Stereophile: Krell KAV-400xi integrated amplifier

Stereophile: Krell KAV-400xi integrated amplifier 02/05/2007 03:03 PM

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Krell KAV-400xi integrated amplifier

Wes Phillips, February, 2005

How times have changed. When Krell first debuted its KAV-300i, in 1996, it risked having people question its high-end credibility simply for having considered producing an integrated amplifier, much less an affordable one. After all, Krell was the company best known for massively overbuilt—and, many claimed, overpriced— power amplifiers that were uniquely capable of driving speakers of ridiculously low impedance. In Martin Colloms' review of the 300i in the July 1996 Stereophile, he asked the question on everyone's minds: "Is Krell risking its reputation?"

As it turned out, no. True, the

KAV-300i wasn't designed to drive

Apogee's 1-ohm Scintillas the way

Krell's massive separates could, but Krell had designed an integrated that would test the proposition that a properly designed single-box component could rival or surpass the performance of more costly separates. It had just been so long since anyone had attempted such a feat that most audiophiles had never even imagined it possible.

Today, high-performance integrateds are, if not thick on the ground, common enough that no eyebrow is raised at the prospect.

Krell obviously took this as a new challenge, and went back to the drawing board. The KAV-400xi outputs 200Wpc to the 300i's

150Wpc, and takes its cue cosmetically from Krell's sleek Showcase line, which uses stout corner posts and milled aluminum panels to create a bombproof chassis.

It also sports a continuous-spin digital volume control, balanced circuit topology, and a slick little membrane credit-card remote—and, at $2500, costs just $150 more than the almost-10-year-old 300i.

It has always been a truism that Krell is serious about build quality; now we know they're serious about that value thing, too.

Truth! stark naked truth, is the word

That post-and-panel aluminum architecture isn't just window dressing—Krell wants the chassis to be rigid and nonmagnetic. And big: The amplifier's 17" depth enables the KAV-400xi to house its massive power supply at a distance from its audio circuit http://www.printthis.clickability.com/pt/cpt?action=cpt&title=Stereop…ereophile.com%2Fintegratedamps%2F205krell%2Findex.html&partnerID=3834 Page 1 of 14

Stereophile: Krell KAV-400xi integrated amplifier boards, which are stacked adjacent to the rear panel's inputs and outputs. The power supply itself, located in the front half of the chassis, consists of an 800VA toroidal transformer, a 55,000µF capacitive reservoir, and discrete regulators for the preamp and power-amp sections.

Krell says the KAV-400xi's gain stages are derived from the same ultra-highbandwidth, low-noise, current-mode technology that the company developed for its

KCT class-A series preamp. The output stage uses six parallel-linked high-speed bipolar transistors for each channel's positive and negative legs (because it's a balanced design, that totals 24). This clever system trades on the rapid response of low-rated output devices without eschewing the brute force of their global output.

And it works—the 400xi is specified as delivering 200Wpc into 8 ohms and 400Wpc into 4 ohms.

The audio circuits are symmetrical and differentially balanced. In keeping with Krell tradition, the circuit is class-A up to the output stage, and the output is DC-coupled to the speakers. The audio circuit board is flanked by two substantial internal heatsinks, and the amp's top and bottom plates are liberally vented to enable heat dissipation. My KAV-400xi got somewhat warmer than body temperature, but never so hot as to discourage catnaps on the part of a tired but relentlessly exploratory kitten.

Volume control is effected by a resistive-ladder network, and the source switches are linked by relays to the rear panel's inputs. There's a single balanced source input (pin 2 hot) and three single-ended inputs, including the tape monitor. There's a preamp output, and speaker connection is by way of WBT binding posts—one of which the no-longer-napping kitten managed to snap off with a flying tackle when I precariously balanced the amplifier on its faceplate to change speaker cables. Even broken, however, it grasped the spade lug securely. There are also 12V input and output triggers, an RC-5 remote control input, and an IEC socket.

The faceplate is sleek to the point of stealth. There's a tiny power/standby pushbutton, a small round IR receptor, and six tiny pushbutton switches (B1, S1,

S2, S3, Tape, Mute), each with a tiny LED indicator directly above it. A small fluorescent display window and a round-capped rotary volume control complete the facilities.

