Krell Industries Inc., founded by its C.E.O. and chief designer Dan D'Agostino, is one of America's largest manufacturers of high-end audio systems. While most of their acclaim has come from their power amplifiers and CD players (their flagship model being the Master Reference Amplifier with a price of roughly $100,000), they also make preamplifiers, loudspeakers, subwoofers, and Super Audio CD players.

Dan D'Agostino was ousted by the investor he brought in, over the direction the company should take.[citation needed] He formed a new company, Dan D'Agostino Master Audio Systems, that competes with his old firm.


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KSA-50

1983 or abouts

Solid-state stereo power amplifier. Maximum power output: 50W into 8 ohms (17dBW), doubles with each halving of load impedance down to 1 ohm.

The KSA-50 is beautifully styled and built. I have never seen any piece of audio gear built quite so solidly, or, when the cover is removed, assembled with such ob vious care. This is Rolls-Royce quality of a kind few competitors are likely to equal.

Like most of the better class-A amplifiers I've heard, the Krell KSA-50 sounds liquid rather than dynamic. 

You get about 70 watts of RMS power with 8 ohms, 150 watts with 4 ohms, and sufficient watts into 2 ohms to threaten my load resistors. There is almost enough power to drive a pair of Apogee Scintillas at their ohm setting

Dimensions: 19" W by 9" H (including feet) by 19" D (including handles). Weight: 60 lbs (net).

Krell KSA-50S

1995 or abouts

The new Krell was significantly better than its predecessor in one important way: that gloriously liquid quality I noted earlier made the earlier Krell sound a little "electronic" by comparison. Hendricks' voice acquired a rather phlegmy edge via the older amplifier; the '50S presented it with a significantly more natural character. The original KSA-50's high frequencies were also grainier compared with the KSA-50S, and slightly sibilant. The new amplifier had altogether a more civilized, more neutral sound, I found. But when it came to the soundstage, the Dresden walls weren't illuminated to the same extent as they had been with the old amp.

While the Krell KSA-50S's bass is not quite as awesomely kick-ass deep as the earlier KSA-50, it has lost some of the slam, the "Wham, Bam, thank you, Dan!," that characterized the original KSA-50.—John Atkinson

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Krell KSA-80

1988

With the Krell KSA-80, honest audiophiles consider this to be one of the finer sounding amps, and one of Krell's best. Although rated at 80wpc, it is very high current and will drive any load.

Though 80wpc, the KSA-80 is a true pure Class A amplifier, so it runs hot and draws enormous amounts of power. Anyone who has power-hungry, tough-to-drive speakers, especially, should keep their eyes open for one of these amplifiers.

It is difficult to find fault with this amplifier for it does so many things well. Its coherence is from top to bottom. The soundstage is very deep and seems to extend well beyond the boundaries of the speakers. Vocalists and instruments have a nice 3D quality. The bass of course is phenomenal with great pitch and control. Its low frequency presentation is very deep and powerful.

The bass slam, in particular, is amazing. The mid and high range are very uncoloured, detailed and fast. In the system, there no grain or glare that can plague some solid state designs. 

Krell KSA-80B

1989-1992 abouts

Same specifications as the KSA-80 but different power supply

KRELL KSA-80B Pure ClassA Power Amp - 1989    KSA-80 KRELL - 中古オーディオ 高価買取・販売 ハイファイ堂

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Krell KSA-100

The start - 1981

Dan plucked the Krell name from the classic sci-fi flick, "Forbidden Planet," and I'm guessing it was Dr. Morbius' line, "In times long past this planet was the home of a mighty and noble race of beings, which called themselves the Krell." that sparked D'Agostino's imagination. Dan and his wife Rondi launched the company with just one product, the KSA 100 amplifier, at the 1981 Consumer Electronics Show. In the early days the D'Agostinos worked hand to mouth, they'd build a few amps, put them in their car, drive them to a dealer, get a check, then build two more and so on.

The KSA 100 could drive any load, regardless of impedance. It delivered 100 watts into 8 ohms, 200 watts into 4, 800 watts into 2, and 1,600 watts into 1 ohm! 

Krell KSA-100 MK2

The KSA 100 could drive any load, regardless of impedance. It delivered 100 watts into 8 ohms, 200 watts into 4, 800 watts into 2, and 1,600 watts into 1 ohm! At $2,200 it was pricey, but less expensive than the market leaders' offerings.

