it on to anyone who comes by this thread.

TheShaggyDA · Joined: May 17, 2008 Posts: 9 Location: UK

New terminology for me - how exactly does one "Lift the ground"?

Kassen · Posted: Sat Jun 14, 2008 12:23 pm Post subject:

factus10 · Joined: Jun 20, 2007 Posts: 158 Location: Buffalo, NY

I have an Echo Indigo and it is a very good card for laptops that have PCMCIA slots. I also have a Lexicon Lamba. Neither eliminates ground noise completely, however.

I've tried lifting the PS ground with both my HP and MacBook laptops. Results were ok but not great.

The solution I use is two DI boxes and I lift the ground with those. They provide absolutely amazing ground noise elimination. I use a pair of inexpensive Behringer DI boxes because, frankly, the power amps in venues just aren't that amazing and the slight loss of bandwidth isn't very noticeable. If it's a problem for you, get more expensive DI boxes.

Coriolis · Joined: Apr 11, 2005 Posts: 616 Location: Stilling, Denmark

I have one of those IBM-noise sources:

-Internal sound on batteries = tons of static/glitchy noise

-Internal sound on AC = somewhat less of the above

- My Focusrite Saffire LE card (firewire) = Nothing. Not a sound.

I have not lifted my ground, but mebbe I should, cause I use the internal card to listen to music a lot. Good thread this - answers some questions for me..

C