Things change. And in technology a radical change seems to happen every year. With the popularity of subwoofers in general and dB Drag Racing (i.e. sound pressure competitions) in particular we've seen an increasing demand among enthusiasts for greater sources of amplification; and this need among consumers is naturally leading to the development of more powerful amps that can drive subwoofers higher and higher. For the most part the proliferation of new classes of amps that employ varying methods for greater power and efficiency was related mainly to a refinement of sound. Now, this most recent development in amps has less to do with sound than pure power, technology responding to the cultural shift. The change may not be revolutionary, but it is radical.
In this review we looked at four very high power amplifiers under special conditions. I'm referring to SPL competitions which require amplifiers that produce huge amounts of power, usually under heavily clipped (distorted) conditions. Often the competitors run these amplifiers at battery voltages as high as 18 volts. Efficiency is important, so we paid particular attention to these numbers. Our tests will reveal power output and distortion just below clipping into a resistive load.
Testing these behemoths required an equally gargantuan power supply. We used a Hewlett Packard 15,000 watt supply. This monster weighs in at 600 pounds! Of course some rather nasty loads were required. I noticed a new addition to the test setup: a fire extinguisher! That's right, Joe Sanchez, the tech running the tests, explained to me that he was just "more comfortable" with one by his side. Hmm...
Normally an amplifier plays into a reactive load (that load varies with frequency). This load remains fairly constant over time, at least while listening to music at moderate levels. But in SPL competitions the speakers are pushed to their limits and beyond. Thousands of watts are pumped into the voice coil, resulting in very high temperatures in just a few seconds as the coil becomes red hot. The load that the amplifier reacts to may start out at 2 ohms, but quickly rises to a much higher number as the voice coil heats up. As the voice coil continues to heat, the resistance of the coil climbs, sometimes burning up. Because of these particular conditions, we also measured power output in a vehicle, as bench testing under heavily clipped conditions does not always reveal the complete picture. A 2000-watt amplifier, driven hard into clipping could produce 3000 watts into a resistive dummy load. If this amplifier is 75% efficient, it would draw nearly 350 amps!
Testing these amplifiers on a speaker requires something with tremendous power handling. For this we chose an Audiobahn AW1508X dual 1-ohm voice coil subwoofer. This was then placed in our SPL enclosure in the back of a 1999 Honda Civic hatchback equipped with a high output alternator and four batteries. We chose to test each amplifier at 50Hz, for this was where we achieved the peak output of the subwoofer at the dash using dB Drag Racing microphone placement. Running an impedance curve on the subwoofer system in the car revealed that the impedance of the sub rises to 5.3 ohms at our test frequency. Each amplifier was then installed individually and the maximum AC voltage of each was measured. Then, using Ohm's Law, we derived the power output of each amplifier (V2/R). As you will see, the results varied greatly.
Remember, sound quality, distortion, and other normal audio specifications are not a part of the criteria for judging in this amplifier test. Rather, these monsters were judged on pure output power! We rated these amplifiers only on power output at 12.5 volts, 14.4 volts, and dollars per watt.
EARTHQUAKE PH-D2
Earthquake is well known in the SPL business and the PH-D2 is the reason why. Considering it's the smallest of the group, this amplifier produces very respectable power. To make this possible, a Harris Class D control IC was used in the design. Circuitry of this type results in very high efficiency, but equally high distortion. This was apparent in our lab results in which the efficiency neared 80% and the distortion exceeded 4%. Additionally, the Earthquake fell short of the 2,000-watt target, producing 1400 watts at 12.5 volts and 1820 watts at 14.4 volts. On the reactive load, the PH-D2 was able to muster up 1684 watts. But at a MSRP of $999.00 the PH-D2 comes in at the highest watt per dollar ratio, making it an excellent value. Also consider that this is the most compact of the group tested, giving it an additional nod in the size per watt.
Layout:
Earthquake's PH-D2 is straightforward and simple to connect. Large power and ground connections protrude from the chassis to accept 0awg wire and it makes use of a setscrew to secure the wire in place. Speaker connections are similar, but in a 10awg variety. As with most Class D designs, a lowpass crossover is always active, in this case a variable 12dB/octave limits the response below 200Hz. Also supplied is an analog remote level control that plugs into the side of the amplifier via a phone cable. And to protect and hide the connections and settings Earthquake provides aluminum end-caps that give the amp a clean look.
Circuit layout is also clean. The power supply uses two main toroid transformers in its unregulated design. Of the group, Earthquake's overall efficiency was the highest.
There is no fusing, except an internal 30-amp fuse on the speaker output. Earthquake elected to use 85*C capacitors for their main supply filters. As we've pointed out in previous reviews, we feel that this is simply too low in any automotive design, and that 105*C capacitors should be used.
CROSSFIRE VR1000D
Crossfire is another big player on the SPL circuit. Their introduction of the CFA1000D back in 1998 helped revolutionize competition, all the while increasing awareness of Class D technology. The progress of this amplifier design since its introduction is substantial, making it one of the most sought after amplifiers in the SPL arena.
The latest version of the company's legendary Class D is the VR1000D. Like its predecessors, it's a single channel amp that uses a true mono-block design. This circuit arrangement makes it possible to bridge two amps together for a combined rating of 2,000 watts into 2 ohms. Linking the two is fairly easy and requires a single RCA connector and a 10" length of 8awg wire. A switch on the amplifier selects Master/Slave configurations per each amp. This allows for all of the functions including the gain setting, crossover adjustments, and subsonic filter to be set on only one amplifier. This is important because we are using two of these bridged together to reach the 2,000 watt spec for this test.
As for the results, the Crossfires mustered up 2250 watts at 14.4 volts and 1800 watts at 12.5 volts. On the Audiobahn subwoofer, max output rounded out to 2477watts, good enough for second place!
