Krell FPB 300cx enough to drive B&W Nautilus 801?

I'm about to purchase the Nautilus 801s, along with the Krell FPB 300cx amp. Would there be any significant improvement if I were to get the Krell 400cx instead? I emphasize the word significant, because price is a major issue. I know the 801s need power, so any opinions as to the sufficiency of the 300cx would be much appreciated. Thanks.
The extra 100 watts derived from the 400cx is equivalent and on the order of only.5dB or about 5 amps. I doubt that you will ever tax the 300cx to anywhere near its limits unless you room is tremendously large or you wish to become deaf in the next few years. Further, I believe the circuit is not much different between the two amps. That is one very nice amp BTW.
The 300cx is plenty.
Thanks to both of you for taking the time to respond. You saved me some money!
I have only knowledge of the 801N with the FPB650 monos. They are great.

Yes the power difference of an extra 100 watts would be only one dB, BUT..........

The 300Cx is based on the FPB200 and the 400Cx is based on the FPB300. There was/is a considerable quality of sound difference between the FPB200 and the FPB300.

Based on that fact, I would do everything I could to swing for the FPB400Cx.

By the way when I went to actively bi-amping my B&W800's, Dan D'Agostino strongly urged me to go for the FPB300, yet he made no urging for me to go to the 600.)
Have you ever try Pass Labs' Alpeh 2 ? Give it a trial, it won't dissapoint you. Arguably best SS !
I have the 300cx driving the 802N. I would first put the extra money into biwiring and then go from there.
Thank you all. Richard (Drrdiamond), I'm alittle confused (and very ignorant). Are you saying D'Agostino encouraged you to go for one stereo amp of 300 watts rather than biamp? Or can you biamp with 2 stereo amps? I thought only monoblocks were used in a biamp scenario. Thanks again.
I auditioned both the 300cx and 400cx in my home system before I bit the bullet and dug deeper to purchase the 400cx. I have Thiel CS6s. The 400cx made an immediate audible improvement in dynamic contrast, air and detail and bass extension and sped with these speakers, which require much current to drive properly. My wife confirmed (thank heaven for small miracles!) The only thing that prevented me from getting a 700cx was simple lack of $$$$$! But I not hesitate if I could swing it.
No, I needed two FPB300's since I used an electronic x-over.

Stevecham, very compelling! The fact that you directly compared both amps in the same system (something I am not able to do) says a lot. It looks like I will be spending the extra money after all. Thanks for the input.
Liszt458: What may have been necessary for Stevecham with his Thiel CS6's, will not be the same for your B&W Nautilus 801's.

His speakers are very inefficient at 86db and yours are much easier to drive at 91db.

Save the money and buy music.
I think what Steve and I are primarily talking about is quality of the power, not the quantity.

I agree with Drrdiamond on this. It was not my goal to simply have more power, and besides, the wattage output gain between the 400cx and 300cx is really insignificant when it comes to sound pressure levels. My goal was to see if there was truly a qualitative difference at the same SPLs I normally listen to (usually b/w 70 to 80 dB with digital meter at 10 ft). The 400cx made a qualitative difference. I wish I could provide feedback about this for speakers that are easier to drive, such as B&Ws, Meadowlarks, Dunlavys and Vandersteens.

Liszt458: please send us your impressions when you're settled in with the 400cx.
Again, thanks to everybody for taking the time. Very informative! I decided to go for the 400cx, and I expect to have everything in place within the next 10 days or so. I'll let you know how it sounds.
a 300 ids not enough power to for a pair of 801's. i know through experience. i owned a pair of 802 and started with a 300 and eventually moved up to a 600 and then upgraded to the 700. the 300 is a great amp, but not enough for a pair of 801's. good luck
I think the 300cx would be more than sufficient power to run the 801's. B&W's are fairly efficient, I have 802'S, same power requirement, and am running tube mono-blocks at 220w/channel. I am NOT lacking power, in fact I haven't turned turned the volume up past about 1/3rd. Unless you are driving music for a auditorium or concert hall the 300 would be fine.
The 300cx is PLENTY to drive the 901's to levels above 100db. How many people listen to music that loud? :O
I am a no count nobody from nowhere when it comes to Hi-Fi equipment, but I have been studying very much to understand how it all works. I am getting into it all and have purchased a set of B&W n802 just recently. To my understanding with all my research, I have discovered that the increase in watts pr channel isn't about more volume. It's about the quality of the sound at all volume levels.
Krell's literature and web page state that the
FPB-300cx, FPB-400cx, and FPB-700cx share the SAME
circuit topology.

It's basically a question of how much power does the
power supply have to put into the same circuitry and
how many output devices share the load.

