LINE PREAMPLIFIER + POWER AMPLIFIER AUDIOMATUS PP03 + AM500R WOJCIECH PACUŁA Translation: Krzysztof Kalinkowski

Audiomatus is a Polish company. Their main points of interest are analog power amplifiers operating in class D. It is worth to mention, that those should not be confused with digital amplifiers – the latter, although also working in class D, have a bit different way of work. In analog class D amplifiers the analog signal goes in and is converted in a sequence of pulses with variable width (in PWM amplifiers – Pulse Width Modulation), or, with a constant width the number of pulses in a given timeframe vary (PDM – Pulse Density Modulation). Almost all class D amplifiers available now on the market use the first technique, the only amplifiers I know that used the second technique, where the amplifiers from Sharp. Anyway, in analog PWM amplifiers the number of impulses is theoretically unlimited – the upper limit is set by the switching ability of the bridged MOSFET output transistors. Most often this frequency is set in the range of 400-500 kHz, what allows achieving high frequency range. In digital class D amplifiers the number of pulses is constant, and relates to 8 bits (the input signal is changed to this value) what gives 256 possible levels. It is worth to mention, that the only digital amplifier I know is the Danish TacT (with a second incarnation in the form of Lyngdorf).

The main assets of such amplifiers are high efficiency and small dimensions. This allows constructing small devices of high power – like the AM500R: in the small boxes we find monoblocs with a power of 500W at 8Ω and 1000W at 4Ω (the dynamic power of the class D amplifier is quite limited, unlike class A and AB amplifiers). It must be said, that small dimensions and low temperature of the output transistors are a fact, but the efficiency is quite problematic. It is said, that the class D amplifiers have an efficiency of 95%. This is true, but only if the amplifier operates at full power. The measurements done by Paul Miller, the editor in chief of “Hi-Fi News” show that at medium volume level this parameter drops to about 20%. This is still a lot, so the European Committee recommends those amplifiers as not contributing to the global warming. We might face a situation, that the class A, and even maybe AB, amplifiers will be subjected to additional “climate” fees. So those will become more expensive as those fees will be charged to the end user. Another problem of class D amplifiers is the susceptibility to loudspeaker cables and loudspeakers themselves. And this is not even about their quality, although this has some influence, but about the construction of the cable and the impedance curve of the speakers. On the output of the amplifiers we talk about, there is an inductive element (a coil) used as a filter, that filters out the “clock” and leaves the musical signal alone – this works like a reconstruction filter on a DAC output. This makes the cable and the loudspeaker a part of the filter. In the ideal situation, the negative feedback loop (which is very strong in those amplifiers) should be connected to the speaker terminals. But this is not done from practical reasons.

We have written about the Audiomatus amplifiers during the test of the AM250 monoblocs – a smaller version of the now tested AM500R (test HERE, there is also an interview with the constructor, Mr. Andrzej Matusiak). Similar to the AM250 the more powerful version is also based on the ICEpower module from the company Bang&Olufsen. This is a ready to use amplifier together with a switching power supply, on one PCB, below which a heat sink for the active elements is placed. As it turns out from my former discussion with the owner of Audiomatus, the company modifies the circuits in a few places – especially the input and the power supply, in a way that the amplifiers sound better than the “raw” modules. There must be something in this statement. The ICEpower amplifiers are used by other companies, like Rotel, Jeff Rowland, Bel Canto and others. And each one of them sounds differently. Probably, big influence on the final effect have the cables and accompanying devices, but I cannot draw a coherent and clear common line about them. Some characteristic elements for this kind of amplifiers can be discerned, about that in a moment, but those are not necessarily relevant to the description of the ICEpower themselves. And this is important. One could have thought that the companies are only busy with preparing an enclosure for the modules, where they put the same product inside. Anyway, even if this is the same product, then the Audiomatus offering will be the cheapest one available. For comparison, the Monoblocs Model 501 from Jeff Rowland (the AM250 are the equivalent of the Model 201) cost around 7000USD. I know, I know, this is a special brand, and we pay for the name, as well as for the unique design of the front panel, but when we resign from that, then the AM500R will seem to be the best opportunity from the very beginning.

