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Electro-Magnetic Interference on... Computer?

post #1 of 10
9/26/11 at 9:39pm
Thread Starter 

I've been having a weird issue lately, and it's got me stumped for the time being.

 

So, whenever I turn on/off a relatively high current "appliance" (i.e. halogen desk lamp, soldering station, etc.) the sound from my system fades out then back in over the course of about a second. Sounds like the system is not getting enough power, but I'm positive it's not due to dirtying up or using up the mains power. My system is: Macbook Pro non-unibody -> Staples USB -> Sonicweld Diverter -> Signal cable digital interconnect -> Assemblage DAC3 -> Homegrown Audio Diva -> 3-channel Beta22/SRM313. This issue happens with all my headphones, whether I'm running off mains power or off battery power from my APC S10 power conditioner/UPS. So, even when everything is physically disconnected from the Mains power, I still get the fade in/out.

 

Do you guys think the soldering station or light could be causing EMI with the computer or cables? I think it's interfering with either the computer or the USB cable, because those are the closest to the lights and the least shielded compared to the other equipment but I'm not sure how to test. I don't have any fancy USB cables to test the effect of extra shielding, and I'm not sure how to shield my computer further. I have both SSD and HDD in my laptop, and it happens when playing from both drives.

 

It's not terribly annoying because I'm not constantly turning my lights and soldering iron on and off, but it would be nice to resolve this.

 

Thanks in advance everyone!

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post #2 of 10
9/26/11 at 10:05pm

so you're saying even when absolutely none of your gear including your computer is plugged into the wall this happens?

 

if so, wow.

 

 

 

 

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post #3 of 10
9/27/11 at 9:09am

Eletrical switching do generate a lot of RF, mainly in devices with coils, like your soldering station, and probably your lamp.  Shielded cables should prevent, or at least lower,  your mac  from interference.  Afaik...

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post #4 of 10
9/27/11 at 9:30am

Are all of your devices on the same ground ( i.e. outlet )?  It could be a simple grounding issue.  Anything with AC current will tend to produce noise into the nearby AC current lines.  I work with laser systems all day and the power supplies produce enough noise that it transfers back down into the AC outlet and into a test bench that has CFL lights.  These lights flicker at the same pulse repetition frequency as the power supply producing the noise.  Motors and fans are almost always the cause of back EMF as they produce AC noise.  Try turning off any motors / fans nearby that are not inside the PC obviously.  Perhaps your soldering station is running a solder smoke fan?  Do you have CFL lights nearby?

 

It could also be simply a lack of current.  If your outlets are rated at 18 amps and you have many devices including halogen lights, fans, etc connected to this outlet when they turn on they are going to steal some current from the outlet.  The current is going to flow to the path of least resistance so if your audio setup is not that path the other sources are going to grab the power first.  If you can plug your audio setup into another outlet that is on a different breaker that should solve the issue.


Edited by NA Blur - 9/27/11 at 9:31am
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post #5 of 10
9/27/11 at 11:35pm
Thread Starter 

Thanks for the replies guys. I did some more brief testing tonight, and it's definitely RFI/EMI from the devices interfering with either the USB cable or the laptop. Not sure which yet, though. When I move the laptop a couple feet away from the lamp the issue subsides. Have to move it a bit farther with the soldering station, though. I'm guessing that's because it's got much more power than the lamp. If I had to take a guess, I'd say the EMI is causing some of the bits going through the cable to be diminished and unrecognizable for the Diverter.

 

NA Blur: thanks for the detailed response, however it's definitely not power related. That was my first thought, but I tried running everything off battery power, and the issue was still apparent. I ran my amp, DAC, computer, etc. all from battery so there was no connection to the wall power at all, and I still got dropouts.

 

I've never been one to buy expensive USB cables, but it looks like I'll have to snag a better one than I have at the moment. I just have a generic Staples USB cable which seemed durable and pretty well made, but I guess it's not shielded well enough. You guys got any suggestions for a really well shielded USB cable?

