Jeff Rowland Corus Preamp & 625 Power Amp (Hi-Fi+)

Solid-state power amplifiers,
Solid-state preamplifiers
Jeff Rowland Design Corus,
Jeff Rowland Design Model 625
Jeff Rowland Corus Preamp & 625 Power Amp (Hi-Fi+)

Absolutes are dangerous things – especially if you are an audio reviewer. No sooner do you declare something to be the “Best” than something else will come along that’s better. Yes, absolutes allow you the luxury of effortlessly embarrassing yourself – and none more than categorical statements that this or that technology, this or that design path, can’t possibly work.

JRDG (Jeff Rowland Design Group) has never been shy of embracing high-tech solutions and the Corus and 625 combination contains enough cutting-edge technology to make any early adopters out there purr with anticipation – whilst sending the resident technophobes diving for cover. Indeed, on paper at least, these products offer a veritable laundry list of features to raise eyebrows if not serious suspicion amongst the less is more, back to the future brigade; op-amps (gasp); switch-mode power supplies (groan); milled from solid aluminium chassis (mutter); connections and facilities to trim, name or adjust every conceivable parameter, as well as incorporate the units into a (shock/horror) home cinema (Pahhh!).

But look a little closer and you’ll find other facets of these designs that should appeal to even the most resolutely retro of listeners: transformer coupled inputs and outputs (tick); ultra-short signal paths (tick); star-earthed circuitry (tick); totally dual-mono construction - even down to physical isolation of the two halves of the circuit (BIG tick).

You see, every time you try to pigeonhole these products, you uncover some detail, feature or function that allows them to worm away from such pat classification. None of the normal labels quite do the job simply because these JRDG units are genuinely different. Those neat, compact and incredibly elegant exteriors are completely at odds with the sheer range of features, functionality and technology crammed inside them.

Each unit is built into a milled from solid chassis, mated to the almost equally massive and Rowland trademark diamond burnished front panel. The complex housing that includes the beautifully sculpted heat-sinks for the power amp has to be one of the most impressively elegant examples of CNC I’ve ever seen. The pre-amp actually consists of no fewer than four separate elements (audio circuit, psu/controller, remote control handset and separate remote receiver) all milled from solid billet. Inside the main audio chassis, the various elements of the left and right channel circuitry are housed in independent pockets, carved from the solid body. The main units each have dimples machined into their bases that locate the Delrin spheres used as feet/high-frequency isolators.

Both the Corus pre and 625 power amps rely on high-speed switch-mode power supplies, incorporating JRDG’s proprietary Power Factor Correction technology. A conventional power supply places rapid, cyclic (100 or 120 times a second) current demands on the AC line, drawing current each time the voltage peaks. This results in substantial ripple and harmonic distortion that gets fed onwards into the audio circuit as well as dumped back into the mains. The PFC circuit aims to precisely synchronize constant current draw with the voltage cycles, thus eliminating this pollution and delivering a pure, high-voltage DC feed to the audio circuits.

The Corus preamplifier employs a fully complementary, ultra-short, star grounded signal path based on Burr Brown OPA1632 op-amps, built onto high-tech, four-layer ceramic circuit boards. The four balanced and two single-ended inputs and two balanced and two single-ended outputs are all transformer coupled, offering improved noise rejection/isolation as well as identical levels across all inputs/outputs irrespective of type. The power supply is entirely isolated in a small (but incredibly dense) milled aluminum outboard chassis. This is linked to the audio circuit with separate DC umbilicals for the left and right channels. Each channel of each input can be individually trimmed in 0.5dB steps, while single-ended Output 2 can also be user trimmed. The phase of each channel can be inverted – ideal for placing and checking speakers, or correcting the overall phase of recordings. Balance can be adjusted in 1.0dB steps, while the optically coupled volume control offers two-speed 0.5/1.5dB adjustment, depending how fast you spin it through its 99.5dB range.

The 625 power amp seems a model of simplicity when compared with its matching preamp, but thus it ever was. Balanced XLR sockets feed an input transformer, separate voltage and current gain stages and a class AB, bipolar output stage in a dual differential, dual mono configuration. A rear switch handles power on, with a front panel standby button, while the IEC AC input is of the large, rectangular 20 Amp variety. One other nice touch is the heavy duty, high-purity copper bus bars carrying current for both the input and output stages. Two sets of speaker connections per channel are provided, although being of the Cardas common post variety they are most at home with spades, although 4mm plugs can be pushed through at a pinch. If your cables are 4mm terminated and the 625 crosses your acquisition radar, factor in the cost (and inconvenience) of re-termination too.