SOUND

The initial plan was to test the stand alone power amplifiers AM500R. That was the way we tested the earlier model AM250. The preamplifier designed to match it was already announced then, but the works and tests prolonged, so that we barely got it for tests now. And actually it was destined to remained in the shadow, as an alternative preamplifier, just for comparison, and not for testing, because although the electrical circuit being final – this is the production version - the constructor pointed to a few missed points in the aesthetics of the enclosure. But when I listened to the power amplifiers with my preamplifier Leben RS-28CX (tubes), with the variable output (tube) from my player Lektor Prime and the preamplifier from Accuphase, the C-2810 (solid state), I came to the conclusion that although the PP03 has its limits, we will discuss later, although it is not as good as the other mentioned preamplifiers, still with those power monoblocs it sounded best, confirming the constructor’s aim. And with this all it costs laughably little, what makes it an absolute leader in this group of devices. Not an ideal one, but standing out from the crowd, within the boundaries of its limitations. A part of the set was also the inexpensive interconnect from Vampire Wire available at Audiomatus, prepared especially for this application. It turned out, that in all other cases, interconnects I used introduced some noise, hum, as a part of the ground loop. Although the quality got better with more expensive cables, it was worse in general, because one cannot live with such hum. So I used mainly the supplied interconnect in the test.

The sound of class D amplifiers is different than the one we are used to in other amplifier classes. I wrote about that earlier, but it will not hurt to repeat. It will be heard easiest, when we compare the amplifiers not in classes, but in the tube-solid state comparison. The sound of those amplifiers, including Audiomatus, resembles the tube offerings with the addition of splendid bass. The latter I will discuss later, because this is an important element of the sound of the AM500R, but first let’s talk about the sound in a more general way. First about this specific model: it is significantly better than the AM250 that was not bad at all; I even liked it a lot. I say more: AM500R with the PP03 is, for me, one of the best class D amplifiers I heard, including offerings from Sharp, TACT (except the Millennium, as this one is in a different category and aesthetics), Cary, Rotel, etc. More again – for me it is one of the favorites in this price range, regardless of technology. Some things are worse, then with the competition, some are better, but when we pull all of those together and look at the transmission, without analysis of all the individual aspects, then it will be apparent how difficult it will be to find something equally nice for such (relatively) low money. Only the amplifiers Trigon Energy, Luxman L-505f and C.E.C. AMP6300 can be another step forward – each one in a different direction, but all of them at a similar level.

The tested set is characterized by a very well sorted, “leisured”, really refined sound. The treble is somewhat rounded, but not as much as with the AM250 and much more substantial than in the Cary CAI-1 I tested for “Audio”. Decisive for the quality of the attack will be interconnects and source. Interconnects must be as good and as short as possible – this is an issue with all passive preamplifiers and the PP03 will not change anything in that aspect. We have also to consider the player, because high output impedance, like in my Lektor, but also in the CD-1 from Ayon (although here we have only 30Ω, then the tube outputs do not always react in a way we would expect them to) may lead to a cut-off of the high frequencies in a unfavorable setting. We minimize this danger with short interconnects, but we do not eliminate it. Anyway, the treble is rounded, but at the same time incredibly energetic and refined. This is not what I usually write about class D amplifiers, because almost always the resolution and frequency response in such devices are a hostages of high noise and significant THD. AM500R is probably not a very particular exception, but in this case the compromises are so successful, that one can speak about thoroughbred treble and midrange. And about very good resolution, albeit in certain boundaries.

