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VictorStagnetti
18-02-2009, 08:35 AM
I have a self powered set of 5.1 Logitec speakers that hums and whines and makes all sorts of other irritating noises apparently coinciding with my hard drive or optical drive spinning. The noise gets louder when I turn the speakers up on either the computer or the speakers themselves and It gets deafening if I burn a CD or DVD. It only occurs when at least one jack is plugged in, but it doesn't seem to matter which one. If I plug in two jacks, it gets a little louder but the third doesn't seem to make a difference. If I plug headphones in, the hum is audible over whatever I'm listening to. I'm wondering if it has something to do with a grounding issue or interference between cables, but I tried re-routing the speaker cables and it didn't make a difference. I also noticed something very strange yesterday when I was playing my bass; if I moved the guitar close to my computer, the bass amp started to pick up the same hum. What is causing this and how do I fix it?

jwil1
18-02-2009, 09:18 AM
If it's what i think it is, I think it is a grounding issue. If it's a laptop, try removing the power lead and see if it still happens on battery :)

Welcome to PF1 too :D

Burnzee
18-02-2009, 10:50 AM
Hi VictorStagnetti

You have a Ground Loop Hum going on.

Two quick ways to stop it. First try plugging the speakers into a different power plug than the one the computer uses.

If this doesn't work, try this. Insert a 100 Ohm resistor into each audio cable grounds.

Let us know how yah get on.

BURNZEE

VictorStagnetti
18-02-2009, 11:35 AM
I tried plugging the speakers into a separate socket and it changed the sounds slightly but didn't make them any better. I don't have any resistors or any immediate access to them, so do you have any other suggestion? It's a desktop, by the way.

Speedy Gonzales
18-02-2009, 11:40 AM
I would go to the forum (http://forums.logitech.com/logitech/board?board.id=51_speakers)

And see if someone has posted a prob / posted an answer

Depending on which 5:1 speaker system you've got

If it doesnt have an answer, I would join it then post the same question there

Burnzee
18-02-2009, 01:15 PM
Hi VictorStagnetti

Here's what you are up against:

Small ground differences between the computer and the speakers cause a current to flow between them inducing hum into the cables. This is called a Loop Current. Whilst small, typically < 1volt, this has a major effect on the audio quality as you already know.

To solve the problem, one needs to reduce the Loop Current to a value so small it won't cause a problem. This where the 100 ohm resistors come in. Simply insert them into the ground cables. If you don't have them, get them. Go to Dick Smith Electronics and buy them. Cost is approximately 20c each. A good idea is to insert them into each of the speaker plugs if possible.
You may even have to buy new plugs if existing ones are moulded on. This is known as the Ground Lift Trick.

Another method is to use a Ground Loop Isolator in each audio cable. This is a small transformer which isolates the computer from the speakers. These are expensive. Jaycars NZ sell some for about $25 each.

There are various tricks - like disconnecting the earth on your electronic gear. DO NOT DO THIS AS IT IS DANGEROUS TO YOU AND YOUR EQUIPMENT!! :groan:

You could try a heavy cable between the computers' and speakers' ground. This can be unslightly and a hassle and might even make things worse.

Check your power plug has been wired properly and is correctly grounded.

Basically, it comes down to three choices, the resistors, < 20c each, the Isolation tranformers, $25 each or get to like the sound of hum!! Your choice!!

Finally, do what Speedy suggested and join the forum. Though your problem is not isolated just to Logitech, you never know there might be a easier way of fixing this well known problem.

Hope this helps.

BURNZEE

VictorStagnetti
18-02-2009, 02:31 PM
Thanks, I'll give that a shot.

VictorStagnetti
18-02-2009, 02:45 PM
Huh. I just noticed that the plug doesn't have a ground prong. I don't how the plugs in NZ are set up, but the ones in the States have three prongs if they're grounded and two if they're not, and this one only has two. It seems like Logitec would not have designed it this way if it needed to be grounded. Also, a grounding issue would not explain the noise on my amp when I bring my guitar near the computer. That sounds more like some sort of magnetic interference, as the guitar is obviously not plugged into the computer. In fact, the amp is plugged in in an entirely separate room. I probably should have mentioned this earlier, but I just noticed. Any ideas?

Burnzee
18-02-2009, 05:19 PM
Hi VictorStagnetti

Thought you were from New Zealand, sorry my mistake.

Think there is a small mis-understanding. When I refer to the grounding loop, this means the AUDIO CABLE, ie screen wire in the cable to the speakers. I don't mean ELECTRICAL ground as in the mains cable. The problem is between your computer and speakers connections.

From your original post, you stated the noise only starts after you plug in a least one speaker lead. Putting in two slightly increases the noise. The third and final plug does not make any difference. This suggest to me you do have a grounding loop rather than a large magnetic induction. With this your speaker leads would pick up the strong signal regardless. You have tried re-routing the cables and things have not improved.

Ground loop hum can and does set up a small magnetic induction hum. Remember there is no effective electrical screen wire. This is the guts of the problem. Pick ups of guitars are coils of wire. Ideal for picking up magnetic induction hum.

How close does the guitar have to be to pick the hum up? Disconnect the speakers leads from the computer, does the guitar pick up hum?

