Replacing my Krell FPB 600 amp with a tube amp

A little off topic . I converse with an Audiophile that collects the Big vintage JBL’s ( 15” woofers ) . He runs McIntosh tubes and class D bi-amped with active an crossover and DSP. Not my cup of tea , but if done right , really impressive . Also no need to worry about subs . I think with B & W or ATC speakers  it would be even better . Cheers , Mike B. 

pesky_wabbit ....Actually i LOVE my Krell FPB 600. I actually feel like it supplies everything i could possible want in a solid state amp and more. I just thought if i am missing something with a tube amp that has that much power and some warmth that tubes provide. I just bought a brand new Ref 6 ARC preamp and besides the ARC Ref 5 se that i only had about 2 or 3 weeks before i demoed the ARC Ref 6 which i found it to be a night and day difference bet the 5 se. This was the first time i ever had a tube preamp. So with that said that is why i was thinking about a tube amp. Another words i would never go back to a solid state preamp. The only thing i could possibly see myself buying to replace the Krell FPB 600 is the ARC Ref 750 or the 750 se amp. for its power. Also my Krell FPB 600 sounds like a match match made in heaven with my B&W 800 Matrix. But always wondered what a powerful tune amp would sound like with my B&W 800s. 

What specifically is it you are looking for in a tube amp that you feel the FPB 600 fails to provide?

Are there elements in the FPB 600‘s repertoire that tube amps fail to emulate that you would find difficult to live without? Ones you may have grown used to without realising?

Although I have never heard a B&W speaker that I didn't find very sterile except the old 801's. I owned the 700C for quite a while and it is a great amp. It's very smooth and powerful with ability to handle any speaker with aplomb. I ended up selling it because someone offered me an amount hard to refuse.

VTL 450MKIII 

Georgehifi
can you get more spread between the speakers, they are very close,

George - the Matrix 800 are a very unique design. They can be set up widely spaced apart and angled in, or close together and shooting straight down the room. Good results are achieved either way.
From the owners manual. (1.5 m or 60 inches) apart will work well.

https://photos.app.goo.gl/9rOuWdINRdBh9ED13

Abbey Road’s placement of the Matrix 800.

https://photos.app.goo.gl/3hL46MQw2ilbHPRf1

There was mention of adding subs on this thread.

The Matrix 800 are a full range - All Out Assault design. A one time effort. They are like having 4 subs in the room - two high - two low. Each cancelling out the others waves; no standing waves. This was evidenced/shown through the Stereophile review (reviewers room) that was linked here. His room was small and the speakers disappeared. The woofer effect is easily tested by disconnecting one set of woofers.

Re: Krell Amp (this thread)

Dan designed his Krell amps around this speaker - I talked with him years ago. He had Matrix 800 in his personal space. B&W and Krell were in partnership - until Dan/Krell came out with their own speaker. This relationship is a big reason behind why Krell is an excellent match with Matrix B&W, and the reason that Dan/Krell came out with their own Krell designed B&W Bass Alignment Filter.

From the Stereophile link that Almarg posted earlier in this thread, there is one Figure 8, that shows the BAF performance with the stock factory BAF. I can tell you the Krell version betters the stock BAF. Would have liked to see those Krell B&W BAF measurements from Stereophile, but the Krell BAF was not available at the time of the review.

That’s fine, to me the stars of your show are the amp and speakers, you’ve, got the megabuck cables, all that left for me with questions is the rest to change/re-configure, can you get more spread between the speakers, they are very close, or have you bought the right one in a couple of feet just for the photo? 
https://systems.audiogon.com/systems/6134

Cheers George

George ......I cant see selling my ARC Ref 6 preamp and Rega Isis cdp to even something really good with a volume control that drives the Krell direct and have it sound half as good as with the ARC Ref 6 pramp. I even upped from the ARC Ref 5se to the 6 just because it was that much of a HUGE improvement over the 5se. The sound that i have acquired with my new ARC Ref sounds phenomena to ME. "I should not mess with a good thing". IMO now. 

tattooedtrackman OP
But i was just thinking how a tube amp would sound and be with these speakers. And i never thought of it sounding disjointed bi amping until you and Almarg briefly pointed out.

That’s my take on it, and as I said before " The better I made all my tube amps sound with mods/circuit changes, the closer they got to the best solid state."

Being all that said maybe id be better off keeping my Krell matched to my 800s.

That’s the way I would go, and for the itchy upgrade feet, I would look at updating the Rega Isis cd player to something really good with volume control that drives the Krell direct,and pocket money selling the preamp.

