The car audio amplifier… its soul purpose is to take a low level signal from the source unit and transform it into a high level signal for activating the loudspeakers.
Amplifiers range in power from about twenty watts per channel to over one thousand watts per channel. Would you believe that the prices range anywhere from fifty dollars to several thousand dollars depending on features, power output and quality! Amplifiers range from one channel of output to as many as eight channels. The most common amplifiers are currently two and four channel models.
Amplifier Power Ratings
Power amplifiers also have “optional equipment”. These features include built-in active crossovers, equalizers, signal processing and speaker level inputs. When shopping for an amplifier consider that all power ratings are not created equal. The only true measure of an amplifier’s power is its continuous power rating or R.M.S. rating ( or root mean square) and refers to the average power output of the amplifiers. Some of the low-quality brands will exaggerate or even outright lie about the power output of their amplifiers which is a good reason to stick with the well known manufacturers.
Car Amplifier Quality: Also keep in mind the quality of the amplifier. A
generally good indication of quality build and the power
output is the size and the weight of the amplifier itself.
Better quality amplifiers will usually have a heavier and
larger heatsink versus a low quality amplifier of the same
power rating.
However there are many top quality amplifiers that do not follow this rule.
Blaupunkt makes a line of amplifiers that have a plastic shell. Because of the high efficiency design of those amplifiers a heavy heatsink is not required. Also a good indication of an amplifier’s true output is the size of the fuse used.
Use your head when buying and keep in mind the brand’s reputation for quality.
If you find yourself on a budget or lack space for many components then the economical thing to do is buy a multi-channel amplifier with the built in features and processors that you desire. By minimizing the number of components the chance of noise entering into the system is lessened.
Some features and aspects of amplifiers to consider are:
Bridgeable: This feature allows a pair of amplifier power
channels to be combined into one channel of greater power.
This is usually used for driving a subwoofer although it
will work with any other type of speaker as well
Channels: The more channels an amplifier has the greater
the installation flexibility it will have. Especially in
terms of options, future add-ons and upgrades.
Class: This refers to the way the amplifier operates. The
three types that are most likely to be encountered are A,
A/B, and D. Class A amplifiers are the least efficient in
terms of power consumption, staying on continually, but
also have better sound in general than A/B amplifiers. They
are very rare in car audio. Class A/B amplifiers are more
efficient than the class A design and are the most common
type. Almost all amplifiers in the car audio market are of
the A/B design. Class D amplifiers are usually reserved for
high power subwoofer amplifiers and can reach efficiencies
in the 80% range. This design can therefore be smaller,
uses less current and produces less heat than the other
classes.
Connectors: This is the method of attachment used for
wires that are connected to the amplifier, including
speaker and power wires. The most common kind is the screw terminal strip. This is a series of screw connectors that can be removed and replaced without compromising the
amplifier. The other main type of attachment is the “Molex”
type connector. This method involves a wire harness that
plugs into the amplifier after the power and speaker
connections have been made with a crimp or solder
connection. If the amplifier is installed in more than one
system these wires can get pretty short over time and
become more difficult and even dangerous to work with. A
variation on the two is a harness that the power and
speaker wires screw into. Then the harness plugs into the
amplifier. This is probably the most convenient of all
connections.
Crossover/Filter: A built in crossover can be useful,
especially if it is many frequencies of adjustment. A
filter is a crossover that only affects one channel, not
actually splitting frequencies but simply reducing a range
of them.
Distortion: This is often given as T.H.D. or total
harmonic distortion. It is the measure of how much an
amplifier will change a signal from the input signal it is
given. Figures below 0.1% are negligible and will not be
heard. Usually the figure can be in the 3% range without
being heard but virtually all high quality amplifiers will
have a T.H.D. below 0.1%.
Efficiency: This is the ratio of of power input (from the
battery) to power output (to the speakers). A 100 watt
amplifier with an efficiency of 50% would take in 200 watts of power from the battery and output 100 watts of power to
the speakers. The other 100 watts of power would be wasted
as heat. The higher the efficiency of an amplifier the
better.
Power Output: The rated power output of an amplifier
should be given into a four ohm load, all channels driven
from twenty to twenty thousand hertz (20Hz-20kHz). Keep in mind that while the low end amplifiers are exaggerated in
their power output, many high end amplifiers are under-
rated in their power output. These are sometimes called
“cheater amps” because they allow a car audio competitor to
compete in a lower power class while in reality having a
larger amplifier. This under-rating can be three times less
than the actual power output.
Power Supply: The two most common types are the IC chip and the MOSFET supply. The IC chip is what is used in most source units (head units) and are only capable of roducing about twenty watts per channel. MOSFET is the more common design and has a smoother sound than the chip design.
Pre-amp Inputs: This is a set of jacks (usually RCA jacks)
that will accept a low level pre-amp signal from a source
or processing unit.
Pre-amp Outputs: This is a set of jacks (usually RCA
jacks) that pass on a low level pre-amp signal to another
amplifier or processing unit. These will sometimes be filtered outputs.
Separate Gain Controls: This allows the gain of each
channel of the amplifier to be set independently of the
other(s).
Speaker Level Inputs: For source units that do not have
pre-amp level RCA outputs this feature may be used to take
the signal from the speaker leads of the source unit. The
signal will not be as clean as a pre-amp level output but
will be adequate for most factory upgrade applications.
Stability: The measure of how low of an impedance load an amplifier can handle (in ohms). Any good quality amplifier
will be two ohm stable while a rare few will go as low as a
quarter of an ohm. Ideally an amplifier should double its
power each time the load is halved. For example, a one
hundred watt amplifier (into a four ohm load) should
produce two hundred watts into a two ohm load and so on.
This is most useful when running multiple speakers off of a
single amplifier or in sound off competitions that are
classed by total power output.
Tri-Mode Output: This feature is available under different
names but is the ability of an amplifier to run a stereo
pair of speakers and a mono subwoofer (or center channel)
from only two channels of the amplifier. Personally, I
would not recommend doing this. Instead buy a good quality
four channel amplifier and bridge two of the channels for
the subwoofer.
Tube Amplifiers: These are the least common amplifiers and are also the most expensive. Rather than the traditional
solid state components they use old fashioned vacuum tubes. They are said to produce a warmer sound and a moother midrange than solid state designs. For most systems the standard design will be more desirable.
Armed with this knowledge, you should now be able to make an informed decision on your amplifier purchase. Interested in more amplifier articles? Check out Putting the “BOOM…BOOM…BOOM” into your system.
Enjoy!
George Steiner
1car-audio.com www.1car-audio.com
George and Judy Steiner from North Carolina have unsuccessfully maneuvered through the teenage eons with their two daughters. The countless boyfriends with modified auto stereo systems broadcasting bone-jarring bass, little room to sit due to the electronic gagets and non-existant trunks, experiences we could have done without!
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