Although Krell has always been strongly associated with Class A biasing it’s their ability to drive extremely tough loads, like the renowned amplifier killer the Apogee Scintilla (1 Ohm version) fullrange ribbonspeaker, that really illustrated the kind of DNA a Krell was made of. Only a few other amplifiers in this era, and most of them were amps with low powerratings, could drive speakers at such low impedences. Opening up the “hood ” of the amp gives you a strong visual indication of the ‘brute force’ method used to get an unflappable amp that could drive anything on the market then and today. D’Agostino’s assault on the highend poweramplifier market was very successful worldwide due to these first designs. After Levinson and Threshold, Krell established itself as a strong contender on the highend audio-market.

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Krell KSA-100S

The KSA-100S, built with legendary Krell attention to construction quality and able to drive difficult loads, is undoubtedly a highly competent amplifier. Its sonic personality is slightly on the soft, forgiving side, which usefully minimized the hardness of many digital recordings. If past experience with Krell products is anything to go by, the KSA-100S is likely to be highly reliable, and will maintain a higher-than-usual proportion of its resale value if (when?) its owner decides to move further upmarket.

The Brystons are well-built (if not to Krell standards), cost about 20% less than the '100S ($4390 vs $5500), and, in the series mode, offer substantially more power. Given my tastes and the components currently in my system, I'd choose the Bryston 7Bs. But the Krell KSA-100S remains a worthy contender, especially for systems that are on the borderline of being too bright.

Krell KSA-150

1990

The music just sounds right with silky smooth vocals and a wonderful piano. Those who have the oportunity to attend a LIVE symphony .... do so for comparison and enjoyment. If you can clearly hear the separate instruments as I can now and they are not a blurr playing the same note you are on the way. With the right material you can forget it's recorded.

The addition of the Krell KSA-150 made the musical experience more real and enjoyable and I have no urge to update my amp having lived with the KSA-150 for six months. With Krell's reputation for taking care of their equipment, build quality, and sound, the KSA-150 is a keeper. I would recommend a good used KSA-150 to anyone looking for a quality amp (new or used)in $1500-$2000 price range, especially if they have a difficult load to drive.

built to deliver power of 150 watts into 8 ohms per channel, doubling with every half of the impedance to 300 watts into 4 ohms, and exceeding 600 watts into 2 ohms & below

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Krell KSA-200

Power!!! Rated at 200w/ch in 8 ohms, 400w/ch into 4 ohms, 1600w/ch into 1 ohm. I dont believe a speaker exists this amp cant drive.

I use a balanced krell pre amp to drive the ksa 200 which drives a pair of huge VMPS super towers R. the sound of the ksa 200 is powerful but surprisingly delicate in the highs and midrange. what surprised me most about this amp was it's ability to run the VMPS's to a legit 120 db level without a hardening of the sound or muddying the bass. All manufacturers hype aside this is indicative of huge power reserves. The transformer is the size of a volley ball and the capacitors as big as beer cans. this leads to the only drawback to this amp, it is huge and weighs 125 lbs and runs hot enough to heat up a small room.

The ksa 200 was only made for a short time before krell redesigned the case and heat sinks [ a good idea].

Krell KSA-200S

Krell explains that their specification defines a pure voltage output which is maintained into successive halving of the load value, to 4 ohms, 2 ohms, and even 1 ohm (where the '200S's rated output power is 1600Wpc!). Only a very-low-impedance power supply combined with an ultra-high-current output stage and low-impedance internal wiring can support such performance. At its rated level into 1 ohm, the amplifier is putting out 3200W, for which it will require at least 4000W from the 2800VA toroid.

Dependable and even-tempered, the Krell KSA-200S gets my recommendation. It may not be exceptional in any one respect, but it is exceptional by virtue of its fine balance of properties. This is as true of the '200S as it is of the matching Krell KRC-2 preamplifier, and positions the Krell at the forefront for amplifiers of its class.

Speculation as to its audiophile status indicates that it would be a Class A contender in Stereophile's "Recommended Components." Its ultimate rating will, of course, depend to some degree on how the performance of the competition shapes up.

OK, it might not be a tube design, but it's damn good nonetheless!

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Krell KSA-200B

1988 - 1989 - Does this model really exist ?

The amplifier was a powerhouse in the bass. While not sounding as crisp or as sharply defined as some competitors, it had terrific slam and reach. Very low frequencies were effortlessly generated at considerable power, the amplifier never missing a beat. On the right system—notably the Apogee Mini Grand and the Wilson WATTs and Puppies—the Krell displayed good pace and rhythm. It was fascinating to hear the lovely but often earthbound Apogee Stage taking off in the actively crossed-over Mini Grand system (footnote 2). It could produce topflight, wide-range bass, mid-, and treble with the '200S as motive power.

