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Old 07-14-2002, 04:33 PM   #1

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My speakers make this high-pitched whine which matches the engine's RPMs.

2.1 My speakers make this high-pitched whine which matches the engine's RPMs. What is it, and how can I get rid of it? [IDB]
The answer to this section was generously provided by David Navone of Autosound 2000. The material in these instructions was adapted from the Autosound 2000 Troubleshooting Flow Chart by Ian Bjorhovde with the permission of Autosound 2000.

This is a set of instructions to debug a stereo installation if there is any noise present after it is completed. Follow each step carefully! If you have more than one amplifier, repeat level one for each amp to be sure that none of them are responsible for the noise.

2.1.1 Level 1: Check out the Amplifier(s)
After you have determined that there is noise in the system, determine if the amplifier is causing the noise. To do this, mute the signal at the inputs to the amp by using shorting plugs. If there is no noise, then the amp is fine, and you can proceed to level 2. However, if there is noise, then use a test speaker at the amp's output. If this stops the noise, then the problem is originating in the speaker wiring, or the passive crossovers. Check to make sure that none of these are shorting with the body of the car, and start again at level 1. If noise is still present when using the test speaker, then there may be a problem with the power supply on the amp. Try connecting an isolated power supply - if this does not get rid of the noise, then there is something seriously wrong with the amp, and it should be replaced. If the noise goes away, then there may be a problem with power supply filtering or isolation. This can be fixed by changing the amp's ground point or b adding external supply filtering.

2.1.2 Level 2: Reduce the System
The amps have been determined to be noise free. If you have any processors between the head unit and the amps, disconnect them and connect the head unit directly to the amp. If this gets rid of the noise, then one (or more) of the processors must be at fault, so proceed to level 5. Otherwise, try running the signal cables over a number of different routes. If you are able to find one that does not produce any noise, permanently route the cables in the same manner, and proceed to level 5. If not, then you must isolate the head unit from the car's chassis (except for its ground!) -- don't forget to disconnect the antenna, since it is also grounded to the car. If isolating the head unit does not solve the problem, the move the grounding point of the head unit. Hopefully the noise will be gone, and you can install the head unit with a quiet ground and proceed to level 5, otherwise go on to level 3.

2.1.3 Level 3: Move the Head Unit
The amplifiers are fine, but moving both the ground for the head unit and the signal cables does not solve the noise problem. Take the unit completely out of the dash, and put it on either the seat or carpet, and run new signal cables to the input of the amp. If this solves the problem, re-install the head unit, one step at a time and skip to level 5. But if the noise persists, then move the head unit as close to the amp as possible and use the shortest possible signal cables. This will verify that the original signal cables are not causing the problem -- assuming the noise is gone, reinstall the head unit one step at a time and go to level 5. Otherwise, there may be a problem with the power filtering for the head unit. As with the amps, power the head unit with an isolated power supply (again making sure that the head unit isn't touching the car's chassis at all). If the noise goes away, you can add power supply filtering or an isolated power supply; go to level 2. But if the isolated power supply does not solve the problem, then you can either replace the head unit and go to level 2, or check the car's electrical system in level 4.

2.1.4 Level 4: Testing the Car
There does not seem to be a problem with either the head unit or the amplifier, and the car's charging system is suspect. To see if this is the case, we can use a system in a car that is already known to be "quiet." Bring both cars together as if you were going to jump one, and use jumper cables to connect the two batteries. Start the engine of the car with the noise problem, and listen to the "quiet" car's system. If the noise does not go away, there is a SERIOUS problem with your car's electrical system (possibly a bad alternator). Have a qualified mechanic check the charging system out. If there is no noise in the "quiet" car, then the "noisy" car's charging system is definitely quiet, so continue with level 5.

2.1.5 Level 5: Adding Signal Processors
We have proven that the amplifiers are good, the head unit is good, and the car's electrical system is good. Now we need to reconnect each signal processor. Repeat this level for each signal processor used in your system; if you have added all of your signal processors, and there is no longer any noise, CONGRATULATIONS! You've removed the noise from your system! Connect the signal processor. If there isn't any noise, then go on to the next signal processor. Otherwise, try re-routing the signal cables. If this cures the problem, the route them permanently over the quiet path, and install the next processor. If not, then isolate the processor from the car's chassis except for a single grounding point. If this works, then permanently isolate the processor, and move on to the next processor. If isolation does not help, then advance to level 6.

2.1.6 Level 6: Processor Isolation Tests
Now, noise enters the system when one particular processor is installed, but regrounding it does not help. Move the processor very close to the amp, and check for noise again. If there isn't any, then re-install the processor, carefully routing the cables to ensure no noise, and continue at level 5 with the next processor. Otherwise, use an isolated power supply to power the processor, making sure that no part of the processor is touching the car's chassis. If this solves the problem, the consider permanently installing an isolated power supply or possibly a 1:1 transformer, and go to level 5 with the next processor. Otherwise, separate the processor and isolated power supply from the car by many feet and re- test. If there is still noise, then there is a serious problem with the processor's design. Get a different processor, and continue at level 5 with it. If separating the power supply and processor from the car does solve the noise problem, then either the processor is damaged, or your tests were inaccurate. Repeat level 5.
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