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?
|Specifications declared by the manufacturer:||
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.
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.
|What "under the hood" is:||
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.
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.
|Measuring the Parameters:||
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.
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.
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.