As well as the nuts and bolts that have gone into the 625 and Corus, considerable thought has gone into the user interface too. The basic input control and labeling functions are a model of simplicity, despite the limited number of control buttons available; and that’s not always the case, believe me. But the nicest touch of all is the housing of the remote receiver in a small, machined “matchbox” connected to the control unit by a two-meter umbilical cord. This means that the electronics can be placed anywhere, even in a closed cupboard, without compromising remote control, just as long as you can see that little box. The display brightness can be set at three different levels, while the display itself can be set to stay on, or switch off after five or fifteen seconds, and the volume readout for the 199, 0.5dB volume steps is large, clear and easy to read, even from across the room. Likewise, the rotary control for the volume is beautifully weighted and speed sensitive for large or small adjustments.

The remote handset is sensibly sized, not stupidly heavy, and offers control over all the pre-amp’s functions and menu settings. It also offers a two-stage mute and inversion of absolute phase (indicated on the front panel) which was to prove very useful indeed.

Listening to the Rowland amps has been both an engagingly enjoyable and rewardingly instructive experience – in no small part because their contribution to the performance of the system (and realizing the performances captured on disc) has been at once both obviously apparent yet hard to pin down. How so? Well – it’s obvious that the system is sounding great, but it’s less obvious exactly why; at least at first. That’s because the JRDG combination’s greatest attribute is their unobstructive, uncluttered fluidity. The musical performance flows unmolested and unimpeded, unsullied by unsightly paw-prints and apparently unlimited when it comes to breadth or scale. I say “apparently” because, in absolute terms (and compared to the best of the competing product sitting in large and generally heavy heaps around the listening room) the Rowland amps do impose some limitation in terms of dynamic range and scale, but they are so evenhanded, so polished and poised in their delivery that short of direct comparison you are unlikely ever to notice the shortfall.

One thing is for sure. Put a Corus/625 combination in your system and you’ll be hearing a lot more of your speakers and front-end. The Rowland electronics have an almost uncanny ability to disappear, leaving the rest of your system sounding more like itself than ever before – which can be a double-edged sword; fabulous if the system is well-balanced and well set-up, but not so great if your previous electronics were selected on the basis of their ability to paper over the cracks. When it comes to the system as a whole, small changes in alignment, level or state of tune are immediately apparent. That absolute phase button on the remote control isn’t just there for show; once you start using it, it’s going to become compulsive. And if you don’t believe that small changes in VTA are audible, you will now. Oh, and while we are on the subject of tweaks, coupling the rock solid chassis of these units to a suitably dispersive surface pays huge dividends.

Does that make the Rowland amps unlistenably critical? Nothing could be further from the truth. Instead, they seem to have an uncanny ability to bring out the best in both partnering equipment and recordings, whilst also responding to the subtlest of tweaks or adjustments. I’ve never had them sound bad – but boy do they respond to careful input.

When it comes to understanding just what the Rowland electronics are bringing to the party, discussion of the sonic attributes of the units is rather less than helpful, mainly because there are so few stand-out aspects of these designs; they do pretty much everything, very, very well. Imagine a three-dimensional plot (rather like the “waterfalls” used to display speaker performance) reflecting the performance of the Rowlands and you’d think that the measurement plane was blank, so mirror smooth would it be, with barely a ripple to disturb the seamless, coherence of the musical “surface”. Which, as impressive as it is, is no help at all in understanding quite what makes them so special – because they surely are.

This is what got me thinking about musical character – and the relationship between that character and the sonically specific. In short, the importance not so much of what attributes a component might possess, but what it does with them – and perhaps most importantly of all, how it balances them. Now clearly, the Rowland is an outstandingly balanced performer (in every sense of that term) but how do we get a handle on what that means in overall musical terms?

One real giveaway is their ability when it comes to throwing an expansive, yet natural image; by which I mean not just big, but appropriate. The Rowlands are remarkably true to the source, delivering width when its present and capable of a remarkably coherent sense of height, depth and space where the engineers captured that information. Carefully constructed soundscapes are beautifully rendered, with soundtrack material as so often, providing the most obvious examples. So, on the Oh Brother, Where Art Thou OST, the hammer strikes of the chain gang that underpin "Po Lazarus" are laid in a beautiful spaced diagonal row, out to behind and beyond the left-hand speaker, while the cup and chain of the water butt are also perfectly positioned. I could mention the incidental restaurant noises on Angel Heart, or just about any of the dialogue sections from Pulp Fiction, but you get the picture.

At the other extreme, recordings devoid of any real acoustic or manipulated separation sound flat and homogenous. 21 is undoubtedly a great pop album (and Adele surely has an impressive set of lungs) but a great recording it isn’t. The Rowlands make the most of the mish-mash of layers and overdubs that create the wall of sound, giving the music a real sense of weight and momentum, but there’s no mistaking the heavy hand of the production. This ability to reflect the spatial content of recordings, the production techniques and venues involved, all without pulling about the music itself plays a large part in the second, less obvious but ultimately much more important attribute, the one that elevates these amps into that select group.

