Trouble Shooting Noise
By: Alan Ward
In this paper, we are going to look at some of the common causes of
noise in your system, and how to track down and eliminate their sources. Some of the
things this page will cover include:
- external interference
- alternator whine
- isolator whine
- trouble shooting step by step ...time to get dirty
The Environment. Sometimes the environment can play
a role in the noise your system is making. Around hospitals, high voltage power lines, and
radio stations (not the public listening type either), you pick up alot of interference.
Also, extremely HIGH humidity can cause problems. A cold start on foggy morning can lead
to some alternator whine thanks to moisture. For the same reason, corrosion builds up
on your electrical connections, causing increased resistance. And the most obvious, you
are at a show and keeping your battery topped off with a charger! AC power lines are very
dirty, and you should disconnect all sources of external power during judging anyhow.
A poor battery. Check the voltage on your
battery with the engine off. IME a good battery will be somewhere around 12.7 volts, plus
or minus 0.2 volts. If you're right at 12, or even under, then try charging your
battery. Constant low voltage is a sure indication you need a new battery, OR have
a charging system problem. Check this link if you suspect
your charging system. If you have a dual battery setup, then it is likely you
have more complicated problems. Differing voltage in a system can be cause for
minute annoying little buzzes. Proper power systems should keep a constant voltage
(although this is next to impossible, it's what you want to work towards. If you have one
battery that's keeping a different voltage, the unbalance between equipment using that
voltage can cause interface problems with equipment not using that source.
Bad grounds. A bad ground is probably the most
common cause of noise. If one of your audio componants is poorly grounded, it's not
getting as much voltage as other componants are. For more on proper grounding, check the
appropriate tech paper.
Isolator whine. Before proceeding to the next
culprit, it is VITAL that you bypass your isolator and make sure it is not the
problem. This is simple to do, and is just as mandatory as checking a fuse when
nothing works at all. To bypass the isolator, unhook all of the wires from it,
there should be four wires. hook the 3 wires from the alternator, battery 1 and
battery 2 together (easiest way to do this is with a bolt and nut) BE SURE and tape the
assembly off so that an accidental grounding does not occur. You could also test the
system with the alternator unplugged, (engine off of course)
Only after you have eliminated the above possibilities should you
begin to tear apart your system and start checking components (unless of course you just
changed amps or something and have good reason to believe it is the system). In the
end use your head, think about it logically. MOST important of
all, write down EVERYTHING you find out no matter how insignificant it may sound, if in
the end you cannot isolate the problem, and have to drop it off at the store your notes
may reveal to a skilled installer exactly what the problem is saving
you A LOT of $$. As you're reading through this,
the idea is to eliminate as much of the electronics as you can between you signal source,
and your speakers. Then, read each componant till you're done.
- You may find throughout this procedure your noise may change in
pitch and volume. This is due to various levels of processing. To counter act
this Set all of your processors, eq curves, bass levels, treble etc to the middle or zero
setting, depending on equipment... working upline to a component that amplifies or alters
a bad signal, may cause a false assumption. (its amplified or altered now and is
misinterpreted as the source, while it is merely amplifying or distorting the source
noise.), .........even though in theory it cant amplify a bad component that isn't hooked
up (further upline), still good to keep this in mind
- Gather supplies: If you don't already have one go to
radio shack and find a cord that turns the headphone output on your walkman or home stereo
into an RCA cable. Use this cable for all source signals
during the testing. Also buy about 4 female-female RCA y splitters...(to be used in
steps 5 and 7), also have handy an extra RCA cable, at least 10 feet long, or long enough
to bridge any two components.
- Now your ready for the fun part, what's behind door #1? Unhook the
RCA's from each of your amps or the suspect amp, feed it the clean signal from the home
stereo... do you have noise?
