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 by adding external supply filtering.


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.


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.


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.






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, then 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.


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, then 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.