Cheers George

Thanks for the nice words, Dentdog. I found that information about the CAT JL2 in the measurements section of this review of the Signature Mk2 version of the amp, in SoundStage. The data provided near the top of the measurements page states "output impedance at 50Hz: 0.7 ohms." And the damping factor measurements shown in Chart 4 indicate a damping factor of about 11.5 across nearly all of the audible spectrum, with a slight decrease to about 11 at 20 Hz and 20 kHz.

I’m not sure what output tap or taps the amp provides, but a damping factor of 11.5 corresponds to an output impedance for an 8 ohm tap of 8/11.5 = 0.696 ohms, and less than that for a 4 ohm tap.

Best regards,
-- Al

The technical guys, Almarg, Eric and a few others are invaluable to this site. If you love these speakers as you say, the advice from these contributors can be helpful in keeping you from making a bad choice.
Had no idea the CAT amp had such a low impedance. 

George.. Thank you for the info. Maybe i would of been better off with this thread in the speaker forum. One thing i know is that i will be keeping these speakers. I will tell you that the Krell FPB 600 cruises with the B&W Matrix 800s. But i was just thinking how a tube amp would sound and be with these speakers. And i never thought of it sounding disjointed bi amping until you and Almarg briefly pointed out. Being all that said maybe id be better off keeping my Krell matched to my 800s. 

Meaning ill be back to the Krell FPB 600??

And others as good and better.
Your 800’s are a pretty nasty load from 200hz down where most current will be needed, 3ohms and up to -55 degrees of - phase angle, this can equate down to around <2ohms in the bass areas as seen by the amp.
https://www.stereophile.com/images/archivesart/88B800fig1.jpg

Trouble with Bi-amping, the internal xover of the 800's is right in the very sensitive area to the ear middle of the lower mids at 380hz and will be sharing this area with two amps, they better be similar in tonal character otherwise it will sound disjointed, as Almarg has also briefly pointed out.

Cheers George

gerorgehifi.....REALLY !!!!!!! "YOU"BE BACK" ...........Meaning ill be back to the Krell FPB 600??

dweller......100% correct !!!!                                                                              

Replacing my Krell FPB 600 amp with a tube amp

REALLY!!!!!!

Haven’t read any of the other posts, all I can say is "YOU"LL BE BACK".
The better I made all my tube amps sound with mods/circuit changes, the closer they got to the best solid state.
The only one that was close/equal to the best solid state was the OTL tubes, but you have to be careful what speakers you drive with them, which are usually the ones I don’t use.

Cheers George

@tattooedtrackman - I believe your ARC is AWSOME! I've had many ARC components over the years and I put them on a pedestal. Can honestly say that my current system meets ALL of my needs. The only way I'd enjoy it more is A. A bigger room (e.g. 25 X 50 feet)  and/or B. Legalized THC. Long live music!

dweller.... That is correct... I will tell you that this ARC Ref 6 is so awesome in sound that it will very likely be my very last preamp. You must hear it to believe and appreciate it. 

I think @rcprince may be right. I have gotten very good results from VTL MB450III mated to my ARC Ref 40 to drive my Q3s. The variable damping factor on the VTLs allows you to optimize for the speakers you are using and address the issues @almarg raises. The VTLs are also very robust with super reliable automated biasing. Even a full on tube failure is handled with aplomb. If you do go the VTL route however you are advised to buy from a VTL dealer as they can be sketchy on support if you don’t have that relationship. Finally make sure to connect the pre and power amp with balanced interconnects.

@tattooedtrackman - It appears that your ARC Ref 6 preamp has two variable outputs and one fixed line out for use with a tape recorder.
You pay your $14,000 but you get what you pay for!

I also remember the Nautilus, a bit cold and analytical yes - I preferred the Dynaudios for that reason. But I felt it was the speakers mainly not the amp. 

So here is my bad take, overall. 

The Krell's that I remember in the day of the B&W Nautilus were cold and analytical as hell. Having heard the top of the line, 5 amplifier setup with Krell crossover and B&W Nautilus speakers I was never wowed, but if you were that's cool. 

If you want to keep that, you want old ARC. If you want something musical and juicy you want Conrad Johnson. 

Almarg - I was not trying to say that the B&Ws are a good match with the Atma amps - most probably not - the OP would have to change speakers in that case. I agree, the zero autoformers is a useful add-on, but again, only if you don’t have an optimal amp-speaker match, which is a far better solution. If the B&W specs say they want 150 to 800 watts (solid state), maybe they would shine with 800 watts or similar powerful amplification - I have no idea, just a guess, based on my Dynaudio experience.

