Krell Full Power Balanced 600 power amplifier Page 4

Imaging, transparency...
Soundstages were very stable, very deep, very wide, and excellently focused. Layering of perspective was most convincing. The big Krell presented the primary image just right, neither too close nor too distant. There was no detectable shift in perspective or depth with changes in loudness or program complexity. Perhaps as a result, the FPB 600 somehow induced the speakers to perform with greater smoothness, showing unexpected gains in driver integration and the sense of musical coherence. Stereo images floated free of their reproducing acoustic sources and were bathed in a luminous, ambient soundfield. With the best program quality, images reached far back into the imagined soundfield.

Traditionally, transparency has not been the strongest territory for big solid-state amplifiers. Audition a well-warmed FPB 600, however, and discover that it ain't necessarily so. In both the mid and treble, this amplifier delivered transparency at a sufficient level to fend off competition from the finest tubed creations, SE or otherwise. Then the fun started. Drifting down from the midrange, it was in the lower mid, the upper bass, and the main bass where the '600 also kept its promise. In context, it showed revelatory transparency in these areas, far better than that of any other design I have auditioned.

In some systems it's possible to achieve a feeling of transparency and fine depth yet lack for resolution of fine detail, the latter an area in which Audio Research's tubed designs have traditionally performed well. This behemoth has bridged the gap between solid-state and such tube designs. The FPB 600 presents the listener with a wealth of fine detail: finely etched, sparkling, immediate, and locked in. This is high resolution in spades.

Classic descriptions serve best here. Take a large choir: Working from previous experience, I expected fine reproduction of solo passages and small group work, but anticipated a noticeable degree of blurring and congestion when the full ensemble opened up. With the big Krell, these same passages were presented in a new light. Yes, the simpler sections were as good as ever, arguably even better than before, but the amplifier's ability to hold focus, detail, and choral registration in the full-bore sections was little short of astonishing. Now the sopranos didn't overwhelm the tenors, nor did the tenors overwhelm the basses. All were accorded equal clarity, their chosen musical weights preserved. Equally, on large orchestral works the approaches to big climaxes weren't dodged—the FPB 600 didn't crunch up.

Neither did it exaggerate highlights in the scoring. In live performances the brass can typically appear to be scored outrageously loud, yet the rest of the band can still make itself heard over such an apparent imbalance. When recorded in purist fashion and reproduced by a hi-fi system, such scoring may not sound so effective. Those same brass sections may overwhelm the presentation, this often signified by a quick reach for the volume control.

With the FPB 600, I found that a number of previously troublesome recordings no longer presented this problem: I could let the system go. All remained in place, the composer's intentions dynamically unsullied. The big Krell got significantly closer to live sound in this respect.

As regards character or coloration, this proved very hard to pin down—of the various technologies employed by Krell in the FPB 600, I really couldn't hear any "at work." The dynamic slide through the sequence of class-A plateaus was aurally invisible; indeed, at moderate volume levels, the cool, stable running of the heatsinks told me that, under these conditions, I wasn't even igniting the second step of class-A operation.

Conversely, if I whacked the FPB 600 hard with loud, percussive rock, it warmed up, quickly growing too hot for more than a momentary touch of the fingertips. Essentially, it drew power only as I needed it, successfully combining the efficiency of class-B with the sound (if there is one) of class-A.

Once it was well run-in, the FPB 600's sound was as close to neutral as I have yet heard from any power amplifier. Somehow the center of gravity was restored with the FPB 600—that common tendency for hi-fi to sound thin and forced was wholly avoided here. This amp was pitched very naturally, with just the right sense of richness and weight. No tone controls are involved here—honest.

Comparing the FPB 600's balanced and normal-input operation, I found that, in absolute terms, the sound quality was remarkably similar. Still, there were minor, subtle differences: Balanced drive favored a slightly deeper and more impactful bass, a tad more air and ambient glow in the soundstage, with a touch more sweetness in the upper treble. Single-ended connection had a marginal advantage in coherence and rhythm. The bass was slightly tauter and more focused, while the upper registers were a little more dynamic and expressive. I used both with equanimity, finding that cable differences, even at the top of the tree, were larger.

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