Srajan
In 1955 Alex Reeves invented the first so-called class D amplifier. Sinclair Radionics released their related X-10 kit in 1964. Its 2.5wpc rating implied ‘f’ for flea power though today would probably read ‘flee’. John Ulrick of Spectron showed Infinity’s first full-range switching amplifier at the 1974 CES. Sony had their TA-N88 by 1979. Calling class D a new or recent development is thus quite in error. True is that broad commercial adoption in more upscale audio did come after tube and transistor amps in class A and AB were already established; and after pulse-density modulation quit pure subwoofer plate-amp employ to look for better-paying gigs as speaker amplifiers. In very basic terms PDM describes an analog waveform as a series of pulses of discrete length, vaguely like what Morse code did for our alphabet’s 26 letters. This requires fast-switching output devices. Today a new breed of switching amplifiers harnesses gallium-nitride aka GaN transistors. Unlike classic silicon parts those are purpose-engineered for class D applications. Cellphones simply won’t work on bigger, heavier, hotter-running less efficient linear power. They need batteries, the smaller the better. Neither would you want linear power in airplanes where weight is an issue. So industries vastly bigger than performance audio keep chasing ever more efficient gain and power circuits. Their suppliers in Taiwan invest serious R&D into creating the necessary parts. It’s no surprise that enterprising hifi designers too canvas industrial catalogues for hi-tech devices which lend themselves to the audible bandwidth at the impedance and power ratings our sector needs.
Hifi Rose from Seoul first set our scene’s eyes aflutter with streamers whose full-width fascias were vertical touchscreens. Their RA180 integrated then launched steampunk knobbery into orbit and added esoteric features like super-tweeter high pass controls. Its radical styling split opinions but nobody denied that it was over the top. The newer RA280 eases up on the excess by trimming some fat fantastic. But it’s still a very sharp looker with selectable ±15dB tone controls centred on 100Hz and 10kHz, MM phono, dimmable VU meters and a magnetic circuit breaker in lieu of a mains fuse. On the audiophile catnip board, Hifi Rose score a hat-trick with GaNFet outputs, 800kHz switching and silicon-carbide Fets in the power supply. Going GaN puts them in the same club as AGD, Java, Merrill, Mytek, Orchard and Peachtree. GaN’s major audiophile claim to fame is 1/10th the transitional dead time between on/off states. That makes for steeper rising and falling edges. Just as that does for digital square-wave transmission, it means higher precision. It’s well known that class D represents the currently most efficient or green form of amplification. It packs the highest power density and converts far more wall or battery power to actual drive power where class A’s always-on parts dissipate most of it as throwaway heat and even class B’s half-wave-on scheme can’t touch class D’s conversion efficiency.
It’s how today’s RA280 can generate 250 watts into both 8/4Ω from gain circuits smaller than a business card then front them with a 500-watt switching power supply no bigger than my hand then pack it all into a handsome box which needn’t weigh more than 9.5kg. For more dry numerology there’s 30mΩ output impedance, 47kΩ input impedance, 0.007%/125W THD and 10Hz – 85kHz ±3dB bandwidth. For i/o we get 3 x RCA, 1 x phono, 1 x XLR and a mono 1Vrms subwoofer output. More catnip comes by way of back-lit VU meters though the furry fun stops short of a headphone port or pre-in to convert this integrated into a pure power amp. Those two nice-to-have features are MIA. But, Hifi Rose are not falling back on OEM modules from Hypex UcD, nCore, Purifi Eigentakt, IcePower, Texas Instruments, Powersoft or Pascal. Their in-house engineering acumen has baked its own solution.
I’ve never attended a single school reunion. If I did for my class of D, I’d have to mention that my current hifi cemetery aka spare bathroom houses a Purifi amp, a pair of early UcD-based Auralic Merak and more recent Nord Acoustic nCore monos. None of them are in play. They’re all gathering dust. The only actively switching output stage belongs to stock Pascal boards inside a pair of Gold Note PA-10 Evo monos from Italy. Those drive my passive dual 15” cardioid sound|kaos sub off a 100Hz/4th-order active low pass inside a Lifesaver Audio Gradient Box II smart crossover. The reason why I’ve benched the other lot is simple. In full-range not knee-capped mode, their high-feedback low-impedance approach sounds too dry and overdamped. In combination those attributes sum to mechanical and flat by varying degrees. In beast mode just for bass meanwhile, those Gold Notes control my mega AudioTechnology cellulose woofers just gorgeously. The class D amps I unconditionally loved in full-range mode cost €15’000. One was a Merrill Audio Element 114 stereo amp. The other was a pair of Alberto Guerra Design Vivace monos. Both drove proprietary GaNFet power. That’s why I wanted to learn what using equivalent parts, Hifi Rose could do at £2’999 whilst still adding preamplitude, defeatable tone controls and phono. For reference, my favourite amps all sing in the key of AB with very wide bandwidth and (most of them) add DC coupling. That entire lot drives lateral Exicon Mosfets. To name names, I mean the Bakoon AMP-11R, Enleum AMP-23R, sundry Goldmund models, Kinki Studio EX-B7 and EX-M7, LinnenberG Liszt and Nagra Classic. Their sound is what coincides with my notions of ‘correct’ and ‘pleasing’. It’s what I judge class D against by classic default of ‘that’s what I got’. Where the AGD and Merrill fell off my cliff was price. Though their performance was similar enough to my own stuff to ring all my bells, their cost was far higher. It’s why I stuck to what I had and sent the challengers packing. However, my mind couldn’t help but mark the three letters GaN. Were those parts the difference makers?
