January 2011

Calyx 500 Monoblock Power Amplifiers
Great audiophile benefits from Class D amplification.
Review By Tom Lyle

  My first experience with Class D switching power amplifiers was back in 2001 when I was sent a stereo amp of said design for review. This was the first of its type released by a rather prominent American audio company, and although like all equipment I am sent for review, I attempted to have no preconceived notions regarding its performance. Yet in this case impartiality was particularly easy, as Class D power amplifiers had hardly reached the collective consciousness of the audiophile community – other than their use in subwoofers and other types of equipment where high power was required, space was at a premium, and sound quality in the frequency extremes was not subject to detailed critique. With this new power amplifier in my system, at first I was mighty impressed by the heft and clarity of the low end and its clear detailed midrange. But from the upper mids on up I was just as unimpressed. This was especially true with its lower to mid-treble, where its sound was grainy, grating, and well, just annoying. Sonic visions of early digital reproduction danced in my head. As anyone who has been following the growing population of Class D amps marketed since these "early days", considerable progress has been made in regards to the sound quality. Of course, as with any type of "new" technology there will always be naysayers. Still, these amps have come a long way in a relatively short period of time.

In an e-mail discussion with head-honcho Seungmok Yi of Korea's Digital & Analog Ltd., the makers of the Calyx 500, he admitted having the same mixed opinions during his listening sessions with early Class D amps as I had. But he and his partners designing the Calyx sensed that these other designers "lacked some knowledge" when it came to designing these types of amplifiers, finding that when he peaked inside the cabinets that they were made from ready-made modules. They simply used these modules, connected their own cables, and assembled the chassis. Not so with the Calyx 500, from which they were confident they could achieve "high-end sound" (his words) from their proprietary technology. They also included their own input circuits and DC power supply circuits to provide more power in its low-frequency response, and increase its transient response. He claims that the Calyx 500 uses "high quality" parts throughout, and is in evidence with its use of its op amps, capacitors, OFC (oxygen-free copper) wiring, and Furutech speaker binding posts. The 250 Watt @ 8 Ohms amplifiers double their power at 4 Ohms, and features both balanced XLR and single-ended RCA inputs. This diminutive amp only measures about 9" wide by 12" deep and only 2.5" high, and weighs a mere 9.6 pounds. A single blue LED is located on the center of its curved edged 0.25" front panel when the unit is powered. Seungmok Yi also shared with me that they also were quite aware that these Class D amps have low current draw which is more than 80% efficient and produces very little heat, therefore are very "green", that is, because of these facts they are friendlier to the environment.

Switching Out
Other than switching out the similarly powered Krell KAV-250a for the Calyx 500 monoblocks, my main system has pretty much remained the same since the last published review. The analog front end consists of a LyraHelikon phono cartridge mounted on a Tri-Planar VII U tonearm which is turn mounted upon a Basis Debut V turntable. The digital front end is mostly 44.1/16 FLAC files stored on outboard hard drives, played via Foobar 2000 upon a Dell XPS 3.2 GHz machine with 8 gigs of RAM running Windows 7, with its USB cable is routed to a Benchmark DAC1PRE digital-to-analog converter. An Oppo BCP-83SE universal player spins physical discs mostly when listening to SACDs or the very few DVD-As in my collection. The preamplifiers are a tubed Balanced Audio Technology (BAT) VK-3iX (with remote and phonostage options), and a Pass Laboratory XP-15 phono preamplifier. Speakers are the Sound Lab DynaStat hybrid electrostatic speakers augmented by a Velodyne HGS-15b subwoofer. Interconnects are mostly MIT, including the excellent Shotgun S3.3 when running balanced XLR (which was used to connect the Calyx 500 monoblocks to the BAT preamp), and power cables are mostly Virtual Dynamics' David Series. All the power cords running from the digital front-end and the preamplifiers are connected to a PS Audio Power Plant P600 AC regenerator, and the turntable's AC is connected to its own P300 Power Plant. The Sound Labs and the subwoofer's AC is connected to a Chang Lightspeed power conditioner, and everything is then connected to two separate dedicated AC lines fitted with Virtual Dynamics wall receptacles. Most of the gear is situated on an Arcici Suspense equipment rack, and the listening room is treated with Echobusters acoustic room treatment panels. Most importantly, LP racks were custom built by NYC's Gotham Cabinet Craft, and my idle CD collection is for the most part used for referencing the booklets sit on IKEA shelves.

