US Amps XT4000D Monoblock

A classic design of Class D bass amplifier with the terminals on one end of a slab of heatsink and the controls on the other. As well as gain and a crossover potentiometer control, you also get a sweepable subsonic filter. Both the crossover and the subsonic filter have really steep 24dB per Octave slopes that really cut the sounds fast below the frequency point selected. This means you can drive more power into a woofer without straining it or the amplifier’s ability to deliver very low energy-sapping tones. It can actually make your bass sound tighter and louder if you don’t own limitless cone area and wattage. The sticky-out bits are plated in Platinum which is both hardwearing and offers a good connection, so is actually better than Gold in my humble opinion. There is a set of line outs as well as the line ins which helps if your headunit has not got lots of RCAs hanging out the back like intestines.
The top bears a logo on a small oblong plate that has a blue LED in it, that matches the colour of the one on the end to indicate that it’s on. The power terminals are huge for the size of the amplifier’s chassis. Then I looked in the specs and saw that it is not vast in output at four Ohms load but goes bonkers as you load it down. The evidence of how it needs the juice to suck on to make the watts is right there on the panel. Three 40A fuses and a set of phat one over gauge power terminals. Designed with rugged internals, the amplifier doesn’t really seem to be too braggily designed and packaged but it does say that it’s good for a whopping one and a half kilowatts RMS into an Ohm. That’d be a dual two Ohm voice coil woofer or two woofers with single two Ohm coils or whatever but it does look as though this amplifier was designed to be run at nail-drivingly low impedances. The manual covers the whole XT Series and it looks good.
– Class D
– Works from 12V to 18V
– Platinum plated RCA stereo input
– Platinum plated RCA stereo line output
– 1 x 200w RMS @ 4 Ohms & 86% efficiency
– 1 x 450w RMS @ 2 Ohms & 84% efficiency
– 1 x 1500w RMS @ 1 Ohm & 76% efficiency
– MOSFET output devices
– Time-delay turn on with opto-coupled muting circuits
– Aluminium heatsink with black finish and blue LED lit logo panel badge on the top at the upper left
– Platinum plated 1/0Ga. Power Terminals with cross headed grub screw bare wire socket connection
– 0 to 12dB Bass Boost @ 45Hz (according to label on amp – says 30dB on website)
– Adjustable input gain
– Mono operation
– Frequency response 20Hz to 500Hz
– Signal to Noise Ratio 80dB
– Subsonic Filter settable between 15Hz to 40Hz with 4dB per Octave slope
– Low Pass Filter 40Hz to 250Hz with 24dB per Octave slope (Butterworth)
– Fuse Rating 40A x3
– HxWxD(mm) 64 x 400 x 222mm
– C/W Wired remote gain control and fixing screws and manual
Review by Adam Rayner
An old classic of a shape perhaps but the internals in here are things like high current MOSFET doodad devices and 35 nanosecond switching diodes. They wouldn’t talk of such things in the manual if this was a simple off-a-Chinese-factory-list type product. This is the result of many years of image building and product development. US Amps have been more famous in the UK in the past and have had their fair share of parcel-to-parcelling with ownership and distribution but the basic facts are that the design of this amp is a bit special.
Just look in the spec list a moment. Signal to noise ratio is standard for a Class D bass amp but the crossovers have 24dB per Octave slopes and so does the sweepable subsonic filter. You can even make it an SPL hitter by filtering all the way up to 45Hz which believe me, with a steep old slope like that, you can really hear slicing out the deep bass. The subsonic filter can be set all the way down to a near-infrasonic 15Hz, although as it is adjustable, I’d have loved to see that settable down at 10Hz for the real breath-pumpers. I set the subsonic at the lowest setting and carefully wicked up the gain and even played heavily with the remote bass gain pot-on-a-wire.
It was plugged into a cunning woofer called a HEX S12.4 made by Diamond Audio that looks like a cast pinecone has been rammed up it. It is in fact the front mounted magnet which is Neodymium and results in a nil-compromise sounding but very shallow mounting woofer driver. It was a fine SQ item as well as being a good and muscular transducer so it was used as the load for the amp.
I connected just one of the dual sets of speaker terminals (all terminals are simple crossheads rather than Allen headed.) which in the manual are referred to as requiring a 1 to 2 Ohms loading, also indicating that this amp is made for sucking on hard.
Lastly, the very voltage the thing can be run at goes nearly up to truck battery levels. Most bits of kit cannot do more than fifteen volts of power input. This puppy can run at 18V so the 16V battery-bank loons will adore this brand. Plus, it isn’t actually that big for what is a genuine 1.5 kilowatts in a box for three hundred smackers.
And here’s another fat indicator of US Amps rock hard intent. There are five logotypes on the box. You might recognise the EMMA one European Mobile Multimedia Association and the IASCA International Auto Sound Challenge Association one. But what about the CEA one? That’s the USA’s Consumer Electronics Association, a mighty organisation who run, amongst other things, the Winter CES in Las Vegas. Then there’s the MECA and USACi logos, standing for Mobile Electronics Competition Association and United States Autosound Competition international, respectively.
The US Amps guys are serious and this amp is really a bit a of a stealth job. Pretty branding with Xterminator and all, but we have seen shite in Maplins with Purple Throbbing Monster printed on it, so the ig’nant would tend simply to not believe the hype of any brand till it’s been tried but the bottom line is an amp that can run at 16V with a single Ohm of load and has the 120 Amperes of fusing and platinum plated one over gauge power terminals to prove it.
The output from the Diamond HEX S12.4 was musical and tightly gripped. It might have been easier to hear the amplifier itself had I grasped a �600 Morel Ultimo 12 woofer to check out the speed of the leading edge of the beats on one of the tracks on Spirit of Sound #6 but this amp is not about that sort of thing. If you want savage bass SQ, you will be buying a far more costly piece of kit (I gather the multi-brand distributor of these has that sort of product too) and so for the cash asked, this represents not just ‘good value’ but a serious bass head competition item, built like a brick outhouse and with one matter in mind.
Eating amperes and excreting watts!
Easily Recommended.
Overall 8.8
Sound Quality 8
Power Output 9
Features 8
Build Quality 10
Value For Money 9