Another winner from MTX

MTX Audio has been around for quite some time, and I always liked their philosophy and marketing. I've owned numerous amps from them dating back to their old Black Gold weries amps. The Black Gold 125x2 amps were some of my favorites. The amp under review now, the Thunder 81000d, is based on MTX's original Thunder amps, which are several generations old now. Those amps were great when they first came out, putting out tons of power for little money. And with the popularity of class D amps in recent years, the power to price ratio is even better these days. The 81000d is a cosmetically updated version of last year's Thunder 1000d. This new model has added chrome on the top of the amp, for improves its looks for some people. Asides from the aesthetics, this amp appears to be pretty much the same as last years model.

The 81000d is a single channel class D amp, designed to run subs only, since it is limited in frequency to about 250hz. Such is the drawback of a class D design, which inherently suffers from high frequency switching noise. Class D amps are great for subs, because subs don't need to run at higher frequencies, and their efficiencies greatly exceed the traditional class A/B design. Most class A/B designs run about 50% efficient at full power, but efficiency drops dramatically at lower power levels (which is more indicative when playing music), to around 25% - 40% at 1/3 power levels. Basically, this means that when a class A/B amp produces 300w, about 600w is also produced in the form of heat. This makes the amp run hotter and it is also hard on the electrical system. Class D amps, on the other hand, are a little more efficient than class A/B amps at full power, with typical efficiencies in the range of 60% - 80% at max power. However, at lower power levels, they maintain their efficiency much better than class A/B amps, so even with music, their efficiency will remain near those levels, which can translate to more than double the typical efficiency of class A/B amps. This translates to less power being wasted in the form of heat, and an easier load on the electrical system. Class D amps are really remarkable for driving subs. To me, it is simply useless to run high powered class A/B amps to drive subs. Despite some people who claim that class D subs have bad sound quality compared to class A/B amps, this is simply not true. While there are measurable differences (higher THD+noise, lower damping, for example), none of these are audible, and this has been proven in double blind tests. MTX has apparently realized this as well, as they dropped their largest class A/B amp (600w rating) and replaced it with 3 class D amps.

The 81000d is rated at 500x1@4ohm and 1000x1@2ohm with 12.5v. They also list a 'dynamic' power rating of 850w at 4ohm and 1500w, both at 14.4v. MTX has been known for underrating their amps, and they include birthsheets with their amps. This particular unit is marked at 1214w at 2 ohm, with a 12.5v input. Car Stereo Review tested last years 1000d a few months back, and found that at 2 ohm, it did 1100w with 12.5v and 1400w with 14v. That's a lot of power from a relatively small chassis, which is approximately 16"L x 9"W x 2"H. At one end of the chassis are the speaker output terminals and power and ground connections. The power/ground are are large insert terminals capable of accepting up to 1/0 gauge wires, which is great. For typical installs, without another other large amp in the system, 2 gauge, and even 4 gauge should be sufficient, as long as wire length isn't that long. Even though the amp is a mono-block (single channel), there are 2 sets of speaker terminals included (which are internally wired in parallel). This allows for easier wiring of multiple subs. On the other side of the chassis, there are low level inputs (rca inputs), a pair of pre-amp outputs (low pass only) to daisy chain more of these amps, gain and crossover pots and a telephone type jack for the optional remote bass module. The crossover is a permanent low pass design (always on, since the amp only works up to 200hz). It is continuously variable from 40hz to 200hz, but I couldn't find its slope rate. The pots are rather small and difficult to adjust, and its hard to tell where the crossover frequency is at, so you'll have to set it by ear. With the EBC2 remote bass module, you can hook it up and mount the control at the dash so that you can control the bass level from the driver's seat. The Thunder EQ is a narrow-bandwidth type bass boost centered at 40hz and has up to 18db of boost.

I got a to play with this amp from a friend who bought it and was to be installed in his car. Since his car was being worked on for performance parts, I put it in my car for about a week. In the box were the birthsheet, manual and an MTX T-shirt. I took the amp out and installed it in my car. Installation was uneventful. I wired the power and ground cables on those giant terminals, hooked up a pair of Hollywood Soundlabs Excursion 15's in series/parallel for a 4 ohm load. I did not have any single voice coil 4 ohm subs to hook up for a 2 ohm load, which would have optimized the power from the amp. Nonetheless, the amp still puts out around 800w at 4 ohm, so 400w per sub should be fine. After the initial hookup, I set the gains to about 1/2 and kept the EQ feature off. The EBC2 unit is optional, and I did not have access to it, but I'm not a big fan of bass boost circuitry. I would have preferred a remote line level control, which would control the output of the subs at all frequencies instead of at only a single center frequency. Also, MTX should include this bass control unit instead of making it optional, as almost all others I have run across do so. Anyway, my HU has a subout level control, so I used it, though its not as easy to use as the knob based control. Upon initial listening, I was impressed with its output, even at 4ohm. My regular amp is a Crossfire CFA1000d, which was tested at 1200w at 1 ohm load. With roughly 2/3 the power, I barely noticed any loss in output from my subs. Everything sound fine as expected, and the amp ran stone cold most of the time, unless I played music with lots of bass continously, during which it got warm. Very impressive, thanks to its class D design. I was a bit skeptical of MTX's smooth heatsink design, which uses no fins. This decreases surface area for heat to dissipate, but the heatsink does have lots of mass, which contributed to the cool operating temperature. After running this amp for about a week, I have mostly positive things to say about it. It has tons of power (lots at 4ohm, and even more at 2 ohm), runs cool and has great power and ground input terminals. I do think that MTX could have used some better pots for the gain, crossover and eq feature. Its rather small, and hard to fine tune, and they could use some labeling. Also, as previously stated, I think MTX should include the remote module for free instead of as an option, and I prefer the type that varies all frequencies instead of a certain bass frequency.

Also, I would like to note that despite the fact that this amp puts out lots of power, and can draw signficantly large amounts of current at peak, for typical everyday usage, the stock electrical system should be fine for most average sized cars these days. My car has the factory 90amp alternator and a $50 autozone battery, and it works fine. I only ran this amp at 4 ohm, but my other amp is run at 1 ohm for 1200w and I only experience minimal dimming with very heavy bass notes. The MTX shouldn't draw much more current than the Crossfire. And remember as I stated above, effeciency remains high at typical music power levels. Running class D amps, with music, the average draw is 1/2 or less than a typical class A/B amp. So, essentially, that's like running a 700w or less class A/B amp, so don't be afraid to get this amp because your electrical system is stock. Most cars should have no problems with it, though some might result in some dimming. This amp is highly recommended. Job well done again, MTX.