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Equipment Review
December 2001

Krell FPB-300c Stereo Amplifier

by Wes Phillips

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"One of those rare audio products that are virtually without fault."

 

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Review Summary
Sound "Transparent and effortless in operation" -- "maddeningly difficult to actually hear"; "over the course of an extended audition, I tried to categorize the FPB-300c's 'sound,' but it simply doesn't seem to have one."
Features Sustained Plateau Bias II, which employs microprocessors to monitor not only the signal level, but also the loudspeaker's impedance; Current Mode Technology allows each output stage of the Sustained Plateau Bias operation to operate in current mode rather than voltage mode, and CAST takes advantage of Krell's Current Mode Technology to transmit signal as current.
Use Unlikely to be taxed by any speaker load; "its CAST technology makes a strong argument for utilizing it in an all-Krell system."
Value "[As expensive as the FPB-300c is,] are there amplifiers that can better [it]? If so, I haven't heard them yet. There are a few others that come close, or possibly even match it. The bad news is, they cost more.

Although Krell has made preamplifiers almost since the company's inception -- and has built top-of-the-line digital components for more than a decade -- Krell's name and fame have always been exemplified by its amplifiers. Hulking constructions festooned with heatsinks and fronted by massive slabs of anodized aluminum -- the gold Krell name-badge screwed tightly down with its six signature screws -- Krell power amplifiers possess a macho mystique attained by only a handful of products. Just as Duesenberg lent its name to a type of superlative ("It's a doozie!") and another car marque, Cadillac, came to personify excellence, "built like a Krell" has come to symbolize engineering and construction quality in the world of hi-fi.

This is not to say that the company is without it critics. Krell amps are unabashedly expensive. Krell's brand of quality does not come cheap -- and yet, to criticize a Krell amplifier for being needlessly rugged or over-engineered is to miss the point. The point has always been to build equipment that CEO Dan D'Agostino likes -- and from the company's earliest days, D'Agostino has demanded that Krell's amps have tremendous transient response, almost limitless dynamic potential, the ability to drive impossibly difficult loads, and a sense of effortless power. And, not so coincidentally, D'Agostino likes nice things -- Italian suits, shoes, and cars; Swiss watches; and haute cuisine -- all areas where excellence has not been achieved unless the product also exhibits a certain sense of style. And all, need I add, areas where a product's expense merely adds a certain cachet.

On the other hand, Krell's biggest competitor may well be itself. No one who has ever bought a Krell amplifier has actually worn it out. The first ones made -- some 21 years ago -- are still working as well as they ever did and will continue to do so for another 20 years, whereas that fancy meal you ate at Daniel last night has probably already turned to, um, a memory.

In mountains, the shortest way is from peak to peak...

Krell's amplifiers have always been based upon class-A operation, which is the most linear, lowest distortion operational mode. But there are inherent problems with class-A operation: The full current needed for full-power operation is continuously carried by the amp at all times, no matter what the signal actually requires. This is inefficient, delivering 10% or less of the amp's total power draw as usable power. The rest of that draw is turned into heat. Thousands of watts of heat end up being dissipated to create a few hundred watts of usable power. This means that class-A amps need huge cooling systems, usually either massive heatsinks or fans, or both, and these add to the amp's size and cost.

A simple solution to this is to bias the amplifier to operate in class AB, where the amp will operate at a much higher level of efficiency (possibly as high as 50%), which permits the amp to be smaller and requires less heat dissipation. The downside is higher distortion.

Beginning with the astonishing Krell Audio Standard amplifier, which I auditioned at some length in Santa Fe, Krell employed a technology called Sustained Plateau Bias. The KAS tracked the musical signal in relation to the amplifier's bias. The bias level was set in several discrete plateaus, so that when the musical signal required a higher bias level to remain in class-A operation, the amplifier would elevate the bias to that plateau long enough to produce the signal needed before ramping back down to a lower bias point. This kept the amplifier operating in class A no matter what the signal requirements, but it reduced the amount of wasted energy.

