This review page is supported in part by the sponsors whose ad banners are displayed below |
 |
 |
With uninterrupted current flow into the capacitor, consider the amount of energy which reaches the output transistors. In a common C-filter, even a large capacitor suffers limited energy storage. It can be topped off only during the short milli-second intervals when the AC voltage exceeds the DC capacitor’s own. In an L-filter, the choke creates an always open rectifier to benefit the capacitor follower during demanding dynamic musical passages. Obviously the energy delivered by the power utility company far exceeds the capacitive storage of any home consumer device. The trick then is designing a choke filter of the right value which leaves the rectifier open but isn't so large that the current flow into the capacitor slows down. This balance is at the heart of NEM’s power supply. The designers’s comparative listening sessions determined that well-designed L-filters always beat C-filters in bass resolution and dynamics.
|
 |
A power supply with a choke makes the power transformer more efficient as current is more evenly conducted without peaks. This reduces transformer heat, makes for better operating conditions and lowers switching noise since the rectifier never fully closes. As long as the load current remains above its critical inductance, the power supply’s DC voltage delivery also remains well regulated. When these requirements are met, they create a near constant filter input waveform for constant DC input voltages.
Our Novosibirsk manufacturer took this theory which was widely practiced in the middle of the previous century to heart. With extensive experience at windings chokes and transformers and armed with oscilloscopes, it nonetheless took the Russians considerable effort to deliver a product that would withstand their own critical scrutiny. Then there was the scrutiny of Andrejs Staltmanis who would only distribute a product that met his high standards.
|
 |
The above two screen shots from their scope clearly illustrate NEM’s contention. Both shots are taken while measuring a similar circuit with the same current and voltage. The first graph shows an L-filter where current is continuous. With the C-filter, current crosses zero to vanish intermittently.
|
|
|
Enough theory. The NEM amp was the first to arrive in our new dwelling. It took some time to get our music room on par with the previous one. At first we had to cope with electrical gremlins. We had to install a dedicated ground circuit including a 3-meter copper ground rod for the listening room; and add a PS Audio Humbuster III to get rid of a nasty DC component on the incoming AC line. Acoustically the room was already treated. We only took one slap on the hand from our acoustic master Franck Tchang who noticed on a photo we sent that one of his 10 resonators was sitting too low. When we finally realized that the floor heating pump produced a 50Hz resonance in the floor itself and addressed that, we were finally ready to recommence our reviewing habits.
The NEM AI-50 has a very sober industrial design. Its black artificial stone fascia is decorated with a vertical aluminum detail that holds the motorized TKD pot. Left and right of that sit two each input selectors and a standby button. Each control is turned from ebony wood. The AI-50 sports three RCA line inputs and that’s it. A multicolor LED indicates standby or power-on. The sides of the 48 x 23 x 49cm (WxHxD) cm amplifier are heat sinks nicely devoid of any sharp edges. At the back things are equally simplistic. Top left and right sit the massive copper speaker terminals that accept a variety of terminations. Down left sits a real power switch, one with a manly lever and a confident clunk next to the IEC power inlet. In the middle the three RCA input pairs are nicely spaced to accommodate even the most exotic connectors and wires.
|
 |
When the amp had warmed up sufficiently we connected the speakers, inputs and hooked the black monolith to our power grid with a LessLoss DFPC via the LessLoss Firewall which in turn connects to the wall outlet with a DFPC Signature with double hot leads. Flipping the power switch lit up the NEM’s indicator to red. The amp stabilizes itself in standby. A push on the standby button or the supplied generic remote turns the LED to green but another 45 seconds pass before the internal safety circuit releases the protective relays. On our 107dB hyper-sensitive horns, the relatively monstrous 50wpc amp only produced the faintest buzz when we put our ears almost inside the horns. The relay transition also proved very well controlled. Turning up the volume during idle did not invoke any noise. This puppy was definitely dead quiet.
