So, again we are keeping in our hands an interesting sample of foreign digital car amplifier. This time the guest is from Brazil, where the company Stetsom has successfully developed and produced car-audio components since 1989. But what could catch the interest of our Laboratory in this sample, among the great number of analogues? Here the saying "Best things come in small packages" is very suitable, because the committed output of this amplifier is up to 3300 watt, but outer dimensions and weight are really diminutive. Such ratio of output to kilos/square centimeters is extremely intriguing. One more interesting fact is that frequency band is very wide for digital monoblock - up to 15000 Hz. So, let's examine this Brazilian more intently.
The package content was nothing of surprise: dense cardboard box, users manual in English, leaflet with interpretation of system error indications, amplifier itself wrapped in the leakproof polyethylene. There is no remote bass controller, and not even a jack on the case for it. Overall outlook of the amplifier is rather ordinary: corrugated aluminum radiator with grey colored powder coating, enclosed in black pressed plates of top-, bottom- and side-covers. The ascetic emblem of Stetsom is placed on the top cover.
Now let's talk about the jacks and controls. On the one hand everything is usual and banal, but there are also pleasant small things. Firstly, 4GA AC power plugs, remote and double-contact jack 8GA that are placed on one side, have uniform size of fixing screw, which is convenient while setting. Secondly, low-pass filter, high-pass filter and level controls are placed on the other side and are implemented as large knobs, what helps to execute fast and accurate setting that doesn’t require additional tools.
Insides of the amplifier turned out to be a little bit unusual, because there no space for placing the multitude of fieldistors. Brazilian engineers have used the simplified circuit of power module with lower coefficient of efficiency, and have created the original converter. The digital part is rather peculiar, but we can talk of success of implementation only after measuring the parameters. The quality of soldering turned out to be not very high and it is rather sad, because even in the output stage the poorly soldered spots can be seen. Let's put mark 4 with great reserve out of 5. The hand assembling has the acceptable quality. There is sufficient amount of heat sink compound and all elements are fastened tightly, that secures good cooling in the process of work. All the inductance and transformer coils are of hand winding and have good varnishing. Power connectors and output connectors do not have gilding, but are covered with simple anodic coating. The single high-speed fan for cooling the system can be seen inside.
What disappoints, it is the noisy buzz of the cooling fan after switching the amplifier on. The developers have not put the circuit for measuring the rotation speed of fans according to the temperature of amplifier, although noise can be heard even inside the car. Another disappointment is high noise background of Stetsom digital transformer. When the amplifier is working it is impossible to listen to the radio, especially if the signal of the radio station is not very strong. That's all about disappointments. I was very impressed by the indication system, which consists of three light diodes: the first indicates the beginning of the "clip", the second one signals of protecting cutout, and the third that informs that the amplifier is on, and what is also very important, indicates the nature of the error at the event of automatic shutdown for exciding the limits of the allowed supply voltage, overheating or short-circuit in the output system.
And now we shall test the compliance of the specifications declared by the manufacturer. Let's start with amplitude-frequency characteristic. I should say that we didn't expect to get acceptable outcome at the segment 20-15000 Hz, because for amplifiers of D-class any frequency higher than bass range, comes hardly. The result gladdened us - the declared variation of 3 dB was even a little bit higher - 3.7 dB, but as for the rest the AFC was rather smooth without high peaks and slumps. Now, a couple of words on Harmonic distortions: the result of the measuring was expectable: in the bass range the index of harmonic distortions fit in 0.9%, as it was declared by the manufacturer. Though when we started increasing the generator frequency, distortions crept up, but even at the end of amplitude-frequency characteristic they didn't exceed 3%. And finally, the most anticipated data - Output. I should mention that we didn't have at hand the 14 volt power supply with power 4 kilovolt. That’s why all the measurements were taken with voltage level - 11.8-12.2 volt. The Brazilians made us forget of all imperfections when we carried out the measurements and the capacity was really unsurpassed for such dimensions. While measuring the low coefficient of efficiency of the power module was felt at once, that’s why for efficient use of this amplifier, you should have good accumulator and generator. Let's pass from words to deeds - here is the table:
And this was with voltage of about 12 volts instead of 12.6 declared!
Of course, tweeters and mid-range speakers should be amplified more carefully, as the character of sound is overlaid with D-class. But I think it is not the task of such amplifier. But concerning basses and Mid-basses, everything is in order. Bass is smooth, energetic, nonmetallic but a little bit 'muddy'. Rather high level of control can be perceived. Musicality is on a good level. What about pressure, here is what my assistant said during measurements: "Stetsom was born to kill with the bass, but not to caress the ear".
Definitely I can tell that this amplifier is unique. Taking into consideration its output to square centimeter and kilo, the minuses we have mentioned, such as loud cooling system, high level of noise of digital transformer, low coefficient of efficiency of power module are compensated with high output, compact size and decent sound. Conclusion could be that Brazilian, definitely, will suite the SPL competition lovers, or those who wish to put 10 mid bass speakers on one door. Quality-price ratio is optimal for SPL.
