During the testing of the amp, I was not surprised to see it meet all of the claimed performance specifications, exceeding them in more instances than not. With its regulated power supply design, the amp makes good power, whether at 14.4 volts or 12.5 volts, although as the voltage drops, the amount of current needed increases. Don't you love the laws of physics?
Distortion measured 0.06 percent at rated 4-ohm power at a battery voltage of 14.4 volts. The specs claimed a THD+N figure of 0.02 percent, which the amp did meet at a battery voltage of 12.5 volts. At any rate the difference is completely insignificant. The amplifier's efficiency was average for a Class A/B 4-channel amp: full power at 2 ohms per channel netted a 62 percent efficiency specification, which dropped to 55 percent at 1 ohm.
The frequency-response bandwidth of this amp was excellent: basically flat from under 10Hz to over 90kHz. This is a nice spec and it speaks to the quality of the parts used, but it really doesn't make an audible difference because the compact disc format uses very steep lowpass anti-aliasing filters at 20kHz that prevent any higher-frequency information (fundamentals or harmonics) from ever entering the amplifier to begin with.
Now is a good time to present a slightly different point of view on a commonly mentioned specification, slew rate. While still a relevant measurement on a bandwidth limited Class D amplifier, the fact is, slew rate is a more or less meaningless specification in a modern Class A/B amp.
Why? Back in the day when transistors were in their infancy, there was a need for audio devices to be able to reach their full switching voltage as quickly as possible. Remember, the ultimate goal of an amplifier is to mimic the input signal exactly, while adding gain. The term "slew rate" is used to define the maximum rate of change of an amplifier's output voltage with respect to its input voltage. In essence, slew rate is a measure of an amplifier's output section's ability to follow its input signal. The unit of measure is volts per microsecond.
Slew rate is usually measured by applying a high-frequency square wave input signal and raising the level to the clipping point of the amplifier. Since the perfect device doesn't exist yet, there will always be some tiny amount of time required for the voltage to rise from zero to maximum. To find the slew rate, you simply look at the output of the amp on an oscilloscope and measure the voltage difference and the amount of time it takes the voltage to rise. Then you divide the voltage difference by the time segment. This is why the slew rate spec is stated in volts per microsecond or V/s.
For many years the speed of the output transistors was the limiting factor in the high-frequency limitations of audio power amplifiers. Consequently, a lot of claims were made about the superiority of this or that amplifier based on a good slew rate. The fact is, slew rate has very, very little to do with the sonics of a modern Class A/B amplifier. These days, transistor technology has improved so dramatically that even relatively slow devices are more than adequate for audio bandwidth purposes. In fact, the slew rate of most A/B amplifiers is from three to as much as 50 times the required slew rate for linear amplifier operation! So, when examining the specs of a Class A/B amp, don't put much weight on the slew rate specification. Because of this, I'm not going to quote an actual slew rate spec, but as the folks at Rolls Royce say when asked horsepower numbers, "Rest assured, it is more than adequate".
There are a couple of other specifications that are over-weighted in terms of real world performance as well, but I'll leave that discussion for another time.
Now, back to the 4200SE... I measured the crossover settings and slopes and found them to be reasonably accurate and functioning as advertised. If you have never heard the difference between a 12dB/octave to a 24dB/octave crossover, you should. I always prefer the steeper filter slope on a subwoofer to minimize high-frequency output and subwoofer localization. Also, it would be worth noting that if you have a -12dB/octave crossover set at a specific frequency and simply flip the switch to 24dB/octave, the -3dB frequency point changes as well. Bass boost measured 0dB to+18dB maximum, with the frequency of boost adjustable between 20Hz and 80Hz. An enterprising installer may realize that the 30Hz highpass filter setting could double as a subsonic filter as well, creating another way to use the amp's bandpass crossover function.
The amp measured well in all respects and protected as it should when I deliberately shorted the outputs. I did drive the amp to full power into 1 ohm, and although I twice blew the 3 x 40A fusing, the amp made prodigious power into 1 ohm and would most likely not blow the fuses with a dynamic musical input signal.
The 4200SE is also equipped with a balanced input jack in the form of a RJ45 connector, not unlike those used for computer networking. Instructions are provided on how to connect the speaker wires of a source unit directly to these inputs, although no connector or wiring is provided.
Thermal performance was measured, and this is one of the better 4-channel amps from a thermal perspective. It easily passed our usual battery of tests and surpassed the performance of many other 4-channel amps by a wide margin. The fan-assisted cooling system on this amp works, and works well. I did notice that as the test progressed, the illuminated logo would turn from blue to red occasionally, and the hotter the amp got, the more frequently this would happen. I didn't find any definitive explanation as to what this meant, but it occured to me that this could be temperature related.
The owner's manual is a rather large book, with a total of 14 pages, covering all the models in the Signature Edition line. I found it reasonably complete and it has excellent diagrams to help you understand the uses and settings of the various controls and connections. Features and common adjustments are clearly explained in a common sense, non-technical manner, so those of you who aren't propeller heads will have no trouble getting the amp dialed in properly.
The only notable exclusion in the manual (and I looked for it for a while) was an explanation of the top lighting turning from blue to red during the amp's thermal testing and protection phases. Extremely curious, I contacted Arc for an explanation. They stated that "the lighting on the amplifier starts blue for normal operation and as the amplifier increases in temperature the lighting will change colors. More frequent color changes indicate that the amplifier is operating closer to its thermal limits -- peaking a solid red as it goes into protection."