Jeff Rowland Corus preamplifier + PSU (Power Storage Unit)
Corus + PSU = heavenly refined and breathtakingly brilliant sound!
Review samples kindly supplied by HVP Audio
This is already the third time that I am reviewing the Corus. First time was in 2013 when my system was quite different than it is now, leading to good results, but it wasn’t until the Corus was again reviewed in 2016 that it showed its true potential and left me wanting one. This third time around it comes as a super attractive package, complete with the brand new Power Storage Unit.
Don’t worry, I won’t make you wait until the end of the review to reveal my feelings about the Corus + PSU. Instead I will state right now that the PSU makes for a change that cannot be called subtle by any stretch of the imagination. The Corus on itself is already a reference preamp, but the PSU really makes for an unbelievable transformation!
Forget about creamy classic sound or clean modern sound, for the Corus/PSU are not about imposing any character on the sound. Instead, you always get glorious, fluid, refined, lively and fascinating sound no matter what you play. Let me state it very clearly: the Corus + PSU are easily the best preamp that JRDG have produced so far.
Well I guess that sums it up quite nicely, I could almost end the review right here! But let me provide some perspective. Do read on!
This is primarily a review of the PSU and how it makes the Corus perform, but as can be read in the previous installments, the Corus in its basic form is also a mightily impressive preamp. Back in 2013 my system was tuned to the sound of classic JRDG components, and as I later learned was also off balance due to room issues. In this environment I had trouble bedding the super-neutral sounding Corus in initially, but when my system was sorted I the Corus was reviewed the second time around, it quickly had me hooked to its superbly transparent and neutral sound.
Even if the Corus on itself doesn’t bring any character to the table and can therefore sound a little overly clean compared to classic JRDG gear, it was difficult for me to go back to the arguably more romantic sounding Coherence II. There is just something highly addictive to the very spritely way that the Corus produces music. Especially its articulate and tuneful bass has to be heard to be believed: completely devoid of excess mass or bloom yet highly elastic and full when it needs to, it is entirely truthful to the source.
The Power Storage Unit is not a BPS: there are no batteries inside. Instead the PSU is filled to the brim with so called Super Capacitors that charge very quickly, can hold massive amounts of energy (233 farads which is 233,000,000 microfarad!) and release this slowly. In doing so the PSU offers the advantages of battery power (clean power), without the drawbacks (high internal resistance). Interestingly, the PSU can feed clean DC power to the Corus pre amplifier and Aeris DAC simultaneously, or the reference phono stage that is currently being worked on.
Wikipedia describes supercapacitors as follows:
Supercapacitors have the highest capacitance values per unit volume and have the greatest energy density of all capacitors. Supercapacitors are manufactured with capacitance values up to 12,000 F/1.2 V, having specific capacitance values up to 10,000 times that of electrolytic capacitors.
With this high capacitance values supercapacitors are bridging the gap between capacitors and batteries. In terms of specific energy as well as in terms of specific power this gap covers several orders of magnitude. However, this high capacitance will in comparison with batteries only be about 10% of the capacity of batteries. While existing supercapacitors have energy densities that are approximately 10% of a conventional battery, their power density is generally 10 to 100 times as great. Power density combines the energy density with the speed at which the energy can be delivered to the load.
Unlike batteries, in the faradaic redox reactions of the pseudocapacitance property of a supercapacitor, the ions simply cling to the atomic structure of an electrode, and no or negligibly small chemical modifications are involved. This energy storage with fast charge-transfer makes charging and discharging of supercapacitors much faster than batteries. Additionally, supercapacitors will tolerate large numbers of rapid charge and discharge cycles.
The PSU has its own on board power supply so the Corus’ external power supply can be laid aside. This means that savings can be made when buying the combo at once.
Although not officially confirmed, to the best of my knowledge the pre-amp part of the Corus is largely identical to that of the Criterion. Apart from the major difference in power supply, the only other difference I can discover is the volume control that in case of the Criterion is a two-function unit that can be clicked as well as rotated, for entering menu items for example while in case of the Corus it is a purely rotary control (entering menu items by exiting the menu).
in the power supply section only. The funny thing is that the Criterion’s display section is actually the combo’s power supply while the blind paneled larger section is the actual preamp. Putting the Corus and Criterion side by side it becomes clear that the Criterion’s housing also has the same dimensions as the Corus, but without the display and operational elements. So, if the difference is only in the power supply, surely the difference can’t be large, right? You’d be surprised!
Tonally, the Criterion has a lot in common with the Corus: it is similarly clean, transparent and refined and is also more finely detailed, with better bass articulation than the more classic JRDG preamps such as the Synergy IIi and Coherence II. Being a battery-powered preamp however makes it sound a little closer to the aforementioned classic designs in terms of sonorous bass and midrange voluptuousness. Like with the Coherence II, the influence of the batteries can be heard also when the preamp is set to AC mode, when they are in circuit but charging while the preamp is fed from AC.