I should also mention that S.P.E.C. of Japan’s implementation of TI-based class D is deliberately informed by and does sonically recall a tube aesthetic whilst Sven Boenicke’s extremist massaging of Powersoft also aims more retro analogue if that’s a thing. These switching amps really were softer, denser, rounder and warmer. They came close to my pure class A Pass Labs XA-30.8. I also still remember E.J. Sarmento of Wyred4Sound’s ICEpower implementations with his custom-baked fully balanced input buffers. Those too were thicker and darker than most class D of its day. The obvious upshot is that like any other class of amplification, class D is a blank canvas upon which crafty designers can leave their own very personal signatures. The word du jour is tuning. For that one needs a clear ‘brain-implant’ notion of what things ought to sound like; then bend one’s chosen technology to it. And my last bit of foreplay must add that in my experience, proper switch-mode power supplies à la Nagra; what LinnenberG use in their push/pull class A monos; what Aavik source from Meanwell for theirs – they beat classic linear PSU on self noise or rather, its absence. They don’t amplify 50/60Hz line noise nor use enormous power transformers prone to mechanical hum. On that score, the RA280 out-silenced my 250-watt Kinki EX-B7 monos which for muscle-amp standards are very quiet but not this ‘off’.
Sonically the Hifi Rose avoided all of my class D complaints with a slightly retro proposition. Unlike other class D challengers which exploit their ultra-low noise floor for soon tiring extremist detail like tiny bright stars on an inky black firmament, the RA280 took the detail off the silver platter. It was on the big table, just not spot-lit. Images weren’t shadow-play cutouts with hyper-crisp edges. They were midfield so gentler not chiselled. Tone textures weren’t wet or decay enhanced like tubes can present them but dry like a warm summer’s day not in a humid climate; comfortable so in no need of moisturizer. With the treble control in bypass, the top end really was naturally extended but lacked the cabriolet effect of roof-down airiness. For that one turns up the tone control a bit. Bass grip and exactitude conformed to popular class D expectations to spell out as sterling. Most music of course lives in the midband’s heartland. That had properly materialized density simply without obvious harmonic distortion thickening. Focus and separation were high but not extreme. Dynamics during peaks had proper swell just as you’d hope for from a bona fide muscle amp. For micro ripples, the RA280 created a calmer surface than my monaural amps of the same 8Ω rating. In short, my two-word catchall for its sonic personality became soft power. Power suggests authority and assuredness. Soft specifies that rather than flashy, show-off macho or edgily muscular, this power was more relaxed and—dare one say it—natural. That segues back at misguided notions of ‘high resolution’ which can seem a bit needly on transient sharpness and overplay the blackground card as though recorded space was a vacuum. It’s not. A good recording will contain ambient cues which, like connective tissue, appears between images as reverb captured by the microphones or injected at the mixing console. Either way, we shouldn’t face an abject nothing between our virtual performers that feels like outer space wherein you can’t breathe. No such effect here. The RA280’s excellent no-noise performance didn’t swallow up recorded ambience like a black hole. In fact, I didn’t hear any class D attributes per se, just good relaxed transistor sound. But now try to pack 250 watts of that into this size chassis with all the other amenities, then make it class AB plus a linear power supply, then price it at €3K. Not. In short, for Cambridge, NAD or Rotel type coin, Hifi Rose give the informed shopper a fully legit alternative to the established brands then throw proprietary solutions, fine workmanship and skilful styling into the mix. As a brand newbie previously exposed only through adverts, webpages and reviews done by others, my first Hifi Rose encounter by way of their RA280 really left a very – uh, rosy impression.
Further information: HiFi Rose
