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 RatingsPower 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. Agenerally good indication of quality build and the poweroutput is the size and the weight of the amplifier itself.Better quality amplifiers will usually have a heavier andlarger heatsink versus a low quality amplifier of the samepower 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 powerchannels to be combined into one channel of greater power.This is usually used for driving a subwoofer although itwill work with any other type of speaker as well

Channels: The more channels an amplifier has the greaterthe installation flexibility it will have. Especially interms of options, future add-ons and upgrades.

Class: This refers to the way the amplifier operates. Thethree types that are most likely to be encountered are A,A/B, and D. Class A amplifiers are the least efficient interms of power consumption, staying on continually, butalso have better sound in general than A/B amplifiers. Theyare very rare in car audio. Class A/B amplifiers are moreefficient than the class A design and are the most commontype. Almost all amplifiers in the car audio market are ofthe A/B design. Class D amplifiers are usually reserved forhigh power subwoofer amplifiers and can reach efficienciesin the 80%+ range. This design can therefore be smaller,uses less current and produces less heat than the otherclasses.

Connectors: This is the method of attachment used forwires that are connected to the amplifier, includingspeaker 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 theamplifier. The other main type of attachment is the "Molex"type connector. This method involves a wire harness thatplugs into the amplifier after the power and speakerconnections have been made with a crimp or solderconnection. If the amplifier is installed in more than onesystem these wires can get pretty short over time andbecome more difficult and even dangerous to work with. Avariation on the two is a harness that the power andspeaker wires screw into. Then the harness plugs into theamplifier. This is probably the most convenient of allconnections.

Crossover/Filter: A built in crossover can be useful,especially if it is many frequencies of adjustment. Afilter is a crossover that only affects one channel, notactually splitting frequencies but simply reducing a rangeof them.

Distortion: This is often given as T.H.D. or totalharmonic distortion. It is the measure of how much anamplifier will change a signal from the input signal it isgiven. Figures below 0.1% are negligible and will not beheard. Usually the figure can be in the 3% range withoutbeing heard but virtually all high quality amplifiers willhave a T.H.D. below 0.1%.

Efficiency: This is the ratio of of power input (from thebattery) to power output (to the speakers). A 100 wattamplifier with an efficiency of 50% would take in 200 watts of power from the battery and output 100 watts of power tothe speakers. The other 100 watts of power would be wastedas heat. The higher the efficiency of an amplifier thebetter.

Power Output: The rated power output of an amplifiershould be given into a four ohm load, all channels drivenfrom twenty to twenty thousand hertz (20Hz-20kHz). Keep in mind that while the low end amplifiers are exaggerated intheir 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 tocompete in a lower power class while in reality having alarger amplifier. This under-rating can be three times lessthan 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 sourceor processing unit.

Pre-amp Outputs: This is a set of jacks (usually RCAjacks) that pass on a low level pre-amp signal to anotheramplifier or processing unit. These will sometimes be filtered outputs.

Separate Gain Controls: This allows the gain of eachchannel of the amplifier to be set independently of theother(s).

Speaker Level Inputs: For source units that do not havepre-amp level RCA outputs this feature may be used to takethe signal from the speaker leads of the source unit. Thesignal will not be as clean as a pre-amp level output butwill 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 amplifierwill be two ohm stable while a rare few will go as low as aquarter of an ohm. Ideally an amplifier should double itspower each time the load is halved. For example, a onehundred watt amplifier (into a four ohm load) shouldproduce two hundred watts into a two ohm load and so on.This is most useful when running multiple speakers off of asingle amplifier or in sound off competitions that areclassed by total power output.

Tri-Mode Output: This feature is available under differentnames but is the ability of an amplifier to run a stereopair of speakers and a mono subwoofer (or center channel)from only two channels of the amplifier. Personally, Iwould not recommend doing this. Instead buy a good qualityfour channel amplifier and bridge two of the channels forthe subwoofer.

Tube Amplifiers: These are the least common amplifiers and are also the most expensive. Rather than the traditionalsolid 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

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!