ne might still laugh at highly efficient and power-saving class D amplifiers – freedom of opinion/speech is one of the very basic rights of every man in this country. But if one thinks about it just for a moment one realizes that this type of device took over some segments of the market where the small size and small power consumption are key factors. This mean portable devices, desk systems, computer audio and car audio. If one checks out the portfolio of such brands as Monitor Audio, Naim, or Cambridge Audio, at least the mass-consumer products, one will realize that ALL such products (all-in-one systems, wireless speakers and so on) sport SMPS (switched mode power supply). A simple balance of pros and cons of this solution tells us this is the only “right” choice for such applications.

But one can notice that this technology entered also a high end market. I believe that what caused it were successful experiments of such high-end brands as Burmester, Naim, Dynaudio, Focal-JMLab and so on, in the field of car audio – this segment of audio market benefited from this technology most. These experiments led to the change of high-end companies' approach and ultimately to development of much better solutions for this type of designs. Today high-end market revolves around three technologies – tubes, solid-state class A, B and AB and, also solid-state, class D. The powerful mono amplifiers by Jeff Rowland – Model 925 – or Mark Levinson's – No.53 – changed the way audiophiles perceived class D.

Top devices, using different technologies, offer a bit different view on how should sound “look like”. The times when “solid-state” meant: bright, harsh, and “tube” meant: warm, sweet, nice are gone. But still each technology presents certain characteristic qualities, or has advantages in certain areas over the others.

In comparison class D amplifiers, I mean the analogue ones, according to stereotypes, seem to offer sort of “tube-ish” sound. Usually it is a warm, smooth sound, easily spoiled by incorrectly chosen cables, speakers, or poor quality source or preamplifier. One has to know though, that also this technology has been significantly developed, improved over last years. The AS125 clearly shows the direction these changes has taken.

It's a stereo power amplifier using a third generation Bang & Olufsen ICE Power module. This means it's a class D amplifier with SMPS. According to the manufacturer it is an improved version of an older model, AS100 – it so happens that I haven't heard this one. The design of B&O module implicates that this amplifier is intended to “drive mid- and high-efficiency speakers in small and mid-size rooms”. “Large output current and very efficient safety circuits allow this amplifier to drive even most difficult speakers with “unfriendly” impedance curve.” Since it is a „second class isolation” device (the ground wire is not connected with device's ground) so it can not be a cause of a ground loop”. This means that it will work very well in systems with computers and streamers as sources.

ANDRZEJ W. MATUSIAK
Audiomatus | Owner, designer

AS125 is an improved version of our previous model, Audiomatus AS100. It is a stereo power amplifier, build around a third generation ICEpower 125ASX2 module. The ICEpower module working in AS125 was modified in such a way, that at the mid-levels of output power the measurable and audible parameters were significantly improved at a cost of a small, 2 per cent decrease of energy efficiency (energy efficiency for small and large output power didn't change). AS125 was designed to minimize noise emission and to reject noise coming from the system.

Despite the fact the 125ASX2 module complies with noise emission norms we decided to place it in a solid (shielded) housing and selected ferrite beads were installed on speaker cables and on power cable. These elements, as well as particular placement of the module within amp's chassis, allowed us to additionally decrease level of noise and to achieve noise emission level few times lower than required by standards.

The input stage of the AS125 sports low-pass filters that eliminate noise at frequencies far beyond acoustic range (these filters do not effect frequency range of audio signal). We minimized length of the internal wiring to even further improve noise resilience.

AS125 is a second class isolation device (the electric ground of the device is not connected to the protective conductor). This solution means that there is no risk of ground loops. All above described features mean, from technical point of view, that AS125 might be used in any audio system, especially in ones with computer source. Such systems often exhibit issues with ground loops and high frequency noise. AS125 should do very well in such system.

AS125 is a power amplifier. Mr Matusiak claims that high input impedance make it suitable for combining it with both, passive and active preamplifiers. It is obviously true but I think that best sonic effect should be achieved with active preamplifiers or with CD Players with adjustable output (but not with just attenuator).

It is important to mechanically decouple this power amp. We all know how important that is for tube devices and many believe that solid-state ones are immune to vibration. But it is not true, especially when it comes to class D amps. So when using such device we should provide it with optimal working conditions. For this test I placed AS125 on Franc Audio Accessories Ceramic Disc feet, and these were placed on the Acoustic Revive RAF-48H pneumatic platform.

The on/off switched is located on the rear panel. Power consumption in idle mode is minimal so one can leave the amplifier on permanently. It is recommended also because this amp presents its full potential after 30 minutes from turning it on, despite the fact that there are no elements that need to achieve optimal temperature.

Płyty użyte do odsłuchu (wybór):

• Carmen McRae & Julie London, Carmen McRae & Julie London Bethlehem/Victor Entertainment VICJ-61458, “Bethlehem K2HD Mastering Series | No. 8”, K2HD CD (1954/2007).
• Depeche Mode, Ultra, Mute/Sony Music Labels SICP-30543, Blu-spec CD2, (2007/2014).
• Dominic Miller & Neil Stancey, New Dawn, Naim naimcd066, CD (2002).
• John Coltrane, Soultrane, Prestige/Analogue Productions CPRJ 7142 SA, (1956/2014).
• Rogers Waters, Amused To Death, Columbia/Legacy/Analogue Productions 5478842, SACD/CD (1992/2015).
• Rogers Waters, Amused To Death, Columbia/Sony Music Labels SCIP-30785, BSCD2 + BD (1992/2015).
• The Beatles, Abbey Road, Apple/USM Japan UICY76978, SHM-CD (1969/2014).
• The Modern Jazz Quartet, European Concert. Volume One + Two, Atlantic/East West Japan, AMCY-1186-7, "Atlantic Jazz Collection, 50 Years", K2HD, 2 x CD (1960/1998).
• The Rolling Stones, Sticky Fingers, Polydor/Universal Music International B.V. 376 483-9, “Deluxe Edition”, 2 x CD + DVD (1971/2015).