The impedance curve for the Matrix 800 that is shown in Figure 1 of Stereophile’s measurements indicates an impedance in the vicinity of 4 ohms in much of the bass region, as I mentioned previously, and more than 10 ohms at almost all frequencies above 1 kHz. That strongly suggests that the speaker is intended for use with amplifiers having low output impedances, and correspondingly having relatively high damping factors. Which disqualifies many tube amps as being suitable matches, regardless of how powerful they are. B&W’s recommended range of amplifier power, 150 to 800 watts, further reinforces a conclusion that the speakers were designed with solid state amplification in mind. (Solid state amps almost always have very low output impedances and relatively high damping factors, those two terms being inversely proportional).

The likely result of driving speakers having this kind of impedance characteristic with an amp having a highish output impedance/low damping factor would be weak bass, precisely what the OP wants to avoid.

While as many here realize I have been a great supporter of Ralph/Atmasphere and his products and his many contributions to this forum, the 2.3 ohm output impedance of the Atma-Sphere MA-1 makes them a non-starter for use with this particular speaker, IMO. Certainly without using the amps in conjunction with a pair of Zero autoformers, and very possibly even with them. And I’m doubtful about the more powerful MA-2 as well, with its 1.75 ohm output impedance.

I’m pretty certain that the CAT JL2 that was suggested, which I see has a specified output impedance of 0.7 ohms, would be a suitable match. As would some or all of the larger ARC amps that have been referred to. Not sure about VTL or CJ.

Regards,
-- Al

@tattooedtrackman "why would i need a subwoofer? "
You may not need one. You could try the ARC 250s first and add a subwoofer as needed. I got the impression that you are a tattooedBASSman and tubes just aren't going to give you the "power and bass slam of the Krell FPB 600". I'm driving my B&W 804 D3s (two 6 inch woofers each) with 300 WPC and I'm using a 12 inch powered subwoofer as well.
With cars it's cubic inches. With Bass it's driver size.

Maybe I am wrong, no expert here, but my impression is that the B&W Matrix 800s are quite a difficult load - or at least, that owners have long been looking for the best ways to get an optimal amp match...On paper, the Krell FPB 600 should be able to drive the Dynaudio Consequence with no problem. In reality that was not the case. It was good, yes, but not optimal. The Consequence speakers were developed using a 1200 watts amp.
Then, of course, there is the question "what kinds of watts". It is hard to say exactly, but I would guess, in terms of loudness, the 140 tube watts on the MA-1 translates to 450 or so solid state watts, it is not as loud as the Krell system, but not far behind. I miss some of the bass action and authority, but not much, due to the fact that I learned from the failed Krell - Dynaudio affair in my system. I bought a speaker system PRECISELY tuned to the amps. In some respects it is simpler than the Dynaudio speakers plus Velodyne sub I had, but the matching makes it stand out. So I think, the place to start is not this amp or that one - but what kind of sound, what kind of speaker match. If in doubt, go for more easily driven speakers. And consider OTL and good tube sound. That was my way, based on listening tests. 

I heard an interesting transformation of B&W 801 Matrix S3 speakers driven by Pass Aleph 1.2 mono blocks (200W/Ch).  They became smooth and rich even in the treble, which before had always had a bit of harshness to them.  So budget permitting if it were me, I would consider a Pass XA amp to replace the Krells. Rowland amps are also "tube-like" although rare on the used market.  I am also not sure that your speakers really need 600W to begin with.  One caveat- I agree with Mr. Holter that the Krell FPB's are very good amps- I had one myself and it was a joy to use- reliable, quiet, unflappable, easy on the eyes, etc.  

Note: my version of the amp does not make it clear when it shifts into class A; the nearest I could get was to feel the heat on the top plate. As soon as I turned the volume up with the Dynaudio speakers, the top plate turned hot, playing loud, very hot. So it may be that the amp was already working in class A, no problem there, but it was striving with my over-controlled speakers, which would have liked double power - 600 watts per channel (I never got a chance to try this).

This was some years ago, but I remember thinking: connecting a 1k dollar set of speakers (the Aurums) to a 12k amp cannot be any good. So I was surprised.

I often wondered if I would prefer a different bias system on the Krell - an option to make it go into class A operation on a lower volume level, or more user-controlled. Maybe it came in a later version (mine was a 1997 first version).