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post #6 of 10
9/28/11 at 10:41am


Let us know if replacing the cable solves the problem.  I know where I work we have a few IC's that are super sensitive to static and we have damaged them before using a poorly shielded RS232 cable.
 

Quote:
Originally Posted by pbandstefanwich View Post

Thanks for the replies guys. I did some more brief testing tonight, and it's definitely RFI/EMI from the devices interfering with either the USB cable or the laptop. Not sure which yet, though. When I move the laptop a couple feet away from the lamp the issue subsides. Have to move it a bit farther with the soldering station, though. I'm guessing that's because it's got much more power than the lamp. If I had to take a guess, I'd say the EMI is causing some of the bits going through the cable to be diminished and unrecognizable for the Diverter.

 

NA Blur: thanks for the detailed response, however it's definitely not power related. That was my first thought, but I tried running everything off battery power, and the issue was still apparent. I ran my amp, DAC, computer, etc. all from battery so there was no connection to the wall power at all, and I still got dropouts.

 

I've never been one to buy expensive USB cables, but it looks like I'll have to snag a better one than I have at the moment. I just have a generic Staples USB cable which seemed durable and pretty well made, but I guess it's not shielded well enough. You guys got any suggestions for a really well shielded USB cable?



 

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post #7 of 10
9/28/11 at 11:26am

Your probley have to use shielded inconnects everywhere in your system, this usb cable here http://www.audiovisualonline.co.uk/product/4603/fisual-havana-usb-cable , has dual sheilds ofc copper braid and foil wrap it's also not to pricey, the lindy cables here http://www.lindy.co.uk/1m-premium-gold-usb-2-cable-type-a-to-b/37651.html , are shielded but only have 1 shield .

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post #8 of 10
9/28/11 at 3:03pm

Another tool that  you can use in your arsenal is this that I found from another thread.

 

http://www.psaudio.com/ps/tips/15-noise-sniffer

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post #9 of 10
9/28/11 at 4:33pm
Quote:

Originally Posted by pbandstefanwich View Post

the sound from my system fades out then back in over the course of about a second. Sounds like the system is not getting enough power, but I'm positive it's not due to dirtying up or using up the mains power



 

What makes you so certain of that? I've experienced lights dimming momentarily when another power hog along the circuit turns on or off.

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post #10 of 10
9/28/11 at 11:57pm
Thread Starter 

Thanks for the suggestions everyone... I will let you know how things turn out with a better shielded cable.
 

Quote:
Originally Posted by JRG1990 View Post

Your probley have to use shielded inconnects everywhere in your system, this usb cable here http://www.audiovisualonline.co.uk/product/4603/fisual-havana-usb-cable , has dual sheilds ofc copper braid and foil wrap it's also not to pricey, the lindy cables here http://www.lindy.co.uk/1m-premium-gold-usb-2-cable-type-a-to-b/37651.html , are shielded but only have 1 shield .


I checked out both those sites, and they appear to be European sites. I'm in the states, so shipping might prove prohibitively expensive. Might check Amazon because I received a tip about some Belkin Gold USB cables that are supposedly pretty good. Hopefully that'll solve my problem!

 



Quote:
Originally Posted by john57 View Post

Another tool that  you can use in your arsenal is this that I found from another thread.

 

http://www.psaudio.com/ps/tips/15-noise-sniffer


That is actually really cool, and I didn't know you could pick something like that up from Home Depot. I'll be sure to check for one next time I'm in the area. Awesome tip! Have you tried it in your system?

 



Quote:
Originally Posted by anetode View Post

 

What makes you so certain of that? I've experienced lights dimming momentarily when another power hog along the circuit turns on or off.


I don't mean to be demeaning, but please read the above posts. I've stated twice already that I'm positive it doesn't have anything to do with the wall power because it happens even when I run everything off battery power. i.e. there is no physical connection to the mains power anywhere in my system.

 

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