The company Audiomatus, housed in Police, is specialized in making solid state, class D amplifiers. We tested earlier two products from that company: the monoblocks AM250 ver.R and the system consisting of a passive preamplifier PP03 and more powerful monoblocks AM500R (HERE). All those products showed the company in a very positive light. And this was really not easy, because amplification in class D is still something new, and there is still a lot of work before the engineers, and finally the audiophile world takes it with a grain of salt.

Just as a reminder – in class D the output transistors are either fully on or fully off. In theory, there are no transition states. Switching of the transistors happens very quick, usually with a frequency above 400kHz. But get any sound out of this “contraption”, the transistors need to be modulated in a certain way; what means the signal must be prepared before it reaches them. Class D amplifiers can work with PDM (Pulse Density Modulation) modulators, where the amplitude is depicted in the frequency an impulse appears – the more impulses per time period, the higher the amplitude – or with PWM (Pulse Width Modulation) modulators, where the width of the impulse is decisive, and not their frequency (density). The last method is very similar to the way, the DSD signal is coded on SACD discs. To retrieve a musical signal from it, we have to create a low pass filter in the amplifier. This is similar to signal processing in a digital to analog converter, this is also the reason, why class D amplifiers are wrongly called “digital amplifiers”. A power amplifier, with the power stage working in class D, can be analog or digital – in the last case, the number of levels (number of bits) is fixed, and in an analog one, it is in theory unlimited, the internal construction is the only limit. In fact there are very few true digital amplifiers on the market, like TacT and its “offspring”, sold under the name Lyngdorf, and recently the M2 from NAD. The new amplifier from Wadia 151PowerDAC mini, designed to accompany the iPod dock from that company, works in a similar way. The NAD utilizes technology designed by the British company Zetex Semiconductors, named “direct digital amplifier”. This name emphasizes the fact, that the signal entering the amplifier is a digital one, and the player works only as a transport. As the example of TacT, and now NAD, this has some advantages, like the ability to use a digital negative feedback loop, which adjusts the signal in real time (opposite to analog loops, which always introduce phase shifts). It eliminates also a DAC. This was appreciated by, for example, Robert Hadley, the editor in chief of “The Absolute Sound”, who praised the M2 in all possible ways in his review titled Inventing the Future of Audio (R. Harley, „The Absolute Sound”, December 2009, Issue 198, p. 136-145). Analog class D amplifiers work in a different way. First of all, the signal supplied is analog, like in a classic amplifier. And only in a modulator it is converted in a sequence of pulses. So for the common user, the amplifier looks exactly like any other, classic amplifier, it is just not so heavy and does not get that hot. This is just the result of the assets of class D – the efficiency of this constructions lies between 80 to 95% (in case of the AS500 it is rather low, in context of class D, 81%), so they practically do not get hot, and do not require costly, big heat sinks. And with powerful amplifiers, like the AS500, this is especially important – this is an amplifier with 2 x 590W @ 4Ω (and 290W @ 8Ω)! They do also not require big line power supplies – most class D power amplifiers work with switching power supplies, integrated on the same PCB, working within the same feedback loop, which corrects not only the power section, but the complete unit. The modules used by Audiomatus are of that type – those are ICEpower modules from Bang&Olufsen, modified in Poland for this particular device.

Audiomatus devices tested earlier:
∙ power amplifier (monoblocks) AM250 ver.R
∙ power amplifier (monoblocks) + passive preamplifier AM500R + PP03

SOUND

Discs used for testing:

• Criss Connor, Free Spirit, Atlantic/Universal Music Japan, WPCR-25171, CD.
• Danielsson/Dell/Landgren, Salzau Music On The Water, Act Music+Vision, ACT 9445-2, CD; review HERE.
• Kazumi Watanabe, Jazz Impression, east west, EWSA-1063, SACD/CD.
• Kings of Leon, Only By The Night, RCA/BMJ Japan, BVCP-40058, CD.
• Marilyn Moore, Moody Marilyn Moore , Bethlehem/JVC, VICJ-61467, K2HD.
• Michael Jackson, Thriller. 25th Anniversary, Epic/Sony Music Japan, EICP-963-4, CD+DVD.
• Sonny Rollins, Way Out West, Contemporary/JVC, VICJ-60088, XRCD.
• The Beatles, 09.09.09 Sampler, Apple/EMI Music, 84414 2 5, 2 x CD; review HERE.

