Noise Troubleshooting Guide -- Eliminate your alternator whine
Found this guide on another forum, and given the slew of recent
threads on troubleshooting noise, thought I would post it here. One
word of warning is that some HEAD Units and/or processors nowadays
have a zero bit mute, which essentially cuts off the output during
low signal passages to reduce noise.....so be aware if this is a
feature your unit has. Onward to the guide;
How can you eliminate alternator whine in a car audio system?
If you have alternator whine in a car audio system and want to get
rid of it, there is only one sure-fire way to do it. David Navone
and Richard Clark from Autosound 2000 in the USA developed the
following step-by-step instructions. If you follow the instructions
EXACTLY, you are guaranteed to trace and eliminate the noise in your
car audio system. Don’t miss a step and don’t assume that something
is OK without checking it.
Each time you check for noise, you should do it with the engine
running at 1500 to 2000 rpm and the headlights on full beam so that
the alternator will be charging. The tests with the CD player
connected should be done with a ‘zero bit’ track playing and the
volume at maximum. Set your CD player to ‘repeat’ if it has that
feature.
Safety. Make sure when doing noise tests that the parking brake is
on and working, and that the vehicle is in neutral or ‘park’.
Perform these tests in an area with good ventilation or use an extension hose on
the exhaust to route the fumes outside.
Step 1. Check the Amplifiers
1a. Unplug the RCA cables from the amplifier/s and mute the signal
at the input by using shorting plugs. This will isolate the
amplifier from the rest of the car stereo installation.
You can make shorting plugs by taking cheap male RCA plugs and
soldering the centre and outer terminals together. This shorts out
the input of the amplifier/s to ensure that it has zero signal.
Has the noise gone?
Yes. Go straight to Step 2. Reduce The System.
No. Go to 1b.
1b. Disconnect the speakers from the amp and connect a pair of test
speakers to it. Make sure the test speakers are not in contact with
the car body.
The purpose of this step is to ensure proper isolation of the
speakers and the speaker leads from the car's chassis.
Has the noise gone?
Yes. Check speakers, speaker leads and passive crossovers for
proper isolation from the car's chassis. Shift passive crossovers to
a location away from power cables and the car’s body.
No. Go to 1c.
1c. Isolate the amplifier from the chassis of the car. There must
not be any electrical contact between the car's chassis and the
amplifier, except for the grounding point.
Has the noise gone?
Yes. Reinstall the amplifier isolated from the chassis of the car.
Make sure that the amplifier is grounded in just one point.
No. Go to 1d.
1d. Supply the amplifier with an isolated power source, for example
an external car battery or a 12-Volt DC power supply.
Has the noise gone?
Yes. Noise is entering the amplifier via the power supply, try
changing the grounding point and add external power supply
filtering. Consider changing the amplifier.
No. The amplifier has some severe problems, is totally isolated and
still noisy. Replace it or have it repaired.
That is the end of Step 1. You have now either eliminated the
amplifier and speakers as a problem or you have replaced a faulty
amplifier. Now you can go on to Step 2.
Step 2. Reduce the System.
2a. The amplifier is known to be OK. It is now time to disconnect
any signal processors (equaliser, electronic crossover, etc.) and
connect the signal from the output of the head unit directly into
the input of the amplifier.
Has the noise gone?
Yes. The noise source must be either one or more of the processors
or possibly the signal route. Go to Step 3. ‘Add Signal Processors’.
If you didn’t have any signal processors and you are using the
signal cable in its normal, installed route then the problem is
solved.
No. Go to 2b.
2b. Run new signal cables over
a new route between the head unit and the amplifier.
Has the noise gone?
Yes. Permanently route the signal
cables in the new route.
Go to Step 3. ‘Add Signal Processors’. If you don’t have any signal
processors then your problem is solved.
No. Go to 2c.
2c. Isolate the case of
the head unit from car's chassis. There must not be any electrical
contact between the head unit and car chassis except for a single
grounding point. Beware of antenna grounds and pullout cases!
Has the noise gone?
Yes. Reinstall the head unit isolated from the car's chassis and any
other metal parts in the dash. Ground the head unit at one point. Go
to Step 3. ‘Add Signal Processors’. If you don’t have any signal
processors then your problem is solved.
