Police is a small, with not even 35000 inhabitants, city in north-west part of Poland. It is a river and sea port on the Oder, in the Wkrzańska Forest (what a SPELLING!), not far from Szczecin, a colony of Greek refugees from the times of the Greek domestic war from the years 1946-1948 – those are the information bits we find in every guide, and Wikipedia. But I did not find any information, that Police is the homestead of the company Audiomatus, the Polish manufacturer of switching amplifiers (class D).Well, this needs to be changed.
We tested the amplifiers made by this company three times already, the last one was AS500, a stereo power amplifier in a newly developed enclosure. The AS250 we test now, is less powerful, although identical on the outside. Looking at the technical data, the amplifiers are not far apart, although we have to admit, that in some points the AS500 looks better – for example it is 1kg heavier. This is maybe nothing, but this is 10% of the weight of the amplifier. How an amplifier with an output power of 2 x 500W (at 4Ω) can weight only 10kg? When it is an switching amplifier. I use this name exchangeable with “class D”, because there is still no clear name for this class of devices. The names used are “Switching Amplifier”, “Class D Amplifier” or “Digital Amplifier”. I think, that the name “Switching Amplifier” is closest to the description of the class, as it encompasses both kinds of class D amplifiers. Those are analog and digital. Their biggest difference is the number of levels used by the PWM modulator – in the first ones it is unlimited, in the second one fixed, and most often the equivalent of 8 bits. There are of course other differences, related to the feedback loop – digital or analog – with the sound path, which can be digital or analog as well, but the first difference is the main one.

The company Audiomatus uses analog switching amplifiers since the beginning of their existence, being the end of the year 2002 (please see the interview HERE). After listening sessions, comparisons, measurements, etc, and also after analysis of the possibilities to improve the complete modules, they chose the offering of the company Bang&Olufsen. This Danish specialist is usually associated with expensive and very expensive designer systems. And this is true – exterior design of B&O are breathtaking, due to innovation, ideation and harmony between form and function. But design is not everything. It is true, what Kalle Hvidt Nielsen, the CEO of B&O said: “Let the beauty of our products seduce you, but also do yourself the favour of going beyond the looks and let yourself be amazed, surprised and impressed by the outstanding technologies on which the Bang & Olufsen products are based.” (source: HERE). And this is not a boast – this Danish company has patents related to almost any audio product, and we used them not even knowing about it. One of the most important technologies from B&O, used in their own products, but also sold to other companies, is the ICEPower module, being an switching power amplifier. Those modules Audiomatus uses in their amplifiers, standing next to companies like, for example, Jeff Rowland, who uses them too. B&O modules are ready for use just after unpacking, because those are compact PCBs, containing and amplifier, power supply (both within a feedback loop), bolted to a heat sink. Audiomatus talks about some changes it introduces to the project. I do not know what they are, but they are surely not big. The differences in sound between amplifiers based on those modules are based on three variables: input circuit, output filters (so called “reconstruction” filters, just like in a DAC) and the enclosure. I heard many amplifiers of that kind, and I was always surprised to the variety of sound they presented. Some aspects were similar, the foundation is the same, but the final effect is – really – very different. Also the Audiomatus amplifiers sound different than others. And there is something more – nobody else offers so solidly applied ICEPower modules for such a low price.

We tested:

• Monoblocks Audiomatus AM250 ver.R
• Monoblocks + passive preamplifier Audiomatus AM500R + PP03
• Stereo power amplifier Audiomatus AS500

SOUND

Discs used for testing::

• FIM Super Sound! II, First Impression Music, FIM XR24 067, XRCD24; review HERE.
• Frank Sinatra, I Remember Tommy…, Reprise/Universal Music Japan/Sinatra Society of Japan, UICY-94599, SHM-CD.
• Jim Hall, Live!, Horizon/A&M Records/Universal Music Japan, UCCM-9225, CD.
• Laurie Anderson, Homeland, Nonesuch, 524055-2, CD+DVD.
• Maria Callas, Maria Callas Live, EMI Classic, 3 31461 2, 8 x CD.
• Martin L. Gore, Counterfeit e.p., Mute/Sire, 9 25980-2, CD.
• Michael Jackson, Thriller. 25th Anniversary, Epic/Sony Music Japan, EICP-963-4, CD+DVD.
• Pery Como, Como Sings, RCA/BMG Japan, BVCJ-37258, K2 CD.
• Savage, Tonight, Extravaganza Publishing Srl/Klub80, CD001, 25th Anniversary Limited Edition, CD.
• Stan Getz Quartet, The Soft Swing, Verve/Universal Music Japan, POCJ-2721, CD.
• Tsuyoshi Yamamoto, Autumn In Seattle, First Impression Music, FIM XRCD 043, XRCD2.
• Vera Lynn, Golden Greats, Disky Communications, MP 790102, 3 x CD.

