Speaker noise issues caused by PC audio out any Solutions?

[dave197878]

My Mk2 cabinet speakers are hooked up to a small amp (cana kit amp)  which  is connected to the PC audio (green) out.

My issue is a have low volume static/hum when there is no volume present.
 
When you play a game it's still there but not as noticeable. Also when im in windows theirs almost a high pitch wine when I move the mouse.

The power supply for the amp is good no noise Is present. I know this because I played music thru the same amp and speakers but with  an mp3 player as the source with no issues.

So this leaves me to believe the PC audio out is at fault. The strange thing is when I hook the PC out to a logitech speaker system (instead of mk2 speakers) the noise seems to disappear.

This leads to my questions is there a cheap pre amp filter I can use to cut out any love level sound??? Maybe logitech has one of these filters in there system thats why it's clean?

So  has got me stumped any help would be appreciaed.

[MTPPC]

Did you try getting audio from the blue jack on the PC?

[BobA]

What are you using to supply power to the canna kit amp?   Sounds like you have a ground loop problem.  These problems manifest themselves by making different noises depending on what the computer is doing.   You can hear disk accesses and overall use of the computer as noises in your audio out.

[GregD]

I am having the same issue.  I thought it was the power supply on my Lepai amp but i tried with another source and it appears to be coming from the pc as well.  Any way to filer the pc output?

[eds1275]

You can try doing a ground lift on the audio line. Try disconnecting the ground wire somewhere between the audio output and the amplifier input. This may or may not end the loop of noise - it may make it worse or solve it completely. It is safe to do unlike other types of ground lifts.

Another few things to try are making sure your computer doesn't have one of those auto-sensing jacks that has decided your amp is actually a set of headphones. If it has you may be getting more noise than you should be. Option 3 would be to try turning down your pc audio from the master control, and turning up the amp.

You could also keep the audio lines away from any power cables in your cab.

[bluethunder]

Seems alot of PC built in audio is fairly noisy.

A cheap fix is a PCI sound card, always are better isolated from noise.

[RamjetR]

Ground loop issue for sure!

Are you running a separate power supply for your Amp on the same AC circuit as your PC? Meaning, do they share the same common earth pin in the AC plug?

Reason Case point:

I have a driving cab with an ATX PC powersupply powering a 5.1ch TA2020 Audio Amp: http://www.ebay.com.au/itm/5-1-Channel-TA2020-Audio-Amplifier-Kit-Class-Board-/230652735126?pt=AU_Electronics_Audio_Amplifiers&hash=item35b3f96e96

For the sake of a test, used a laptop to inject the audio/video and to control the PacDrive LED controller for the 5V lighting (buttons) and used the 12V ATX power from the same supply as the audio amp for the 12V LED strips.

Problem was this, every time the LED's pulsed there was a MASSIVE thump in the speakers.

Result was the following; The Laptop uses an isolated powersupply which mean't there was no common earth return back to the ATX powersupply from the PacDrive. The current for the 12V LED strips had to travel from the PacDrive, down the USB cable earth, then back up the Ground pin of the Audio cable (because it had nowhere to go? Kirchov's Law right!) and through the 5.1 amplifier ground and finally back up the Ground wire to the ATX powersupply. This would raise the ground reference, which would appear as DC injection on the audio signal. It would be amplified and appear as the DC THUMP! on the speakers!

Now I never had this issue with my normal cabinet. But the difference was that the PC supply and the external ATX supply both share the common earth ground from the AC adaptor. This was my only earth link but enough to equalise all the grounds to the same potential. Hence no problems... but once I went to isolated powersupplies, it was a world of trouble.

This is why checking your ground wires and earths are critical.

Make sure that if your using multiple powersupplies (1 in a PC and another for other 12V/5V stuff) they share the same ground on the AC powerboard, or better still, tie a ground link wire between the chassis of both 12V ATX powersupplies (NOT THE CRT CHASSIS!!! They can often be live chassis!).

Take the time to sketch out how your cabinet is wired in terms of the DC and the audio, LED controllers, PC etc... block diagram would be sufficient. Post it up and we'll take a look at it for you.

Ramjet

[kahlid74]

As has been stated by several before me, you've got a groundloop.  You need to identify how the power is being provided to your amp and then identify the power in your PC as well.  If you plug the amp into one outlet and the PC into the other and you're still getting the static you need to identify why your PC isn't properly grounding and is instead grounding into your amp.

Every time I've seen these problems it stems from either a bad PC Power Supply or some type of light on the bulb/lighting device on the line that's making this pissy.

[yaksplat]

I solved this by adding a $50 USB creative sound card into my cab. It works great and has more than enough outputs.

[dave197878]

The amp and PC is running off the PC atx power supply (12V Yellow and black wires). I plugged in head phones to the audio jack to test and theirs no noise. So at this point i figured it was the amp creating the noise but as mentioned above with the same power supply and plunging an mp3 into it as the source it works fine.. So the ground loop only appears when both the amp are plunged into the power supply and pc audio jack. Only when one of these factors is removed the issue seems to go away.

