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This seems like a simple solution but the real trick is to dimension the coils in such a way that the rectifier—in fact four diodes—remains open always to feed the capacitor follower. Such an L-filter design warrants sufficient current on demand. Where one power supply might be insufficient, the NEM DAC 1394 uses three all of which are choke filtered and tube rectified. That's the reason for the 22 kilos - those large copper-wound chokes next to the massive transformers. The other two rectifier tubes are 6C5S. Andrejs left us a spare Telefunken AZ1 and Rogers 5X4G for the 5C3S just in case. Each main part of the DAC relies on its own dedicated power supply - the FireWire to I²S board and the DAC board with current-to-voltage conversion. The output stage is transistor based without feedback and of course equipped with yet another transformer*.
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* In this age of switch-mode power supplies, NEM's unusual combination of a tube-era choke-filtered power supply replete with valve rectifiers yet a transistor output stage is another lovely example of unusual 'hybrid' circuitry. - Ed
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Once the enclosure's Faraday cage is opened the beauty of simplicity is out in the open. That is, whatever mounts above the double bottom. One large choke assembly, three smaller chokes in a row, two transformers and hookup wires in bright red contrast with the black metal used elsewhere. In the back is the piggy-backed FireWire to I²S PCB with the DAC board atop, in-between a row of large Nichicon capacitors and the three tubes snuggly mounted upfront.
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Neither Amarra nor Audirvana offer lossless volume control so we had need for a preamplifier to tame the 2.6Vrms the NEM DAC can deliver at its 250Ω output. We started with some of the tracks Andrejs had collected on his PC. For test purposes there were various albums available in 16/44.1 as well as 24/192. The NEM DAC 1394 SE locked to any sample rate without hiccup. For more familiar music we added some from our own collection of WAV files in various resolutions via the computer's USB 3 port.
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For us telltale music is Dolce Pontes’ Momentos. If something is slightly off, this recording makes it painfully clear. Senhora Pontes’ voice becomes sharp and poignant from jitter. Lack of dynamics renders the Portuguese guitar dull and uninvolving. A high noise floor downscales the image. With the Avantgarde XA pre and power combo, the NEM DAC offered a rich large sound, rich in the meaning of generous and welcoming rather than colored, large in the sense of a big cinerama picture. That same impression persisted albeit with a little more pronounced and snappier transient processing when the XA Power was swapped for the Ncore monos. |
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NEM advertises the DAC 1394 SE with a noise floor of -80dB which on paper isn't impressive. Here one may find one reason for this sonic richness but we say better a richer than thin and brittle sound. In combination with the Audio Note Meishu running WE 300Bs itself not devoid of richness (6SN7 drivers) and adding its own noise level, things admittedly got a bit much. A rather better marriage was achieved with the Trafomatic Reference One preamp and matching Kaivalya monos when tube amplification was on the listening menu.
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