Krell KSA-250

Internally, the KSA-250 is a study in simplicity as well as a technological tour de force. The 4.5kVA transformer, which by itself weighs 85 pounds (!), is located just behind the front panel, and is in turn followed by four 47,000µF capacitors covered by a printed circuit board. It is important to note that there is no wiring in the signal path, all connections being made via the pcb in the front end, and gold-plated copper-beryllium busbars in the output stage. There are 24 output devices per channel, all operating in class-A mode down to 3 ohms, where the amplifier reverts to class-AB (see Sidebar 3). The KSA-250 utilizes class-A circuitry throughout the audio and power-supply regulation stages, and can actually generate 320Wpc into 8 ohms. 

This amp draws an enormous amount of current (12A continuous, a not so pleasant side-effect of class-A operation), and should be, according to Krell, placed on its own dedicated 20A AC circuit. I would have to say, after listening to the KSA-250 in several AC mains modes (dedicated 15A and 20A lines, and non-dedicated lines) that their suggestion should be taken seriously.

Something else you might take into consideration before purchasing and installing a KSA-250 is the amount of heat produced. All class-A amps run hot, and this one is no exception. Even with the cool fall weather outside, our listening/family room turns into an inferno within 45 minutes after powering up. 

The Krell KSA-250 is a truly extraordinary piece of audio equipment. It is ruthlessly revealing of everything upstream and is, in this respect, the finest reference amplifier currently available. It will drive virtually any load, and is the first amplifier this listener has heard that successfully combines ultimate musical finesse with sheer dynamic brawn without sacrificing much along the way. While the KSA-250 does not quite measure up to the finest tube electronics in the area of harmonic accuracy, and falls somewhat short of the best solid-state in the ability to resolve vocal and instrumental attacks, it wins the prize in overall musical and sonic honesty. But if you're thinking about buying one of these, be darn sure that your front-end electronics are the very best, or else you may be disappointed.

We can see it clips (1% THD) at 325W into 8 ohms (25.1dBW), at 635W into 4 ohms (25dBW), and at over 1000W into 2 ohms (actually 1066W at 0.97% THD, or 24.3dBW). When driving 1 ohm, the KSA clipped at 1548W (22.9dBW). This is approaching perfect voltage-source behavior, and could be expected.

Weight: 140 lbs.

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Krell KSA-300S

1994

Stereophile ALWAYS sums it up very well....

Again, Rickie Lee Jones's "On the Boardwalk" clearly displayed the differences between the two amplifiers. As the music began, quietly and slowly, the 250 initially appeared airier and more open. As it progressed, the 300S's smoother, more grain-free sound took over, the 250 now seeming a bit lean and etched in comparison. The 300S had more punch and weight, especially through the midbass, and a more fluid, coherent sound overall. Both amplifiers impressed equally in the deep bass. The 250's relative leanness gave it a more superficially open quality, but at the cost of richness and a fully developed sense of weight and drive. The KSA-250 is still a very fine unit. But it has more than met its match in the 300S.

The sound here was also superb, though certainly displaying a different set of strengths and weaknesses due largely to the change in room and loudspeakers. It was a big sound, less intimate but more open and expansive than that in the smaller room. The KRC and KSA-300S used here were different samples from those discussed above, but despite all the system and room differences, nothing in the sound persuaded me to change my opinions of the Krell amplification. Somehow I had never quite been comfortable with the KSA-250 driving the Stages, though the results were certainly more than acceptable. The KSA-300S with the Stages, however, was a different, and more pleasing, proposition altogether.

Conclusions
Sam knew he was in trouble as he watched Jim disappear down the front walk, stuffing a down-payment check into his pocket. How would he explain this to Mary when she returned from visiting her mother? Oh, well, maybe she wouldn't notice the change. Uh-huh.

That new amplifier does look a bit like the old one, though its black, front-panel trim pieces and less art-decoish heatsinks sort of give it away. But how will he explain the less-toasty listening room? A mod, that's it! He'd had the old amp modified! Explaining the preamp would be more of a challenge...

This Pioneer AM/FM stereo receiver model SX-838 dates from 1972.

Rated at 50 watts per channel, RMS.

Looks very similar to the SX-939 that came few years later.

Beautiful blue display.

Krell KMA-100

1984

they are capable of delivering 100 watts into 8 ohms, 217 watts into 4 ohms and 380 watts into 2 ohms and nearly 800 into 1 ohm! All in pure class A. They are completely original in every part. Consecutive serial numbers.

Pick-up in person or delivery by our means is preferable to be agreed.