- NO I don't have any more noise: then your
in good shape this means the amp(s) AND the speakers are OK, hook the RCA's back up
to each amp, move to the end of these RCA's (your not at the next piece yet, its time to
check the RCA's themselves leading to the amps. move on to step 4
- YES I still have noise: check for the following, since you have
noise you can assume for now that the problem is in your amp, speakers, or speaker wire
- Power supply problem, if you went through the beginning of this
paper and did not find anything wrong, then it is safe to rule this possibility out,
though be sure and make a note of it.: TAKE NOTES
- Possibly poor speaker mounting/wire routing: Unhook the
speakers from the amp and test them from an external source, do you still have noise?
- NO: Good then you know your speakers are OK, this means that
your amp is a likely suspect. read on.... and TAKE NOTES.
- YES: either your speakers or the crossovers (if you have
components) are bad, you can test each driver individually in this case in order to rule
out the speakers, leaving the crossover as the culprit
- Bad amp: if none of the above criteria solve your problem
then your amplifier is probably bad, or the power supply to it, you can test the power
supply with another amp you know is good, or you can just "fiddle", checking the
grounds and wire routing.
- Check the RCA's: Again feed a clean signal from the end
of the RCA's to each amp. This may require a female-female connector from radio shack, our
king-of-connects. Y-splitters work very well and serve a dual purpose for later on
when you test out the crossovers. Do you have noise?
- NO: Good then your RCA's are not damaged fried or poorly
routed* (*keep in mind that the other RCA's and wires don't all have
power and signals at this point. TAKE A NOTE OF THIS. proceed to step 5
- YES: Check the routing of your RCA's for help on this refer
to the tech paper on "wire routing", also, check to make sure that none of your
RCA cables are physically damaged. Damage on the outside may be a sure indication
that the inside of the cable is also damaged. Have a spare RCA, a cheap-o will do
fine. Use this cable and test again for noise. If you still have noise then
re-check your amplifier in step three. This is rather bizarre, I would not expect
anyone to have such luck, if so mail firstname.lastname@example.org
- This step will be repeated for each set of signal processors,
in-between each step refer back to step 4, and check each set of RCA's. AS you move
up the line, hook your signal processor up to the RCA's leading down to the amps, remember
we already know that every thing in this particular setup is good, so if there is noise,
then the processor is causing it. Do you have noise?
- NO: If you don't have any noise then your first processor or
crossover is in good shape, proceed to check the RCA's leading up to the next level. (step
- YES: If you have noise then your crossover/processor, is the
problem, likely causes for this may be:
- Poor ground on the crossover, see the tech
paper on grounds. Damage due to insecure mounting, (internal breakage) is the
crossover spliced into the amps power supply? that's a NO NO, as I read in another paper
once....what happens in the shower when you flush the toilet?
- NOTE: If you're looking for the source of turnoff - pop, and you
now have turn off pop, it is because your processor is cutting of the signal before the
amp shuts down, remedy? you need to create a circuit with a diode, and capacitor to keep
the EQ on longer. (mine stays on for 30 seconds after shut down) a good explanation
of this can be found in the RAC-FAQ,
look for turn off pop. It will explain how to wire up the diode.
- At this point refer back to step 4, and then 5, and then 4, and
then 5, etc until your at the head unit. Each time testing the system with an
external source. TAKE NOTES ! ! If you make it up to the head unit with no noise,
after having completed step 4 once again... remove the head unit, your problem may be:
- Bad Ground: check the ground on your head
unit. tech paper on grounds
- Poorly mounted, is your head-unit in an other-than-stock location?
If so, is there a heat vent blowing on it 24-7?
- Mechanically bad mount, does your head-unit dance around
inside the dash every time you hit a bump, when you hit a bump do you look at your HU and
sigh relief that it still works? If so, FIX IT.
- The dash contains a lot of vents, and such, it may be that your
head-unit is just dirty, you may try blowing it off gently with an air
- Bad Head-Unit: Get it fixed or purchase a new one.
- Once you have found your faulty component, by-pass it and make sure
the system works well without it, this is where the RCA Y-splitters come in handy, mainly
if a crossover is your problem.