Japanese version of the discs can be found on CD Japan

In a blind test, the AS500 can be taken for a strong, tube amplifier with KT88 power tubes. This sound, this way of presentation, this timbre, reminds me so much of the MC2275 McIntosh! I do not claim, that the Polish amplifier is as good, but I want to turn your attention to that, what – in my opinion – is most important to it: it has a very saturated, well balanced sound. Like all devices, loudspeakers, cables, etc, also the Audiomatus was compared to my reference amplifier, the Luxman M-800A, which costs ten times as much, weight five times as much and consumes much more energy. Only changing elements 1:1 in my system, I know what has changed. And after plugging in the Audiomatus, there were no significant changes in terms of presenting timbre. This is a very saturated sound. This is not the same kind of saturation, like from the MC275 Commemorative Edition McIntosh, because in the AS500 there are no such big virtual sources, but in this aspect, the Mac is hard to beat. And in this case, that competition is not needed here. The AS500 plays with a very mature sound, where the medium and lower range, are very well controlled. Looking at the parameters, seeing the maximum power output, it is hard not to imagine a monster, playing with a contoured, dreadfully precise sound. It is hard, but only reading the table with the specification, because after listening to the first disc – at least I think so – then we will reach the conclusion, that this is a “big tube” without tubes, which has nothing in common, with big amplifiers like Krell or Bryston. Did you ever hear an VTL amplifier, or the top Manley (like the Neo-Classic250)? That is the direction./p>

And at the same time the bass is really splendidly controlled. As I say, this is not due to hardening of the attack, we do not deal with a “clear”, what means random, power, but rather with something more physiological, something that moves us, audio-maniacs sitting in front of the loudspeakers, more. I am sorry for that “us”, but I sometimes personalize with my Readers… Anyway, this is a smooth, but saturated, and surprisingly detailed, bass playing. This can be heard very well with a contrabass, like on the disc Jazz Impression Kazumi Watanabe, Way Out West Sonny Rollins, as well as with synthetic bass from Thriller Michael Jackson. Those are completely different recordings, with completely different instruments, and the way those were recorded, and yet, they were connected by the AS500 with a common divider: they were strong, saturated and slightly soft – the latter just like my Luxman.

Low sounds got really very deep, and only with electronic power from Sounds Of The Universe we could hear, that on the deepest edge, it gets slightly rounded and loses some of its resolution. But the differences were incredibly small, and only expensive gear I tested, like the Krell EVO402, sounded better in that aspect.
Due to that shape of this sub-range, the sound is big. It is not “pumped up”, like in some amplifiers, especially the tube ones, but just big. The virtual sources were not flattened, or made smaller, and if the sax on the disc has a big volume, then it will be big, if Watanabe’s guitar is full and big, then it was reproduced like that. So the recordings from the disc Only By The Night Kings Of Leon sounded great. This is not the best recording made, and it lacks saturation. Medium class amplifiers tend to thin even that, emphasizing the slightly coarse treble. But with my Luxman, and with the Audiomatus, there was nothing like that. The disc sounded with fantasy, with a nice base, and much lower midrange. Because the midrange is big and saturated. Voices have big volume, and are reproduced a bit to the front. This is similar to what Cyrus devices do – the vocal is to the front and bigger, than I am used to. This is the reason, that the voice of Michael Jackson from Billy Jean, which is in reality weak, and placed deep in the mix, was stronger here, almost at the same level as the rest of the instruments. On the other hand, when everything is quite OK on a disc, like on Torchy!, where Carmen McRae sings, then the AS500 did not push the voice forward, it did not destroy the balance. Yes, McRea sang closer than with the Luxman, a bit stringer, but did not cover the instruments.

Till now I concentrated on the bass and midrange, so you could think, that now it is time to show problems with the upper ranges. But no. I left it for last, because Audiomatus succeeded in creating a class D amplifier, that does not have withdrawn treble, or a softened one. Usually such devices have a very smooth, creamy treble, where the upper part is visibly softer. This is where the comparisons to tube amplifiers and SACD discs come from. And the AS500 sounds with strong, well articulated treble. It is in a very good balance with the midrange, and resembles very much that, what I get from my Luxman. Its character is close to Cyrus and Naim amplifiers – we get a rich timbre palette, the attack is quite quick, but not sharp, and the timbre differentiation can be heard very well. This is still much more rounded sound, the cymbals are slightly smoother than with other solid state amplifiers (like the Aaron No.1.a or Cambridge Audio Azur 840A) and not as resolved.