 DIMENSIONS:

 … Width 19.0”  483mm

  … Height  8.9”  226mm

  … Depth 18.9”   480mm

  * PESO 55.0 lb / 25 Kg  each

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These are huge amps with huge transformers, pure class A that keep doubling down right down to a half ohm load! Up to 2000wpc of pure class A!

Krell KMA-100 MKii

MK1

MK2

Krell KMA-160

1989

These are the big, brutish looking Class A amps from Krell. At 8 ohms, they put out 160W of pure Class A. They double up to 320W in 4 ohms, 640W in 2 ohms and an astonishing 1280W in 1 ohm. Running them on a dedicated outlet is strongly suggested because they really draw a lot of “juice”. If you have a lightning appliance sharing the same electrical line, it can dim when the Krells are turned on. Such is the might and requirement of the Krells. The amps are capable of driving any speakers with ease. They have a lovely warm overtone, tremendous amount of bass impact and very sweet highs. When fully warmed up, they sound almost tube like but with a tighter rein over the bass section. 

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Krell KMA-200

A perfect fit to drive your Apogee speakers...

The KMA-200's are one of Krell's early amplifiers, and many people believe they were some of the best sounding. They pump out 200W which isn't much for an amplifier in this size and weight by today's standards.  But they do so in pure Class A operation, which produces an unbelievable amount of current and therefore they are capable of driving the most difficult loads.  From the look of the power transformer, size of the capacitors, and output copper buss bars, it looks like you could arc weld with these monsters.  Folks with Apogee speakers often search these out for this reason, and as a result they are becoming harder and harder to find in decent shape.

Krell KMA-400

1988

Very little into it seems.

Early versions dont have balanced inputs. Later versions are balanced. This is a great amplifier. Don't look here for tube warmth though, but if you value speed and breadth of stage and bass and bass and bass.

Very rare monster mono block KRELL power amps kma-400's for $5500 cdn a pair. these are the even harder to find super rare balanced version with 400 watts per channel of pure class-A into 8 ohms and 800 into 4 ohms 1600 into 2 ohms 3200 into 1 ohms and will even drive .5 ohms at 6400 watts per channel. a true power house of superior sonic enjoyment with any speaker regardless of it's power or current demand. weight is over 400 pounds for the pair.

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Krell MDA-300

1992

These were monoblock versions of the KSA-150, but did not use conventional channel bridging. Instead, the amp circuit has two separate hemispheres to amplify the normal and inverted version of the signal in a differential manner, not referenced to ground. Bias current was increased over the KSA-150 to enrich class A operation and global feedback was eliminated. The result is a 90 lb. (net), 32 output transistor, 1.8 kVA transformer-equipped monaural powerhouse with Stygian bass power and control. I listened to these first at my dealer's driving the big B&W 800 system. After hearing this system reproduce large orchestral works with ease, I decided to try them at home. These amps had a warmer sound than most solid-state, with a sweet, relatively grainless top end. Dynamics were effortless, soundstaging was wider and more upfront than the KSA-150 when the material lacked depth (the midrange and presence region of the KSA-150 is depressed, giving extra depth which can be a euphonic effect)

Power
300 watts at 8 ohms
600 watts at 4 ohms
1200 watts at 2 ohms
2400 watts at 1 ohm

Weight 105lbs/ea

Krell MDA-500

1991

When only the best will do, the Krell flagship MDA 500 are performers. These are by far the most incredible amplifiers I have ever used. 500 watts of KRELL power doubling its output all the way down to 1Ω and 4000 watts, I do not know of a pair of speakers that they can not drive with control and uncompromising clarity! You are not just buying an amplifier you are purchasing part of a legacy. 

DIMENSIONS 19.0" WIDE 24.0" DEEP with handles 8.5" HIGH with feet 144 pounds 


Tech Specs: Continuous power: 
8 ohms 500 watts 
4 ohms 1000 watts  
2 ohms 2000 watts  
1 ohm 4000 watts 

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Krell KST-100

1991

The KST-100 is quite compact by Krell standards, its heatsinks contained within the overall width of the alloy front panel. Described as class-A to half power (more on this later), it is quite powerful at 100Wpc into 8 ohms (20dBW); ie, 50W 8 ohms class-A, with the specified power doubling into successive halvings of that impedance; with 800W quoted into 1 ohm.

Simple removal of the top cover provides access to a mono switch which allows the amplifier to perform in unbalanced bridge mode, working as a monoblock delivering 400W into 8 ohms and 800W into 4 ohms (both equivalent to 26dBW, footnote 1). Given the past history of Krell products being able to drive low-level impedances, these figures are believable.