There is no balance control—but the KAV-400xi uses a balanced resistor ladder for volume control, so of course the amp's balance can be adjusted. That's where its credit-card remote comes in. I'm probably just stupid, but I had the dickens of a time figuring out the remote. It's a universal model that also works with other Krell components, and it has a pair of source switches at the top, labeled CD and Pre. It wasn't immediately obvious to me that I had to press Pre before every command or the 400xi wouldn't accept it. I suspect that wired remote input on the rear panel is the giveaway—Krell assumes its customers will be using a system remote or home automation system such as those made by Crestron.

If you've a yen for incorporating your two-channel system into a multichannel hometheater setup, the KAV-400xi's assignable Theater Throughput mode toggles the designated input into and out of unity gain.

I am as true as truth's simplicity

The KAV-400xi doesn't require any real setup. Just connect the inputs, speaker cables, and AC cable, and turn it on. It sounded pretty good straight off, seemed to blossom a bit after about 10 minutes, and that was that. I didn't notice much improvement with additional burn-in.

The Krell DVD Standard DVD player is fully balanced, so I used the B1 input on the amp and plugged the Musical Fidelity Nu-Vista 3D CD player into S1. I couldn't detect a noticeable difference between balanced and single-ended operation, but the 400xi is balanced from input to output; if your most critical source offers balanced outs, there's no downside to using it, and some theoretical advantages.

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Stereophile: Krell KAV-400xi integrated amplifier

So why not?

The KAV-400xi is hefty at 36 lbs, but not brutally massive the way Krell's biggest components are, which means you don't have to hire an architect to design a shelf that will hold it. It bounced along contentedly on Solid-Tech's elastic-banded Feet of

Silence (no, I didn't make that name up), which are not designed for massive loads.

You do want to give the 400xi a lot of breathing room, however.

The amp appears to be fairly easygoing when it comes to speaker loads, too. I challenged it with Krell's own $8000/pair Resolution 2s, a 4-ohm load with a claimed sensitivity of 89dB. Ignore the specs, however; I found the Rez 2s to be speakers that really wanted to be spanked by their amplifier—they sounded best when dominated by a big brute.

The 400xi was well up to task, demonstrating that it's not just the sons of Krypton who hide their powers behind mild-mannered exteriors. Yes, the Krell was super— both of 'em, actually. However, I felt that auditioning an amplifier solely with a loudspeaker born in the same stable was a tad too cozy, so I wired up a pair of

PSB's $4999/pair Platinum T6 Towers: 4-ohm speakers that don't seem substantially more sensitive at 90dB, but that subjectively seemed to require less boot. The T6 is the next model down from the $6999/pair Platinum T8, which John

Atkinson reviewed in November 2003. The KAV-400xi was in complete control of both sets of loudspeakers, producing balanced sound from bottom to top.

I enjoyed the sound of the KAV-300i when it was released, but that was eight years ago, and since then, solid-state design has come a long way—at least, the best of it has. The KAV-400xi retained the 300i's best qualities-control and unpixelated timbre

—while improving on it across the board, especially at the frequency extremes. The older integrated's bottom end, which I admired in its day, seems overemphatic compared to the 400xi's deep, taut, natural bass.

I hadn't expected this. I once joked to JA that the only newsworthy review of a Krell amplifier would be one that could scream "Krell designs component with no bass response!" The company has certainly not done that this time out, but neither does the 400xi have big bass sound. Its low end just sounds accurate.

Did I say "just"? That's not simply rare, it's a daring move for a company known for its big bass. I suspect that a certain number of consumers might misinterpret the accuracy of the 400xi's bass response for something else: excessive leanness.

More on this anon, as one of my erstwhile editors was fond of saying.

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The 400xi's top end, however, was the real revelation, exhibiting the sort of air and unhyped detail that I've heard from only a few other solid-state designs (most notably, some Krells with breathtaking price tags). What was apparent from the getgo, however, was that the Krell was uncommonly uncolored. Spanish Legends, http://www.printthis.clickability.com/pt/cpt?action=cpt&title=Stereop…ereophile.com%2Fintegratedamps%2F205krell%2Findex.html&partnerID=3834 Page 3 of 14

Stereophile: Krell KAV-400xi integrated amplifier guitarist David Russell's new CD of works by Llobet, Segovia, Pujol, and de la

Maza (Telarc CD-80633), was impressive in its combination of delicacy and authority. Recorded in the somewhat dry acoustic of the Peggy and Yale Gordon

Center for the Performing Arts at Owings Mills, Maryland, the disc places Russell's instrument some distance away within a large space, as opposed to the current trend in recording the guitar of crawling into the instrument's sound hole. This perspective emphasizes the intellectual rigor with which Russell approaches these delightful works, allowing us to luxuriate in the extended architecture of his phrasing, the delicacy of a note's decay, the velocity with which the sound of a plucked string flowers into full bloom . . .