In that matter, the difference is only 1.25 dB.

The "quality" is really a function of how much of the amp's
capacity you are using. The smaller the fraction of the
amp's capacity - the more "linear" the response.

So you have to push a 300cx a little more than a 400cx to
deliver more power - and thus drive it more toward the
non-linear regime. However, you only push it 1.25 dB
more than the 400cx - so the difference will be marginal.

Dr. Gregory Greenman
I currently own a pair of B&W Nautilus 801's and the fpb 300c amp. There is absolutely no need to for the 400 amp. You'd be wasting your money. The amp provides more than adequate power. Any louder your ears will start bleeding. believe me it's plenty.
The 300c would be more than enough power as I was previously using one on my 801n's in a large room
without any strain. I replaced the 300c with a MAC
MC2000 and according to its meters very loud levels
are about 13 watts. The MAC sounds much better on these
and has no problem controlling the woofer. If you want SS
I would look at the MAC402 or 501's.
If money is no object buy the 400. The 300 is a great amp and will sound great. I doubt you will be disappointed
I was looking at getting the 300cx for my thiel 2.4 before settling with the Classe' ca401 which has a little bit more power. The 300cx has more then enough power but I believe that it is not how loud you want to push an amp but how well the amp performs when playing in the same sound level. A higher power amp will always performs better. Just think if 300cx can play loud with most speakers then why they need a 700cx!
With the CA401 I can listen at very low level and yet without losing dynamics. Just like driving a big V8 at cursing speed, smooth with great ease!
Well I don't entirely agree with a lot of you on here. I for 1 have two speakers the MBL 111B and the B&W 801N. First, for the Diamond series: the diamond tweeter does sound a little darker(ie less bright) and the crossover was improved somewhat, but keep in mind the diamond tweeter diaphrame is heavier and not metalic so yes it does sound a little smoother. Modifying the crossover in the 801N will get you some great results but be prepared to spend money on some on high end parts. The woofers were also changed for lack of a better word in the 801s Im not sure about the other models? The 801's are fairly effient and rated for 1000 watts (the MBL's are 78db and 2200 watts)but they are a difficult load, a stronger amp with a beefier power supply and robust output stage is going to get the most out of them. The MACS arn't even class A of course they run cool, the 801N's are generally a 3-4 ohm load, I listened to the MACS but was not that impressed so far, maybe it wasn't the right system or something. I was looking to switch over to MACS but gave up on that after hearing them versus the Krell on some 800D's. There is more to this than just the Power you guys are discussing, take for example my FPB350mc's they put out 485 into 8 ohms, the FPB450mcX puts out the same amount, 485 watts, on the test bench but being an "X" amp it does have improved circuit boards giving it a much wider bandwidth and honestly a better sound. I'm not saying anything negative about the FPB350m or mc, they are amazing amps they can even run my MBl's very very hard without any compression, if the wall voltage is held to 117 volts they are smooth as silk they only get that agressive sound when you get into the 125 volt range like we have here in CA. The MONO amps are far superior to the stereo amps, I hate the guys that exagerate so much on here but please understand me it is a night and DAY difference, the imaging, depth, hieght, and power of the mono amps is easily heard. I have a FPB300c for the rear channels and it was my first "c" amp, when I got the MONO's my wife said WOW that's a lot better, she claims not to be into it but she is totally an audio snob. Her granfather was an audiophile, her dad and she married one, enough said. You think the sound improvement from the earlier amps to the later is the wattage but it's the same it's the circuitry that's improved, in the case of the "c" amps it's mostly the driver stage. For the "X" amps, the circuitry is so good the bandwidth goes from 0-150mhz to 0-450mgz with the given increase in sound quality. What's the bandwidth on those MACS again??? he he he

Again the FPB 600 and FPB700 amps are not equivelant to the MONO brothers. The stereo amps are bridged designs. so the specs look the same except for the transformers of course which are much lager in the MONO amps. I personally think the FPB750mcX is the finest amp I have ever heard, better than the EVO units (except the 1&2) to my ears. I have not heard a good comparison with the EVO "e" series amps yet but I understand the circuit boards are better on those. I also have the FPB650mc amps and want to upgrade them to the mighty FPB750mcX amps and upgrade my KRC3 preamp to the EVO 202. the EVO1&2, best I have ever heard in my life!

The lower line FPB200 and 250 mono's just never sounded right? I'm not sure why they do not carry the torch but they just don't? I do listen to mine pretty loud at times but not 1000 watts, my 650's only put out 975 watts into 8 ohms anyway. But there is not a ton of difference in sound between the 350's and the 650's but for whatever reason the 650's do sound some how a little better, and believe it or not slightly stronger bass too.

