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Rev D

Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz Hifi, Tidal Hifi, Fore Audio DAISy1, COS Engineering D1, Denafrips Terminator, Soundaware D300Ref,  AURALiC Vega 
Preamplifier: Nagra Classic, Wyred4Sound STP-SE Stage II, Vinnie Rossi LIO (AVT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1 monos, F5, F6, F7; Goldmund/Job 225; Aura Note Premier; Wyred4Sound mINT; Nord Acoustics NC500 monos; LinnenberG Audio Liszt monos
Loudspeakers: Audio Physic Codex; Cube Audio Nenuphar; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V & VI & Submission; German Physiks HRS-120; Eversound Essence
Headphones: Raal Requisite SR1a [on review]

Cables: Complete loom of Allnic Audio ZL3000 and Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Ocellia OCC Silver
Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps/sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands 
Sundry accessories: Acoustic System resonators
Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room, hence no wall behind the listening chairs
Review component retail: £887.50/ea. with SI 990Enh for a new set of MkII amps; £549/pr for just buffer boards with SI990Enh opamps; £200 for 4 x Sparkos 2590

"Wanna dance? Well, more rock 'n' boogie. We launched the above new Rev D buffer board for the NC500 and it makes a dramatic difference in performance. Do you fancy trying them? And updating the review?"

That was Colin North of Nord Acoustics. From him I'd bought a pair of Ncore 500 mono amps a few years ago. For our then hardware arsenal, I'd wanted a cost-effective example of high-power class D with steep damping factor to manhandle speakers I might be asked to review for which I didn't have proper drivers. With swappable discrete dual opamps from Sparkos Labs and Sonic Imagery, I could even season sonics. Since that purchase, I'd not used them that much. With our residential speakers which don't need their power, I preferred our traditional and admittedly rather costlier class A or A/B specimens. Perhaps the new buffer board and revised opamps would reshuffle domestic favourites?

"Assuming that I can do the surgery myself—plug'n'play and all that jazz—absolutely."

"Yes, simply pull cables off and slide buffer out."

To revisit Colin's gambit, "we start with discrete voltage regulators from Sparkos Labs. These provide ultra low-noise and accurate power with very fast transient response feeding the NC500 and discrete opamps. Discrete opamps simply sound better. Their design and size allows the use of large capacitors and high current not possible in ICs due to size and heat dissipation. Our buffer board uses tight tolerance metal film resistors and audiophile polystyrene capacitors throughout the audio stages. High-quality gold plated sockets make for easy opamp changes. The board is fully interchangeable with the standard Hypex board and accepts previous 8-pin opamps."

If you're still foggy, remember how sundry brands distinguish their Ncore, Hypex or ICEpower amplifiers with custom input buffers to tweak sonics. Without that front-end shift, they'd all sound alike, give or take a little for dissimilar connectors and housings. But mess with the buffer and sonic variability is your uncle. Enter two new versions of discrete opamps in the Sparkos SS2590 [upper right in the header image] and Sonic Imagery 990Enh [upper left] plus an all-new buffer board. With this lot, my two-year old Nord Acoustics One SE Up NC500MB amps (yep, they're a bleeding mouthful) could be supercharged and rejuvenated. Original review here. Only an idiot would decline. And I wasn't quite there yet. Older, yes; senile, no. And… I seemed to recall that I'd worked at Mesa Boogie before. Hadn't I?

To be safe, "let's boogie" it was.

And to round out the intro, in the original review's assemblage with my silver amps, we see their old buffer board and piggy-packed opamps. The new stuff was clearly different. And doesn't hope spring eternal for something better just around the corner? I really and truly was cornered. Here it is in writing:

"The new board uses two opamps per channel and runs even deeper into Class A, delivering up to 250mA into the Hypex NC500 module. The result is more tonal depth, dramatic bass improvement, greater soundstage depth, slightly more detail all wrapped in a balance of rich texture and harmonics… After intense development and evaluations, we tried three opamps from John Hardy, Sonic Imagery and Sparkos Labs. Despite excellent reports on the John Hardy 990C, we preferred the Sparkos 2590 and Sonic Imagery 990Enh. Both are excellent. The difference is less than with the previous versions we used. We prefer the Sonic Imagery. The power section's Panasonic electrolytic capacitor's value was chosen to deliver the best and fastest combination of attack and sustain in the bass. Small values have faster flinch capacity to deliver crisp bass. Too small and they run out of power to deliver sustained bass. We evaluated multiple devices before settling on 22μF. The new Rev D buffer accepts the previous SI994 and SS3602 opamps in DIP8 packages. We also further enhanced the peripheral circuit implementing further counter noise reduction. The new Rev D board is 100% compatible with our previous MkI amp." If you own 'my' amps and feel so inclined, you duplicate what I did for this review: remove the old buffer, insert the new, then season to taste with your choice of new Sparkos or SI opamps. FlexiFi.