In creating the KST-100, Krell has succeeded in trimming the fat from the audiophile KSA series. This recent introduction is definitely not a cheap version of the old KSA-80; rather, it is a cost-effective cousin of the new KSA-150. In absolute terms it equals the sonic performance of the KSA-80 and has a comparable power-output delivery, though it did not sound quite the same. Here you have to balance performance in terms of the bass speed of the KST and the absolute slam of a bigger Krell, or the lively, quick, detailed midrange of the KST vs its mild zippiness in the high treble.

Krell MRA

One of the most extreme amplifiers EVER built!!

Krell MRA mono amplifiers. The best Krell ever made. Only 50 were made I read somewhere. These were $150,000/pair when new.

These are the best Krell amplifiers ever made. Incredible size and weight 770 lbs each in the crate.

The MRA chassis was amazing. We looked at the output transistor array and wondered if we could even physically pickup the driver board! National sales manager, Bill McKiegan, proved it was possible, but it wasn't something he wanted to carry for a long period of time! Two MRA amplifiers were nearing completion while we walked by. These beasts were each perched atop a heavily reinforced cart that was labeled with a 1000 lb load maximum warning. It seemed very appropriate looking at these brute force monster amplifiers. Each time the impedance load on these monsters is halved, they respond with double the power. This doesn't stop until the limits of resistance are reached and a short is all that is left.

Try 16,000 watts of current based power on your fractional impedance speaker load and see what massive muscle can do with grace and maximum resolution added! How can you get this amount of current?

Each amplifier requires 40 ampere 220V connections for ideal power.

I heard these monos hooked up with the Wilson X-1s. They are truly incredible, I was blown away by the sheer power of the setup. Bass ripped through my chest. Massive transient attack etc. But it doesn't involve me musically. Wehn I listen the first thing I do is check the hairs on the back of my neck. I they are standing I know it is a good product. While the Wilson/Krell setup made me feel like I was in a Maxell commercial, alas, they did not move me the way much much cheaper electronics do. For me the reason to lissten to music is to be transported away. To be enveloped in the magic sound, transcend time and space. These amps never let that happen. True I did hear ever last drop of detail in the recording, but I don't care about that. I suppose this proves to me once and for all that transistors cannot touch tubes. I know that this opens up a whole can of worms but I'm sorry. If this is solid state at its finest (which it had better be damn close to for $125,000) I feel sorry for those who purchase it. Not because its a bad product, it very well might be state of the art, but because music can be so much more involving.

This is an 80's child.

Tuning range: FM, MW

Power output: 30 watts per channel into 8Ω (stereo)

Frequency response: 10Hz to 50kHz

Total harmonic distortion: 0.05%

Damping factor: 35

Dimensions: 450 x 142 x 306mm

Weight: 8.2kg

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Krell FPB-200

1997

"The FPB-200 is fully balanced, input to output, and also features fully regulated output devices, meaning each output transistor has its own high-speed active regulator to ensure that fluctuations in rail voltage cause no sonic degradation. Krell amplifier power output spec’s have always been rated very conservatively, and with both channels driven, and always operating in full class-A, this guy is capable of 200W into 8 ohms, 400W into 4 ohms, 800W into 2 ohms, and is stable driving even a 1 ohm load. This is possible because the power supply is built around a 2 KVa transformer!"

This whole series of FPB amps, from the 200 to the monster 650m monoblocks, absolutely rocks. The amps are so effortlessly dynamic that you will swear you have purchased new speakers. The sound is wide, well-delineated, with a tube-like sweetness.

The bass is deep, structured and crisp (unlike most tube amps). I don't know how anybody with an ear for music and any experience with live performances can say otherwise. Well, there are obviously those who have an anti-krell bias. Some of them are on this webpage--ie, MR B's reviews are obviously bogust--he "prefers Plinius" here, but on the Plinius page he "prefers Krell."

Krell FPB-300

1997

If your speakers present a difficult load, this Krell "Full Power Balanced" amplifier is the answer.

Capable of delivering clean high-current power in a class A configuration, and rated at 300W for 8 Ohms with up to 1200W at 2 Ohms.

Utilizes Krell's "Sustained Plateau II Bias Technology" to keeps things in check, and a fully balanced design from input to output which ensures the best stereo separation possible.  Since this amp is direct coupled (meaning there are no coupling capacitors in the signal path), careful consideration should be made when choosing and connecting a preamp.  Let us know what preamp you'll be using so we can make adjustments prior to shipping.