Japanese versions of the discs available on CD Japan

If you can remember, some time ago Audiomatus offered a passive preamplifier. But not any longer. Since some time they work on a reference preamplifier – but this work is being delayed. I asked Mr. Andrzej Matusiak, the owner of that company, about that, asking also about a possible integrated amplifier, as a natural addition to the offered product line:

“There is no integrated amplifier in planning. I tried the idea twice, we have even built two prototypes of integrated amps, but we could not achieve satisfactory results at reasonable costs. Switching amplifiers influence other circuits placed in the same enclosure in a negative way. So complicated and expensive shielding is required, and still the result is worse, that with a preamplifier and power amplifier in separate boxes. Currently works on a SET preamplifier, with C3m tubes, battery biased, are very advanced [I’ll just remind, that the preamplifier Ayon Audio Polaris II uses those tubes, and I use this preamplifier in my reference system – editors note], with output transformers and without any feedback loop. We have tried stock transformers from Lundahl, Electra Print and Cinemag, now I am waiting for custom trafo’s from Lundahl and Cinemag. Electra Print went out of the competition. All this takes time. Initially the preamplifier was to be introduced in the beginning of September, but the time needed for the custom transformers to be manufactured stretches, and I am not sure, if I will be ready in the beginning of November.”

And everything is clear. This is the reason, that I used the amplifier with my Polaris II, the Manleya Jumbo Shrimp and the Accuphase C-2410. I attached it also directly to the variable output from my CD player Ancient Audio Air and the output of the Benchmark DAC-1 PRE (USB version HERE), which I tested for “Audio”. This is not the full scale of possibilities, as I did not have the opportunity to try a passive amplifier, but one thing was clear from the beginning – the device sounded better attached to a tube preamplifier or the CD, which also has a tube output. So it seems, that a passive preamplifier may be a good choice. But the problem is in the price of the Audiomatus, completely incredible, taking into account how it sounds. Because there is no good tube preamplifier to be found for comparable amount of money. But I warmly recommend to try it with the CD-07 Ayona, or – even better – with the mentioned Manleyem or the preamplifier Absolutor – it will be beautiful!

The Audiomatus amplifier has a very smooth, incredibly pleasant timbre. Rephrasing the Merovingian from the second part of the Matrix (dir. Andy and Larry Wachowski, 2003) listening to music with the Audiomatus is like wiping your arse with silk… Music sounds in a hypnotizing way, draws us into its own world, similarly to some tube amplifiers. I will not run away from this comparison. It is repeated in tests of class D switching amplifiers quite often, especially when we deal with B&O modules. Probably they were tuned like that, and their creators did not want to fight their shortcomings, but rather use them to their advantage. I noticed this smoothness, silkiness and slight warming while listening to the disc Golden Greats Verra Linn, with old recordings, limited frequency response, weak dynamics, etc. The whole was shown in a nice way, but as a whole. Linn’s voice was round, warm and had a very well reproduced volume, what means, that it had significant size, and was not squeezed out like a raisin. This is important, because the Audiomatus does not narrow the sound to a point, but rather shows something like a sphere – an instrument of significant size and around it a kind of “fluid”. This is the reason, that monophonic recordings sound so well, so natural – the sound comes perfectly from the middle line between the loudspeakers, but it takes some space between them, and it is not a sharp knife looked at from the edge.

The midrange is without question the most important subrange in this amplifier. It is fondled, strong, saturated. Sometimes, like on the disc Live! Jimmy Hall, where the leader’s guitar is very warm, the sound of the Audiomatus goes a step too far in the direction of saturation and warmth. Not that it is unpleasant – in contrary, it sounds incredibly nice, but then the sound lacks some edge and differentiation of the playing – everything has similar timbre. Especially in the midrange, so in the place, where Hall’s guitar operates. In general this is a very good way to have a sound, that will resemble much one of very elaborated, total systems, at a fraction of their costs. There is nothing dangerous in it, nothing painful. This is a sound, with which you can listen to music for hours without getting tired, without irritation, even at high volume levels. And it does not need to play loud, the AS250 will sound well at low and at high volume levels, no problem there. Of course the sound will be best at a certain level (we have to find it ourselves, and it will be different for each and every recording), what is the result of discs being recorded and mastered at a certain sound level in the sound recording studio. But in this case the differences are not so big, so that we do not have to adhere to this strongly.

