Rogers High Fidelity KWM-88 Corona Integrated Amplifier

High-Tech Meets Tubes

Equipment report
Integrated amplifiers
Rogers High Fidelity KWM-88 Corona Integrated Amplifier

Of course, as with any amplifier review, no subwoofer was used. Otherwise, I would be listening to the sound of the 1200-watt subwoofer amplifier instead of the Corona. The Corona took longer than normal to completely warm up. 

A thin line is scribed on the volume control to show its setting, but from my listening position about ten feet away it was hard to see. I wished for an LED on the volume knob to show the volume setting better at a distance—or a numeric readout in the computer window. The remote-control app installed on my iPhone 7 worked just fine. There was a bit of latency as the amplifier’s volume setting tracked the input, but I got used to it. The range of the remote control was much further than standard remotes; I could operate the Corona several rooms away from the amplifier. That’s cool and useful.

The Corona impressed me as a highly linear, neutral amp with explosive dynamics at all levels. I noticed one unusual trait, however: The channel balance varied a bit with different recordings. And there was no balance control to adjust that balance. This was not a show-stopper problem, just a perceptible one. (Well, I guess it could be a show-stopper for some listeners, who are ultra-picky about channel-balance adjustment.) 

I started my formal listening with the KT88 tubes inserted in the amplifier. Generally, KT88 tubes had good harmonic accuracy and lots of detail. I began the formal audition with old favorite Folia: Rodrigo Martinez 1490, a realization of a truly old piece of music played by Jordi Savall and his band of Renaissance instrumental specialists. In triode mode, this information-rich piece was reproduced with lots of detail, especially in the percussion where leading-edge transients were unusually audible, though the soundstage was skewed to the left. Bass had plenty of rhythmic energy and descended fairly deeply. Band leader Jordi Savall solos on the viola da gamba (an instrument similar to the modern cello), and his tone was just a smidgen less harmonically rich than with some amplifiers. In the Ultralinear setting, the Corona was more explosive, exhibiting taut bass impact, but with the same slight leftward skew in channel balance that I heard in triode. The viola da gamba tone was ever so slightly bleached.

Moving on to “Miserere” from The Tallis Scholars Allegri’s Miserere & Palestrina’s Missa Papae Marcelli, an a capella setting of Psalm 51 performed by a small choral group with a smaller solo group some distance behind the main group. In the triode setting, lots of nuance and shading was delivered with ravishing finesse from the main group; however, the distant solo group was immersed in more reverberant echo than usual. Nonetheless, their lyrics still sounded perfectly enunciated and defined in space with not a hint of bloat or splashing. The solo tenor’s voice had a dense filigreed texture, free from distortion. In the Ultralinear setting there was still some left skewing of the channel balance, though the distant solo group was immersed in less reverberation than in triode. 

The song “Snilla Patea” with Bjørn Kåre Odde, the composer, expertly playing a fiddle, backed by the Schola Cantorum chorus under the leadership of Tone Bianca Sparre Dahl, is an MQA-encoded piece. My DAC won’t decode MQA, but the recording still sounds great. In triode setting, the piece seemed better centered than the other pieces. The composer’s solo fiddle was not as harmonically vivid as it is through some amps. The chorus also sounded slightly less detailed than I’ve heard. In the Ultralinear setting, the soundfield was well-centered. The chorus sounded quite lucid, and the fiddle produced a full harmonic tonal envelope. The chorus was remarkably agile. 

Next, I replaced the KT88 tubes with KT150 tubes. My first impression was that the KT150s sounded wide open and relaxed. In the Triode setting, Folia: Rodrigo Martinez 1490 enjoyed a well-centered channel balance. The opening cascabels were more distinct—it was easy to distinguish each strike on the bells from the other strikes. The initial transients of percussion instruments were (appropriately) dissimilar. Bass was deep and impactful, and it was easier to tell the pitches of each note. Savall’s viola da gamba sounded harmonically complete and tuneful. In the Ultralinear setting, it was also easy to tell difference between cascabel notes. Likewise, percussion instruments were distinct and realistic. Castanets swarmed like bees. Bass was ever so slightly less impactful. I could even tell the difference between baroque guitar and harp as they repeated the same musical passage, where the two instruments often sound identical. I’ve seldom heard this much detail from an amplifier. Dynamics were also unusually forceful. 

In “Miserere,” channel balance in the triode setting was skewed slightly to the right—barely perceptible. The solo group sounded buried in reverberant echo, but was still clear. The Ultralinear setting produce slightly less bright highs, but the solo group was less detailed.

In the triode setting, “Snilla Patea’s” soundstage was well-centered. The fiddle sounded a little bright. On the other hand, the chorus was articulate, airy, and dynamically agile. In the Ultralinear setting, the fiddle exhibited the same very slight brightness. 

So which tubes are better, the KT88s or KT150s? I slightly preferred the latter, but several visitors preferred the KT88s. I guess that makes it a personal choice.