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Krell FPB-600

1997

I suspect that even the Krell team was surprised when the Full Power Balanced 600 began to take shape. On paper, it was simply a power-doubled FPB 300 delivered at a moderate and appropriate hike in price. In practice, the FPB 600 has gone much further. Great as the '300 undoubtedly is, the '600 holds all the aces, with a potential to severely embarrass a wide sampling of top-brand power-amplifier references. I'm quite certain that it redefines the art. It will certainly dictate a vigorous shakeup of the current stack of Class A power amplifiers in Stereophile's "Recommended Components." Since a Class A rating means "the best we know," I feel that, in the light of this design achievement, the rest will have to be re-classed (footnote 2).

The FPB 600 advances substantially on the FPB 300 in particular, and on the art of the power amp in general. In fact, I suspect that the Krell designers are now acutely embarrassed at the audible shortfall in matching preamplifier performance. With no disrespect intended to the KRC-HR (Stereophile, October 1996, Vol.19 No.10), just use one in conjunction with the KPS-20i/l and the FPB 600. Then bypass the KRC-HR by simply linking the existing balanced cables input to output, with no other changes whatsoever—and hear the system take off. Such is the '600's transparency that care in system alignment, choice of cable, and quality of connectors all offer substantial payoffs.

The FPB 600's sound quality was at the leading edge. The Wilson X-1 Grand SLAMM proved as nearly perfect a match as one could wish for. The overall quality and dynamic range available from this combination was both stunning and breathtaking.

Add into the equation its huge, uncompromised peak loudness, the incomparable power delivery confirmed in its excellent laboratory results, and the Krell FPB 600 is something quite special among power amplifiers. And, lest I forget: at the price, and taking everything into account, this big Krell is actually good value for money.

I confidently dub the Full Power Balanced 600 the "Grand Slam" of power amplifiers.

The '600 matched this achievement by measuring 945Wpc continuous into the same load (935Wpc into a scaled 8 ohms). This is a huge output, well nigh on 30dBW, and sounded it! Rated output level is 28dBW, 600W, 8 ohms—and this amplifier could hold to this level at all loads and frequencies, 20Hz-20kHz, 8 ohms down to 2 ohms.

I wasn't able to run my long-term continuous testing at 2 ohms, but compromised with five-second bursts—long by peak-measurement practice (eg, 20ms). The FPB 600 could sustain a 29.3dBW level into this load, corresponding to 3.4kWpc—an extraordinary figure.

Driven on a toneburst equivalent to peak program duty at 8 ohms, it reached to touch the 1kW line, while at 4 ohms it attained 1.85kW, and for 2 ohms 3.53kW. And for 1 ohm—wait for it—an amazing 6kW! These are single-channel results, but, measured as short-term ratings, they should be available from both channels simultaneously.

Krell FPB-250M(C)

1997

I have used the old Krell KSA250, KSA300s and recently upgraded to FPB250mc. FPB250 is even more transparent with better sonic separation and expansive sound stage than the fantastic KSA300s. This is particularly so when you play large symphony music with multiple instruments. The sound is fast, lively and fresh to the extent that you can imagine that you listen to live music. They make me want to listen to classical music more often. Bass punch and control are exceptional, but the body of the bass itself is slightly less than the 300s. For mid-range vocal, I feel FPB250 is very neutral but not as warm as the KSA300s. The KSA300s seems to give more body and character to the singers. I still like the KSA300s a lot as the “s” series has its uniquely sweet character. So, it is the matter of personal taste. Both amplifiers are exceptional in their own ways. As for the old KSA250, the KSA300s beat it in every aspect so the upgrade was an easy choice.

This review is for the 250m and not the 250mc. The main difference (other than cosmetics) is Krell's new CAST technology which (unless you're using other CAST components) means that any used pair of 250m will be a true bargain compared with the 250mc.

At this price range, however, any review of amps is more about personal musical preferences and component synergy than simply better/worse.

I bought these after reviewing a number of high end models. I found them brighter, punchier and more detailed than the Levinson 332. Within the Krell family, they had better soundstage and warmer mid-range than the FBP 350; FBP 350 has more grunt and bass slam.

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Krell FPD-350M(C)

1997

350 WPC into 8 ohms. 700 WPC into 4 ohms and 1200 WPC into 2 ohm loads. These Amplifiers are class A rated and are fully balanced. If you know anything about KRELL Amplifiers, Their known for their Bass Slam and total control of the speakers. These amplifiers will drive any speakers on the Planet!

