Page 1 of 14 1234567891011 ... LastLast
Results 1 to 10 of 139

Thread: Induced noise/Ground loop trouble shooting guide.

  1. #1
    FLAC
    Join Date
    Sep 2004
    Location
    Falls Church, VA
    Posts
    904

    Induced noise/Ground loop trouble shooting guide.

    work in progress...

    So you just installed all of your expensive new equipment and it works! HURRAY! Except for one annoying aspect - You have a strange buzzing noise that mimics the reving of your engine. This noise is commonly caused by a ground loop. Lets see what we can do to help.

    Almost all car audio is based off of 12v dc which requires a circuit to operate. What it means is that you need to have 12v coming in from the alternator/battery and it must return to the battery via a ground. (Purists: Yes, 12v actually runs from - to + in US vehicles, but lets not confuse the point). Electricity is sneaky, and rather moody. It will try to find the easiest path to create this circuit. We want to ensure that its easiest and most efficient route is through the ground wiring of the unit. This brings us to our first potential cause for your noise...

    "Your ground is not ground"

    Yes, I'm sure you think your ground is enough but its not. Always make sure your ground is the same gauge wiring as your 12v +. Make sure that the wiring is a large enough gauge for your needs (Google or read your manual). Get good quality crimps and make sure that you are using a freshly stripped end of wire. Crimp the wires solidly making sure little strands are not pokeing around wildly. Now find a grounding point. This is tricky! Yes, that stock bolt looks like it may be good and it even tests as ground with your mulitimeter (which i KNOW you have purchased...) but its not. Its awful. Car manufacturers coat all of these pieces to prevent corrosion. This coating causes resistance and makes the ground less efficient. This will cause your component to seek out more inviting grounds which we want to avoid. What you need to do is find a new point in solid metal and make your own grounding point. Again, sounds easy but its not. Most modern cars are built on the uni-body concept. Metal portions are tacked together with high power tack welders. The welds are awful for grounds and can cause a real hassle. You want to make sure you have found a solid piece of metal, preferably on the base of the vehicle. This should be a thick piece of metal away from the GAS TANK! Make sure its easily hidden by carpet and begin your sanding. I use a piece of course sand paper or a wire brush and scrape away all the paint and coating for about a silver dollar size circle. Using a self taping screw or a bolt, i will create a new grounding point. Once i have attached the ground to this new point, I will use electrostatic grease to cover all the bare metal. Don’t want it to rust on us. If you dont have electrostatic grease, you can use vasoline or undercoating. This is usually my last step as the ground you choose may wind up being a bad ground.
    I also want to point out the same meticulous care should be taken for your 12v+ wiring. Make sure you use good crimps, adequate gauge wiring and LOTS of contact at every connection. That means your connection to the battery should have a ton of surface to surface contact. The more the better as I have seen numerous people just shove a little bit of a ring terminal into the battery terminal. This does NOT make the proper type of connection. I usually tug on my wiring after i connect it. Give it a decent tug. If it comes loose, it wasnt a good enough connection/crimp.

    Our next potential cause of noise is something called Electromagnetic Interference...

    This stuff is everywhere. Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. This interrupts, obstructs, or otherwise degrades or limits the effective performance of those other circuits. It can be induced intentionally, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like. It is also known as Electromagnetic Interference or EMI. phew...

    What this means is that if you are not careful with the quality of your components and where you place them, they hold a strong chance of picking up EMI. Shielding on cables can help reduce this effect but the cost of cables is rediculous. A standard RCA cable from a decent manufacturer purchased outside of Radio Shack should be sufficient. Looking for single shielded cable. Plan on spending about $1.00 to $1.50 a foot. These cables are very important to your system and should not be the weakest link. Make sure you route your cables as far away from RFI sources as possible. Your power cables are a source, your PC is a source, strange electrical component boxes around the vehicle are sources. Basically anything that carries an electric signal can produce this unwanted nuisance. Keep your cables as far away as possible from them all.

    Now you may ask what about your amplifiers? your PC? Your radio? Are they also susceptible to picking up EMI? They sure are. In the trouble shooting proces, it is important to determine which component is picking up the EMI. I will get into how we do this later in the article, but for now lets talk about what we can do to help combat or defend ourselves...