What emerged after lengthy listening to the Rowlands – and what links them to the other products mentioned above – is the uncanny ability to bring a natural voice to recordings; to allow them to speak for themselves. It’s something that’s perhaps most apparent when listening to different performances of the same classical piece; to hear not just the sound of a different orchestra and venue, but more importantly, to be drawn into a different interpretation. But it’s actually just as critical with any form of music, and just as obvious once you realize what you are looking for. Listen on the Rowlands and the difference between the graceful, easy momentum, the natural flow and holistic shape of Barbirolli’s reading of the Sibelius 2nd Symphony (beautifully re-issued by Chesky from the Reader’s Digest tapes), and the dramatic contrasts and dynamic fireworks of Berglund’s EMI recording are laid bare. One is carefully shaded, sweeping and emotive, the other a study in black and white, a tour de force of musical and emotional contrasts. But by the same token, the character and attributes of Elvis Costello on My Aim Is True stand starkly against those of Ian Dury’s New Boots and Panties, despite being the product of the same time, the same social and musical milieu. In fact, the two albums are separated by only a couple of months, but by a gulf of personal experience, the one energetic, bright, sensitive and chippy, the other darker and deeper with a very different kind of power. Turn to something altogether lighter like Getz/Gilberto and you’ll marvel at the difference between the sonic and musical quality of the original Verve CD issue and the recent LIM re-issue with its incredibly natural sense of flow and expression, an infectious rhythmic integrity to rival the best analog pressings.

And that’s exactly what makes the Rowlands special; the fact that whether it’s a great performance, a great recording or one of those all too rare occasions when the two coincide, they are going to let you hear that. By allowing recordings and performance their own identity and character they allow them their own voice, their own emotional connection and impact. In so doing, they lean slightly to a smoother, more progressive presentation, one that favours overall shape above the construction and juxtaposition of individual phrases, a subtle elevation of the what that’s being played above the how. But combine that with the solid, grounded and contained quality they bring to performances and there’s an unburstable confidence and presence to the music they deliver. Yes, the Connoisseur/Berning combination gives you greater transparency and separation, greater insight into individual technique and a perspective that brings smaller scale acoustic recordings to life, but that comes at a price. The Rowlands are great all-rounders, taking anything and everything in their stride, without fear or favour – and well able to interface with all but the most demanding of speakers (there’s a mono version on the way for that!). They also act in concert.

Both world class products, I’d rate the 625 as the stronger performer of the two (just), sounding slightly less contained than the line-stage, breathing a little freer and easier. But, impressive enough on their own terms, use these two products together and that’s when they really deliver. It’s their completeness that makes them so special; the completeness of their musical presentation, their all-embracing functionality and elegant aesthetic; their versatility and polished performance. In every sense that matters, from the way they look to the way they work, but most importantly of all, the way they sound, the Corus and 625 really are the complete package, allowing you to simply listen, the mechanics of reproduction receding into irrelevance.

In a world where every review seems to be good and so many products exhibit so few specific, identifiable sonic flaws, these Rowlands represent a different level of achievement. It’s that attention to detail, that perfectionist insistence on the right over the easy, that has created them – and recreated the musical performances they’ve played to such emphatic effect.
If you are feeling jaded and you are losing confidence in the promise and performance of high-end audio, the JRDG Corus/625 combination is just the antidote you need. Exquisitely constructed components with their feet planted firmly on the path to musical gratification – they’ll plant yours there too.

Technical Specifications

Corus Preamplifier
Type: Two-box solid-state line-stage
Overall Gain: 20dB
Inputs: 4x balanced XLR*, 2x single-ended RCA*
Input Impedance: 40 kOhms
Outputs: 2x balanced XLR, 2x single-ended RCA,  2x record out (1x XLR, 1x RCA)
Output Impedance: 60 Ohms
Dimensions (WxHxD): Audio Chassis: 394 x 99 x 311mm, Power Supply: 119 x 99 x 279mm
Weight: Audio Chassis - 10kg
Price: £11,995

Model 625 Stereo Power Amp
Type: Class AB solid-state amp with bipolar out put stage
Overall Gain: 27dB
Inputs: 1pr balanced XLR
Input Impedance: 10 kOhms
Rated Output Power: 300 Watts into 8 Ohms; 550 Watts into 4 Ohms
Outputs: 2prs Cardas binding posts/channel
Dimensions (wxHxD): 394 x 146 x 413mm
Weight: 24.5kg
Price: £12,495


Jeff Rowland Design Group
UK Distributor: Musical Design Company
Tel: +44(0)1708 229308

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