Japanese CD editions are available from

I quickly found out that this was a very god product. It so happened that I had known its price before the test – it does not happen too often – and so I appreciated it even more playing one album after another and comparing it also to Soulution 710 power amplifier.

It delivered a very smooth, liquid sound. These sound qualities are always welcome – they create an impression of a “completeness” of the sound. At first I thought that treble was slightly rolled-off compared with a midrange. By after a closer evaluation, using The Modern Jazz Quartet's European Concert. Volume One + Two and Carmen McRae & Julie London I found out it wasn't true at all. This impression of a very gentle treble comes from a soft leading edge and not from a roll-off. It is also responsible for this smoothness I mentioned before.

AS125 differs from previous Audiomatus amplifiers (and from most competitors based on B&O modules), sounding more like Jeff Rowland's amplifiers. Namely, sound is much more resolving and carries much more information. What before was very pleasant and easily acceptable for a listener on almost “cellular” level, now gained a new, deeper, better differentiated meaning. It is still a bit “round” sound, but with much wider tonality pallet, phrasing, more precise positioning on the stage.

Polish amplifier delivers all the recordings in an enjoyable fashion. But at the same time it differentiates them pretty well, too. Sound is different from one album to another, even if the general sonic character remains similar. What we get is a big, rich sound with a solid bass foundation that smoothly supports midrange. The much more resolving sound allows us to “see” that lower midrange is not as rich as the other parts of the range surrounding it. Almost all other class D amplifiers hide the same feature by emphasizing the other parts of the range. This might result in a spectacular sound, like with Jeff Roland's Continuum II integrated amplifier, but it also provides information on a specific sonic quality of the class D technology.

The amplifier under review delivers sound of truly special clarity. No, it is not brighter, it is clearer, it delivers more information. With some recordings, like with Depeche Mode's Ultra, Abbey Road by The Beatles and New Dawn by Miller & Stacey it is indicated by a removal of some information from 400-600 Hz range. This is an insignificant sound modification and might even go unnoticed, but we should be aware of its existence.

Without direct comparison with expensive and very expensive systems, Polish amplifier will be an excellent example of a well made and wonderfully sounding power amp that combines smoothness, richness and density of the sound with ability to deliver a lot of information from any recording. It's (subjective) frequency range seems very wide and only at the very top and very low end one might find some “imperfections”. But those are really small, and it is easy to not even notice them. Combine it with some fine speakers like, for example, Chario Reflex Prima or Xavian Perla, and the final effect will satisfy even very demanding audiophiles.

Summary

Me proposing Italian, and Italian-ish speakers is no accident. The philosophy of the sound is similar, the understanding which elements might and which might not be compromised. Richness, fullness and smoothness – three key-word, that for AS125 have even more meaning that ever before. Dynamics might not be as significant element here as in many other products from the same range, like offered by Marantz, Denon, and also NAD or Music Hall. Also the depth of the soundstage was not that impressive. But AS125 did a great job surrounding me with sound when I played Ultra by Depeche Mode (listen to the beginning of The Love Thieves!) and the new remaster of Roger Water's Amused To Death – sound wasn't “offensive”, but I really appreciated full, stable phantom images located at the sides and even behind me.

All my remarks came from comparing this amplifier with my reference one. When we start to consider prices of both devices my findings won't matter anymore. It is a true bargain – you won't find any other device for this price that would offer this level of performance so as long as you will accept the aesthetics you should not hesitate. A fantastic device. RED Fingerprintfully deserved!

Some things change, some don't – and while sonically AS125 differs significantly from its predecessors from Gorzów Wielkopolski, its looks remained, more or less, the same. It sports a thick front panel of a brushed aluminum. There is only a company's logo on it and a small hole for a red LED. Nice and simple. Cabinet is made of steel. Small feet are made of plastic. Rear panel holds solid, gold-plated speakers posts, high quality RCA inputs and IEC socket with mechanical on/off switch. Placing on/off switch in the back suggests that amplifier should remain switched on all the time.

The PCB inside is rather small. One can spot there a SMPS and a modulator with output transistors. Radiator used for the latter is also quite small. A separate PCB hold input stage with RCA sockets. Internal wiring was well thought-through – the power cable is placed in sort of holder that keeps it at required height. Even cables providing power to LED in the front panel is nicely fixed to amplifiers bottom panel. There are ferrite beads on speaker cables that lower RF level. Similar beads are placed on power cables, too.

Specifications (according to manufacturer):

Power (THD+N 1% 10 Hz < f < 20 kHz):
- 2 x 68 W/8 Ω
- 2 x 125 W/4 Ω
Nominal loading range: 3 – 16 Ω
Efficiency @ Po=120W/4 Ω: 81%
Frequency range: 5 Hz – 100 kHz
Dynamics @ Po=125 W/4 Ω: 114 dB
THD+N: 0,003%
(@ Po=1 W/f=1 kHz/4 Ω)
Max. THD+N: 0,1%
(100 mW < Po < 100 W/10 Hz < f < 20 kHz/4 Ω)
IMD CCIF: 0,0005%
(14 kHz, 15 kHz Po=10 W)
TIM 3,1 kHz, 15 kHz Po=10 W: 0,003%
Input sensitivity: 0,8V (@ Po=120 W/4 Ω)
Input impedance: 100 kΩ
Damping factor (@ 1 kHz/8 Ω): >1000
Power consumption:
- idle: 8W
- max.: 350W
Weight: 5,4 kg
Dimensions (including feet and sockets):
440 x 85 x 288 mm (W x H x D)