I was pleasantly surprised at the musicality of this product. Traditionally (for me), Krell has lacked warmth and palpability, yet these monoblocks really excelled at capturing the soul of the music - a cardinal feature. Associated equipment included Utopia and Mezzo-Utopia spkrs, dCS front-end and C-J 16LS preamp, Transparent Ref cable/IC's.

CAST your fate to the wind
Incredibly, I found, the Krell 350Mc monoblocks were more self-effacing than the slightly-more-expensive Linn Klimax, my current solid-state reference. The Krells actually drew less attention to themselves from the midrange on up through those sweet, engaging yet detailed highs; attractive enough to pull me right into the music, but fairly subtle about it all. Imagine.

The bottom end was powerful, just what you'd expect from a Krell. It was impressive, no doubt about it. In fact, I couldn't help being aware of how great the bass was. Is that a good thing or not? I dunno, you might feel inclined to argue about it, but not me. I just enjoyed it.

The Linns had slightly better microdynamics, the Krells slightly better macrodynamics. The Klimax sound a touch "white" and more transparent on top in comparison to the Krells, the 350Mc were slightly darker and seductively sweeter.

So...is it all just a matter of taste? Yep. And if your tastes runs to their sound, don't even hesitate. The FPB 350mc is a classic class-A design if there ever was one. Highly recommended!

Maximum power delivery of a monstrous 475W into 8 ohms (26.8dBW), way above the specified power. 850W was available into 4 ohms (26.3dBW) and while I measured 1060W into 2 ohms (24.2 dBW) rather than the specified 1400W, the AC line in our Santa Fe office was sagging significantly for this measurement.

Krell FPB-650M(C)

1999

Put away your low flea powered triodes. They CANNOT do what this amp does. Take the midrange magic of the 600 Krell and double the power (tests have indicated this amp puts out 950 watts into 8 ohms) and you have a magic amp. Listen to Morrisey come alive in your listening room or gunshots sound as they do at the range 🙂 Hello? I'm sorry, I've heard a lot of amps and cannot say there is one that does music and movies better or more accurately. Cannot imagine why there is not more extensive press, except maybe Jonathan Valin's glowing reviews of this in the Absolute Sound as well as the synergy with the KPS 25Sc. The absolute best amp I've ever heard. Go listen and hear for yourself. Sweet, Subtle, Powerful, Musical, Live... Worth every dollar.

Power output: 650 watts into 8Ω (mono)

Frequency response: 20Hz to 20kHz

Total harmonic distortion: 0.03%

Gain: 26.4 dB

Input sensitivity: 3.39V

Signal to noise ratio: 121dB

Dimensions: 318 x 267 x 673mm

Weight: 63.6kg

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Krell FPB-300c(x)

2001

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.

Krell FPB-400cx

Killer amp. Completely invalidates the old stereotypes about Krell amps sounding 'cold' or 'bright'. I had shopped this amp against the top tube amps among others, and the Krell was just as warm, without being in any way dark or veiled like the Mark Levinsons.

I had previously owned the well-reviewed 400wpc Classe CA-401 (very similar to their highly touted CAM 350 monoblocks), and the Krell BLEW IT AWAY. I ran the 2 amps back-to-back in my living room, and the Classe sounded small, pinched and anemic compared to the Krell. I'd enjoyed the warmth of the Classe, but Dianna Krall through the Krell was just as pleasingly absent any solid-state hardness, and was even smoother and more full-bodied.

The difference was surprisingly dramatic given that I was starting with such a natural sounding amp in the Classe, but it was like I'd made a switch upstream from a hard-sounding, cheap solid-state pre-amp to a world-class tube pre-amp.

And the bass - Oh My God - that's the part about the Krell stereotype that is 100% true. Immense, powerful, super deep yet absolutely controlled.

Price (RRP): £12000

OUTPUT POWER EACH CHANNEL DRIVEN: 8 Ohms 400 W 4 Ohms 800 W 2 Ohms 1,600 W

OUTPUT VOLTAGE: Peak to Peak 170 V RMS 60V

UNIT ONLY: 110.0 lb., 50.0 kg 

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Krell FPB-700cx

2003

Bring it on home….

The longer I participate in this endeavor, the more I realize that there is no magic bullet. What was just last months greatest component since Edison's' Dictaphone often finds itself listed on the vast audio wasteland that is Audiogon.com. Driven by the hopes and dreams of the latest upgrade and the hope that it will bring us everlasting musical bliss, we are forever searching.