Put Aside
I thought that any preconceived notions regarding Class D amplification had to be put aside, at least for a while. That is, at least until after I broke-in the Calyx 500 and started more serious listening sessions with these amps in the system. Admittedly, I have not had many Class D amps in my system of late, and even though it was a while ago, I still had a bad taste in my ears since I first tried that lone unit early in the century. "But that was then, this is now", I told myself.

The first thing I noticed was that these amps sound much louder than their power rating suggests. I've had lots of different amplifiers in my system over the years with a claimed power rating of at or near 250 wpc @ 8 Ohms, and none of them were able to reach what I consider "normal" listening volumes with the BAT preamp set at such a low read-out number on its front panel. OK, everything is relative, but in this case it should, at least in theory, reduce the background noise level. Perhaps not the noise from the rest of the signal that feeds into the amps, but at least from the preamp feeding it. I mention that it this might only be in theory because I've never felt that the BAT was anything other than very, very quite not only for a preamp, but especially for a preamplifier powered by vacuum tubes. Still, the background of the Calyx 500 was pitch black, and music emerged from this darkness – and of course, the residual background noise from the recording and/or pressing process – but that's the nature of the beast. But these comments regarding the lack of any background noise if far less important than the fact that these amps sounded huge, with a striking amount of bass control and just plain ole' bass wallop when called for. I've been using my Sound Lab speakers for years now, and the only time I've heard them controlled so admirably was when they were powered by the massive Rowland Design Group Model 7 monoblocs that pump out 350 wpc into 8 Ohms. Considering that I'm comparing the control of the featherweight 9 lb. Calyx 500 to amps that were too heavy for one person to lift without risking injury should give one an idea of at least one of the benefits of Class D amps. Again, it is the sound that matters, and in the area of bass and bass control the Calyx has nothing to fear.

I'm also happy to report that the Calyx 500 did not have blatant shortcoming of upper-midrange/lower-treble glare that plagued earlier designs of this type. Nor was the sound overly detailed as some lesser solid-state units tend to be. Even more importantly, to repeat the oft repeated cliché: music played through the Calyx 500 sounded like music. Playing the illustrious EMI LP of Andre Previn conducting the LSO on Prokofiev's cantata of the film Alexander Nevsky (EMI ASD 2800) illustrated this fact. The first track on side two, The Battle On The Ice starts with the double basses playing the frightening intro shortly before the bass drums begin to disrupt the proceedings. Of course this demonstrated the Calyx 500 extremely stentorian bass, but even more undeniable was how the lifelike percussion that litters the stage during the entirety of the movement. I've heard many a component render percussion with this kind of realism, but more often than not it comes across as merely a parlor trick rather than a true rendering of the live event. This is largely due to this "lifelike" percussion simply draws attention to itself.

How many times has one attended a live performance and uttered "wow, listen to that lifelike sounding triangle and snare drum!"? Not very often, in fact I suppose never. In a live situation it just is what it is, a part of the piece written into the score for a reason. Of course I'm not going to deny that approaching the holy grail of reality is part of the thrill of being an audiophile, this suspension of disbelief, so it is noticeable for a reason. There is nothing wrong with that. But this percussion is integrated naturally into the rest of the sound of the orchestra, and similarly, just as the string sound on this LP is one of the best of its breed, the rest of the orchestra is laid out before the listener illustrating what Prokofiev's meanings were in scoring of this Soviet era propaganda film.

