Krell KSA-300S power amplifier Page 2
The other aspects of the KSA-300S's design are more conventional, though by no means conventionally executed. The amplifier is direct-coupled; there are no capacitors in the signal path. Instead, electronic servos are used to eliminate unwanted DC. The circuit is fully complementary from input to output. Front-end driver circuits are high-bias, true class-A. First-rate materials are used throughout, from the anodized and hard-coated (a process said to be much harder than simple anodizing) front panel to the four-layer printed circuit boards. But exotic, expensive parts are not used where, according to Krell, they wouldn't have real benefits. Protection circuitry is provided for DC, short circuits, oscillation, AC power problems, high ground resistance, or out-of-phase ground. There are no fusesonly a single rear-panel circuit breaker.
Both balanced and unbalanced inputs are provided, and two pairs of output terminals are furnished to facilitate bi-wiring. The latter are superior-quality, gold-plated custom units optimized for spade lugs (they do not take banana plugs). They are also designed with a hex-head and may thus be easily tightened with a nut driverunlike some of the otherwise excellent custom output connectors we have seen which omit this feature and therefore can only be hand-tightened. (A nut-driver is not a torque-wrench, and should be used only to ensure a secure connection, not a permanent one.)
But the KSA-300S's power supply is its most awe-inspiring feature. The 5kVA transformer occupies a huge portion of the amplifier's interior (and a large portion of its weight). The filter capacitance is 272,000µF (more than a quarter of a farad). Heavy bus bars connect much of the critical power supply and output circuitry. The supply is fully regulated. The net result is an amplifier rated to deliver power into loads down to 1 ohm, with a power supply so prodigious that the output is specified to continue to double for each halving of the load impedance below 8 ohms (300Wpc into 8 ohms, 2400Wpc into 1 ohm).
One might easily argue that the KSA-300S's design is engineering overkill. Do you really need, for example, its race-carlike performance into low impedance loads? Or a backbreaking weight that requires two strong people to move it? (footnote 2) Clearly, not all loads are difficult loads, and not all listening situations require enormous power reserves. Potential buyers of an expensive, bulletproof amplifier such as the KSA-300S should remain conscious of what they're buying and approach such a purchase with their eyes open. But the KSA-300S is an amplifier which is unlikely to be taxed by any conceivable load, now or in the future.
"Get a grip," said Sam as he peered more closely at the KSA-300S's strange yet familiar visage. As he put aside thoughts of those dark-side forces that must've replaced his space-heating KSA-250 with this cooler, yet oddly seductive, new presence, he turned to the rest of his eclectic yet clearly high-end system: the Wilson WATTs/Puppies, the Rowland Consummate and Krell KRC preamplifiers, the C.E.C. TL 1 transport, and the Levinson No.35 D/A processor.
"You should have waited," Jim had bellowed as he walked into his stock room with a newly arrived Krell Audio Standard monoblock amplifier under each arm. Jim, Krell dealer and pundit, had chided Sam for selecting the Levinson. "We've got the new Krell processors coming in next week." But Sam's system was working great. What would the new Krell amplifier do for itor to it?
My reference system began like the one described above. In addition, Kimber AGDL digital cable linked transport and processor, TARA Labs Master RSC (unbalanced) linked processor and preamp, Cardas Hexlink (balanced) connected preamp and power amp, and TARA Labs RSC loudspeaker cable ran between amp and speakers.
There was no question, even from the opening bars of the first musical selection I played, that finding fault with the KSA-300S would be an uphill battle. Its reproduction was grainless and three-dimensional, without a hint of stridency, dryness, or identifiable coloration. Its soundstage was focused and tactile, with a neutralneither forward nor recessedperspective and, when the recording allowed, a full, spacious ambience. Its top end was silky and liquid, sounding sweeter than previous Krell amplifiers of my acquaintance, yet in no way lacked for detail. Nothing was veiled or obscured: voice, in particular, popped out of the sonic fabric in a manner that sounded natural, unforced, and alive, without a hint of edge or bite. And the 300S's bottom end was powerful and full-bodiednot super-taut. But this limitation seemed more a function of the room and loudspeaker than of the amplifier. There was certainly nothing lean or mean about the sound.
Christmas Time with the Judds (MCA MCAD-6422-2-R) has some of the cleanest, most lucidly recorded upper octaves around. While impressions of a slightly reticent extreme top continued, nothing really seemed to be missing from the 300S's treble reproduction on this recording. Again, nothing was obvious or overdone, but fine detailsthe delicate touch of fingers on guitar strings, the gossamer-smooth sibilants, the slightly breathy quality of the children's chorus backing the Judds on a number of cutsleft no doubt as to the Krell's capabilities. I couldn't have hoped for a cleaner, more subtly shaded performance. On the other hand, the Krell's clean coherenceits complete refusal to slice and dice the soundbenefited less pristine recordings as well.
Willie Nelson's City of New Orleans (Columbia CK 39145, footnote 3) is a classic example of a good bad recording. It's totally unnatural, with Willie's voice awash in artificial reverberation, little bottom-end weight, and more than a trace of lower-treble edge. Although I suspect this album will be unlistenable on many systems, it has certain strange attractionsnot the least of which is its almost spookily focused vocal track floating ethereally between the loudspeakers. The Krell captures this quality with eerie precision. And its slightly forgiving top end makes the recording more than listenable. Of course, no amp I know of (including the Krell) can be expected to salvage truly bad bad recordings. Accuracy demands that the good, the bad, and the merely ugly be distinguishable.
The Jurassic Park soundtrack (MCA MCAD-10859) belongs in the "good recording" category. It falls shy of excellence, but I've been using it a lot lately because of its exceptional bottom end and well-developed, atmospheric soundstaging (footnote 4). The Krell, despite its apparently forgiving nature, didn't conceal this recording's slightly fizzy top end. But it left nothing to be desiredwithin the extension limits of the Wilson WATTs/Puppiesin its deep, solid bottom end. Nor did it do anything to conceal the topflight soundstaging performance of the Wilsons (and the recording).
Footnote 2: A can of worms for thought: Does the combined 350-lb weight of the KSA-300S and the KSA-250, side by side between the loudspeakers on the suspended floor of Stereophile's listening room, have any effect on the system's sound by damping loudspeaker-induced floor vibrations? Methinks it does.Thomas J. Norton
Footnote 3: Egad! I seem to have gone Country here. However, I own exactly four recordings on CD (out of 700+) by Country performers. I've just named two of them, each of which is very useful for listening evaluations, although for very different reasons.Thomas J. Norton
Footnote 4: Soundtrack recordings are, in general, artificial constructs. Yet when produced/engineered with intelligence, they can be very effective. JP's music-scoring mixer was Shawn Murphy, whom I have mentioned previously. His name on any sound credit's list is a solid assurance of an intelligent music mix, frequently distinguishable by an effective use of depth and space.Thomas J. Norton