Laptop power supply, PCMCIA card and digital hash noise in new monitors

chikin

New member
Hi all,

I'm new to this forum, so please be gentle with me.

My setup is a Dell Inspiron laptop with an Echo Indigo PCMCIA audio card for recording, the output of which goes to the TAPE IN inputs of my little Behringer Eurorack mixer. The TAPE OUT outputs of the mixer go to the input of the audio card. I have some Sony monitoring headphones, a mic, guitars, etc. Everything's been peachy up until now.

I went out today and bought a pair of KRK TR5s for monitoring. (Regardless of what you think about those speakers, they fit well with my music and I thought they sounded the best to me. I'm not here to fight over monitors--I got bigger problems.) For starters, I hooked them up to the control room outputs of the Eurorack mixer via 1/4"-RCA cables and used the unbalanced inputs of the monitors.

Anyway, everything is fine when the laptop is running off the battery. There is no digital noise whatsoever. The output from the monitors is nice and clean. The problem comes in when I plug my laptop's power supply into the laptop. All of a sudden, there is a TON of digital hash and noise from the soundcard output. I notice the very same thing when I hook up the TR5s directly to the soundcard output rather than taking the output through the mixer. When I plug my monitor headphones into the soundcard output, I don't really hear the noise. It just dawned on me now that the noise is probably more prominent in the monitors due to the fact that they are amplifying everything at the input, whereas the headphones aren't.

I am aware that switching power supplies are noisy little beasts, but there's really no way I can record using battery power alone--the CPU usage with all the verbs and compressors I throw on the tracks takes a lot of juice.

So what should I do? My first instinct is not to blame the cabling. I figure that the PCMCIA soundcard, being powered by the laptop supply, is picking up all that nasty crap, and I should be using some sort of external USB device. Furthermore, I believe I should get an externally-powered USB device, you know, one that uses a little plug-in wall wart (or, better yet, a 9V battery or something), so that it won't use the power on the USB line, which, after all, would still come from the laptop.

I humbly ask for any advice or assistance:
1. Does my hunch sound correct? If so, can anyone recommend a fairly decent externally-powered USB audio device (better yet, one that maybe takes batteries)? I don't need much in the way of features--just a stereo 24-bit input and output would be fine, though I'm open to other features, and of course, good driver support for XP.
2. If someone suspects something else, maybe the cabling, or some other techniques I should try, I'd appreciate it. I've tried relocating the laptop power supply to different outlets, trying different cabling, etc., with no success. But as soon as I pull that laptop power supply and go on battery power, everything is clean as a whistle.

Thanks all,
chikin
 
Hey Man,

I've run into the EXACT same problem with a novation USB x station and an RME multiface. It's definately the computer, not the soundcard. I'm trying to find a solution but as of now, it's just not happening. I'm using this set up for live stuff by the way so when they crank the gain on the keys you hear that terrible noise. Let me know if you figure something out.
 
Mindset said:
Power Conditioner

Won't help. The problem is not the power lines. The problem is that your computer wasn't designed for audio. The shielding of your computer is connected to its ground plane, and since it doesn't have a grounded power supply, when you hook it to external audio hardware, the shortest path to a true ground for all that electrical noise is through your audio cables.

That noise level goes way up when you run on a power supply, presumably because of a noisy charge circuit. However, in theory, you could still see problems even while running on battery. I very much doubt a USB interface will help because you're still sharing a system ground with the computer, and that's where your noise problem is coming from in all likelihood.

Indeed, Dell Inspirons are well known for this problem. I didn't have any trouble finding people complaining about their ungrounded power supplies on the net.... Fortunately, you should be able to fix it easily if you know what you're doing. :)

There is exactly one way to fix this correctly: ground the living s**t out of your computer's ground plane. The only way I know of to do this (without voiding your warranty) is to build a grounding pigtail.

First, find an unused jack on the computer. It doesn't matter what type of jack you pick, so long as you can do without it while recording. For example, if your audio interface provides a headphone jack, you might not need the one on the computer. Or you might have a spare USB port.

Next, find a plug that fits in the jack you picked. Connect the shield of that plug to the ground contact of an electrical plug using a heavy gauge (e.g. 10AWG) wire. Plug the plug into a wall outlet and plug the other end into the unused jack on your laptop.

