Voltage = Power

DD Audio Tech Talk | WRITTEN BY AARON TRIMBLE | 22 June 2017

What do you see when you look at an amplifier’s spec sheet? In many cases, you’ll see a couple impedance values followed by their respective wattage numbers. If you’re lucky, you’ll see what voltage these values were derived from as well. Very often you will see these amps rated at 13.8v or 14.4v, a value which some vehicles are capable of maintaining on lower wattage amplifiers. However, when the topic of big amplifiers (>2,000 watts) comes into play, lower test voltages become far more relevant.

Here at DD Audio we make some pretty big amps, and we know that low voltage is a reality for many bassheads. Take for example the créme de la créme of the DD Sub amp line, the Z2c. The Z2c is capable of almost 18,000 watts of power if we’re not concerned with how much distortion is involved. It’s a monster. If we’re talking about clean, unclipped power (<1% THD+N), the Z2c is still good for a whopping 14,360 watts at 16v of input. When we reduce the power to 14.4v the amp is still pumping out a massive 11,660 watts, and if we reduce the input power further, say down to 12.6v, the Z2c can still manage a laudable 7157 watts at a 1 ohm load.

Chart: Z2c THD+N at a given output wattage based on varying input voltages.

Now, why is this information important, especially for big amps like the M series and Z2c amps? The unfortunate truth is a lot of people will buy amplifiers that are too big for their electrical systems. If someone spends all of their money on a 5000 watt M4b amplifier and doesn’t plan batteries and an upgraded alternator into their budget, they’re probably going to run into some voltage related issues.

An amplifier can only draw as much power as it is provided and if your system is bigger than your electrical, then you’re going to see some voltage drop. The voltage will continue to drop until it reaches a point where the battery can supply the necessary amperage at a given voltage. If the system is run too long or too hard at an electrical deficit, or the system is simply too large to be effectively powered by the vehicle’s electrical some scary things can happen. When an amp drops below 11 volts, the output devices can start to generate more heat as their switching speeds slow down. The combination of this along with some clipped signal from the output loss can cause some real damage. At 10.5v on all DD M Series amps the voltage meter on the bass knob will display “LO” as a warning to the user that the amp is being run at dangerously low voltages. If the amp is run below 10v the MOSFET’s can no longer reliably switch. MOSFET’s are driven by voltage, and when there isn’t enough voltage to turn the FET’s on or off all the way, they become resistive and the current passing through them begins to be sloughed off as heat. When too much heat accrues in the FET’s, they fail and they can take gate resistors and audio drivers out with them. Power supply MOSFET’s can also be taken out in a similar fashion.

It never hurts to have an extra battery or a bigger alternator. It will extend the life or your equipment and help the amp deliver all the power that was promised to you. Most systems should be running between 12.5-13.8 volts. If you notice that you’re running below 12v, it’s time to look for some electrical upgrades!