With the Krell FPB 700cx, I can say with certainty that we have an amplifier that should find itself a permanent home in all but the most obsessive, tweaky and ultra-deep pocketed audiophile. I for one could easily retire with an FPB 700cx and never look back. Built with uncompromising attention to detail and backed by a company that is in the game for the long haul, not an insignificant point in these troubled economic times, the FPB 700cx finds itself on a very short list of candidates in the super-amp category. Capable of truly engaging sound, the FPB 700cx always kept my attention pointed were it should be, connected to the excitement and life of the music. While some designs and technologies may focus their attention on perfecting a particular part of the musical spectrum, few can match the FPB 700cx's ability to blend its overall sonic strengths into what is a singular musical experience.

The FPB700 EXCEEDS the following measurements of the FPB-600

I wasn't able to run my long-term continuous testing at 2 ohms, but compromised with five-second bursts—long by peak-measurement practice (eg, 20ms). The FPB 600 could sustain a 29.3dBW level into this load, corresponding to 3.4kWpc—an extraordinary figure.

Driven on a toneburst equivalent to peak program duty at 8 ohms, it reached to touch the 1kW line, while at 4 ohms it attained 1.85kW, and for 2 ohms 3.53kW. And for 1 ohm—wait for it—an amazing 6kW! These are single-channel results, but, measured as short-term ratings, they should be available from both channels simultaneously.

Krell FPB-350Mcx

The bottom end was powerful, just what you'd expect from a Krell. It was impressive, no doubt about it. In fact, I couldn't help being aware of how great the bass was. Is that a good thing or not? I dunno, you might feel inclined to argue about it, but not me. I just enjoyed it.

The Linns had slightly better microdynamics, the Krells slightly better macrodynamics. The Klimax sound a touch "white" and more transparent on top in comparison to the Krells, the 350Mc were slightly darker and seductively sweeter.

So...is it all just a matter of taste? Yep. And if your tastes runs to their sound, don't even hesitate. The FPB 350mc is a classic class-A design if there ever was one. Highly recommended!

Monstrous 475W into 8 ohms (26.8dBW), way above the specified power. 850W was available into 4 ohms (26.3dBW) and while I measured 1060W into 2 ohms (24.2 dBW) rather than the specified 1400W, the AC linewas sagging significantly for this measurement.

  • Output Power, Each Channel Driven: 8 Ohms = 350 W, 4 Ohms = 700 W, 2 Ohms = 1,400 W
  • Output Voltage: Peak to Peak 138 V, RMS 49V
  • Unit Weight (each): 68.0 lb

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Krell FPB-450Mcx

There isn’t really much to say about these amps that you have not heard or read about them in reviews and user feedback. They are simply reference level monoblocks that will just about drive any speakers. They start off at 450W in 8 ohm, double up to 900W in 4 ohm and an astonishing 1,800W in 2 ohms. Each monoblock is a massive 98lb of pure audio muscle.

No where is it more noticeable in the sound difference than using these amps to drive a pair of Magnepan MG20.1s. The Maggies are not easy speakers to drive but the Krell drove them without breaking a sweat. Bass was clearly tighter, more controlled and the mids were more robust with higher extensions on the highs.

These amps were operating in a higher plane than our other resident amps. If you are looking for a used pair of monoblocks that didn’t cost more than $10,000, these should be on the top of list. There will be other brands and even some Krell models that will crowd this price range but if you want a starting power output of 450W, there are only a handful that will meet that spec and probably only the FPB-450MCx that will give you that audio completeness.

Krell FPB-750Mcx

Full Power Balanced 750MCX, Monoblock  Amplifier

The question is not how good this amp is and it is tremendously good, but why aren’t more amps this good? Through hole construction, 6000+ watts of transformer in each one, pure class A, CAST which was a huge bold step forward. Dan is an amazing guy to buck the norm with CAST and I know he endured a lot of crap from the industry for it, he’s an innovator and this is a perfected product thanks to his bold efforts.


MONO is the way to go with FPB amps, it’s in the details but the difference is obvious and we have had both. You don’t have to be an audiophile to hear how good and graceful these amps are, they are all about the music. They do not shove detail in your face, they do not exaggerate dynamic swings nor do they compress anything.

The detail with the CAST connection is beyond or equal anything I’ve ever heard, hard to say, but it’s at the level of the Momentum amps and FM acoustics, the detail is not exaggerated it’s just all there.

OUTPUT POWER EACH CHANNEL DRIVEN: 8 Ohms 750 W 4 Ohms 1,500 W 2 Ohms 3,000 W

OUTPUT VOLTAGE: Peak to Peak 240 V RMS 84V

UNIT ONLY: 140.0 lb., 63.6 kg

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