John
Derailed. This isn’t the product that I initially intended to cover this week. Instead, what follows is the result of an unexpected discovery: an entry-level amplifier that when partnered with the KEF LS50 produces seemingly magical sounds.
Rotel’s RA-10 isn’t a new model; it first went on sale in 2012. The RA-10 isn’t even a current model; it was superseded by the A10 in 2016.
I wasn’t particularly looking forward to disconnecting the Vinnie Rossi LIO so that the Rotel RA-10 integrated could take its place in the driver’s seat of the KEF LS50. A £349 street price on the RA-10 suggested expectations should be downgraded accordingly. A 2012 birth date suggested that the Rotel might already be old hat.
But no.
With a heavy nod to 6moons’ “3 x 1 = 5¾” column that documents a series of fortunate events, the RA-10 proved to be a knockout performer with the LS50. A glorious discovery of an improbable partnership between loudspeaker and amplifier where the results kick the door down on expectations, taking a large chunk of the competition with it.
First, some background.
I’ve lived with KEF’s LS50 standmount for almost five years. Why this loudspeaker and why so long?
Firstly, I like the way it looks, especially in Racing Red. I like the way it sounds too. As do many others. That makes it a common reference point among more readers; and perhaps more so than any other loudspeaker in its class.
Secondly, ongoing exposure permits a deeper than average understanding of the LS50’s sound profile. This in turn makes it easier to discern differences affected by upstream electronics, especially amplifiers whose performance can vary wildly. Not just with the LS50 but ANY loudspeaker.
Loudspeaker selected, how many amplifiers does the average hifi enthusiast try before settling on one? And for the audiophile forever seeing the grass as greener elsewhere, how many of the world’s amplifiers can be brought home before the financial strain becomes too much or domestic harmony is threatened? And what of the time required by the amplifier churn?
No one audiophile – not even professionals – can hope to systematically eliminate all possibilities in pursuit of The One. It’s why forums are littered with posts asking after “Best amplifier for loudspeaker X?”.
Choosing an amplifier for one’s favourite loudspeaker is a game of mix and match, trial and error.
Previously DAR articles on suitable amplification for the LS50 – here and here – were derived from first-hand experience – aka listening. That said, specifications and measurements can help us narrow the field.
Loudspeaker sensitivity is an important factor. A flea-watt tube amplifier will quickly run out of steam driving a sealed standmount clocking in at 86db. Big-kahuna Class D would be overkill for 100db+ horns.
There’s little doubt that the Devialet Expert 200’s higher watt count is what makes Steffi’s Fabric 94 mix sound big, bold and majestic when heard through the 85db LS50.
Careful though: the amplifier selection game isn’t only about raw power.
A loudspeaker’s input impedance should also be taken into consideration. Here be monsters. The figure quoted by the manufacturer is only nominal – a summary value.
In reality, a loudspeaker’s input impedance varies with frequency. To the amplifier designer, these variations are largely unknown. The amplifier must be designed so that is capable of delivering current consistently as the loudspeaker’s input impedance moves up and down. Not only for the LS50 but for an enormous range of loudspeakers.
The LS50’s impedance plot, as measured by John Atkinson at Stereophile, can be found here. They barely dip below 4 Ohms so a 4 Ohm-stable amplifier should do.
Generalising for the sake of simplicity: a lower input impedance calls for higher amplifier current provision. Vinnie Rossi’s LIO amplifier module arrives with a mere 25wpc up its sleeve but its strength is with current push; possibly why the LIO has become my preferred LS50 dance partner. Despite its 25wpc rating, LIO doesn’t run out of steam when the music calls for big drama. Neither does it forego music’s subtleties.
We hear tonal colour as more deeply inked via the LIO than the Devialet when driving Talking Heads Naked in the baby KEFs. A quality that transcends either amplifier’s specifications sheet.
I now hear the LIO as a more natural-sounding piece. More organic. More believable. Which amplifier measurement can give us an a priori indication of such subjective qualities? And how reliable would such a measurement be, should it exist, when so much depends on the loudspeaker in play?
With a more substantial build budget, the amplifier designer can specify a larger transformer, a more sophisticated power supply, higher quality capacitors, more tightly specified resistors and better output devices from which comes the possibility of higher output power, wider bandwidth, faster slew rate or higher damping factor.