I went up the Krell line of amplifiers in the 1990s, and ended with a FPB 600, which deserves high praise, but has certain - let me say - conditions. In my system, it sounded much better when it 1) got a dedicated power line, 2) a solid slab of stone below, 3) a good tube preamp rather than a mid-line Krell or other solid state (the manual warns of possible problems with a tube preamp, a jumper can be used, but I noticed much better sound without it, and never had problems), 4) using balanced inputs, and 5) matching speakers. The ones I had (Dynaudio Consequence) were a bit too much even for the 600. So the sound went from good to marvellous only on a quite high volume level (the amp shifting into class A operation). Even this power beast could not really unsettle the rather Germanic Dynaudios and make them sing and dance. Experimenting a little with speakers, I marvelled at how good the amp could sound driving an easier load. Since it was not possible to add another 600 amp to my setup, I ended selling both the amp and the Dynaudios, and bought Atma-sphere MA-1s instead.

I could say "I have never looked back", which is mostly true, but having lived with the Krell for ten years I have a lot of respect for it, it is a classic in some ways, and I have often wondered if there was even more potential to it than I managed to exploit in my setup. It is a bit of a paradox, the FPB 600 was sort of a "solve-all" when it came, it should not matter what speakers you gave it, it ate them all, and so on - but my experience was different, this amp is so good that everything you do - in terms of speaker matching, and the points mentioned above - is well worth it. Just before I sold it I had the Krell drive my small Aurum Cantus 3 speakers to great heights. 

aoliviero..... I just read your review and i really did like what i read about it. Especially compared to the Krell FPB 600. Wonder how it compared to the ARC Ref 750se. 

I replaced my FPB600 with a CAT JL2.  Noticed no lack of bass control.  I’m fact the CAT gear is powerful and transparent across the full frequency range plus many other positive qualities.  You can ready my review on it.

rcprince ...... I was also thinking the same thing that a tube amp wolnt control my speakers as well as the Krell. Unless i buy the ARC Ref 750se.    lak.....Thank you but im really not interested in Carver....

Ozzy has some great comments that he has made about his new Carver mono's. He also started a thread here on Audiogon...

You could try a higher-powered VTL amp, but I still don't think a tube amp will control your speakers as well as the Krell does.

dweller.....My Arc Ref 6 does not have a variable preamp out...                       almarg.....Wow i would of never guessed that. Thanks...                                 dweller..... I too now dont see any advantage to bi amping                               dweller......Question....If i was going to go with tube amps , say ARC Ref 250 se, why would i need a subwoofer? My B&W Matrix 800s have plenty of bass, even more so with my Krell B&W Bass alignment filters when is called for.

I don’t see any advantage to bi-amping in this case. That’s why my first suggestion was for tube amp(s) with a subwoofer. I, myself, am using a BAT integrated (mid & treble) and using the "pre-out" to drive a Bryston 4B3 (bass). The BAT is 150 WPC @ 8 ohms and the 4B3 is 300 WPC (twice as powerful). Since the gain of the amps is the same, 29db, the volume is the same. There is just more headroom for bass dynamics.
The crossover issue sounds like it is handled by the internal crossover of the speaker. The mid-treble speaker input just ignores any bass content and the bass speaker input ignores the higher freqs.

A point to keep in mind regarding passively biamping the FPB600 with a tube amp, in addition to the gain matching concern that was mentioned, and in addition to the possible effects on coherence of driving the speaker with two very different amps, relates to the fact that in a passive biamp configuration (i.e., without an electronic crossover "ahead" of the amps) both amps must put out voltages corresponding to the full frequency range of the signal.

Your speakers have impedances in the vicinity of 4 ohms in much of the bass region. The FPB600 is rated to provide up to 1200 watts into 4 ohms. If you were to passively biamp it with say the ARC Ref 150 you would be reducing the usable power capability of the FPB600 from 1200 watts to not much more than 150 watts, because if you were to turn the volume control up high enough to utilize more of its power capability the lower powered amp would be driven into clipping.

Good luck. Regards,
-- Al

Probably the ARC Ref 150? Just make sure your amps have equal gain and it really helps if you pre-amp has a variable "pre-amp out" as well as a "main out". Otherwise, you'll have to use a splitter to feed both amps.

What would be a good ARC Ref amp to bi amp with my Krell ?

Atma-Sphere should be on your list.
B

Conrad Johnson Premiere 12s

Best,

Erik 

jimcgrogan2....I have thought about that a while back . Maybe its time really consider that again. Thanks

I'd think about some Carver mono's and an awesome subwoofer (why put all the burden on a single amp?). Also, Carver claims to run his tubes in a manner that they last 20 years (instead of the usual two).

Oh forgot to mention i am also running B&W Matrix 800s tri wired and Krell bass alignment filters (2) balanced