    Grounding a components chassis can help create a shielding barrier by passing the interference back into the ground. Depending on how the system is designed, this can be good or bad as it can create a ground loop. We haven’t gotten to ground loops yet, but we will. For now I recommend grounding the chassis of your PC to the same grounding point that you ground your amps and PC. This will help in creating that barrier protecting components in the PC from an EMI environment it was never intended in. I recommend the same thing if you use an inverter.

    Some amplifiers will also pick up EMI. Usually these are inexpensive amps where they cut corners in the design. If you have determined your amp is the problem, try mounting the amp to metal. It may help the situation. HUGE NOTE: grounding the chassis of an amp can cause the exact symptoms we are trying to avoid, so only try this in your trouble shooting process. I usually recommend AGAINST mounting directly to metal.
    Keep in mind that those external crossovers (passive AND active) can also pick up EMI. Be careful where you place them.

    Finally the most famous culpret... The Ground Loop.

    In electrical engineering and electronics, a ground loop refers to an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, for example ground potential, but are actually at different potentials. In english, this means that one component has found it easier to ground itself through another component.

    Remember in the beginning when I spoke about grounds and making them as clean and efficient as possible? Well this is where its important. If a component does NOT have a proper ground, it will look to ground itself through the easiest means. This is by grounding through the next component down the line. How does it do this? Through those nifty RCA cables. The outer shielding of the RCA cables is actually a common ground (in most cases). If your PC's ground is not so great, it will try to ground itself through your amplifier's ground by passing its ground through the RCAs and into the amp. This is where all that noise comes from. This can happen if the ground potential of any one component is higher/lower than another. We combat this by making sure our ground are sufficient (first paragraph).

    There are devices called ground loop isolators which are a band aid for this problem. They will filter out and isolate that ground loop on the signal path. Some people claim this can alter the sound. Maybe it can but i question whether you can pick it up in a car environment. Regardless, they are out there and everyone should pick one up. I use mine as a ground loop detector. I will use it in cases with ground loops to help pick up which components are causing the loop and then work on grounding potential issues.

    There is one other scenario that can cause this issue and its easiest explined as a burned up component. Bad grounds and ground loops can actually burn up the grounds on the signal path of components. When this happens, you will NEVER be able to remove that whine. The unit has to be repaired. This is a bit more advanced and will not be covered in this article. If you suspect this is the issue, please make a post and I will try to help diagnose.

  2. #2
    FLAC
    Join Date
    Sep 2004
    Location
    Falls Church, VA
    Posts
    904
    Finally, how do we troubleshoot a system?

    Isolation, Isolation, Isolation

    We have to separate each piece from the system and test it. Consider the system below:

    [Source (PC, HU)] ----> [amplifier 1,2,3...n] ----->[passive crossover] ----->[speakers]

    We just installed the pieces making sure to properly ground all devices and keep signal path away from EMI emitting devices. We have discovered that we still have a ground loop somewhere. How do we find it?

    Lets get that ground loop isolator out and plug it in at any of the -----> points. This will tell us where the ground loop is and help us determine which components to look at.

    My personal preference is to break the chain right in the middle. I will unplug the RCA's going into the amplifier and plug in my shorting plugs (see my faq on troubleshooting tools). You can try to use an ipod as well, just make sure its battery powered and you keep the RCAs away from power. Is the sound still there? If yes, we know we have a problem (may not be all of the problems) with the amplifier or the speakers. Next step is to disconnect the speakers and grab a test speaker. A test speaker can be any old working full range speaker. Even factory speakers will work. Attach the test speaker and listen for the sound. If the sound is gone, the problem is in your speakers or passive crossovers. Check to make sure you have not put a screw through your speaker wires and they are not touching a metal ground somewhere. Relocate your passive crossovers as they may be picking up the sound. If the noise is still there, Its your amp. You may want to try mounting the amp to metal, relocating the amp or changing your ground. If none of these work, I would say you have an issue with the amp and get it looked at.

    If no whine is detected from the above, its the RCAs or the source. You can use your shorting plugs on the source ends and determine if the RCAS that are picking up interference. If they are, look for a screw that has gone through the RCAs or consider rerouting them. It could be a lousy pair of RCAs so you may want to have another pair to test with.