What is the best amp, literally the FPB750mcX but my favorite is the FPB350mc MONO's, they are stunning in bang for the buck. Not easy living with all the dedicated power lines, heat and power bills but they cost less to operate than the EVO's lol. My wife hates the power bills here in CA and the heat in summer, but she only whins about it nothing serious.


Second: I have a few different Krell systems
Well first step done, I did get the FPB750MCX amps yesterday and got them set up last night. I love em. With the 801N's they are so smooth I think they would be even smoother with the 801D? There is a little more air up there with the X amps, it's only been one day but I would swear the new amps have a little more bass control? They seem to have a smoother mid-range too more like the Pass amps. They definitely do not care that the 801N's have a 15" woofer they push it around like it's an 8", sooo much definition and punch! It's amazing to me how much finesse and articulation these have and are still so smooth and effortless, I think these speakers were designed for these amps? They just get everything there is to get out of the 801N's, who the hell needs a sub? Top to bottom they just make it sound so easy, no strain at all. I running them with all 2ft runs of Krell Path speaker cable. Big chorus works are just amazing I can point to every singer, I can tell what kind of mallet they are using on the bass drum so easily. How they make the 801's start and stop like that on Michael Jackson's "This is it" I don't even know, you hear absolutely everything but it's not at all or ever harsh. I just feel like compared to the MC amps there is a little more air, bass definition and I can hear further into the music somehow? but honestly we are talking like that last 2%-3% here. Only from memory, but these amps look like they are even cleaner inside with the circuit design, it's like art in there. I can't remember for sure, but I think the little transformer in there for the circuitry is new too? I don't think my MC amps have that?

Can't wait to get a better preamp but I do love the KRC3, no regret's there it's so musical. I like to tweak and improve things like most all of you, but I do love the way this sounds right now, it's just so effortlessly musical. I can live with it for a long time like this.

Hey Rob,
Check out Dan's hour long video interview on his web site News section -- He talks about Krell and other things very interesting -- you will love it -- lots of great info -- but he also talks about other amps he thinks are great -- "PASS"
-- Keep up the good info on your system -
Nice amps!
That is a great video!I would like to listen to some of his new stuff. I think I want to try a pair of the 801D's now? One thing I have noticed with the 750mcx's driving the 801N's is that they really don't get that warm. Compared to driving the MBL's they are warm to the touch maybe hot if played loud but driving the MBL's you can cook on them. I like both the 801's and the MBL's for completely different reasons. If I had to pick one it would be MBL all the way but the 801 when driven by the krell's do not lack anything sound wise and you don't need a sub I love how tight and punchy the bass is in particular with the 801's. The MBL's just have such a huge gigantic soundstage and a nicer midrange and treble, the base is good but not equal to the 801's in my room anyway.

OK, one of the FPB750MCX amps has failed and was drawing in excess of 15 amps from the wall at idle so I boxed them up for repair. I sold all my extra amps so now for this system the only extra amp I have lying around was a S300i. I set the little amp up in theater pass through mode for the mean time, and set up the 801N's again, it dosn't sound too bad when you bypass the preamp, the preamp is the real weakness of the S300i. Well ok, listened to a little led Zeppelin then some Michael Jackson from the this is it blue ray, turned my trusty Krell preamp up to about 50%, after about 4-5 minutes the amp went into thermal overload which it stated nicely on the display. Once it cooled off it shut itself off I turned it back on and it played fine. I could see from the P-1200 it's hooked to it was drawing a lot of power for a little amp. Can't wait to get my babies back.

On another note I spoke with Dan Daugustino a fare amount when he was here at the show in SF recently, he said the Krell amps should be running at 220 volts and they will sound a lot better. Come to find out they are all designed originally for that voltage, the MRA amps were designed to only run at 220. So looks like I have to save some pennies and do some more work on the house here...

Have fun guys,

Just an update, sold the B&W 801N's and have some Apogee Calipers (ultimate version) and waiting for my Diva's to be finished (also the Ultimate version, all metal ribbon). Finally found a KCT that was literally brand new and hooked it up, WOW what a step up. I run all siver cables except the Balanced cable to the amp which is silver coated copper. When the amps finally come back I'll be using the transparent CAST cable. Just using the KAV 2250 right now but I never thought it could sound like this, just stunning can't wait for the big amps.

I have the Krell FPB 400CX with The KCT with CAST cables running my B&Ws and my system never sounded so good. The KCT is a must have with the Krell amps. You are going to love how your system sounds when you get your BIG boys back. I would love to see what my system would sound like with the Krell FPB 750MCX amps.