Please
'Boom' Responsibly As
most of you have noticed, the noise ordinances have
become much tougher lately. Most of this is due to
idiots, yes IDIOTS, who drive through residential areas
with their windows down while their system is playing at
full power. To make things worse, the music they listen
to has all sorts of foul language that's not suitable for
small children, (who may be playing outside). There are
even a few people, who are even beyond idiot status, that
play their systems at full power through residential
areas after 10:00 PM (when many people go to bed). I
don't believe that this type of behavior is good for the
industry. If the fines get too stiff, people will stop
buying large systems. If this happens, more people will
get out of car audio (who wants a mediocre system).
People get interested in things because they're exciting.
A deck and four 6.5" speakers are not going to
interest many of the younger car audio enthusiasts. If
car audio enthusiasts keep annoying more and more people,
the fines will keep getting tougher. All of this will
only reduce interest in the equipment that fuels the
industry. If you want to listen to your system at full
volume, get out on the highway where there's little
chance of bothering anyone. When you get to a red light,
turn it down. If the only thing attractive about you is
your 'system', you have some work to do. Bottom line...
Think about what you're doing. Think about other people.
It's not the end of the world if you have to turn the
volume down for a little while.
Head Unit:
The term head unit will be used
instead of radio or tape deck or cd player or...
well you get the point.
Power Connections:
Most head units have 2 power
input connections that have to be connected to a
12 volt source. The 'battery' or 'memory' wire
has to be connected to a constant source of power
(has power on it at all times - even when the
ignition switch is in the off position). The
other power wire (the 'ignition' wire) is
connected to a power source that's controlled by
the ignition switch and therefore will only have
power on it when the ignition switch is in the
'on' or 'acc' position.
Speaker Outputs
Most head units have outputs
that are designed for driving 2 to 4 speakers.
These outputs provide the audio output power to
drive the speakers. The power output from a high
power head unit is limited (by battery voltage)
to approximately 20 watts per 4 ohm speaker. All
of the manufacturers that say their head units
can produce 30 or more watts of real power are...
how can I say this? Hmmm... Full of it!
Note:
On "high power"
units, the internal audio amplifier will be instantly damaged if a speaker output wire is
allowed to contact anything except a speaker
terminal, even if the volume is not turned up. Be
sure that there is no power to the unit when
making any connections. This
link explains why the outputs will be damaged if
they contact ground.
Preamp Outputs
Preamp level outputs are audio
outputs that are used to drive an amplifier (or equalizer or crossover...).
Preamp level outputs do not have enough output
current to allow them to drive speakers directly.
They are generally included on higher end
equipment. In virtually all cases, they will have
RCA type connectors. Some units will have only
one set of preamp outputs (would likely be a
'rear' output). Other units have multiple pairs
of outputs for front, rear and subwoofer signals.
Remote or Power Antenna Output
There may be one or more
switched 12 volt outputs on your head unit. These
outputs are usually called remote outputs. They
are used to control power amplifiers or power
antennas. If your unit has only one
remote output, 12 volts will be sent through it
when any audio source is
being used (tuner, CD, tape, aux...). It will be
'hot' (have 12 volts on it) when the head unit is
on. It will have no voltage when the head unit is
off.
If the unit has two
remotes, one wire (generally a dark blue wire
with a white stripe* for aftermarket radios) will
be for your power antenna and will only have 12 volts on it when you are
using the tuner. It will have no voltage on it when
the head unit is switched to CD, tape, aux or is
switched off. This is so that your power antenna
will go down when it is not needed. The second output (generally a dark blue wire*
for aftermarket radios) will be marked amp
remote (or amp
turn-on) and will have 12 volts switched to it
when any
source is in use. The diagram below only shows a
single remote wire. There is a diagram on the test light page that shows both types of
outputs.
Please note that the remote
wires for stock (OEM) radios will be of a
different color (probably not blue). You can
refer to the following page for the color code
for your vehicle. Street Dreams
*Some radios use blue
with a white stripe for the power antenna and
others use it for the amp turn on wire. Just keep
in mind that if it has 2 dark blue wires and one
has a white stripe and the other is solid blue,
those wires are for amp/power antenna control.
You'll have to refer to the deck's owner's manual
for the color code.
The following diagram will give
you an idea of what the wiring on the back of a
head unit might look like.
Again with the fuse thing...
Most remote outputs are
switched through a very small transistor. This
means that they are EASILY damaged by excessive
current flow. They should be fused close to the
head unit with a .5 amp fuse. A 1 amp fuse may
not protect the switching transistor, which
supplies power to the remote output. Do not try
to use the remote output to power fans
directly.
If you use an LOC,
you will have to set the gains
on your amplifier so that the amplifier reaches full
power before your head
unit's volume control reaches 1/2
volume. Most radios' speaker
outputs will start to clip
at about 1/2 volume. This is far earlier than the
point where the preamp output signal starts to
clip on most radios. The only time that I've seen
a preamp out start to clip along with the speaker
output is when the preamp output signal is
derived from the speaker output via a voltage
divider network (sort of a cheap internal LOC).
This is usually only done on the
bottom_of_the_line head units.
If you blow a fuse when
installing your head unit, consult your owner's
manual for the proper replacement fuse size. By
proper size I don't mean physical size. I mean
amp rating. If an electronics manufacturer
specifies a certain size fuse, they do it for a
good reason. They know what the equipment and
internal electronic devices can handle. More than
half of the head units that I serviced would not
have been damaged if the proper fuse would have
been used.
TECH TIP:
Speaker Connections
If you are not using your
speaker output wires, cut them off so that there
are no copper strands sticking out of the
insulation AND tape up or otherwise insulate the
end of the wire. You may be able to pull on the
insulation so that it stretches over the end of
the cut off copper wire.
REASON: If the
speaker wires on a high powered radio are allowed
to touch to any grounded piece of metal, the head
unit's internal amplifier will be instantly
damaged (even if the volume is not turned up).
RCA Cables
Do not allow any source of
power (12 volts) to come in contact with the
shield (outside metal part) of the RCA cables.
REASON: The
shield is grounded to the case of the head unit.
It is the reference for the preamp audio signal.
If it comes in contact with a source of power,
the ground connection inside of the head unit
will be damaged. This may cause lots of problems
including blown tweeters, engine noise, lack of
bass and many more.
Aftermarket Wiring Harnesses:
When installing an aftermarket
head unit, you should not cut the factory plug
from the vehicle's factory wiring harness.
Instead, you should buy an aftermarket wiring
harness that would plug into the factory harness.
These harnesses (such as those made by Metra)
will have each wire marked with it's function
(ignition, battery/constant, speakers...).
You would connect the harness
to your radio with butt connectors (or other
connectors) and then simply plug the harness into
the factory harness. If you want to reinstall
your factory head unit at a later date, you'd be
able to plug it right back into the factory
harness.