Mathias Duplessy L’Hermite Voyageur was the first CD loaded into our PS Audio Perfect Wave transport. After the first few notes it was clear that the new arrival was a real music lover. Deep colorful bass response was one of the first things we noticed. Not only the lowest bass but up to middle C was produced with supreme ease but no reckless bravura. On Marco Beasley’s tenor voice on L’Arpeggiata’s Homo Fugit Velut Umbra, the overtones never lost their connection with the fundamentals and the full timbre of his extraordinary voice was present. In depicting stable images, the NEM impressed again. Large orchestral works as found on Kaleidoscope with overtures and dances by various composers played by the LSO under Charles Mackerras contain—when recorded purist as here—a rich amount of venue information. When the full brass section exploded on a tutti, the sound never broke up or turned overly bright. The NEM remained unfazed over the full spectrum. On this recording a triangle is struck at a specific time. If you know the piece you imagine the percussionist all the way in the back of the orchestra eagerly counting down to hit the steel at just the right time. When he does, it releases an avalanche of overtones but the fundamental pitch gives away the location of the instrument. The piercing sound held on beautifully and decayed slowly Here the multi-transformer amplifier proved its stability once more by not blurring the single triangle experience into a dull single tone.
|
|
|
Even at low volumes the NEM proved capable of revealing the slightest nuances of upper harmonics even though such musical components then were maximally subdued in output. That they weren’t veiled by noise was testament to the very low noise floor of the AI-50. Our 19-ohm Avantgarde Duo Omegas are truly merciless when it comes to noise. In fact, the NEM begged for low-level listening and required no SPL compensation to cover up design flaws. The first watt is important but the first milliwatts are even more so. Here this combined with rock-solid stability of dimensional cues not as the dreaded soundstage but proper localization. Only perfect stability recreates a sense of realism wherein micro dynamic fluctuations make the difference and involvement enters. NEM does not publish damping factor values but for what it’s worth, the NEM AI-50 did not cause robotic artifice for lifeless punches below the belt. Bass was present in abundance but in a natural state. A large drum whack had proper attack, bloom, short sustain and decay at any level. Though 50wpc were available, here they were best considered as a reserve for a really rainy day.
In order to assess the amp with less sensitive speaker, we pulled out the 90dB Podium Sound panels. It takes a while to switch your brain over to their diffuse sound because there is a disconnect between visual expectations—sitting three meters always for a near-field experience—and hearing an actual presentation that mimics a large concert hall somewhere in row 10 or 12. Again we enjoyed the naturalness of our temporary amplification especially with orchestral numbers where timbres and timing came together beautifully and coherence prevailed. With a 17dB lower voltage efficiency, the NEM needed to be turned up a little more than over the Duos. This caused no changes in sound quality however nor any desire to play louder.
|
 |
Listening to the NEM AI-50 reminded us of an experience we had with the Luxman C-1000f and B-1000f preamplifier and monos. Priced ten times higher, the Japanese manufacturer placed equivalent emphasis on their power supply. Neither design showed off its power reserves which were simple available. Ditto for tonality in musical neutrality - no ice-cold rendering of individual tones, no smeared harmonic warmth. Even the idiosyncrasy of the designers was similar. Luxman uses negative feedback though dynamically and only when needed – which is still a no-no in certain high-end circles. NEM refrains from any feedback but puts a tube in the signal path to get a scolding from a different sector of purists.
Louis Motek was right. This is a very special amplifier. With a short signal path comprising only 5 elements and a very robust power supply for the output transistors, this amplifier takes the less-is-more principle to heart. Well designed and solidly built, this hybrid zero feedback class AB integrated offers a sumptuous musical feast. |
|
Quality of packing: The amplifier was hand delivered without its 12 kilo wooden crate
Ease of unpacking/repacking: Unknown.
Condition of component received: Perfect.
Completeness of delivery: Includes generic remote control.
Quality of owner's manual: No manual available.
Website comments: Simple and in German and English.
Pricing: Reasonable for the musical qualities.
Human interactions: Heartwarming and very responsive.
Suggestions: Offer more on-line information on the NEM factory.
|
|
 |
 |
