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| Thread ID: 97483 | 2009-02-17 19:35:00 | Constant Speaker Hum? | VictorStagnetti (14630) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 748791 | 2009-02-17 19:35:00 | 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? | VictorStagnetti (14630) | ||
| 748792 | 2009-02-17 20:18:00 | 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 |
jwil1 (65) | ||
| 748793 | 2009-02-17 21:50:00 | 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 |
Burnzee (6950) | ||
| 748794 | 2009-02-17 22:35:00 | 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. | VictorStagnetti (14630) | ||
| 748795 | 2009-02-17 22:40:00 | I would go to the forum (forums.logitech.com) 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 |
Speedy Gonzales (78) | ||
| 748796 | 2009-02-18 00:15:00 | 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 |
Burnzee (6950) | ||
| 748797 | 2009-02-18 01:31:00 | Thanks, I'll give that a shot. | VictorStagnetti (14630) | ||
| 748798 | 2009-02-18 01:45:00 | 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? | VictorStagnetti (14630) | ||
| 748799 | 2009-02-18 04:19:00 | 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 (6950) | ||
| 748800 | 2009-02-18 04:34:00 | 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 |
Burnzee (6950) | ||
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