Resolution is the keyword of this test. AM500R presents a solution to the problem that brought substantial benefit. We have brilliantly drawn, in the sense of saturation and naturality, virtual sources and much worse presented elements between them. I am coming with the explanations. The space with the AM500R is good, but only in the sense of locating the instruments in space, because we get a deep and broad stage, presented with real swing. But there is not much happening between the individual events. Even the costing 2000zl tube amplifier from Xindak, the MT-1, I just tested for “Audio” is capable of more. Maybe this is not the summit of precision, but there is something there. When we listen to the brilliant, beautiful disc Antiphone Blues Ame Domnérus in the exceptional re-master from First Impression Music (Proprius/Lasting Impression Music, LIM K2HD 026, K2 HD CD), we will see, that the saxophone is beautifully set in space, it is not brought closer or pushed away, and it has a full, live sound. The same with the organ – only a background, but what beautiful background! Between those two instruments there is quite dark space. This is a lot of space, and only two instruments, what predestines it to sound like that, but the Audiomatus amplifiers underlined that, took the main sources of sound from the reverbs and privileged them. In the tested devices everything was set so on purpose, that the emphasis was placed on the main sources, their multi-dimensionality, saturation, fluency, etc. We get an incredibly vivid and credible sound, that is a bit “created” and not “re-created”, but this creation might be the one and only that touches our heart. Just like the title role of Dominika Ostałowska in the film Łagodna (dir. Mariusz Treliński, 1995) or Salma Hayek as Frida (Frida, dir. Julie Taymor, 2002) – one and only.

When I played the disc Revolver The Beatles (Toshiba-EMI, TOCP-51117, CD), then from the first moment, when the vocalist starts to count down the start, I had a big, convincing transmission. All instruments got the right frames, there was no discussion about any lacking, thinning and there was no warming. Everything was incredibly, for the given money, palpable. That is the way more expensive power amplifiers from Pass (like the X150.5, test HERE) or Accuphase (like the P-3000, test HERE) sound, and those cost a dozen thousand zlotys or more. This is of course partially due to the mentioned smoothing of what happens “between” the sounds. Because when we make one of the elements quieter, then the other seems louder. But the way this was done here should gain special recognition. When I switched to the Audiomatus system from my set Leven + Luxman (M-800A), it could have been heard, that the sound “sits down” in terms of clarity and resolution – this is not the same league. But also the money is different – I could buy the Audiomatus for the money spent on the cable connecting my devices and still have some left in my wallet. And this changes the perspective, doesn’t it?

I wrote about the treble, and partially about the midrange. It can be easily deducted, that it is full, saturated and smooth. Yes – smooth. All sounds in this amplifier, and in other class D amplifiers, seem to “glide” on a Teflon floor, they are reproduced so smoothly, so fluently they transit from one to another. In the real world of sounds, at least in my system, this is not so even, and from those internal tensions, from the friction between the elements comes the vision of reality, a complicated set of dependencies, that we might not even realize, but that constitutes what we hear. When Ray Brown plays a solo on the contrabass on the disc Happy Coat (Shota Osabe Piano Trio, Sho Studio of Music/Lasting Impression Music, LIM K2HD 031, K2 HD CD) the sound of this instrument is defined in a way how it bounces in the room, how it reacts with the sound of the resonating body, etc. The Polish amplifier showed the playing technique very well, the melody, and similar, but it smoothened, drew back the “air” around the strings, around the performers. We could shorten all this, and say that the Audiomatus simplifies everything, maybe not in the area of individual happenings, but looking at the whole picture. One could do that, and it would be even conform to the Ockham razor, reducing unnecessary existences, what I also strive to do. But in this case this would be too much of a reduction: even if in the light version we can say about ‘simplification’ in the hard version, closer to the truth, it does not fully describe the phenomenon. This is an element that differentiates the tube amplifiers from the AM500R. Although the timbre of those type of devices is similar (there is no way of “digital” sound, such kind of comparison comes from another galaxy), but the way of drawing planes and edges puts the tubes in a better position.