02/05/2007 03:03 PM

That's the long way around the barn. What it really means is that the Krell got me lost in the whole music thing rather than in the whole audiophile emphasis on what music sounds like.

I assumed this would be less true with Buddy Miller's Universal United House of

Prayer (CD, New West 6063 CD), because his albums usually don't exemplify an undue emphasis on audiophile purity (translation: he do like his compression). To a certain extent, I was right: I was able to approve of the righteous reedy wheeze of

Phil Madeira's accordion and the churchy burble of the Hammond B3—and, as always, I was agog at Miller's guitar virtuosity and his signature tone, dripping with scads of compression, deep tremolo, and chiming Vox AC30 overdrive.

Yes, it was easy to get all critical and right-brainy about that stuff, but the minute

Miller began singing with his wife, Julie, the gospel duo of Regina and Ann McCrary

(daughters of Rev. Sam McCrary, who refounded the Fairfield Four in 1942), or bandmate Emmylou Harris, I'd lose perspective, getting swept along by the sheer emotion, which completely pegged my meters. "Emotional overload" is not a charge many reviewers have ever leveled at Krell products.

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And don't get me started on the interplay between drummers Brady Blade and

Bryan Owens. Pace and rhythm are not areas where anybody's "affordable" products are expected to excel, but the 400xi broke the mold here. It aced the toetap, hip-wag, tripe-faced-boogie test.

I don't mean to give the impression that the doughty integrated made UUHoP sound any better than it was. The album was recorded in a home studio, and it doesn't have much breath to it—the proceedings have that homogenized digital workstation gloss, and your front wall is in no danger of "disappearing." On the other hand, the

Krell didn't emphasize sonic flaws until I couldn't hear the music that lay beneath them.

An exaggeration is a truth that has lost its temper

Taken on its own, almost any high-fidelity component of a certain quality sounds better and better the longer you listen to it. Eventually, its sound becomes the "real thing"—or, even worse, becomes preferable to the real thing. This is why so many hi-fi buffs complain about the "rolled-off top end" when they hear a live orchestra in a big hall for the first time. It's why Stereophile reviews compare new products to components that have already been reviewed in its pages.

Fortunately, my office system is built around the direct-marketed, 100Wpc Portal

Audio Panache integrated amplifier ($1795) Sam Tellig praised so highly back in

February 2003. Like Sam, I rate the Panache quite highly—it does rule the system I listen to more than eight hours most days.

The Panache lacks a remote control—or a preamp section, really. Sam described it succinctly as "a power amp with a volume potentiometer (ALPS), a volume control, a balance control, and a selector switch." This isn't a problem in my office system, because it sits beneath my computer monitor, which puts it within reach for volume adjustment and source selection. In my listening room, however, I found myself remarkably surly about having to get up to make those changes. (Why, back in my day, none of us audiophiles had remote controls, and we liked it that way. . . . But I digress.)

I don't need to preach about the convenience of remote control, the logic of adjusting volume and balance from your listening chair, or the exquisite luxury of putting Eminem on hold to catch the latest scores on the sports channel. You know how you feel about that. Of course, the extra 100Wpc the Krell offers is perhaps, to many audiophiles, a more [ahem] powerful argument—and so it proved with Krell's own Resolution 2s, which darkened considerably when driven by the Portal.

On "Ladies in Mercedes," from the Steve Swallow/Ohad Talmor Sextet's L'histoire

du Clochard (The Bum's Tale) (CD, Palmetto PM 2103), everything sounded tuned down—Meg Okura's violin was more like a viola with the Portal, Greg Tardy's clarinet sounded thicker, and Swallow's taut bass sound was plummier.

Switching over to the PSB Platinum T6s, the Panache sounded a lot happier.