It doesn’t take an audio expert to tell us that some amplifiers sound better than others – that much is obvious.
Less obvious is that matching an amplifier to a pair of loudspeakers is an unpredictable game of trial and error.
My preference for the LIO has only arisen after months of listening to it and other amplifiers – the Devialet Expert 200 (€6990/~US$8000), the AURALiC Polaris (US$3799), the Peachtree nova300 (US$2500) – drive the LS50 in turn. This is where personal curiosity overlaps with professional duty.
Less scrupulous readers-turned-commenters might use these findings to advance an anti-Class D agenda. Of the four here, only the LIO is a Class A/B design. The Polaris and Peachtree are both ‘Class D’ switching amplifiers. The Devialet is a Class A / Class D hybrid.
My preferences for LS50 dance partners amongst these four boxes fall loosely along price lines. The Devialet outperforms the AURALiC. The AURALiC outperforms the Peachtree. Just as we might expect. Only Vinnie Rossi’s LIO (ever so slightly) bucks price-derived expectations. Specifying LIO modules for RVC volume control, DAC and phono stage to bring it into functional line with the Devialet et al sees us checking out at US$6520.
In other words, we get what we pay for…or so the theory goes.
Exceptions do exist.
The Rotel RA-10 is an integrated amplifier offering 40wpc. It’s an all-analogue deal in which an MM phono stage and a 3.5mm headphone output augment four line-level inputs, a tape loop and pre-outs.
An internal DAC is conspicuous by its absence; and entirely forgivable at the RA-10’s £349 (~US$450) price point. This is Rotel’s most affordable integrated. At least it was until discontinuation in 2016 after four years of entry-level service. (Its replacement is the A10).
I purchased the RA-10, full price from a local dealer, in order to get up and running with music as soon as possible after arrival in Berlin. Something cheap and cheerful to tide me over until bigger guns arrived.
Paired with the ELAC Uni-Fi F5 floorstanders, the Rotel sounded very good but without comparative data points, I was none the wiser as to its audible talents. None too dissimilar to an audio show demo. Maybe – just maybe – this amplifier was a little bass shy but there was no questioning its enthusiasm for dynamic alertness.
Soon after the arrival of PS Audio’s megasystem, the Peachtree nova300, the Devialet Expert 200 and Vinnie Rossi LIO, the Rotel was boxed up and stashed in the cellar. Thanks for the memories.
It would take another six months and an intensive week of comparative listening for the RA-10’s talents, as they relate to the KEF LS50, to be discovered…
The RA-10’s headphone stage comes on as more powerful than a smartphone but not as juicy as Schiit’s Jotunheim headphone amplifier. Nothing out of the ordinary there. Both the Final Audio Sonorous III and AudioQuest NightOwl Carbon are driven nicely by the Rotel’s 3.55m socket and – more importantly – without the power shortfall that leaves the Sennheiser HD800S sounding threadbare.
The phono stage can only be judged as ‘good’ given the absence of potentially performance-triangulating outboard solutions.
Evening up the feature set odds came the AURALiC Aries Mini. A Roon Ready streamer with a terrific sounding DAC on board, lassoed to the Rotel with AudioQuest Yukon interconnects.
Connecting this combination to the Racing Red LS50 a set of AudioQuest’s Rocket 88. Those grumbling about the speaker cable costing more than the amplifier itself are advised that this choice was made for the sake of consistency — this is the same make/model loudspeaker used by this reviewer for the last four years. The same that has interceded between LIO and LS50, between Devialet and LS50, between Polaris and LS50, between nova300 and LS50. The same cable that wrings a better performance from each amplifier/loudspeaker combo than does $10 phone wire.
The $10 cable sitting inside the sideboard might indeed be more price commensurate. Had I gone with that instead, I might not have heard all that I did from the Rotel/KEF pairing and dismissed the RA-10 as just another entry-level integrated; which it isn’t. At least, not with the LS50.
The KEF standmounts mark the beginning and end of this piece’s loudspeaker-matching scope. Those wondering why I didn’t also pull up the ELAC floorstanders from the cellar are reminded that this discovery arrived out of the blue whilst investigating the sonic capabilities of an entirely different product. In other words, I’m squeezing this review in.