And finally the bass. Looking at the specs, we see that the AM500R can deliver 500W to 8Ω and 1000W into 4Ω, so one could expect a flooding, a heap, and monstrual amounts of bass. One might expect that, but only in case he or she never came across such amplifiers. Because the truth is, that the more powerful the amplifier is, the less it draws attention in that aspect. When I compare my Luxman with the fantastic system EVO 222+402 from Krell (let me remind you – this is 400W at 8Ω, 800W at 4Ω and 1600W at 2Ω), the biggest difference is that the Luxman clearly colorizes the bass (clearly – only in comparison, and not objectively) trying to generate bigger bass than it (probably) should. The Krell behaved like an aristocrat in this area, placing accents in the right place and right time, exactly when it was needed. Audiomatus was similar, I never had the feeling that something is exaggerated, that there is too much or too little of anything. Whether it was the disc Thelenoious Monk & Sonny Rollins (Prestige/Universal Music Japan, UCCO-9274, CD) with quite light recorded contrabass, or significantly stronger present contrabass from the disc Loverly Cassandra Wilson (Blue Note, 507699, CD) the bass was fantastically dosed, one would like to say, controlled. But control is a word that describes the way an amplifier deals with a bass driver, describes the balance between those two powers. With the AM500R, just like with the Krell before and even earlier with the Gryphon Diablo, this category escapes description. We do not have the idea that there is any fight going on, that there is something struggling with something else. There is no trace of those doings that are sometimes audible as tight bass but with a lockjaw. In the Polish amplifier this is aided by quite abundant upper bass. It is a bit similar to the one my Luxman generates. Remembering, that the Krell reproduced this sub-range clearer, in a bit softer way, one might think, that the AM500R, similar to the M-800A, exaggerates a bit. But together with the control – better than in the mentioned Japanese power amplifier – of the lower bass it gives a very natural sound. Because everything was led very well, there was not a trace of stiffening or hardening. Sometimes, but really sometimes, I had the impression, that the mid-bass is a bit harder than it should be, but it turned out that this was depending mostly on specific loudspeakers – this amplifier reacts quite lively to the impedance curve (similar to tube amplifiers).

I already mentioned that, but I will repeat this with joy: this is a very good amplifier. I mean the set: the preamplifier PP03 and the power amplifiers AM500R. It has its limitations, nothing happens without a cause and effect, but it presents some advantages over classic amplifiers with a price tag two or three times higher. This is not a hi-fi sound in terms of blindly following the “fidelity”, seen as not adding anything. This usually ends in thin and stringy sound. Here we have the following of the musical matter. Sublime recordings will sound fabulously, but much better – and this is the real SOMETHING – the worse ones in terms of the recording quality. That was the case with the farewell disc (issued at the end of the cooperation with EMI Records Ltd.) compilation The Best of Radiohead (Parlophone/EMI Records, 2758828, 2xCD). I received this disc for review, but I did not make it. The sound was too bad, especially with recordings from discs before the Kid A. It sounded splendid with the Audiomatus. Seemingly, that something between the sounds what annoyed me so much earlier, some kind of hash, sand, and a reminder from the digital processing was softened by the Polish amplifier. Equally well, or even better, sounded the single with the piece I.F.Y. Vader (Croon Records, CsCD-002, SP CD). This is a remake of the piece I Feel You Depeche Mode, that is why I listen to it from time to time. In this system, with the AM500R in the role of the engine, the voice of Peter was dark and shady, just like it should be, and at the same time it was clear. I may exaggerate a bit, but if I would listen to metal, also trash or death, on high class equipment, then I would stay with the Audiomatus. But we do not need to limit ourselves to that kind of material. We should listen, if this isn’t what WE were looking for earlier, but could not find it: a tube without a tube and with bass from a completely different tale.