Okura's strings gained a lot more of their zing, and Swallow's bass had a lot more bloom and body, sounding meaty and richly resonant.

That was a problem, actually. Swallow isn't a bass player who plumbs the depths.

He has a unique ability to walk bass lines really high up on the neck (which a lot of bass players can do) while retaining perfect intonation (which makes him pretty much unique). An integral part of Swallow's identity therefore lies in the tension of his uniquely lean bass sound—and the Portal put extra meat on its bones. It was big-chested and brawny.

I confess that I liked it that way. It's a prettier sound than Swallow has had when I've heard him live, and I wouldn't be surprised if many audiophiles also preferred it to the Krell's more accurate portrayal of Swallow's slightly nasal drawl. They might even call it "better"—but that's confusing preference with reality. That's not what high fidelity is supposed to be about.



Interesting, isn't it? Everyone knows that Krells have "good" bass: deep, rich, and plenty of it. Yet one of the KAV-400xi's biggest appeals for me was its absence of audiophile bass and its true-to-life delivery of real bass power and depth. Go figure.

Yes, there are amplifiers—many of them made by Krell—that can offer a level of shake-the-earth solidity that the 400xi doesn't have, but at least it tells the truth as it sees it, within its capacity to do so. If you want to storm the gates of hell, you have to give the devil his due—and I think ol' Patch comes a lot dearer than $2500.

Neither the Krell KAV-400xi nor the Portal Audio Panache is going to challenge the reigning soundstage champions for depth or sonic holography. That's something that most tube amps (and Krell's Reference Series) still do better.

Sviatoslav Richter's recording of Beethoven's Piano Concerto 1 (CD, JVC XRCD

JM-24018) offered a good example of this. While I've heard it sound more threedimensional, the 400xi didn't exactly reduce it to wallpaper. Not by a long shot. The

Krell presented a stage as wide as the spread between the speakers and stretching back beyond them about 3'—all the way to my room's front wall, in other words. The

Portal delivered similar stage width but didn't go as deep—still performance that, as

ST put it, "could give solid-state a good name."

I'll continue to use the Panache in my office system, but I suspect I'll often wonder,

"How much better would this sound on the Krell?"

Memories are made of this.

Dearer still is the truth

Eight years after introducing its crowd-pleasing KAV-300i, Krell has followed it up with an integrated amplifier that is more elegant, more powerful, and just plain sounds better. And for a scant $150 more, it's an even greater bargain.

When JA picked up the 400xi for measurement, I called it "my favorite Krell ever."

That surprised me, because I've reviewed a whole passel of Krell components in my career: the KPS-28c CD player; DVD Standard DVD player; KRC-HR, KCT, and

Krell KAV-280p preamplifiers; and the Audio Standard, FPB-300, FPB-300c, and

KAV-2250 power amplifiers. None was less than superb, and some were sublime—

I still wake up some nights from dreams of the KRC-HR-Audio Standard system.

But what I blurted out to John unedited was the truth: Even though Krell has most assuredly built better products, the KAV-400xi is special. Not because it's

"affordable," not because it's exquisite audio jewelry, not because it meets some watts-to-dollar ratio of goodness, but simply because it's as faithful to the music as I am.

Well, to tell the truth, more so.

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Sidebar 1: Specifications

Description: Solid-state, remote-controlled, stereo integrated amplifier with 5 linelevel inputs (1 balanced, 3 single-ended, 1 single-ended tape loop) and 1 set of single-ended preamplifier outputs. Power output: 200Wpc into 8 ohms (23dBW),

400Wpc into 4 ohms (23dBW). Output impedance: 0.17 ohm. THD: 1kHz <0.04%;

20kHz <0.25%. Input impedance: 47k ohms. Input sensitivity: 644mV RMS. Power consumption at idle/standby: 20W.

Dimensions: 17.3" (444mm) W by 3.5" (90mm) H by 17" (436mm) D. Weight: 36 lbs (16.4kg).

Serial number of unit reviewed: 57803100160.

Price: $2500. Approximate number of dealers: 200. Warranty: 5 years, transferable.

Manufacturer: Krell Industries, 45 Connair Road, P.O. Box 0533, Orange, CT

06477-0533. Tel: (203) 799-9954. Fax: (203) 799-9796. Web: www.krellonline.com.