    Lets suppose that the RCAs are not the culprit. That leads us to the last unit, the PC. Keep in mind that the PC was NOT intended for the environment we are putting it in. There are MANY factors that can cause havoc with the pc and you may NEVER eliminate the noise (component related). Plug a set of headphones into the output of the sound card. Do you hear the noise? Well then we know that there is something internal to the PC that is picking up EMI or a ground trace is burned up. We can check the later by swapping sound cards. If its EMI, you may need to relocate the PC or ground the chassis.
    I have found low quality sound cards will cause this issue as well as power supplies. I recommend picking up a Xfi as it seems to be well isolated but for many this is not an option. My message is try not to skimp on this area. I had noise issues with my integrated sound card that never went away until i upgraded. Its due to improper shielding and sometimes you just cant get it far enough away from EMI sources. I have also found many power supplies are not designed to properly shield the EMI they produce. The first DSATX caused this but have subsequently been redesigned.

    This system is simplistic as its more of a methodology than a checklist. As you add on USB sound cards, things get much more complex. There are several posts to help out so search. Hopefully you will have an idea on the methodology behind troubleshooting and you can adapt my methods to help you locate and isolate the problem. Once you have isolated it, you can further search the forum for more details on how to solve it.

  3. #3
    _
    Join Date
    Mar 2004
    Location
    Little Elm, Texas
    Posts
    13,500
    *bravo!*
    Jan Bennett
    FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

    Please post on the forums! Chances are, someone else has or will have the same questions as you!

  4. #4
    Raw Wave kickercivic1's Avatar
    Join Date
    May 2003
    Location
    Florida
    Posts
    2,031
    I am glad you started this thread. I just installed most of my stuff yesterday. I have monster power inverter in my car to run my pc. It makes this loud *** noise thru my speakers. When i hook up the car pc with extenstion cable from my house and noise is gone. Inverter is ground right, but i just can't figure out the noise.

    NOte: its not the engine noise. The level of the sound stays constant no matter the rpm of the engine.

  5. #5
    FLAC
    Join Date
    Sep 2004
    Location
    Falls Church, VA
    Posts
    904
    Isolate isolate isolate!

    Ground loop again is my guess. I will need you to list your components and try a ground loop isolator before the amp. Tell us if the noise goes away. Do you hear the noise using headphones?

    Otherwise it could be the inverter. Is the inverter grounded to the same point as the PC chassis? Did you ground the inverter chassis?

  6. #6
    Raw Wave kickercivic1's Avatar
    Join Date
    May 2003
    Location
    Florida
    Posts
    2,031
    i have rca going from computer to 4channel amp, i have not bought ground loop isolator yet... I have my Gain screen pluged into my cig lighter plug. when i turn the computer on everything work, when i unplug the screen power wire from the cig lighter sound even gets louder.

  7. #7
    FLAC
    Join Date
    Sep 2004
    Location
    Falls Church, VA
    Posts
    904
    bad ground

  8. #8
    Raw Wave kickercivic1's Avatar
    Join Date
    May 2003
    Location
    Florida
    Posts
    2,031
    Quote Originally Posted by Will Albers
    Isolate isolate isolate!

    Did you ground the inverter chassis?
    Are you suppose to ground the chassis?

  9. #9
    FLAC
    Join Date
    Sep 2004
    Location
    Falls Church, VA
    Posts
    904
    Not always, depends on the invertor but it may help. Gonna have to try it and see

    The fact that the noise changes when your lilliput is plugged in tells me that something is grounding itself through the lilliput. Somewhere the differential between grounds is off to a degree where its grounding through your cigarette lighter.

    Is your PC ground grounded as well?

  10. #10
    Raw Wave kickercivic1's Avatar
    Join Date
    May 2003
    Location
    Florida
    Posts
    2,031
    When i ground the chassis the noise is gone. So does that mean i need to find a better ground for the inverter?

Page 1 of 14 1234567891011 ... LastLast

Similar Threads

  1. I tried everything, can't get rid of this ground loop
    By intense in forum General Hardware Discussion
    Replies: 3
    Last Post: 07-10-2005, 09:58 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •