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. Here's a short list of things to check for:
This is the tricky part! It's also the part where you need to pay the most attention.
- 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.
Why not use the stock bolts in the car?
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.
Typically you 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, create a new grounding point. Once you have attached the ground to this new point, use electrostatic grease to cover all the bare metal. Dont want it to rust on you. If you dont have electrostatic grease, you can use vasoline or undercoating. This is usually the last step as the ground you choose may wind up being a bad ground.
Power Wires (+12v)
It should also be pointed out that the same meticulous care should be taken for your 12v+ wiring.
- Make sure you use good crimps
- Make sure you useadequate gauge wiring
- Make sure there is a LOT 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 just shoving a little bit of a ring terminal into the battery terminal does NOT make the proper type of connection. You should tug on the wiring after you 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.
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. We 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 havent gotten to ground loops yet, but we will. For now it's recommend that you ground 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. It is recommend that you do the same thing if you are using 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.
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. Usually it is recommended to NOT mount 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 we spoke about grounds and making them as clean and efficient as possible?
Well this is where it's 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. They are out there and everyone should pick one up. You can use it as a ground loop detector. Some 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.
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.
A good starting point is to break the chain right in the middle. Try to unplug the RCA's going into the amplifier and plug in the shorting plugs (see 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. Step 3:
If the noise is still there, it's your amp. You may want to try mounting the amp to metal, relocating the amp or changing your ground. If none of these work, it's safe to say you have an issue with the amp and get it looked at. Step 4:
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.Step 5:
Let's 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.
It has been shown that low quality sound cards will cause this issue as well as power supplies. One recommendation is to pick up a Xfi as it seems to be well isolated but for many this is not an option. The message here is try not to skimp on this area. Many users report noise issues with the integrated sound card that never go away until an upgraded sound card is added. Its due to improper shielding and sometimes you just cant get it far enough away from EMI sources. Sometimes, power supplies are not designed to properly shield the EMI they produce. The first DSATX caused this but have subsequently been redesigned.Conclusion
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 these 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.
Article written by Will Albers