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Sidebar 2: Associated Equipment

Digital Sources: Krell DVD Standard DVD player, Musical Fidelity Nu-Vista 3D CD player, Polk XRt12 Reference XM satellite radio tuner (w/Musical Fidelity X-

DACV3).

Integrated Amplifier: Portal Audio Panache.

Loudspeakers: Krell Resolution 2, PSB Platinum T6.

Cables: Interconnect: Audience Au24 SE, Shunyata Research Aries balanced &

SE. Speaker: Audience Au24, Shunyata Research Lyra. AC: Shunyata Research

Anaconda.

Accessories: Shunyata Research Hydra AC Power Distribution System; Solid-Tech

Rack of Silence equipment stand, Feet of Silence & Discs of Silence equipment supports. Room treatment: Phillips-Manes fiction archives.—Wes Phillips

Article Continues:Measurements

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Sidebar 2: Measurements

To precondition an amplifier before testing, I run it at one-third power into 8 ohms for an hour. For an amplifier with a class-B output stage, this thermally stresses the amplifier to the maximum extent. To my alarm, after 15 minutes of driving 67Wpc into 8 ohms, the top panel of the KAV-400xi above the internal heatsinks was way too hot to touch, implying a temperature well above 60ºC; the chassis was also too hot to touch and smelled of hot insulation. More alarming, the distortion level, a good 0.05% when the amplifier was cold, had risen to 0.15% and was continuing to rise. Worried about the amplifier being damaged by thermal runaway, I concluded the preconditioning at that point.

The Krell is one of an increasing number of wide-dynamic-range amplifiers that do not have sufficient heatsink area to allow continuous high-power operation. This tradeoff may permit a product to be competitively priced—using appropriately sized heatsinks for a 200Wpc amplifier would significantly increase its cost—but it needs to be pointed out. While it is unlikely the Krell will overheat in normal use, it may well do so when used for a party.

The KAV-400xi's input impedance at 1kHz was a usefully high 47k ohms, double that for the balanced input. The amplifier was noninverting through both balanced and unbalanced inputs, and the maximum voltage gain was 35.7dB. (Assessed at the preamplifier output, which has a lowish source impedance of 198 ohms, the maximum preamp gain was a sensible 10.2dB.) The 152-position volume control operated in approximately 0.2dB steps at the extremes of its range, these increasing to 0.4dB steps in the middle of the range and 0.7dB steps around the unity-gain setting of "39." The "0" position mutes the output.

The output impedance was a little higher than usual for a solid-state design, at 0.35

ohm across most of the audioband, this rising slightly at 20kHz. As a result, the modification of the amplifier's frequency response reached ±0.25dB, when it drove

Stereophile's simulated speaker load (fig.1, top dotted trace). Into resistive loads, the response was flat in the audioband, with a very slight rise below 20Hz and a high-frequency -3dB point of 134kHz, which correlates with excellent 1kHz and

10kHz squarewave shapes (figs.2 and 3), there not being any hint of overshoot or ringing. The response was the same through both balanced and unbalanced inputs, and was not affected by the setting of the volume control.



Fig.1 Krell KAV-400xi, balanced frequency response at 2.83V into (from top to bottom at 2kHz): simulated loudspeaker load, 8 ohms, 4 ohms, 2 ohms

(0.5dB/vertical div., right channel dashed).

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Fig.2 Krell KAV-400xi, small-signal 1kHz squarewave into 8 ohms.



Fig.3 Krell KAV-400xi, small-signal 10kHz squarewave into 8 ohms.

Channel separation (not shown) was excellent in the audioband, at better than

85dB, L-R, and 80dB, R-L, in the treble; beneath 1kHz, the crosstalk was buried in the noise floor. With the high gain, however, the amplifier's signal/noise ratio (ref.

1W into 8 ohms) with the input shorted and the volume control set to "151" was good rather than great, at 62.2dB, wideband. This increased to 71dB when Aweighted.

