Kenwood Excelon XR-4S Reference Fit Amp Review

A Test of Kenwood's Compact Amp

Back in the day, the car audio customer didn’t feel like he was getting his money’s worth unless the woofer or amplifier he bought weighed at least as much as his spare tire. Surfboard-sized amplifiers and subwoofers that required a trailer for the magnet were all the rage. An added benefit was that you only had to pay for lowering the front of your ride—the weight of the system took care of the back!



Efficiency boosting technologies like Class D and Neodymium magnets were around, but there was not much demand for them. Maybe it’s the price of gasoline, or the fact that we’re driving smaller, greener cars. Maybe we’re just more environmentally conscious these days. Or it could be that people want easier install solutions for amplifiers. Certainly compact amps make life easier for installers. Whatever the case, efficiency is becoming a stronger theme in the audio world. Savvy audio enthusiasts want higher performance than ever, while demanding smaller and lighter components. And where there is more demand, technology advances…
 
Product Description

The Kenwood Excelon units have long been the most highly regarded products in the Kenwood family. Even if you couldn’t afford it, we all knew it was good stuff. And one of the best units in the Excelon family is the XR-4S Compact full range Class D amplifier.

The XR-4S is a four by 120W amplifier that measures a tiny 9-¼ x 7-9/16 by 2-1/16 inches. Each pair of channels sports a switchable dual range 12dB per octave crossover that can be set for highpass or lowpass operation (or off, of course). For the low range, the frequencies go from 50 Hz to 200Hz, and 2.5kHz to 10kHz for the high range.

All controls are on one end of the amplifier, and all the connections are on the opposite end. The amplifier is all black with rounded corners, and the connectors are all recessed under the endcap for a very neat installation. The power connectors accept 4awg cable and the speaker connectors will take up to 8awg. There are two 30A fuses on the connector end.

Inside

Well, you’re definitely getting your money’s worth in here. Sure, it’s a small amplifier, but there’s a lot of stuff in here, and it’s all very tightly arranged to fit into the small package.



There are two smaller aluminum heatsinks: one has all of the power supply switchers and rectifiers mounted to it, and the other is a heavier piece with the output devices attached. When the amp is assembled, these two blocks are thermally connected to the outer case. Framed between the blocks are two large capacitors, dual power supply transformers, four sets of output inductors and capacitors, three power filtering inductors, and a myriad of smaller components on the main board.

The input connectors, low level controls and all the processing circuitry is actually on a second, smaller circuit board that is connected to the main board by way of a 23 conductor ribbon in zif connectors. Oh, yeah, there are also two small cooling fans attached to the case.
 
On the Bench

Power measurements came in better than rated. At 1.0% THD+N and 14.4V, each channel puts out 127 watts into 4 ohms and 155 watts into 2 ohms. Measured frequency response is 3Hz to 40kHz (+0, -3dB), so you won’t miss anything. The crossover frequencies came in right where they were supposed to be, and the signal to noise ratio (CEA2006) was right on mark at 73dB. (The noise did go up substantially when the cooling fans were running, but you’ll have the music too loud to notice if you get the amp warm enough to turn on the fans!)
 
Measured

Output Power:

14.4V B+, 1.0% THD + Noise, all channels loaded
 
4 x 127W @ 4-ohms Stereo
4 x 155W @ 2-ohms Stereo
2 x 308W @ 4-ohms bridged
 
Manufacturer rating:
 
4 x 120W @ 4-ohms Stereo
4 x 150W @ 2-ohms Stereo
2 x 300W @ 4-ohms bridged



Frequency Response measured:
 
3Hz to 40 kHz (+0, -3dB)
 
Manufacturer rating:
 
20Hz to 20kHz (+0, -1dB)
 
Signal to noise ratio (CEA 2006): 73dB
Manufacturer rating: 73dB
 
Conclusion

In my opinion, 120 watts per channel is perfect for driving a high quality set of component speakers for the front and rear corners. Even better, the crossover ranges make it a great choice for biamping a single set of high quality components. At 80 cents per watt at retail, this is quite an affordable unit. Efficiency at max 2-ohm power is a respectable 69%, rising to 72% at rated 4-ohm power.
 
If you’re looking at this amplifier, you’re probably also checking out the Alpine PDX4.150 (MSRP $750) and the ARC 125.4 (MSRP $519). The Alpine is also a Class D unit, but uses Direct FET technology. It puts out more power than the XR-4S (cost per watt is about the same) but has a more limited crossover frequency range of 30Hz -300Hz vs dual ranges on the XR-4S. The ARC is actually a Class G amplifier rather than Class D, putting out less power (about 20% less). It also has more limited 40Hz to 500Hz crossovers and has a bass boost for about the same price. Efficiency at max 2-ohm power is a respectable 69%, rising to 72% at rated 4-ohm power.

MSRP $499
 
Visit Kenwood for information on the Reference Fit amps.