And, as always, a review is a slice in time. It is constrained by the clock and the gear to hand. This forces the reviewer to prioritise: what makes the cut and what doesn’t. For my own writings, if it’s not in the review, I didn’t do it and if I didn’t do it, it’s not in the review.
Out of the gate, The Magnetic Fields’ Love At The Bottom Of The Sea and Neil Young’s Decade tells us that the 40wpc Rotel (w/ Aries Mini) is an exceedingly articulate vocalist. The midrange here, it leans in toward the listener. More so than the Expert 200 or the Polaris.
In overall gestalt, the RA-10 is closest to Vinnie Rossi’s LIO, almost matching it in terms of tone colour saturation – almost – but bettering it with one of my favourite qualities: dynamic elasticity. Kick drums sound more like balls hitting the floor, their outer shells flexing before bouncing back. The dull thud of inferior amplification is nowhere to be found.
The LIO is better extended in both directions and takes us deeper into the mix than the Rotel but the delta is smaller than we might expect when comparing a multi-thousand dollar unit to one that asks us for ‘mere’ hundreds.
Criticisms? Sure.There’s no remote control so getting out of one’s seat to change the volume is a proper first world problem. Neither is RA-10 the airiest or most detailed amplifier available. Player definition can get a little woolly at times; and the stereo image between the speakers doesn’t have the sharp focus of the aforementioned – and let us not forget – considerably costlier rivals.
The RA-10 instead evinces with righteous get up and go. An uncanny ability in extracting maximum rhythmic poise from Ellen Allien & Apparat’s Orchestra of Bubbles is nothing short of revelatory. Fun!
The low-riding Rotel’s eerily precognitive way with rhythm shows up again with a run through Lawrence’s Yoyogi Park. Some amplifiers have a tendency to present this album of tightly-structured, mid-paced tech house as somewhat pedestrian. The Rotel pulls a little more swing from the 4-4. Note the purposefully sidestepping of slippery terminology like “musicality”, which talks loud and says nothing.
Modeselektor’s “Pretentious Friends” plunges deep into the lower registers. Not all hifi systems are capable of digging it back out. As standmount speakers, the KEF are intrinsically limited in this respect. The Rotel feed helps them make a more than decent fist of it. Not as accomplished in this respect as any of its rivals the RA-10 compensates any shortfall in bass depth with real punch. Kapow!
The standout quality here is musical excitement and, therefore, listener engagement. This Rotel is emphatically an amplifier to be enjoyed more than admired for its uber-high-end qualities.
I find the RA-10 impossible to ignore and, on a more personal note, I’d take the Aries Mini + Rotel RA-10 over the Polaris or nova300. And I really dig the Polaris and the nova300. That’s quite some conclusion: a thousand dollar two-fer supplanting a pair of considerably more expensive all-in-ones.
The gotcha: this freakishly glorious discovery is specific to the LS50. How the RA-10’s performance translates to other loudspeakers is for other reviewers (or readers) to learn and report on. What Hifi’s 2012 (!) review of the RA-10 points to a less than satisfactory result with ATC and Dali Zensor 3 but that paydirt arrived with the Acoustic Energy 301.
The broader conclusion here is that amplifier matching isn’t a black art. Engineers aren’t Jedi Knights. There is no mystical Force in play.
For the amplifier designer pulling together a universally successful circuit means one heck of a challenge. End users claims of ‘synergy’ have their root not in The Ministry of Magic but in an copacetic electrical match between amplifier and loudspeaker, specifically with impedance and current supply (among other factors).
Readers with a better understanding of audio engineering than I are invited to explain possibly why the Rotel RA-10 defies price point expectations. I’d wager that its transformer, handwound on-site at Rotel’s Zhuhai factory, plays a significant role.
Amplifiers built for passive loudspeakers are derived from a ‘one size fits many’ thinking. Is it any wonder we audio enthusiasts have a tough time finding the optimal dance partner for our favourite loudspeakers?
I played the amplifier lottery with the KEF LS50 this week and netted a sensibly-priced jackpot in the Rotel RA-10. A gob-smackingly wonderful pairing.
Further information: Rotel