The noise presumably contributes to the shape of the THD+noise curves plotted against output power (fig.4), where the downward slope with increasing power is due to the reducing proportion of a constant noise level. However, looking at the distortion spuriae on an oscilloscope revealed there to be distortion harmonics in the noise, and, as I found with the preconditioning, this level increased as the amplifier got hotter. The important point to note from fig.4 is that the Krell comfortably exceeds its specified output power. No fewer than 290W were available with both channels driven into 8 ohms (24.6dBW) at our normal 1% THD definition of clipping, with 350W available into 4 ohms (22.4dBW). However, with one channel driven into 2 ohms, that channel's rear-panel 3A fuse blew at 500W output

(21dBW), which is why the trace in fig.4 ends at that point. Replacing the fuse restored the amplifier to normal operation.

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Fig.4 Krell KAV-400xi, distortion (%) vs 1kHz continuous output power into (from bottom to top at 1W): 8 ohms, 4 ohms, 2 ohms.

Concerned about the temperature-dependent nature of the amplifier's linearity, I measured the manner in which the KAV-400xi's THD+noise percentage varied with frequency at a moderately high level (16V) into 2, 4, and 8 ohms. The results are shown in fig.5: the audioband distortion is nicely below 0.1% into 8 ohms, with the right channel a little more linear than the left. A rise in THD above the audioband gets more severe into the lower impedances, but this is nothing to be concerned about. I then repeated the measurement after running the amplifier at 67Wpc into 8 ohms for 15 minutes. The results are shown in fig.6. Again, the rise in distortion above 20kHz can be seen, but now the audioband distortion has tripled!

Fig.5 Krell KAV-400xi when cold, THD+N (%) vs frequency at 16V into (from bottom to top): 8 ohms, 4 ohms, 2 ohms (right channel dashed).

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Fig.6 Krell KAV-400xi when hot, THD+N (%) vs frequency at 16V into (from bottom to top): 8 ohms, 4 ohms (right channel dashed).

Of more subjective importance than the absolute level of an amplifier's distortion is its spectrum, with low-order harmonics being more benign than high-order.

Unfortunately, the Krell's distortion waveform (fig.7) suggests the presence of both, the spikes in the waveform coinciding with the zero-crossing points. This measurement was taken with the amplifier very hot, hence the highish distortion level of 0.47%. The level was lower with the amplifier cold, but the spikes increased in amplitude as it warmed up.

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Fig.7 Krell KAV-400xi when hot, 1kHz waveform at 2.3W into 4 ohms (top), 0.47%

THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale).

This is shown in a different manner in fig.8, the spectrum of the amplifier's output while it drove a 50Hz tone at half power into 4 ohms. A regularly decreasing series http://www.printthis.clickability.com/pt/cpt?action=cpt&title=Stereop…reophile.com%2Fintegratedamps%2F205krell%2Findex.html&partnerID=3834 Page 12 of 14

Stereophile: Krell KAV-400xi integrated amplifier of odd harmonics can be seen, interspersed with a lower-level series of even harmonics. The fact that the harmonics decrease in level with increasing order might mitigate their audibility, but I must admit to some alarm at seeing this behavior. Finally, the decrease in the circuit's linearity at high frequencies, referred to earlier, results in rather more intermodulation products than I like to see in the high-power, high-frequency intermodulation test (fig.9), taken just below the level that caused visible waveform clipping on the oscilloscope screen. However, this is at a very high output power; the spuriae fell rapidly with decreasing power.

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Fig.8 Krell KAV-400xi, spectrum of 50Hz sinewave, DC-1kHz, at 100W into 4 ohms

(linear frequency scale).

Fig.9 Krell KAV-400xi, HF intermodulation spectrum, DC-24kHz, 19+20kHz at

350W peak into 4 ohms (linear frequency scale).

Summing up the Krell KAV-400xi's measured performance is difficult, as some of its odd behavior will not be an issue when it comes to playing back music at normal listening levels. It is also possible that our sample was defective, though the fact http://www.printthis.clickability.com/pt/cpt?action=cpt&title=Stereop…reophile.com%2Fintegratedamps%2F205krell%2Findex.html&partnerID=3834 Page 13 of 14

Stereophile: Krell KAV-400xi integrated amplifier that both channels behaved similarly is evidence for that not being the case. But I would avoid pairing the amplifier with loudspeakers that drop below 4 ohms—such as Krell's own Resolution 1—and would make sure it had adequate ventilation.

—John Atkinson

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Stereophile: Krell KAV-400xi integrated amplifier

Krell KAV-400xi integrated amplifier

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