If you plug the headphones directly into the computer do you get the hum?

From what you say, I gather the computer mains plug has three prongs, is this correct? If it has then the thing that worries me is when you burn a CD or DVD. This indicates the major cuprit is the computer. Open it up and check the mains earth connection is clean and in place. Check the mains cable for any breakage too. Disconnect mains first.

The volume of the hum is controllable via the volume control, either on the computer or the speakers. This suggests the problem is at least the hum is coming in through the leads.

Is it possible to open up the main Logitech main box and simply solder a resistor into one ground lead. If this is possible try just that lead.

BURNZEE

Burnzee
18-02-2009, 05:34 PM
Hi VictorStagnetti

Just had a thought. Leave the speakers where they are but plug in say an ipod, Mp3 player or Walkman. Do you still get the hum?

BURNZEE

VictorStagnetti
18-02-2009, 05:46 PM
No, the hum is gone. It's also gone on my laptop. I also discovered that the orange speaker jack isn't actually connected to anything, and the green jack is driving the front 2 speakers as well as the center and sub channels. I wonder why there even is an orange jack...

VictorStagnetti
18-02-2009, 05:49 PM
Oh, and I forgot to mention that if I record something with a microphone or direct line on either the back or front panels, the hum is present in the recording.

Speedy Gonzales
18-02-2009, 05:59 PM
You've probably plugged the wrong plugs into the wrong connections

VictorStagnetti
18-02-2009, 06:02 PM
I've tried them in every configuration I can think of. Could be a sound card driver issue? I'm using the onboard soundcard on my motherboard, but it has it's own driver. Maybe I should look into updating it.

Speedy Gonzales
18-02-2009, 06:07 PM
Umm even if its onboard, you would have to install the drivers or it

You didnt install the sound drivers through windowsupdate did you?

Have you read the mobo manual, which will show you what goes where?

VictorStagnetti
18-02-2009, 06:27 PM
I installed the drivers from the CD when I built the computer, but I hadn't updated them untill just now. I just tracked them down from the Foxconn website and updated, but it didn't make a noticeable difference. Any other ideas?

Burnzee
18-02-2009, 06:56 PM
Hi VictorStagnetti

Ok,we can forget strong magnetic induction hum because the hum is gone when you plug something else into the speakers.

When you plug a microphone into the computer the hum is present in the recording. This is not surprising, you have simply replaced one ground loop, (the speakers), with another, (the microphone).

You are looking for the magic bullet but I can not help you further if you don't answer all my questions. I repeat:

How close does the guitar have to be to pick the hum up? Disconnect the speakers leads from the computer, does the guitar pick up hum?

If you plug the headphones directly into the computer do you get the hum?

From what you say, I gather the computer mains plug has three prongs, is this correct? If it has then the thing that worries me is when you burn a CD or DVD. This indicates the major cuprit is the computer. Open it up and check the mains earth connection is clean and in place. Check the mains cable for any breakage too. Disconnect mains first.

Is it possible to open up the main Logitech main box and simply solder a resistor into one ground lead?


BURNZEE

VictorStagnetti
18-02-2009, 07:41 PM
The amp starts humming a few feet away. It gets louder as I bring the guitar closer, and it seems strongest toward the front of the case where the hard drive is located. This happens regardless of whether not the speakers are plugged in to the computer.

Headphones hum whether or not they are plugged into the computer directly. I've tried plugging them in on the front and rear panels, and there was no difference.

The computer power cord has three prongs. I checked where the power cord connects to the PSU, and the connections look fine there. I poked around the case, but I didn't see any broken or bald wires, or anything that looked like a faulty ground. I pulled out all of the motherboard audio leads to the front panel and made sure they were clean.

The Logitec box is potentially openable, but it would take some major surgery. I can unscrew the panel where all of the speaker wires enter the box, but I can only pull the panel out 1/4" or so. I would have to cut and re-solder all of the internal wires, and I'm sure that would cause more problems than it would fix.

Just out of curiosity, what is the voltage of the wall sockets in New Zealand? I've been there once a long time ago, but I don't remember. The ones over here are 110.

Burnzee
18-02-2009, 08:47 PM
Hi VictorStagnetti

The mains voltage in New Zealand is 240Vac @ 50hz. Think you Yanks have 110Vac @ 60hz. Is that correct?

Don't expect you to stuff your speaker set up so don't open it.

Everything you say seems to confirm the problem really starts from the computer. Wondering if you are able to confirm true mains earth to your computer using a multimeter. Use this to check continually from the mains plug to the chassis of your computer. If there is a earthing problem here it could be dangerous to you and the computer.

If there is true electical earth to the computer and assuming the house mains are earthed correctly, (to check this you might have to move your set up to another house as a test!!), my best suggestion is to buy one Ground Loop Isolator. This simply plugs in between the audio lead and the computer. Test using this lead only.

If this works then you can buy as many as you need to to fix the problem.

BURNZEE

VictorStagnetti
19-02-2009, 05:27 AM
Yeah, ours are 60Hz.

I would guess that the house is grounded right because I had it set up in a different location a few months back and still had the issue while wearing headphones. As for the computer itself, I'll see if I can track down a multimeter to check it out

Thanks for the help!