KR Enterprise VT8000 MK monoblock power amplifier Michael Fremer returns
I've been reviewing audio gear for 13 years now, and never, never has the discrepancy between what I heard and what was measured been so great as it was with the KR Enterprise VT8000 MK monoblocks (Stereophile, November 1999). I didn't see the amps' disappointing measurements until the final review was faxed to me for fact-checking. I almost went into toxic shock. I am much more used to having John Atkinson or Tom Norton confirm what I heard; eg, the Audio Physic Virgo review, my first for Stereophile (September 1995, p.121).
Have I, in one review, destroyed my credibility with you? I hope not, though I almost destroyed my credibility with me when I read those measurements. How could something that sounds so good, that seems to have so much power in reserve, measure so poorly? Chip Stern took a healthy swing at an answer in last month's "Letters" (p.13), in his response to a similar gap between what he heard from the Mesa Tigris in the August issue and what TJN measured.
I was extremely disappointed and surprised to read the discrepancy between the KR's claimed power (75W) and measured power (40W and lower, depending on load impedance and distortion). While the Amati Homage is 92dB-sensitive, it does not present the easiest load to an amplifier. The Virgo is less sensitive, and also does not present an easy load. Yet the KR amplifier had no trouble, or so it seemed, driving either speaker to +100dB levels without audible clippinggranting that, as Chip pointed out in his reply, tubes approach clipping gradually and generate more euphonic even-order harmonic distortion.
Everything measured surprised me, especially the high-frequency rolloff into an 8 ohm load (2.75dB at 20kHz). The amplifier's high source impedance, hence its wide response variation into the magazine's standard simulated speaker load, was also a shocker, as were the curvaceous squarewave response and high distortion measurements. There was nothing good in those measurements. Then came the news of instability and ultrasonic oscillations. Say what? Those are not acceptable "performance" characteristics under any circumstances.
But I needed to get the amplifiers back to hear once more in light of the measurements. Was I fooling myself? Were the many listeners who'd spent time in my room fooling themselves as well?
As it turned out, I was finishing up this issue's review of the Musical Fidelity Nu-Vista 300 power amplifier, for which is claimed 300W into 8 ohms, 600W into 4 ohms, and 1000W into 2 ohms! The literature claims 80 amps peak! How about putting that powerhouse up against the underpowered, unstable, high-distortion, rolled-off, round-squarewavereproducing "tone control" of the KR VT8000s?
That's what I did. My new room is not gigantic, but it's not tiny either: 19' long by 14' wide, with an 8' ceiling. I drove the Amatis to 100dB SPLs and higher with both amps, using raucous, bass-heavy source material like the Stones' "Can't You Hear Me Knockin'?" and "Rocks Off," along with mellower fare like Nat King Cole's "When I Fall in Love" and Roxy Music's "Avalon," played at lower SPLs.
As I observed last time, the KRs had no trouble with the raucous, bass-heavy stuffnor, obviously, did the Musical Fidelity. With "Can't You Hear Me Knockin'?" positively shaking the house, I could detect no clipping or strain. In fact, I sensed plenty of power in reserve, though I had no desire to crank up the KRs further to find out. It was more than loud enough. Nor did transient response seem particularly softened or lacking in "edge." The amps rocked fine, and the bass was deep and well controlled. On "Avalon," the bass extension and definition seemed fine, while the percussion was sharp and well focused.
Did the same tunes sound the same through the Musical Fidelity amp? No. Nor would I have expected them to. Without showing you my reviewing hand, let's just say the MF, which is also a hybrid design but in the other directiontube (Nuvistor) input stage, solid-state outputoffered a somewhat leaner, more sharply focused, "faster" picture. Looking at the KR's abysmal measurements, I don't hear what I seeat all. [Which is why we don't allow the magazine's reviewers to see the measurements until after they have submitted their texts. See this issue's "As We See It" for further discussion, as well as "Manufacturers' Comments" for the KR response to the review.Ed.]
In the KR review, I wrote that the VT8000s were free of "...grain, glare, etchiness, edge, 'ripeness,' compression, midbass 'lumpiness,' etc." I still find them free of almost all that, but they do sound somewhat on the "ripe" sidemeaning harmonically rich and inviting, as in real music, though perhaps the "reality" is the effect of additive distortions.
I've just listened, through both amps, to a fabulous test pressing of Art Pepper Meets the Rhythm Section (Analogue Productions APJ 010). There were differences in overall character, not "wrongness" or "rightness." If the satisfying musical performance I heard through the KRs was the sonic result of the awful errors that showed up in the KR's measurements, I'm at a loss to reconcile the two. But Randall Smith, Mesa Engineering's designer and president, did an outstanding job of trying to do the same in his response to Chip's review and TJN's measurements (August 1999, "Manufacturers' Comments," p.137). I hope Riccardo Kron takes the same thoughtful tack in his response to my review and TJN's measurements.Michael Fremer