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Conclusion. Each and every amplifier misrepresents reality by distorting the signal fed to it. The true art lies in eliminating distortion, noise, interference as much as feasible and to select all the necessary parts in a way that adds up to good sound. Shelling out well over 100.000 zlotys for an amplifier makes us entitled to expect wonders. The Momentum Stereo is such a miracle. We might even say "little miracle" compared to the size of its main solid-state competitors. It's designed by one of the founding fathers of American high-end audio through whom we all have learnt a lot over the decades. You can hear how he must have had fun designing it by starting from scratch without the burden of Krell's heritage binding him to a certain path.

Here we have an amplifier which boasts a very tasteful sophisticated sound that resembles the best tube amps whilst being better than their vast majority. The Momentum Stereo has its own character. It's not some wire with gain, a notion to which it won't even pretend. It approaches things in its own way to create envy. Here is another solid-state amplifier which denies getting trapped in the stereotype of cold dry sharp transistor sound. Many tube amps sound far colder, drier and harder yet are praised left and right. I will instead praise Dan’s amplifier and feel perfectly honest about doing it.

Review methodology: The amplifier was tested in an A/B comparison with both A and B known. The reference was primarily the Soulution 710 amplifier with the Ayon Audio Polaris III modified by Gerhard Hirt as preamp. It was also fed directly from the variable output of the Ancient Audio Lektor Air V and Aesthetix Romulus CD players. It sounded best without preamp fed directly by the Ancient Audio player. Take care of providing the best possible source. The Momentum Stereo will show off any difference. During the test the amplifier sat on the Acoustic Revive RST-38 anti-vibration platforms (two) and not on its own feet but rather on three Fat Padz from Symposium. It was powered via the Acrolink Mexcel 7N-PC9300 power cord.

Design. The Momentum Stereo from Dan D’Agostino Master Audio Systems is an extraordinary amplifier. Small, beautifully finished, styled as a steam punk or watchmaker’s work of art (you decide), it's already been recognized as such around the world. Its enclosure is made of very thick panels. The side walls are flat copper bars with through-holes acting as heat sinks. As shown by John Atkinson in his Stereophile measurements of the Momentum monos, the heat sink area is insufficient for the amp to work at its quoted max power for long (Michael Fremer, Dan D'Agostino Momentum, Stereophile, February 2013).

It's very unlikely however that it will ever be placed in this kind of condition. In normal operation even with very high sound levels, overheating protection will never get triggered and heat dissipation will be perfectly adequate. The rear panel is made of thick aluminium plate with a milled recess for the connectors. No screws or bolts are seen anywhere except for the bottom.

What primarily catches our attention is the output indicator meter designed to resemble a ship's porthole (that of Captain Nemo from Jules Verne's novel perhaps) or certain luxury watches. It’s illuminated green. The power switch is nowhere in sight and found on the belly near the frontal edge. On the back panel we find an IEC power input with integrated fuse, two pairs of speaker terminals, balanced XLR input connectors and small switches to set the sensitivity of the power meters and their backlit brightness. The speaker terminals are very closely adjoining and I would be very cautious using larger spades. One channel's output is also very close to the power cord. Detailed measurements in HiFi News & Records Review showed how this results in a 5dB lower S/N ratio for that channel, a small difference which shouldn't be audible. Inputs are balanced exclusively. With an unbalanced preamp use the supplied adapters.

The unit rests on four pretty solid feet but you are well advised to upgrade to something better. The manufacturer offers a special stand which elevates the amplifier significantly. Our Polish distributor instead sent along three Fat Padz Symposium footers. The electronic assembly is upside down similar to tube amps, i.e. suspended from the top panel. To improve shielding a thick copper plate bolts to it from the inside. The electronic circuit spreads across a few PCBs. The input section is situated close to the rear panel. The circuit is fully solid-state with fantastic parts, from Dale precise resistors and Cornell Dubilier CDM mica capacitors to polypropylene Wima capacitors and others. This section has its own separate power supply with a dedicated toroidal transformer. The latter is mounted to an aluminium plate, shielding from its bottom side the arguably widest toroidal transformer I've ever seen. Power for the output stage is filtered by eight very good Panasonic caps. The output-stage PCBs mount to either cheek and feature six pairs of output transistors each, 2SA2223+2SC6145 from Sanken. Here too the passive parts are top notch. The interior looks beautiful and adds to the pleasure of watching the machine from the outside.

Specifications (HFN&RR measurements):
RMS output power: 240/390w 4/8Ω
Instantaneous output power: 300/550/970/1, 3W (8/4/2/1Ω)
Output impedance (20Hz - 20 kHz): 0.28-0.29Ω
Frequency response (+0dB/-1.9dB): 20Hz - 100kHz
Input sensitivity (0dBW/200W): 175mV
Signal/noise ratio (A-weighted): 113.8dB
THD: 0.07 -0.1%
Power consumption (no signal/full power): 99/690w
Dimensions (WxHxD): 318 x 109 x 470mm
Weight: 40.8kg
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