No. Go to 2d.
2d. Move the head unit ground to a quieter grounding point. Test a
number of points and also try grounding the head unit to the same
point as the amplifier.
Has the noise gone?
Yes. Reinstall the head unit using the quiet grounding point. Go to
Step 3. ‘Add Signal Processors’. If you don’t have any signal
processors then your problem is solved.
No. Go to 2e.
2e. Move the head unit as near to the amplifier as possible. Then
connect output of the head unit to the amplifier with the shortest
possible RCA cables.
Has the noise gone?
Yes. Reinstall the head unit one step at a time. Check for noise
after each step during the reinstallation. Once you have the head
unit installed, noise free go to Step 3. ‘Add Signal Processors’. If
you don’t have any signal processors then your problem is solved.
No. Go to 2f.
2f. Supply the head unit with an isolated power source, for example
an external car battery or a 12 VDC power supply. Make sure that car
chassis is not in contact with the head unit.
Has the noise gone?
Yes. The head unit is sensitive to noise in the supply voltage. Add
power supply filtering to the supply voltage for the head unit or
use an isolated power supply. You may be better to change the head
unit. Once you have a head unit installed noise free, go to Step 3.
‘Add Signal Processors’. If you don’t have any signal processors
then your problem is solved.
No. There is a serious problem with the head unit. Go to Step 4
'Check the Vehicle' and/or change the head unit.
Step 3. Add Signal Processors.
At this level the amplifier is known to be good. The car's
electrical system is OK and the reinstalled head unit is working
fine when connected directly to the amplifier.
3a. Connect one of the Processors back into the signal path.
Has the noise gone?
Yes. Go to 3a for the next processor. If there are no more
processors, the problem is solved.
No. Go to 3b.
3b. Run new signal cables over
a new route between the Head-unit and
processor and between the Processor and the amplifier.
Has the noise gone?
Yes. Permanently route the cables on the new quiet path. Go to 3a
for the next processor. If there are no more processors, the problem
is solved.
No. Go to 3c.
3c. Isolate the processor from the car's chassis except for a single
grounding point. Connect the processor ground to the same grounding
point as the head unit.
Has the noise gone?
Yes. Provide isolation between the Processor and the car's chassis
and permanently route the cables on the known quiet path. Go to 3a
for the next processor. If there are no more processors, the problem
is solved.
No. Go to 3d.
3d. Since new cables and re-grounding does not help, it is time to
relocate the processor very near the amplifier. Connect the output
of the processor to the amplifier with the shortest possible RCA
cables.
Has the noise gone?
Yes. Reinstall the Processor one step at a time. Check for noise
after each step in the reinstallation. Be careful when routing the signalcables.
Remember that the car's chassis is a conductor. Go to 3a for the
next processor. If there are no more processors, the problem is
solved.
No. Go to 3e.
3e. Power the processor with an isolated power supply. Do not let
the processor touch the chassis of the car.
Has the noise gone?
Yes. The processor’s power supply in not sufficiently isolated from
its audio circuitry. Either replace it or consider the permanent
installation of an isolated power supply (1:1 DC/DC converter). This
type of device provides a permanent power source that is well
isolated from the car's chassis. Go to 3a for the next processor. If
there are no more processors, the problem is solved.
No. Go to 3f.
3f. Physically separate the processor and the isolated power supply
from the rest of the system by many metres. Use long signal cables.
Has the noise gone?
Yes. Something is seriously wrong with either the processor or your
install/test procedures. Please repeat this level from the
beginning.
No. Change Processor -- this one has design problems. Go back to 3a
for the new processor.
Step 4. Check the Vehicle
The suspect car's charging and electrical systems can be checked by
using the previously installed sound system in
a "known quiet" car.
4a. Connect jumper cables between the batteries of the two vehicles
and start the engine of the suspect car. Turn on the headlights on
the suspect car and listen to the stereo on the "known quiet" car.
Is there now noise in the quiet car’s system?
Yes. Have a qualified auto electrician check out the car’s charging
system.
No. The suspect car's alternator and charging system is now proven
to be quiet. The problem must lie in the car
stereo installation --
not in the vehicle.