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Discussion Starter · #1 ·
Hi, I have connected my pc to the QSC K10 to play backing tracks, I connected using the headphone out mini jack at the rear of the PC, to the RCA connectors on the QSC speaker, the tracks play fine, but when I stop the music there is a buzz or hum from the speaker, this does not happen if I play the backing tracks from my ipod, or minidisc player. I am assuming this is computer noise I can hear, it disappears when I turn the gain down on the back of the speaker, any suggestions would be appreciated.

Thank you.
 

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Distinguished SOTW Member, Forum Contributor 2007-
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This could well be a grounding issue that I've experienced before. Get a three prong to two prong electrical plug in adapter and then don't connect the ground wire when plugging up the K10. Or just take a three prong extension cord and break off the ground prong from either end, then use that with the K10. Basically, you don't won't the amp grounded to the same circuit that the PC grounds to. Ungrounding the amp often works fine.


Grounded_AC_Plug_Adapter_3_prong_to_2_prong.jpg

These are usually about $3 or less.


PS: The very best way I've found to connect a PC to a mixer or amp is fiber optic cable. Many PC's have a fiber optic out port. Just buy a $20 digital to analog converter to go fiber optic to RCA at the mixer or amp. These work great to go from the mixer back to the PC too for recording.
 

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Thanks for these tips. I'll file them in memory. I have a pair of QSC K12s (for big ballroom gigs like last nite), and a K8 (for playing on someone's back deck at a private home tomorrow). While I currently run backing tracks from an ipod or ipad, there may come a time when I use a laptop....
 

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Discussion Starter · #5 ·
Hi, thanks for the replies, I wondered if the headphone socket was part of the problem, as there is no noise when I connect the ipod or phone to the rca connectors to play the same baciking tracks, yes the speaker does have xlr connection, and the analog converter looks like a good solution. as does the usb peavey,

thank you all.
 

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Get a three prong to two prong electrical plug in adapter and then don't connect the ground wire when plugging up the K10. Or just take a three prong extension cord and break off the ground prong from either end...
View attachment 37189
This is a great way to electrocute yourself. Never, EVER, EVER defeat the ground connection on an AC plug. When you do that, there is no where for the electrical current to go to ground if it shorts, except the next easiest connection to the ground, i.e through your body. And the user manual for these speakers, on page 2 specifically states:
9. Do not defeat the safety purpose of the grounding-type plug on the three-pronged “Edison” style power cable. The grounding plug has two blades and a grounding prong. The third prong is provided for your safety. If the provided plug does not fit your outlet, consult an electrician for the replacement of the obsolete outlet. Do not cut off the grounding plug or use an adapter that breaks the grounding circuit. This apparatus must be
properly grounded for your safety.
If you need to use a ground lift to get rid of a 60Hz hum, you can use it on the particular XLR line that is causing the problem, one of these XLR ground lift barrels will work fine. Don't EVER lift or defeat the ground on a high voltage AC line. It can electrocute you or someone else, and stands a very real possibility of starting a fire. It's unsafe, and stupid. Just don't do it.

The problem is likely that there is a short in the 1/8" to RCA cable that you are using.Try a different one, or use an 1/8" to two XLR-male cable and connect your PC that way. Using a USB adapter interface is great, but often times more trouble than they are worth. Of course the best solution is to use a small mixer and run your iPod and computer into that and then connect your mixer to the QSC speakers.

On second thought, there could also be a problem with the power supply and battery charging circuitry on your laptop (I'm assuming you're using a laptop). This is pretty hard to fix. I had a laptop that would do this when recording with Protools. You couldn't hear it while recording, but upon listening back there was a hideous digital distortion. Sometimes it happened sometimes it didn't I finally traced it down to a bad battery that was not supplying the proper voltage to my USB recording interface. Ordered a new battery, problem solved. (Yes this happened even while plugged on, since the laptop ran from the battery, and the AC plug just continually charged the battery). Until the charging circuit finally died. Then I bought a new laptop.

Basically, you don't won't the amp grounded to the same circuit that the PC grounds to. Ungrounding the amp often works fine.
No, actually that is exactly what you want. All of your audio gear, including computers, should be on the same circuit, or have the same ground. Putting different pieces of equipment on different circuits will spread the load out so that you won't trip a breaker, but if those different circuits have different paths to ground, then you will get a hum. Even the biggest touring shows that use 400 amp, 3 phase power go to great lengths to make sure that their equipment all has the same path to ground.

If you are running your laptop (or desktop computer even) plugged in to the AC power, but it is on a different AC circuit than the speaker, plug them into the same AC circuit and this will likely cause the hum to go away since both pieces of equipment will now have a common ground path (i.e. they are not creating a ground loop).
 
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