And although the midrange is ruling here, the vocals are not especially favored – neither in terms of timbre, nor space. Frank Sinatra and Perry Como, from discs issued in two years distance, but very distinct in timbre, had the right volume, rich tonal colors and dynamics, but did not jump in front of the instruments. With pop recordings, like Michael Jackson or Savage, we could even talk about slight absorption of the voices by the background. Those recordings are difficult to reproduce, because we need really outstanding resolution to extract the voices in them, and show them as independent points. Audiomatus does not cost really much, and is no champion in that aspect, this is why Jackson and Zanetti were placed in one line with the instruments.

The way the AS250 sounds has influence on how the sound stage is constructed. Although the voices do not stand in the first row, yet the first plane is most important here. It is dense, pithy, many things are happening here – this is absolutely different to most solid state amplifiers in the 5000zł price range (we need to add a preamplifier to the AS250), which come out battered from such comparisons, offering nothing but “points” on the sound stage and attack. Audiomatus has such a slightly softened attack, that the sound is fleshy, palpable and close. This results in the effect of the presence of instruments, the sound is big and it makes a good impression. But the further planes are shown worse. Maybe not even worse, we should rather say, that our attention is not concentrated there, so they seem quieter. The recordings are not flat, because the vividness of the things near to us is splendid, but it is hard to talk about swing – when in the recordings from the sampler FIM Super Sounds! II the orchestra enters, then it is shown by the Polish power amplifier as one mass, in a way interesting in terms of timbre, but without perspective. Even such recordings profit from big sound. But it seems, that smaller ensembles sound nicest, jazz, solo recitals, quartets, etc. In their case the attention of the listener is concentrated on the close plane, and depth plays a lesser role, than with a large orchestra. And here, if I remember well, is one of the differences between this version and the stronger AS500. The more expensive amplifier was also not outstanding in terms of sound stage, but it fared better than the AS250, it sounded with greater swing, and this made the depth seem better.

Like I say, the Audiomatus sound similar to tube amplifiers, like the Leben CS-600. It means quite a warm sound, and the resolution not as good, as in other amplifiers from the 5000-10000zł price range. But this is not “sticky” sound. To see how differentiation of this device works I compared a few discs together – most of all two different pressings of the solo EP from Martin Gore Counterfeit e.p. and two version of the recording Autumn In Seattle Tsuyoshi Yamamoto. In the first case only the pressing is different, and both versions come from USA, and were issued on Mute license by Sire. One of the discs was pressed by WEA Manufacturing Inc., in Olyphant Pennsylvania, and the second one somewhere else – there are no marking on the disc. There is of course a variable I do not know nothing about, which subsequent copy it is (XRCD is pressed in a very limited number of copies from a given matrix, this is one of the reasons for the high price of those discs), this is why this will not be a “clean” comparison. But the differences are significant, so I will forget about the hole in the research. The more, that Audiomatus showed them quite clearly, and correctly. The WEA version is more resolved and better settled. The unmarked disc sounds in a more dynamic way, but in the form of “attacking” the listener. WEA differentiates the timbre of individual elements better and combines them together better. The treble is treated in a different way – clearer on the WEA and withdrawn on the other disc. The element, in which the AS250 did not show many differences is the midrange. In both cases it was warm and shown rather as one event, although on the WEA it is a bit more differentiated. So I knew, that Polish amplifier, despite its limitations, differentiates the recordings well. Better than – seemingly – better resolving, open and having a better attack amplifiers Cambridge Audio Azur 840A and Marantz PM8003. In case of the tested power amplifier it was not about showing of things “outside”, in a way of speech, about underlining differences, but about showing how this influences the whole emission. Thus the differences found by it are built into the sound in such a way, that we do not notice them directly, but we perceive the whole sound differently. This was confirmed when comparing two version of the recording Autumn In Seattle. This is the title piece from the 2001 recording of Tsuyoshi Yamamoto, written by this Japanese musician especially for Winston Ma, the owner of First Impression Music. So it should not come as a surprise, that Mr. Ma issues this disc each time, when he finds a better way of transmitting music. So I have this recording on an XRCD2 and XRCD24. I wrote about that some time ago, but it does not hold me from repeating: XRCD2 sounds fantastic. This is a very resolving and dynamic version. But you need to listen to the XRCD24 to know, what it misses. The 24 bit signal processing (because this is the only difference between them) resulted in a more natural, more – I have to say that – “analog” sound, in the sense, that the midrange is warmer, and not limited from the top, and it is also more coherent. It was clear with the Audiomatus, and I did not need to listen very carefully to confirm this difference once more.