Layout:
Circuit layout is OK, but not as clean as the other amplifiers tested. Like the Earthquake and US Amps, Crossfire elected to use 85*C capacitors for their main supply filters instead of 105*C that we feel should be used in any automotive design. Power connections are smaller on this amp, only 4awg, which is sufficient for this 1000 watt class D amplifier. They, along with the 8awg speaker outputs, use a gold-plated brass design that requires a bare wire end to be inserted and secured with a setscrew.
US AMPS USA2000X
The USA2000X by US Amps is the odd-amp-out in a couple of respects. First off, this was the only one in the test to use class A/B topology. Under normal conditions when an amplifier is not being pushed to extremes, class A/B amps are not nearly efficient as class D or T. However, SPL competitions present a different situation. As these monsters are often played into a serious clip, the efficiency of a class A/B amplifier can measure closer to that of a class D or T.
The USA2000X also is the only 4-ohm stable amplifier of the group. However, this did nothing to deter the beast from producing impressive numbers. Our in-lab results showed it to be quite powerful, making 1685 watts with 12.5 volts, and a more impressive 2100 watts with the juice increased to 14.4. This placed it third in both categories. But placing the USA2000X on a reactive load drastically changed things. Here it took top honors with a very impressive 3010 watts. This is largely due to the 4-ohm impedance design (as opposed to the 2-ohms in the other amplifiers in this test). Therefore, the USA2000X should make more power at the test frequency of 50Hz where the impedance of the speaker rose to 5.3 ohms. In many ways it is fair to say that US Amps had an unfair advantage in our test since the output would likely be higher at this impedance.
It must be noted that during initial testing, this amplifier went into protection above 1850 watts (above 14.4 volts). After calling US Amps, we modified the circuitry. Following this modification, we were able to get 2,100 watts.
Layout:
This amplifier was the largest of the four at more than two feet long! The circuit board is cleanly laid out with a huge ground plane to accommodate the high output. The unregulated power supply is substantial, using two toroid transformers, by far larger than any found on the other amplifiers tested. Interestingly, the USA2000X uses four power and ground connections. These are the typical spade-type that normally accommodate 10awg wire. As with the Crossfire and Earthquake amplifiers, the 2000X employs only 85*C capacitors.
Protection and control come via a microprocessor. US Amps calls it Smart Amp Technology, or SAT. This is controlled through a port on the side of the amp. But the SAT controller was not provided so we were not able to test its capabilities.
ZAPCO C2K 9.0XD
The Zapco C2K 9.0XD is in a class of its own. It is very apparent that this amplifier was not designed just for the SPL competitor, but for the serious listener who is an occasional volume junky. Its build quality is second to none, as is the flawless and well thought out exterior.
This amp uses the Tripath Class T drive module. Unlike the class D amplifiers, it is capable of full range audio, even though it is not likely that someone will be using this much power on anything other than a subwoofer system.
The Zapco is the only amplifier of the bunch that employs a regulated power supply. While this type of design allowed it to produce the greatest amount of power at battery voltages of 12.5 volts, unlike the others its power did not increase but slightly at higher battery voltages. This can be seen in the results, as this amp produced 2100 watts at 12.5 volts and 2108 watts at 14.4 volts. This achievement merited first place in the former category and second in the latter. As for the reactive load test, this amplifier produced 2439 watts, good for third place, just slightly off the pace of the two Crossfires that wrapped up second.
The C2K 9.0XD includes a control unit that can be mounted in an area that is easy to reach, and remote display to show your adjustments. The control unit allows the user to adjust turn-on delay, enable the limiter, control gain, and select the display mode (these can be adjusted at the amplifier as well). The remote display also presents average and peak power, battery voltage, supply voltage, and internal temperature. A very nicely packaged and easy-to-use feature. Note: There is a 4-ohm version of this amp.
Layout:
This amplifier does not compromise on layout. Twelve low ESR, high temperature capacitors are used on the power input. Eight low ESR capacitors are used in the supply's power output section. Dual toroid transformers are used in the power supply. As this supply is regulated, it employs dual output chokes. Zapco also uses surface-mount components as well as through-hole throughout the PCB. Control functions are accomplished by a 16-bit microprocessor, while dual uP controlled fans are used for additional cooling. Power and ground connections are similar to the Earthquake's and can accommodate 0/0awg wire. However, the speaker outputs are standard spade-style that accept 10awg wire.
Final Opinions
Ideally, a competitor would want to use the 4-ohm versions of these amps if available for much higher SPL scores. In any case, it is truly amazing the kind of power that car audio amplifiers can produce these days. I suspect that all of these amplifiers will produce very close SPL levels in the various vehicles and enclosures used in today's SPL competitions. As actual impedances rise in the vehicles during SPL (and because competitors tend to use very high battery voltages) I feel the Crossfire will likely benefit the most. The Zapco and US Amps prove to be very versatile and potent in or out of the SPL arena. The high distortion (nearly 5%) of the Earthquake amp confines this to SPL, in my opinion.
And when it comes to cosmetics, the Earthquake and the Crossfire were judged best looking, by some pretty geeky guys, of the four amplifiers tested.
 EARTHQUAKE PH-D22,000 watts...  EARTHQUAKE PH-D22,000 watts into 2 ohms |
 CROSSFIRE VR1000D 1000 watts...  CROSSFIRE VR1000D 1000 watts into 1 ohm 2000 watts bridged pair. |
 U. S. AMPS 2000X stereo 1000...  U. S. AMPS 2000X stereo 1000 watts/channel or 2000 watts bridged. |
 ZAPCO C2K 9.0XD stereo 1100...  ZAPCO C2K 9.0XD stereo 1100 watts/channel or 2200 watts bridged. |