And probably only in resolution and dynamics, and dynamics only in sense of differentiation, shading of the attack, we can look for this devices weaker points. In the end this is a product coming from human hands, and in addition a surprisingly cheap one. This is why we can hear, that the Polish amplifier unifies the sound planes to some extent, and although it builds a big, vast sound stage, still the instruments are shown close to each other, they are reproduced as one thing, something common, without special depth. But this is not something endemic, something that happens only to the Audiomatus, because other devices, for the given money, cannot differentiate the instruments on the stage either. It can be done better, but at a given price. For a comparable price, we can buy the integrated Cambridge Audio Azur 840A (II). It is a splendid, well equipped amplifier, beautifully made and nice sounding. And although it works in a class called XD by the manufacturer, it has nothing in common with class D – it is just a modified AB class unit. Aldo Cambridge is able to control many speakers, and reaches very low. And has a better selectivity. But it is “thinner” in terms of timbre, and none of the sub-ranges is equally saturated. Also the treble is simplified in comparison with the Audiomatus. On the other hand we have the Heed Obelisk Si (class AB) (test in a system HERE). This one has its timbre close to the Audiomatus, deep, dense and saturated. Its treble is nicely differentiated and has good “weight”. But is has no chance with the AS500 in terms of controlling the speaker and with reach of the bass. Here the Polish amplifier declasses everything that moves. This is why I have seen it power, without problems, the Magnepan MG 1.6/QR , and for me this a very big recommendation. Those panels show all the shortcomings of timbre in accompanying devices, and like to be controlled well. This is of course only one aspect, but a very important one. The other goes in a completely different direction –Harbeth bookshelf speakers, especially the small P3ESR, based on the legendary KEF LS3/5a. Those speakers are difficult to drive, because of the low effectiveness, and on the other hand, they love tubes – so two things, that are difficult to combine. Here the timbre and power of the Audiomatus will introduce and added value, like no other amplifier. Those are of course only examples, because I would give Dynaudio Excite and Monitor Audio Silver Rx a listen, but I would start with the ones I mentioned in the beginning.

DESCRIPTION

We have tested an Audiomatus amplifier before, which used the same B&O modules. But this time we deal with a stereo unit: the AS500 is a stereophonic amplifier working in class D. It is small and very solid. The front is made from a thick slab of brushed aluminum, where there is only one, red LED, which indicates power on state. Because the amplifier consumes only 15W when idle, we can leave it on all the time. The power switch is on the back. But fortunately it is big and easy to use. Above it, there is an IEC power socket. In the middle we have the fantastic, American RCA sockets, from the company Vampire Wire, and to the sides single loudspeaker terminals – nice Chinese products, used also by Rotel or Canor. And that’s it.

The enclosure is made from very rigid, heavy steel elements, and those are making the weight of the amplifier. Inside we will find two B&O ICEPower 500ASP, version I modules (identical to those mounted in the monoblocks). Those are complete modules, with integrated power supply. The signal is supplied by short interconnects, that come from small PCBs soldered to the RCA sockets, which seem to have a DC-servo circuits – two transistors and two capacitors. On the short internal loudspeaker cables double ferrite cores were mounted, which, create a low-pass filter, needed for the amplifier to work. The same cores were also used for power cables. Switching power supplies generate lots of high frequency noise, which is “thrown” into the power grid. So it is worthwhile to equip devices used together with the AS500 with mains filters, even the simplest ones, like Audience ones. Because the modules are bolted to heat sinks, that are also their supports, and those are on their turn bolted to the bottom plate, the whole enclosure acts as a heat sink. I think, that an integrated version of this amplifier would be a nice thing.

Technical data (according to manufacturer):
Output power: 2 x 290W/8Ω | 2 x 590W/4Ω
Load impedance: 4-16 Ω
Total efficiency (Po=500W/4Ω): 81%
Frequency response: 5Hz-80kHz
Dynamics (500W/4Ω): 112dB
THD+N (4 Ω/f=1kHz/Po=1W): 0,006%
Max. THD+N (4 Ω/10 Hz IMD (CCIF 14kHz, 15kHz/Po=10W): 0,0005%
TIM (3.1 kHz, 15kHz Po=10W): 0,003%
Input sensitivity for full power: 1V
Input impedance: 100kΩ
Damping factor (1kHz/8Ω): >1000
Input: 1 x stereo RCA
Energy consumption: idle 18W | max 1500W
Weight: 9.8kg
Dimensions (with feet and sockets WxHxD): 440 x 85 x 390mm