DESCRIPTION

The preamplifier PP03 and the monoblocs AM500R from the company Audiomatus are small boxes, in a form similar to devices from Cyrus or Audionemesis, meaning narrow fronts, of about “half rack width” and deep. The PP03 is less deep than the AM500R. Both have a similar front plate from 12mm thick aluminum. It bears the company logo and a round window in the middle. In the monoblocs it is lit red when operating, in the preamplifier it remains unlit – as it is a passive device, not connected to mains. We just have two knobs at our disposition, with a nice retro look of the 70-ties. However they have no markings on them, and have to be set guessing (unless this is only the case in the unit I received for testing, and the production items have the right markings). The knob to the left is the volume control; the knob to the right is the input selector. We have only three unbalanced RCA inputs at our disposal. The RCAs are splendid, much better than in many hi-end products, and were bought from the company Vampire Wire. Besides the three inputs on the back panel there is a single power amplifier output. Passive preamps, if they are to perform well, need a very minimalist environment to work in, so there is no tape loop, or a second power amplifier output, what makes bi-amping a bit more troublesome. It is a pity, that there is no remote. I know, this would require a power source, but it could be in the form of an external plug power supply. Maybe this is possible, but it would increase the costs for sure.

The enclosure is made from thick plates and extremely rigid – the to cover is screwed close by means of 18 thick screws, what made me sick, when I was opening the enclosure for photography. Inside we have only two elements: the input selector and the potentiometer both placed near the back plate, with the axes elongated to reach the knobs in the front. Please note, that the device is available in a few different variants – with different selectors and different potentiometers. The tested unit was equipped in a TKD potentiometer 2CP2511 and a standard input selector, so it was not the most expensive version, and still the effect was splendid. I will just quote the company materials on that:
“Two types of potentiometers are mounted inside, on the request of the purchaser: black ALPS RK40, or a product of the Japan specialist of studio potentiometers, the company TKD. There is also a possibility to fit inside a potentiometer from Penny&Giles, this on special request. Those potentiometers were and are used in home and professional gear, costing thousands and hundreds of thousands dollars. The superb sound and reliability of those potentiometers is legendary. In studio consoles they last dozens of years. An uncompromising solution for the most demanding people. And you do not need to have a mortgage. In the PP03 we use selectors, which detach all leads, including ground, from the not used inputs. This way of switching prevents any noise to come from the unused inputs and prevents issues with the ground loop. This helps in achieving the highest possible dynamics of a system and in reproducing the finest details. Depending on the demand of the customer we can use one of the following switches: a standard one, or a highest quality one coming from the company Elma.”

The signal is led by means of short, not shielded cables, no PCBs are used. The whole stands on rubber feet, which should be exchanged for something better.
The AM500R enclosure is slightly deeper, what makes the top cover to be fixed with… 20 screws. The cover has venting holes. The device does not get very hot (so it can be fit in tight places), but the airflow is kept, just in case. The inside is occupied by one large module – the ICEpower 500ASP in version I. This is a large PCB with many SMD components on it. 2/3 of the surface is occupied with an elaborate switching power supply, including a large, for the purpose, transformer, two large BC capacitors and a few smaller ones. Two more large capacitors were placed in the amplifying circuit. On the power supply input we find a big - filter, and on the power supply cables ferrite tubes. This is done to minimize the high frequency noise generated by the amplifier itself. It is also important to plug the amplifiers in filtering power strips or conditioners – they should be separated from the CD player as much as possible. The audio circuit is made around the LM61721 IC on the input, where short interconnects lead from the input. Behind it we have the modulator and immediately the output section: drivers and the power amplifier bridge – medium power MOSFET transistor followed by two more MOSFETs per branch. The latter are screwed to a heat sink, which makes the construction bar for the circuit that gets fixed to the bottom plate of the AM500R. The diodes and transistors from the power supply are also attached to the same heat sink. From the PCB we go to the speaker terminals by means of speaker cable (two thick twisted copper wires per branch), over which three ferrite tubes were placed – this is the output filter, and it is an integral part of the amplifier, and it does shape the sound. The speaker terminal is the very nice WBT 0765, and the input RCA is the same Vampire Wire element as found in the preamplifier. The whole is nice looking and well made. The device is placed on small rubber feet. Unfortunately the places Audiomatus modified on the PCB are not visible – one has to know where to look for, otherwise the modules look like stock. The back plate terminals are not labeled. The preamplifier has a description on the bottom plate, which is not very useful, once in place we will not revert to it. One more thing – the RCA sockets are mounted the other way round as normal, meaning “red” for the right channel is near the top, and “white” for the left channel are near the bottom.

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