The AS250 is a splendid amplifier. But it has a clear character, thus is not a universal device. It is easiest to compare it to tube amplifiers with the EL34 on the output, for example – like I said – to the Leben CS-600. Both have a very comparable timbre, dynamics and resolution. They differ with the stronger treble of the Audiomatus, also sweet, but still more visible. The higher midrange of the AS250 is slightly withdrawn, hence the “safety” of listening. But if the Polish amplifiers sounds like a tube amplifier, why buy it, and not some tube amp? I prepared some arguments in its favor:

AS250 does not cost much, and even if we add a preamplifier to it, still this combination will sound better than most tube amplifiers for that money.

AS250 is small, does not get hot, so it is safe for to use (kids!) and can be placed even on small shelves

AS250, although it has a slightly round, similar to a good tube, bass (not as well controlled as in the best solid state amps for the money), then it sounds almost as well, without any change, with difficult and easy, small and big, loudspeakers. The tube does not.

Dynamics and distortion of the AS250 are not dependant on the volume level, and the timbre does not change with the volume being turned up.

Its elements do not age as tubes do.

AS250, at normal operation, does not need any servicing.

AS250, due to high efficiency (up to 82.5%),is very environment friendly (as it is to the household budget). I think, that it is much, even for the tube lovers. The best amplifiers with tubes on board, for comparable money, like the Linear Audio Research IA-30T, Leben CS-300 X(S) or Manley Stingray have some more breath in the sound, are more resolving and are … tube amps. So as usual, it will be the case of assumed priorities, housing abilities, rest of the system and ideology.

DESCRIPTION

AS250 is a stereo power amplifier, working in class D, in analog mode. Its dimensions are identical with the dimensions of the more expensive version AS500, the amplifiers only differ slightly in weight. Despite the high power, the amplifier is rather small. This is the result of using class D modules, mostly due to their high efficiency – the manufacturer quotes 82.5% (at full power) while a classic AB class amplifier has an efficiency of 40-60%, and in class A even half of it. This means, that less power is dissipated as heat, and in consequence, big, heavy and expensive heat sinks are not necessary. The unit is made extremely carefully, on a normal, world level, never suggesting a small series production. The front is made from a thick slab of brushed aluminum, and there is only one, red, LED in the middle of it. The chassis is made from thick, steel plates. To make it additionally rigid, the top cover is mounted to the lower with 14 bolts. On the back we have two pairs of nice, Chinese, gold plated loudspeaker terminals and splendid, American RCA sockets. There is also an IEC socket with a mechanical power switch on top of it. The inside is very clean and neat – actually there are only the modules and cables. On the input there are small PCBs with a DC-servo circuit, from where short cables lead the signal to the ICEPower modules. Those are the 250ASP Ver.1. Most part of the module is taken by the power supply, a switching one, filtered with a “Pi” filter from the AC side. As it is commonly known, switching power supplies generate much high frequency noise, which we have to get rid of. Hence additional filters in the form of ferrite cores on the power cables – those are separate for the left and right channel. The filtering capacitors in the power supply are not big – those are mostly two Elna 200μF each (for 200V) and some for lower voltage, also from Elna. On the output we have the HIP4081 HV Labs driver, which controls the output MOSFETs, working in a bridge. In this case we have two pairs of transistors per channel. Those are mounted with clips to an aluminum heat sink, on which the whole module is placed. This heat sink is bolted to the lower plate of the cabinet, so the whole enclosure works as a heat sink. The loudspeaker output is coupled with the terminals by means of two ferrite rings, placed on loudspeaker cables, which create a “reconstructive” filter. Nice, solid work.

Technical data (according to manufacturer):
Output power: 2 x 130W/8Ω | 2 x 250W/4Ω
Load impedance: 4-16Ω
Total efficiency (Po=500W/4Ω): 82.5%
Frequency response: 5 Hz-80 kHz
Dynamics (130W/4Ω): 108dB
THD+N (4Ω/f=1 kHz/Po=1W): 0.0055%
Max. THD+N (4Ω/10Hz<20kHz/100mW<500W): 0.1 %
IMD (CCIF 14kHz, 15kHz/Po=10W): 0.0009%
TIM (3.1kHz, 15kHz Po=10W): 0.003%
Input sensitivity for full power: 0.73V
Input impedance: 100kΩ
Damping factor (1 kHz/8Ω): >1000
Input: 1 x stereo RCA
Power consumption:
- without input signal 14W
- max 700W
Dimensions (with feet and sockets; W x H x D): 440 x 85 x 390mm
Weight: 8.8kg