The FPB, or Full Power Balanced, line of amplifiers employs Sustained Plateau Bias II, a refinement that employs microprocessors to monitor not only the signal level, but also the loudspeaker's impedance. That way, both signal and load are monitored and constantly adjusted so that the amplifier constantly operates in the class-A bias that yields the lowest possible distortion with the lowest possible heat dissipation at all times. In theory, it's a win/win situation. And, in practice, that's what it seemed, too. I auditioned the Krell FPB-600, and it was powerful, transparent, nuanced, and reliable.

But that was the FPB-600 -- would all of that still prove true in a power amplifier rated at half the power? We'll get there, but the $10,000 USD FPB-300c is also the recipient of several far newer, proprietary Krell technologies: Krell Current Mode and CAST, Krell's novel analog connection scheme.

Krell Current Mode allows each output stage of the Sustained Plateau Bias operation to operate in current mode rather than voltage mode, which is the norm. CMT permits low overall impedances to be employed within the circuit, which preserves low-noise and high-bandwidth operation without having to resort to large amounts of overall negative feedback. In CMT, Krell uses a "moderate" amount of feedback to provide both gain and thermal stability.

In an ordinary audio system, signal is transmitted in the voltage domain and every component and connecting cable operates as a separate entity that interacts with the other system elements in its own peculiar way. CAST takes advantage of Krell's Current Mode Technology to transmit signal as current. This has several advantages -- for one thing, it causes the entire chain of CAST components to behave as if they were a single global circuit. Rather than dictating that the preamp's output be low and the power amplifier's impedance be high, which creates a situation where the interconnecting cable's impedance can affect (even distort) the signal voltage operating the amplifier, CAST transfers current from a high-impedance source to a low-impedance load, minimizing (if not outright eliminating) the cable's effect on signal transmission. And, if you're using a CD player, the signal can be taken straight off the DACs without going through a I-to-V conversion stage. Krell claims CAST is responsible for a 6dB noise reduction alone. Of course, if you're not using an all-CAST system (read: Krell), you don't reap any of these benefits. For details about the CAST system in operation, refer to my full Krell CAST system review at onhifi.com.

On top of these proprietary technologies, Krell also employs several fundamental construction philosophies that have served well over the years. For one thing, the amplifier is fully complementary (balanced). This doubles the amount of circuitry involved, but, of course, Krell maintains that symmetrical circuit paths independently running the positive and negative amplification signals not only reject noise and insure integrity, but also lock the speaker into a push-pull relationship. In other words, balanced operation guarantees speaker control.

Krell also believes in regulation big time. Krell's Active Regulation instantly corrects any change in supply voltage no matter whether the source is a variation in the AC-line voltage or a change in output-stage current delivery. The output stage in all FPB amplifiers employs a free-floating feedback arrangement wherein ultra-fast regulators independently monitor the output stage and respond to the smallest drop in current or voltage with regulator response that is all but instantaneous.

Add to this, Krell's usual high construction and parts standards, which include the company's proprietary output and driver transistors, and you have a product that lives up to its nameplate. Yes, it's built like a Krell, measuring 19"W x 10 1/4"H x 20"D and weighing 110 pounds. It even boasts two pairs of the best-connecting, easiest-to-tighten speaker connections I've ever used. From the largest details to the smallest, the FPB-300c simply screams pride of ownership.

...But that requires long legs!

Try to imagine the perfect amplifier. What would it be? It would have no sonic signature of its own and it would drive any loudspeaker.

Sounds like a description of the FPB-300c. The amplifier is maddeningly difficult to actually hear! Whether driving small speakers, such as Krell's LAT-2 or Dynaudio's Contour 1.3 Mk IIs, or larger reference speakers such as Dynaudio's $30,000 Evidence Temptations, the FPB-300c is transparent and effortless in operation.

Over the course of an extended audition, I tried to categorize the FPB-300c's "sound," but it simply doesn't seem to have one. And I didn't just use it with its matching preamp and CD player, either. I had an Ayre K-1x and V3, a Niro Control Engine and Power Engine, and a Conrad-Johnson Premier 17LS in house and in system over that time -- and while I could clearly hear differences in each combination of gear and speaker I tried, none of those differences could be laid at the feet of the Krell.