This is true of the Jaws-like pumping, the snare drum tap-tapping, the tambourine at the rear of the stage, and the Psycho-like strings. Not to get all audiophile on you (but that's my job, really), after the full chorus entered and as f turned to fff, I became aware that I was anticipating that the system would start breaking up – that I should soon at least start to hear a bit of tracking distortion added to the pandemonium, or perhaps the amplifiers not being able to handle the complexity (I was listening to this at, of at least near or even slightly above, realistic orchestral levels after all), but this distortion never occurred. Of course this is testament to the rest of the system, especially the speakers being able to handle volumes much louder than your average electrostatic panel. And of course the analog front-end, and especially to the marvelous Bishop/Parker producing/engineering team for delivering such a coherent recording in the first place. Oh, yeah, and the unflinching Calyx 500s. But really, it doesn't get much better than this. Then – the climax of the climax occurs: the tympanis pound quarter notes, the trumpets blast and blare, the chorus sings and shouts at the top of their lungs, and the orchestra nears Rite Of Spring dissonance atop the din. Whew. Good job, Calyx.

I've been listening to a lot of 'Stones lately. I guess it might be all the attention they've been getting around the time I'm writing this, including of course, Keith Richard's autobiography. I'm glad I added a bunch of their SACD hybrids to my collection back in 2003 when they re-remastered most of the catalog, as they are now indispensable (and out of print). Perhaps the record company neglecting to even mention on the outer-covers that these were hybrid discs hastened the formats US demise. But I digress. On their pivotal 1969 release Let It Bleed, the only cover on the album, Robert Johnson's "Love In Vain" comes across extremely well through the Calyx 500s. Even though Keith Richard's acoustic guitar is rendered too large due to its close mic'ing, the larger than life guitar's steel strings resonate realistically on the left side of the large man-made studio soundstage – provoking me to scribble in my listening notes "the guitar sounds real!". Even if there was some studio overdubbing, the track seems to have been recorded live-in-the-studio, and each instrument and part of Charlie Watts' drum kit occupies its own distinct sonic space, including the stellar mandolin playing by guest RyCooder. It's easy to picture in one's mind's ear Mick Jagger, alone in the vocal booth laying down the vocals, the tasteful amount of reverb added to his voice. It doesn't take away any of its immediacy.

The Calyx's also provides on the classic "Live With Me" the ability to discern that the bass playing was done not by Bill Wyman but instead Keef, his plectrum coming down on the strings driving the song forward from the start of his unaccompanied intro. The dual pianos of Leon Russell and Nicky Hopkins panned left and right never clash with each other, and Bobby Keys' sax, his first appearance on a Rolling Stones album, wavers in and out of the song – probably not because that is the way it is mixed but because it sounds as if he is purposely varying the distance from the mic in response to the song's vibe. Charlie Watt's kit is especially impressive during this song, too much space would be necessary to describe the individual characteristics that impel the song forward, but it as I could see the tension on the kick drum skin expanding and contracting with each hit, and when the song ends, the splash-splash-splash of his crash cymbal sizzles as it cuts through the fray.

Last but not least I listened to the 44.1/16 FLAC files of Maurizio Pollini playing Debussy from a 1999 DG release. His solo piano preludes came across as charming as I have always thought. One can debate Pollini's approach to these miniatures, and I guess that's part of the fun of listening to different pianists play these works. Objectively, the sound of the piano recorded in a hall in Munich is up to DG's fine standards, although with a bit more hall sound than direct sound from the keyboard's soundboard. Still, there is no denying Pollini's talent, and no denying that the Calyx 500 is able to relay his approach via the speakers unto which they are connected. Because of the relatively distant mic'ing technique it wasn't as if the piano appeared to be playing in the listening room, it was if sonically viewing the recording through a clear window into the hall. Yet sometimes I felt as if Pollini's exacting approach combined with the Calyx’s exacting approach might be a bit too much of a good thing, which brings me to...

