Amplifier Power and Voltage

Did you know your vehicle's charging voltage can affect the power output from many car audio amplifiers? Many car audio amplifiers have what is called an unregulated power supply. The power supply is what converts the vehicle's charging voltage into power that the amplifier can use. And if the power supply is an unregulated design a boost in voltage from the vehicle means a boost in power from the amplifier.

Regulated vs Unregulated Car Audio Amplifier Power Supplies

So what makes an amplifier's power supply regulated versus unregulated? It's basically up to the amplifier's designer. As with anything there are pros and cons to the two different designs. Some designers like to use an unregulated design because an increase in vehicle voltage will give an increase in amplifier power output. But on the other hand a decrease in vehicle voltage will cause a decrease in amplifier output power. In both cases the voltage must stay within a certain range or the amplifier will shut down. Usually the range is somewhere between 10.5-16.5 volts.

A regulated power supply will put out the same power regardless of the vehicle voltage. So even if your vehicle's voltage drops to eleven volts it will still put out the same power as if the vehicle's voltage was fifteen volts. And looking at it from the other way, if the voltage goes up the power output will not go up.

The Effect of Vehicle Voltage on Unregulated Car Audio Amplifiers

Let's put regulated supplies aside and focus on the unregulated power supply. How does this design help us? Quite honestly this is really designed more with car audio competition in mind. An amplifier with an unregulated power supply can be rated for low power output at a nominal 12 volts but will actually put out a good deal more at "real world" charging system voltages. This lets a competitor competes in a lower power class while actually having wattages of a higher power class. It's the same type of edge car audio amplifier companies create with high current, low impedance driving designs.

Time for some quick math. How does an increase in voltage affect power output in watts? Let's say we have an amplifier rated to for X watts into four ohms with an input voltage of 12.0 volts. What will the real output of that amplifier be with an input voltage of 14.4 volts? We'll have to start with Ohm's Law. From it we know:

NOTE: These values are relative and don't represent actual watts produced by the amplifier. There are other factors involved but this example will show you the percentage increases gained with increased supply voltage and a given impedance (load).

Power = Voltage x Current, (P=E*I)

We also know that Current = Voltage/Resistance, (I=E/R)

So we know the voltage and the resistance but not the current. But with a little substitution we can put in Voltage/Resistance for every value of Current in the Power Equation (P=E*I).

Power = Voltage x (Voltage/Resistance)

OR

Power = (VoltagexVoltage)/Resistance, (aka, Voltage "squared" divided by Resistance)

SO

Power = (12x12)/4 = 36

Increasing the voltage to 14.4 volts gives:

Power = (14.4x14.4)/4 = 51.84

That amounts to a percentage increase of (51.84/36)-1 = .44 or 44%

If we increase the voltage to 16.25 we get:

Power = (16.25x16.25)/4 = 66.02

That's an increase of (66.02/36)-1 = .83 or 83%

Because power increases with the square of the voltage a small increase in supply voltage will give a large increase in power output. So if our amplifier's output at 12 volts was 100 watts then at 14.4 volts it would be 144 watts and at 16.25 volts it would be 183 watts. This assumes that the amplifier can handle voltages as high as 16.25 volts (it might not).

How Do You Get the Edge

For starters you can make sure your vehicle's charging system is working properly. Alternators, regulators and batteries all go bad and can lead to the slow demise of your charging system. Have your system checked out by a qualified mechanic and make sure everything is in good shape. Also check the connections at the battery and of the negative battery cable where it grounds to the vehicle (often on the engine block). If these are loose or corroded anything else you do will be a waste. It's also a good idea to have the ground cable from the battery upgraded to a larger gauge wire. Moving lots of current requires a big pipe on both ends, not just the positive cable. The same goes for the charging cable that runs from your alternator to your battery, especially if you've upgraded the alternator to a larger unit.

Another option is to change the set point of your alternator to a higher voltage. This is NOT a good idea if you're running a single alternator, single output system. This is what almost every vehicle on the planet has. The danger here is a change in the output voltage of the alternator will increase the voltage for the entire vehicle, not just the amplifier. You could pretty easily end up frying delicate electronics and causing all sorts of other fun problems if you did this. But if you're running a multi-alternator setup, with one alternator for the vehicle and a separate charging system for the audio system you could set the output of the audio's charging system higher without affecting the vehicle voltage. This would be a very unusual and extreme case but some competitors do have it, especially in the unlimited SPL shootouts.

There was once a product made by Jacobs Electronics called the Accuvolt that was designed to increase the voltage up to a maximum of 16.25 volts. US Amps also made a similar device. Using this device in conjunction with an amplifier that has an unregulated power supply would give an advantage in car audio competitions. It was also separate from the rest of the vehicle so increasing the voltage of the unit will only affect devices that are connected to it (amplifiers in this case). Non-competitors are generally better off buying a larger amp since they do not have the power class restrictions and do not have to use devices such as this to increase power output in their system.


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