To me it sounds like the “battery sound” is simply switched between low and high modes by swithing from AC to battery only mode. The influence of the batteries can be seen as a blessing or a curse, it depends on the rest of the system and on user expectations. I won’t hide the fact that for the longest time I have found batteries to add romance and take away and overt cleanness that could spoil my musical pleasure when not in place. Especially when I still used the quite clean sounding Magnepan MG3.6R magnetostats. This is why I used BPS-6 power supplies with the model 6 power amps, and is also why I liked the Coherence II so much, in addition to it having a bigger and better power supply than the later Synergy models. But my need for batteries, and romantising the sound has been revealed to have been rooted elsewhere in my system and these days I feel that batteries are best avoided if you want the best transients and the most propulsive sound. This is just my long-winded way of indicating that the Criterion’s sound has aspects that place it somewhere between the classic Rowland sound and the modern Corus sound, and that this can be viewed as being either detractive from the clean and lively Corus sound, or the perfect antidote for an otherwise clean sounding system.
Above: during the Corus/PSU review, the PS Audio Directstream DAC and Memory Player were also visiting, and they paired excellently.
Between the Corus without PSU and the Criterion my vote would probably go to the Criterion because it offers a very large chunk of what makes the Corus so excellent, while adding body and substance to the upper bass and lower midrange, producing a more organically flowing and arguably emotionally more appealing sound which comes in handy when using speakers that are themselves also very clean sounding. But this is a relative matter that ties in with taste and system synergy.
At the time that I am writing this review I have had the Criterion in my system for a few months and during that time I have grown very fond of it, but I must also admit to having missed the Corus’ cleaner sound and more articulate bass.
Corus + PSU
I was in the fortunate position to have at hand the Coherence II, Criterion and Corus, all at the same time. Surely this must count as a slice of Jeff Rowland heaven! The Coherence II is a true classic, and truth be told even in this elevated company it still sounds very good. Sure it cannot begin to match the recent preamps’ levels of transparency, detail and refinement and it is definitely not as articulate or as dynamic, but it has a rich smoothness and sonorous authority to it that is quite unique for a solid state preamp, and indeed has served me very well for over 10 years.
As described above, there is room for interpretation between Corus and Criterion, but when the PSU comes into play, it is quite quickly and very decidedly game, set and match. The PSU does not detract any of the aspects that make the Corus so great, but adds to them in a wholly coherent manner. The PSU makes the Corus sound every bit as energetic as it does when using an AC connection, but without any of the grain or hash that comes along with direct AC power, compared to the more silent, but more rounded and slower-sounding battery operation.
Most obvious is the deeper soundstaging that it provides, with better layering front to back while more clearly delineating the performers in that stage. There is an overwhelming sense of continuousness to the soundstage.
Corus with standard external power supply
The PSU also removes the last trace of what I will refer to as “switching power supply noise”, for a lack of a better description. There is no doubt that switching power supplies can outperform traditional linear power supplies on many levels, especially in terms of agility and dynamic contrast, but very often they can also make a component sound “impatient” and somewhat gray, and this is one of the areas that a linear power supply, or batteries can address. In my experience thus far however always resulting in less articulate transient behaviour.
The PSU provides constant, utterly clean DC, but when required it delivers this extremely quickly. In more ways than one it sounds like a super-fast, low impedance, extra powerful battery. The result is a complete and utter continuity and coherence combined with a highly neutral and natural feeling of elasticity, much as is the case with live music.
The level of detail is also greatly enhanced, but without adding any edge or a forward nature to it, as often happens when the level of detail is perceived to be enhanced. This is an aspect of sound that is hard to describe but hink of it this way: just like a Retina display on the iPad doesn’t look artificially sharp but makes a non-retina iPad seem crude and low-res, the PSU raises the overall resolution of the sound, top to bottom, without creating a typical “hifi” sound. Put another way, I feel that the PSU further raises the Corus’ levels of detail, while simultaneously bettering the already superbly organic and naturally flowing nature of the battery-powered Criterion.
Sure, no matter how smoothly they operate or how nicely made the Corus and PSU are, 29.000 euro is a big pile of money, and I understand the “diminishing returns” sentiment, meaning that more and more money needs to be spent for ever smaller increases in performance.
There are two arguments to defend the cost of this super combo. First: the PSU can also power a second JRDG component. I sold my Aeris some time ago when I felt that some of its aspects were bettered by a much more affordable product, and now definitely do regret this, for I am told that the differences heard with the Corus are apparently even greater with the Aeris. I firmly suspect that the very aspects that made me want to sell the Aeris will actually be addressed by the PSU. This means that the PSU not only enables true reference level pre-amplification, but also quite possibly true reference quality DA conversion.
Second, if you want true reference quality, then you have to be prepared to open your wallet a little further. But just look around at what’s available at the very top, and it is easy to see that 29.000 euro is not even close to the eye-watering cost of some of its competitors.
Third, just view it as the nice car that you are not buying. Nobody views buying a new car as being in any way extravagant, and the Rowlands sure hold their value better than most cars.
But let’s move away from the cost factor and return to what it is all about: the sound. Going from my experience with a very large chunk of the Jeff Rowland preamp portfolio I think it is obvious that a power supply is the single most important part of a preamp, it can make or break the performance.Let me be very clear about this: the PSU makes for a change that cannot be called subtle by any stretch of the imagination.
The Corus with PSU truly comprise the ultimate JRDG pre-amplifier. Not only is this the best JRDG preamp I have heard but the combo puts in the best overall performance that I have heard in my system. It took only moments to make me decide to put my money where my mouth is and use a credit loan to purchase the combo.
Impeccably machined remote control and receiver