Suitable
Obviously, not all amplifiers are not going to be suitable in every situation. While 250 wpc is more power than many are going to need, it is unlikely to be too few for the majority of listeners. But even if only a hint of tube amp characteristics are what you crave, I'm afraid one is going to have to look elsewhere. This is in many cases a good thing, if by tube characteristics one is alluding to rolled off frequency extremes and loss of transient response. But if one has in mind characteristics that the best modern tube gear possesses such as very neutral sound, fine transient response, and an added glow in the midrange and treble, than you are out of luck. In fact, I'd say this might be the Calyx 500s Achilles heel – even though I'm well aware that these are solid-state amps and I assume are designed to take advantage of all that solid-state has to offer. And good luck with the size and heat (not to mention cost) of a tube amp that provides 500 wpc into 4 Ohms. But the Calyx 500s lean much more toward a solid-state sound than an ideally neutral one. It is level of articulation edges slightly towards the analytical, and its sound couldn't be considered romantic sounding by any stretch of the imagination.

I also heard a hint of the dreaded rise in upper-midrange glare than I'd like at times. But to be fair, the Sound Lab speakers tend to accentuate the midrange over any other frequencies, so this certainly might be system specific. Do these concluding comments void all the praise I heaped upon these amplifiers in the body of the review? Of course not. It wasn't until I put the resident Krell KAV-250a back into the system that I really noticed most of these traits, and as usual I'm exaggerating a bit to make a point. And even though some might balk at me using the 1990s classic Krell as a reference, I've compared this amp to many current models of solid-state amplifiers, some costing upwards of $7000+, and it compared not only as at least the equal to almost every one of these, but sometime superior to them. To the Calyx's credit, the Krell was not as loud or powerful in the bass, nor was it as detailed or quick in the transients. But the Calyx lacked some of the sparkle, the magic, and beauty that the Krell imparted onto acoustic instruments recorded in a real space. And even though the Krell is also a solid-state unit, its upper-mids and treble were more neutral than the Calyx. Again, I hope one doesn't think that these comments reflect too poorly on the Calyx, as I'm being hyper-critical. Why? Because, well, that's what I'm here for, and since you are reading this, I assume you are also very critical.

Still, judged on their own, they are fine amps, as one can easily tell from my sonic descriptions of them in the musical examples. They are more than worth their asking price if high power and especially if space is at a premium. They provide every ounce of the benefits that Class D amps have to offer – especially small size and efficiency – that makes this class of amps so attractive to many in the first place. And too my relief, they provided very few of the drawbacks that have plagued the earlier incarnations of Class D amps.

Specifications
Type: Class D monoblock power amplifier
Power: 500W into 4? per mono block 
THD+N Ratio: 0.005% @ 1kHz, 4?, 10W
THD+N Ratio at Max Power: < 0.1% @ 1kHz, 4?, 500W 
Signal to Noise Ratio: 110 dB @ Balanced Input, 1kHz, 4?
Noise Floor: 145 dB
Voltage Gain: 32 dB
Damping Factor: > 1000
Input Impedance: XLR = 47k ?, RCA = 57 ?
Bandwidth Limit: 80 kHz @ 8?
Total Efficiency: 81% @ 1090W, 8?
AC Input Voltage: 110 - 120 V (Voltage set a factory)
Dimensions: 9 x 12 x 2.5 (WxDxH in inches)
Weight 9.6 lbs.
Price $1250 each

Company Information
Digital & Analog Co, Ltd.
4F, Changbu Building
1458-4 Gwanyang-dong
Dongan-gu, Anyang-si
Gyeonggi-do
431-060 South Korea

Voice: +82 31 422-5690
E-mail: ask@calyxaudio.com
Website: www.calyxaudio.com

North American Importer
Obad imports
Voice: (778) 968-3044 
E-mail: sasha@obadimports.com
Website: www.obadimports.com