Integrated Amp Reviews

The owner's manual is well written and informative. A quick peek under the Mystère's hood revealed a beautifully laid out design. The wiring was well done indeed, and even insulated with silk, I'm told. If this is how China can make audio gear, I don't see how anyone can find fault with it.

"I am here to fix ze problem viz yer pheaun."
After setting up the ia21 and letting it cook for a day or two, I sat down and gave it my first real listen. Something was not right. The sound was grainy and rough, the soundstage was not happening, and the frequency response seemed very lumpy. I switched to the 8 ohm taps, tried a different input, replaced the KT88 tubes with EL34s, and let it cook a while longer. Still no dice. This was not the sweet-sounding amp I'd heard at CES.

Suspecting that the review sample had been damaged en route to my house, I shipped it to John Atkinson for testing to confirm what my ear was telling me. Indeed, the amplifier was busted: One channel was putting out 10 times the distortion of the other. (See "Measurements" sidebar.) After exchanges of e-mails with Kevin Deal and JA, it was determined that something had happened to the amp after it was tested at Mystère USA and before its arrival at my house, and a second sample was sent to me. All of my comments on the ia21's sound are based on that second sample, which worked perfectly.

With the new ia21 in place, I began the battery of trial-and-error tests to which I usually subject tube amps, to see how best they might work with my system's front-end, a Bel Canto DAC 3.5VB with VBS power supply (review underway), and drive my Revel Performa F30 speakers. Sain Line Systems' Silver single-ended interconnects gave me the most open, neutral sound—the ia21 didn't need the added warmth that copper interconnects tend to impart. Next, I determined that the ia21's 4 ohm taps gave my Revel speakers (nominal impedance 6 ohms) the most even tonal balance, the best dynamic range, and the least grainy highs.

"And oh how they danced . . . the little children of Stonehenge."
The Mystère ia21 offers a choice between KT88 and EL34 output tubes, and I had sets of both, made by Shuguang in China. I gave each output tube about 100 hours of playing time before switching back and forth between them to pick apart their sounds. I began with the KT88s, which offer more power and are similar to the KT90s I've been using in my Rogue M180 monoblocks. The sound was marvelous: extremely rich in harmonic colors, a nice, wide soundstage, and very even tonal balance. There was just enough tube magic in the midrange to make me smile. Bass was reasonably controlled, if not as dynamic as what I hear from the Rogue M180s or the Plinius SA103, which I will be reviewing in a future issue.

Though the KT88s offered fine, balanced performance, there was a certain thickness, an almost chunky quality to the music—it was all just a little too sumptuous. As I wrote in my listening notes, "If music is a turkey dinner" (I wrote this around Thanksgiving), "then the KT88s are a yummy but thick gravy drizzled over the whole plate." Specifically, the KT88s added a bit of thickness in the upper bass, a slightly congested lower treble, and good but not great spatial separation between instruments. Don't get me wrong—the sound was lovely—but it was on the thicker, richer end of absolutely neutral.

This effect was very apparent as I listened to Robert Silverman playing Brahms' Variations on a Theme by Handel and Schumann's Symphonic Etudes, from a forthcoming Stereophile release that I'm producing. The piano sounded very full and rich, but Bob's dense left-hand work in the Schumann got a little claustrophobic, with bass notes sounding too full and smearing Schumann's thick writing. For kicks, I also tried a set of Electro-Harmonix KT88 tubes borrowed from a friend. These offered a bit less grain in the treble than the Shuguangs, but the thickness remained. Perhaps this effect comes from running the tubes in pentode—my Rogue M180s sound far more quick and lean with KT90s in ultralinear mode. The KT88s were particularly kind to thinner, brighter recordings, making Animal Collective's "My Girls," from Merriweather Post Pavilion (CD, Domino 219), sound great. Don't get me wrong—I'd always prefer the richness of the Mystère ia21 with KT88s to some god-awful threadbare sound—but however pleasant the KT88s were to my ears, they did have a definite if lovely character. This is the sort of "problem" I wish more amplifiers had.

Then I switched to the EL34s. Now we were talking turkey. When the EL34s lit up against the Mystère's black-gloss finish, so did the sound. Harmonically, at least in my system, these tubes really got it right. The chunky quality of the upper bass was gone, and the treble didn't bunch up as much in the 5–8kHz region. The top end was also sugar-sweet and silky, though maybe not the last word in terms of extension. Separation between instruments and notes was far greater than through the KT88s—remarkable performance in this regard, especially considering the price. Soundstaging—width, depth, layering, projection—was excellent. So much music sounded so right through the ia21. For me, the EL34 tubes gave me harmonic color in spades, but also let the air in. The EL34s sounded like a successfully made soufflé; the KT88s' baking effort may have fallen.