Associated Equipment

Loudspeakers – Dynaudio Evidence Temptation and Contour 1.3 Mk II, Krell LAT-2.

Preamplifiers Ayre K1x, Conrad-Johnson Premier 17LS, Krell KCT, Niro Control Engine.

Power amplifiers – Ayre V-3, Musical Fidelity Nu-Vista 300, Niro Power Engine.

Digital – Musical Fidelity A3CD, Krell KPS-28c and Sony CDP CX-400 CD players; Bell Canto DAC1 and Perpetual Technologies P-3A DACs.

Interconnects – AudioTruth Midnight and DiMarzio M-Path.

Speaker cables – AudioQuest Dragon and DiMarzio Super M-Path.

Digital cable – Illuminations Orchid, Kimber KCAG.

Accessories – OSAR Selway Audio Racks, Audio Power Industries Power Wedge Ultra 116.

Room treatments – ASC Tube Traps, Slim Jims, and Bass Traps.

This is more than frustrating, to a person in my position -- it's career-threatening. If everybody came out with products that had no sonic signature whatsoever, I'd be out of a job. So trust me when I say I wanted to hear the FPB-300c in operation.

Usually, when you have an amplifier capable of anything approaching 300Wpc, you can throw a lot of huge orchestral works at it -- or something with a synthesized bass -- and just revel in the power for a while. And I certainly did that with the FPB-300c. Daniel Barenboim's new recording of Stravinsky's Le Sacre du Printemps, Debussy's La Mer, and Boulez's Notations VII with the CSO [Teldec 8573-8170202] arrived in the mail just in time to test the Krell's mettle.

It’s a great recording -- you can hear the vast volume of Orchestra Hall before the first note is played, all that air just sitting there. Then come the insanely high bassoon notes that open Le Sacre, and the CSO is off. The Krell was seamless; from those tortuous first notes to the full orchestral stomp and chuff that follow, the music never changed character. And the sound of those massive chords dying in the hall was as crisply delineated as the tuttis.

What a great performance of Le Sacre this is! And what a workout for the whole system. But the Dynaudio Temptations were perfectly controlled by the Krell. I could hear through them both down to the direction of the nap on the carpet (well, almost).

At times, the Stravinsky actually acoustically overloaded the hall; there was that acoustic compression that occurs in concerts when a big band really lets loose. That’s why, in some regards, the disc's companion piece of La Mer was even more satisfactory. The orchestral colors -- and the sound of the hall itself -- came through with phenomenal clarity and detail. What a great orchestra the CSO is -- and what a truly grainless, transparent recording of them this is. I recommend it to anyone in need of an hour's beauty. Don't be put off by the Boulez: it ain't Debussy, but Barenboim and the CSO find true ecstasies of logic in it. You may not ever find yourself humming it, but it's worth having.

Oh damn! Once again I forgot I was listening to the Krell, not the music. Oh well, it happens.

Of course, the sneaky thing to do with a big amp is to find something small and filled with grace. A lot of large amplifiers stumble when you don't actually need their massive output. They can't get out of their own way.

To that end, I can think of almost nothing more delicate than Ralph Kirkpatrick's harpsichord rendition of Das Wohltemperierte Klavier [DG 413 891]. (Well, actually I can, come to think of it. I once heard Kirkpatrick perform the work on a clavichord, but that was so delicate, I doubt even he could have heard it clearly.) After listening to Glenn Gould's crystalline clarity, it's refreshing to hear Kirkpatrick's stately, unhurried, unabashedly emotional reading of this towering work. Of course, he did write the book on interpreting the piece (Interpreting Bach's Well Tempered Clavier, Yale Press, 1984), but there's nothing pedantic about Kirkpatick's unrelentingly rhythmic flow, which emphasizes the different voices and interior beats without detracting from the headlong forward momentum.