Now for the warnings:

1. If you aren't used to electrical work, find someone who does. 110VAC is dangerous....
2. You'd better make darn sure that your house's ground really is grounded and that you connect the wire to the right contact.
3. You should also use electrical tape to cover the unused hot and neutral (or hot and hot in the case of a 220VAC circuit in some countries) contacts. You really don't want the wire to short against a hot contact if it comes loose inside the plug.
4. If possible, use a pre-molded power cord and cut it in half. That way, you don't have to worry about #3.
5. If you do anything described in this, you do so at your own risk. I will not be held liable for any damage to your equipment, whether caused by your error or mine.
 
Thanks for your help. I definately don't have the electrical know how to do what you described and my laptop is more important to me functioning and not running clean audio than it is running clean audio and possibly dying (I use my studio desktop for all recording). However, I recently went to radio shack and bought one of those 3 pin to 2 pin power cable converteres and it completely got rid of the digital noise. (granted I have a quiet 60 hz hum now but it's much easier to deal with than the digital stuff). My question is, am I in danger of hurting myself or my laptop by using this converter? I've used it now at one show and for some on the go recording with no injuries or broken electronics. Thanks in advance.
 
I use a Dell Inspiron for mixing. It hums like crazy if I use the internal soundcard's line out into my monitoring system, unless on battery power. Doesn't hum at all going out through my Digigram VXPocket PCMCIA card that has balanced in's and out's. BTW, none of the humming is digital noise. It's analog.
 
An alternative solution is a DI box between the mixer and the monitor.

BTW, ground lifting the laptop is probably not a good idea.
 
Strave said:
Thanks for your help. I definately don't have the electrical know how to do what you described and my laptop is more important to me functioning and not running clean audio than it is running clean audio and possibly dying (I use my studio desktop for all recording). However, I recently went to radio shack and bought one of those 3 pin to 2 pin power cable converteres and it completely got rid of the digital noise. (granted I have a quiet 60 hz hum now but it's much easier to deal with than the digital stuff). My question is, am I in danger of hurting myself or my laptop by using this converter? I've used it now at one show and for some on the go recording with no injuries or broken electronics. Thanks in advance.

I think you're in more danger by using that ground lift than doing what dgatwood described.
 
I was just about to post about this problem when i read this post
then i went through a direct box i had around the problem is fixed...
amazing!

thank you much freddy

noah
 
Strave said:
Thanks for your help. I definately don't have the electrical know how to do what you described and my laptop is more important to me functioning and not running clean audio than it is running clean audio and possibly dying (I use my studio desktop for all recording). However, I recently went to radio shack and bought one of those 3 pin to 2 pin power cable converteres and it completely got rid of the digital noise. (granted I have a quiet 60 hz hum now but it's much easier to deal with than the digital stuff). My question is, am I in danger of hurting myself or my laptop by using this converter? I've used it now at one show and for some on the go recording with no injuries or broken electronics. Thanks in advance.

Ground lifts on power cords are very dangerous. If anything goes wrong electrically with the gear and one of the hot connections inside shorts to the case, you could touch the device and get electrocuted.

I assume you're lifting the ground on whatever is plugged into your laptop, right? Because I didn't think the Inspiron laptop supply had a third prong. If I'm wrong about it being a two-prong adapter, then there's something really, really wonky about the power supply design. :D
 
I use an insiprion too, by the way.

after about a week of using a direct box between the computer and the mixer i started to realize different noise patterns.. the audio was also going through minimal clipping... it drove me just as nuts as the first problem.

I was just wondering, chikin, if you had found a soloution.

Thanks, Noah
 
I am not convinced by the assertion in this thread that a ground lift is that big of an issue. Quite a few laptops out in the marketplace don't even have grounded plugs on the AC adapters.

My fiancee's Gateway's AC brick has a ungrounded power cord with the 2 pin polarized plugs on it.
 
A 2-pin device will be double-insulated, like a power tool that only uses a two-prong plug. A third prong means it's needed, and shouldn't be removed.

Besides being potentially dangerous, removing the safety ground voids the warranty on most equipment.
 
Don't most power bricks have fuses? Everything coming into the brick is 110/220V AC, but everything coming out is 12-18V DC.

If there was a problem, the brick would die before the actual laptop was affected...
 
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