So yes its a ground loop issue.. I have a ground loop isolator 3.5mm in my car for my sirius radio I use it to remove the alternater sound so I gave it a try on the PC out and it worked...

Anyone see an issue with this fix.. it is a bandaid fix but it does work. Should I worry about the ground loop causing any other havoc? Can it effect the crt or do any damage? TY for the help every one.

[RamjetR]

The amp and PC is running off the PC atx power supply (12V Yellow and black wires). I plugged in head phones to the audio jack to test and theirs no noise. So at this point i figured it was the amp creating the noise but as mentioned above with the same power supply and plunging an mp3 into it as the source it works fine.. So the ground loop only appears when both the amp are plunged into the power supply and pc audio jack. Only when one of these factors is removed the issue seems to go away.

So yes its a ground loop issue.. I have a ground loop isolator 3.5mm in my car for my sirius radio I use it to remove the alternater sound so I gave it a try on the PC out and it worked...

Anyone see an issue with this fix.. it is a bandaid fix but it does work. Should I worry about the ground loop causing any other havoc? Can it effect the crt or do any damage? TY for the help every one.

Headphones aren't connected to another earth, thats why you wouldn't hear it.

Are both the PC and AMP running on the same ATX supply from the PC? or a separate power supply and the PC still has it's own?

Reason I ask is this:

If it's on the same ATX power supply as the PC is running on, then is there enough current on the available on the 12V rails to run your PC and the AMP? You'd be suprised to know how much current the amp may need. But on the plus side, it wouldn't be an earth issue. But you may be seeing voltage regulation fluctuations appearing as audio hum.

If they are on different powersupplies, then just run a link wire connecting the case of the powersupplies to each other. That should be all you need.

The noise isolator from your car, is that an 3.5mm line level audio filter? If it's truely an isolator then it's probably separated the earths properly, but the issue is just going to arise again when you connect stuff from one powersupply to the PC which is on the other one.

Ramjet

[GregD]

Sorry to hijack the thread but you guys seem to know what you are talking about.  My setup has separate power supplies for the pc and the amp, both plugged into the same smart strip.  I tried plugging the amp into a different outlet but I got the same noise.  Do I just have a bad power supply for the amp? 

[dave197878]

I am using one power supply for both Amp and PC.   The Amp is small 20 W @ 12V =1.6 amps  
Does not seem like allot for a 12v rail...

 

Headphones aren't connected to another earth, thats why you wouldn't hear it.

Are both the PC and AMP running on the same ATX supply from the PC? or a separate power supply and the PC still has it's own?

Reason I ask is this:

If it's on the same ATX power supply as the PC is running on, then is there enough current on the available on the 12V rails to run your PC and the AMP? You'd be suprised to know how much current the amp may need. But on the plus side, it wouldn't be an earth issue. But you may be seeing voltage regulation fluctuations appearing as audio hum.

If they are on different powersupplies, then just run a link wire connecting the case of the powersupplies to each other. That should be all you need.

The noise isolator from your car, is that an 3.5mm line level audio filter? If it's truely an isolator then it's probably separated the earths properly, but the issue is just going to arise again when you connect stuff from one powersupply to the PC which is on the other one.

Ramjet

[RamjetR]

Dave,

Well, without actually doing an Ohm test on your grounds between your Amp and PC ground, I can't think of anything else to tell you. It shouldn't be an earth problem if your using the power from a standard 4 pin utilux connector that you would plug into a DVD/burner drive. Obviously the earths would be tied together nicely.

The mouse noise is interesting though. I'm suprised that you'd hear that if it weren't being induced somewhere. I've had that issue years ago with an old wireless mouse which generated noise on my long 3.5mm audio lead to my stereo. I just changed it to a smaller cable and it went away. Unless your mouse is on another USB hub with it's own powersupply maybe? Do you have any other USB hubs with external power? maybe HDD's too? Unplug everything except the necessary stuff to run and slowely plug them back in till the noise comes back? It's a long shot but it's possible something else is doing it?

Otherwise, I'm pretty much out of advice without actually being there to check with a Multimeter.


GregD:- Need more info mate, A sketch is the best way to show us what your setup is. Keep it block diagram if detailed electronic schematic symbols aren't a strong suit. Two separate power supplies though, try tieing a wire between the case of the powersupply in one and the other one. See if that helps.

But from experience, I've found that unless your going audiophile quality amplifiers... you never truely get a quiet amp on a PC. But I'm assuming your problems are noticeably louder than background white noise.

[eds1275]

A dimmer switch on the same circuit would also potentially add noise. If you've got one on your marquee try turning it all the way up to see if it gets better, and then around 50% to see if it gets worse.