Dynamically, we're talking fractions of degrees here, yet -- as the FPB-300c clearly illustrates -- in the hands of a master, a few degrees can speak volumes. The interior dances and contrapuntal figures that make up these preludes and fugues are as delicate as butterfly wings, yet the Krell amp manages to make them sing and gambol as they ought to.

And that's an accomplishment that few of your micro-watt single-ended amps can brag about!

'Tis a gift to be simple...

My long-term reference amplifier is the Musical Fidelity Nu-Vista 300. It's not perfect, but I like it and know its shortcomings (which are relatively easy to ignore) well. And it, unlike many high-output contenders, was affordable, costing about half as much as the Krell.

The Nu-Vista exhibits a mild warmth in comparison to the FPB-300c -- this is most noticeable in a mild softening of deep-bass information such as the immense drum thwacks in Barenboim's Le Sacre. The Krell kept control of these immense percussion blasts -- they were lean and taut, crisp and well-differentiated. The Nu-Vista thickened the transient -- and this is not so much a result of its mild warmth as it seems a blurring of the initial attack.

However, in the reproduction of the Wohltemperierte Klavier, the Nu-Vista's signature sweetening did seem to manifest itself. The Krell reproduced Kirkpatrick's harpsichord with a tad more zing and an extended crystalline clarity that let the plucked-string overtones float in the ambient sound longer before decaying -- a slow process that remained audible deep into the room sound.

The Nu-Vista imparted less zing. The plucked strings sounded heavier and the sound was not so crisp -- and this is an effect some listeners might actually prefer. However, the decay of the string overtones was far more rapid, blending with the room sound faster and being masked by it sooner.

These don't sound like night-and-day differences -- and they weren't. But they were repeatable and noticeable. The Nu-Vista is an amazing amplifier and one heck of a bargain, but the Krell FPB-300c is clearly more transparent and capable of extracting even more low-level detail from my musical sources. This doesn't mean I'll stop using the Musical Fidelity as my reference -- after all, I own it already -- but I can no longer trust it as the last word in accuracy.

I love those that yearn for the impossible

The Krell FPB-300c is one of those rare audio products that are virtually without fault. If it can sound strained or produce ugly sounds that aren't indigenous to a recording, I certainly wasn't capable of forcing it to do so -- and I gave it a thorough workout. Still, I suppose a sufficiently dedicated soul could do so, if he tried hard enough. But why would anyone want to?

I auditioned the Krell FPB-300c with a wide range of associated gear and it worked like a dream with all of it -- from tube preamp to $30,000 loudspeakers. It always performed like a trooper, although I have to say that its CAST technology makes a strong argument for utilizing it in an all-Krell system. However, audiophiles don't seem to cotton to all-one-brand systems, so it's good news that the Krell is so versatile.

It is $10,000, however, and there's no getting around that. It would be great if you could get it cheaper, but its build-quality is impeccable -- as is its parts quality. Factor in the cost of Krell's construction methods, which are essentially hand assembly, and it's not hard to see where the money goes.

There are some mighty tasty amplifiers out there that cost less money. You might possibly even be happy with one of them -- I certainly could be with quite a few amps in the $4k-$6k range. That money will buy an awfully good amplifier. But I'd be a liar if I said those amps were as good as the Krell FPB-300c. Is the difference between the next level down and the FPB-300c vast? No. To get that last bit of performance, you pay quite a price. But make no mistake, what it buys is real. Are there amplifiers that can better the FPB-300c? If so, I haven't heard them yet. There are a few others that come close, or possibly even match it. The bad news is, they cost more. Some, like the Mark Levinson No.33H, are monoblocks that cost a lot more.

On the other hand, buying the FPB-300c gets you off the audiophile treadmill. You're done. All you need to do now is sit back and enjoy. And you will. You will.

...Wes Phillips
wes@soundstage.com

Krell FPB-300c Stereo Amplifier
Price:
$10,000 USD.
Warranty: Five years parts and labor.

Krell Industries, Inc.
45 Connair Road
Orange, CT 06477-3850
Tel: (203) 799-9954
Fax: (203) 891-2-28

E-mail: krell@krellonline.com
Website: www.krellonline.com

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