My laptop is feeding noise into the PA

MikePeartnoy · #1 05-11-2010, 12:27 AM

So my band has recently purchased a PA system, and I have a Mandala Pad in my kit. So naturally, I found a 1/8" to 1/4" converter cable so I can connect the laptop on which the software brain resides to the Direct In on the mixer. I used to do this to an old amp before on a different laptop, and everything was fine.

Right now though, the laptop, or one of the cables, or the 1/8" converter is feeding noise into mix. I'm suspecting the laptop, since the noise basically corresponds to whatever's going on with the laptop. I.e, I click to open a new window, and as its loading, the noise intensifies. The screen dims, it lessens, etc. So I'm assuming that I'm picking up way more signal than just what should be going through the headphone jack.

To add to that, I've discovered using certain Guitar Pro tabs for example, that instruments panned to 0 couldn't be heard, while instruments panned to either side could be. What's going on here?

Any advice on what to do? Is it the headphone jack perhaps? How do you even replace something like that? Cables? Converters? Anybody had a similar problem?

chathamight · #2 05-11-2010, 04:41 AM

noise coming through the headphone port of your laptop could be many things. loose/faulty port, soundcard on its way out, bad cable, cold soldering, signal levels between consumer (laptop soundcard) and professional (pa) equipment, etc. i don't know b/c i can't see your setup.
i would consider getting an audio interface. the soundcards on laptops aren't the best. plug the audio interface into the laptop via usb/firewire, then outs from the interface to the pa. the noise from the computer should be eliminated, since the signal is coming out of the usb/firewire port as data, then converted in the interface instead of your laptop's cpu.

MikePeartnoy · #3 05-11-2010, 04:53 AM

Thank you, sounds like a great idea actually.
I'm gonna look up some prices when I get the chance.

audiotech · #4 05-11-2010, 04:05 PM

Are you certain that your laptop is feeding into a high level input jack on your mixer and not a microphone level input?

Dennis

MikePeartnoy · #5 05-11-2010, 04:54 PM

I was under the impression that microphones fed specifically ONLY into XLR jacks, no? But there are two 1/4" inputs on the mixer: "Line In Bal or Unbal" and a "Insert I/O." I'm running through the Line In.

audiotech · #6 05-11-2010, 07:27 PM

Quote:

Originally Posted by MikePeartnoy

I was under the impression that microphones fed specifically ONLY into XLR jacks, no? But there are two 1/4" inputs on the mixer: "Line In Bal or Unbal" and a "Insert I/O." I'm running through the Line In.

No there are balanced microphone inputs using XLR connections and also unbalanced mic connection using 1/4" jacks. Both of these can be low level inputs. It does sound as if you have your laptop connected to the correct inputs of the mixer. High level or line inputs vary between -20 db and +8 db depending on the mixer.

Dennis

MikePeartnoy · #7 05-11-2010, 11:16 PM

They must be, in fact, I just connected it to the other one for the sake of troubleshooting, and the noise was far more pronounced.

diosdude · #8 05-12-2010, 12:42 AM

Are you running clean power through all of your gear? do you use a power conditioner?

catlover · #9 05-12-2010, 02:44 PM

Noise is coming from "earth" or "ground" connexion through AC power !
Try disconnect laptop AC plug, using only battery, and noise is gone.

Use external USB soundcard... or cut "earth" connexion of AC plug (not recommended ...)

gallonsloth · #10 05-17-2010, 03:08 PM

I'm having this problem too... I only have the noise when the laptop is plugged in through AC power, but even going through an external sound device doesn't seem to do the trick.

MikePeartnoy · #11 05-17-2010, 05:08 PM

I returned to the cable I used before and I got stereo sound back, and disconnected the laptop from AC while playing -- success.

Thanks Catlover.

Now I just have to put faith in my battery.

Numberonefan · #12 05-18-2010, 10:18 PM

You should be running your laptop into a mono or stereo (depending on your needs) DI a few feet from you then DI to the PA.
Use a single stereo earphone to Y ¼’s then XLR back to the snake and board. All your noise will be filtered by the transformer in the DI regardless of DC or AC operation.
This also protects your laptop from 48V phantom power. The lower end boards that don’t have switch able on each channel so it’s sent out to all including your laptop….

MikePeartnoy · #13 05-20-2010, 05:17 PM

So then something like this?

http://www.zzounds.com/item--BSSAR133

Numberonefan · #14 05-20-2010, 10:23 PM

Sure but that puppy is really expensive and all that is important in the transformer inside. You’re in Canada like me and I use the Yorkville ones but really any will do… Only exception would be Behringer. Most if not all the components in these are bad Chinese knockoffs of name brad parts. They will work but suffer from poor performance and almost always premature failure.
You should be able to get one for 50 to 75 bucks locally in any pro audio shop. Look for whoever is you local live sound rental company and these guys should be able to steer you right and will have the right cables as well.