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Thread: would a VGA "amplifier" solve LCD hum??

  1. #11
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    [QUOTE=OldSpark;1496322]What do you mean by "shileding is sorted with the signal grounds"?

    i mean that, each of the 3 signal cables, has its ground twisted around it (un-insulated), and in touch with the "shield sleeve" wich in turn, touches the overal shield sleeve. i know that those sleeves are suposed to conduct only from one side, but if you mesure resistance across the 15 pins, you will see that all the grounds, have resisstance to one-enother (meaning they touch), and all have resistance with the shield...

    i have read that CAT5 is better for longer distances, (maybe cause of the solid cooper inside??) , than a normal VGA cable. and yes its not shielded, nor do i think that the twisted cables will do everything about the "noise". i just wanna check if, properly insulated grounds, and maybe better quallity cable has to do anything with the signal degradation.

  2. #12
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    That IMO sounds like crap cable. There is little point having grounds (and shields) touching each other when the interface and connector keeps them separated.


    Anyhow, the Cat-X will certainly preform better than that (as might a "proper" video cable).

    Cat-x is better because of its twisting method which tends to cancel noise - including what one conductor induces into the others (which builds up with increasing length unless "cancelled").

  3. #13
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    There is a BIG difference between CAT5 and VGA cable.

    CAT5 relies on twisted pair and differential for noise cancellation whereas VGA is shielded (for noise) and single ended.

    A "good" VGA cable has each video signal individually shielded and then wrapped with an overall ground.

    Most CAT5 cable is several twisted pairs and a ground.

    Reference this:

    http://www.dougburbidge.com/vgaovercat5.html

    Some more info:

    http://answers.yahoo.com/question/in...8230023AAfh3mY

    The bigger the resolution, the more noise you get.
    Last edited by heavymetals; 08-18-2013 at 04:36 PM.

  4. #14
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    well. vga over cat5 certainly did not solve anything >_>. in addition to the noise, it has some extra distortion in picture (shadows or something like that, behind the icons. ghosting i it's called)
    Last edited by settra; 08-19-2013 at 10:15 AM.

  5. #15
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    Quote Originally Posted by settra View Post
    the classic hum. its preiodic, with some spikes now an then, but, it gets stronger with longer vga cable. 1.8 meters, and i have no noise. add enother 1.8 , and i got enough noise. 5 meters are noisy as ****.
    although i dont know if it is the same noise, but in the speakers, you can hear noise that has its peak at 1khz , and goes up with my RPM (2000rpm = 2khz and so on... )
    In my humble opinion (and I may be wrong) you are tackling the noise problem from the wrong end.
    While the VGA cable is indeed contributing to the noise with the extra length I assume the noise(hum) is coming from the audio side not the video.
    If I am right that means you are getting the hum but the video itself is not corrupted.

    If that is the case, I say leave the VGA cable alone and try to isolate the noise from the audio end by trying to clean up the audio not the video.
    Ground loop isolators would be a good place to start.
    I also had a really loud humming noise in my setup originally and to clean things up I first properly grounded the CarPC, then installed ground loop isolators at both ends of the audio path.
    I made a custom cable by splicing in the GLI (ground loop isolator) where the RCA cables connect to the PC and another where it connects to the head unit.
    I can remove one or the other of the GLIs without any noise any more but prefer to keep both.
    This is a bit of overkill if you ask me but I wanted to make sure I am not chasing the problem ever again

    If however your video itself is affected because the noise is getting into the VGA cable itself then disregard my post.

    I wish you luck getting to the bottom of your problem as I know how annoying that hum can be.
    Last edited by Dluvr22; 08-20-2013 at 04:00 PM.
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  6. #16
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    Quote Originally Posted by settra View Post
    well. vga over cat5 certainly did not solve anything >_>. in addition to the noise, it has some extra distortion in picture (shadows or something like that, behind the icons. ghosting i it's called)
    If you had read the link(s) I provided, you could have saved some time.

  7. #17
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    Did you say 5m which is 15feet?

    That is likely too long of a cable and your signal is too weak. If the shorter cable is working fine then this is an indication that this is your issue. We used to use VGA cables in the lab where I am at and anything over about 6' you had to deal with noise or use an amplifier of some sort.

    If you can mount a USB video card near the monitor and run the USB cable to your computer this might be your best bet to reduce the noise since you are isolating the monitor from your computer and using a short video cable.

  8. #18
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    typo - "By" to But

    Quote Originally Posted by heavymetals View Post
    If you had read the link(s) I provided, you could have saved some time.
    LOL - maybe they read the Yahoo! reply further down - "it can be any length" (or length does not matter etc).

    But that first Yahoo! answer was brilliant.
    Alas it is rare I see "good" answers on Yahoo!. Most are akin to that crap one I mentioned above.
    Last edited by OldSpark; 08-21-2013 at 07:43 AM.

  9. #19
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    heavy metal i did read it. it just wasent enough to stop me, becouse, apart the fact they both sed it is best for long distances, i wanted to be sure that each ground is grounded alone and not with all the others

    redhead , yes it was 5m as we say 15feet

    dluvvr, i have the sound completly isolated anyway. even with everything disconected from the PC, (except the LCD ofc) the noise presists. i am no longer trying to find the source of the noise, becouse on my long run to do so, i have fried so many mobos and screens... i am trying to HIDE it.

    redhead, the usb idea is not bad. but it would not help, becouse the noise tyravels through the USB as well ( i know cause of the noise in my usb sound card). BUT i have found out recently, that there are some things called USB isolators (like 50 euro for a discent one), that completly isolate the usb from the pc (but minimizing the speed to just full speed 12mb.) i think a HUB after that usb , could solve MANY noise and ground problems. my only problem is, if 12mb are enough for a usb to vga converter...

    i have ordered an amp. by the end of the month we will now.

  10. #20
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    Did you use shielded cat5 cable?

    And it sounds to me as if you haven't determined the noise source. Though it varies with (vga) cable length, you mentioned its frequency dependency with RPM (not that Hz would be 1:1 with RPM for anything other than a crank sensor).

    Are you sure you have signal/vga cables separated from power and EMS signals, and the PC/vga card source power etc separated from the same?

    Have you tried suppression caps (22mF, 0.01-0.1uF, 1000uF etc) across alternator outputs (and field if external regulator), IgCoils, PC input power etc - else chokes?

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