Krell versus Pass Labs

I have been a a Krell loyal fan for years and years. Recently I upgraded through several speakers to finally settle on the Apogee Diva Ultimate made by Rich Murry in NV. I've also owned the Caliper Ultimate but this new version of the Diva with all ribbon drivers and no transformers is simply amazing. Last weekend I listened to a recently rebuilt version of the Apogee full Range, one step up from mine and these are honestly probably the finest speakers on the planet and I've heard and owned a lot of others over the years, B&W, MBL and so on. One thing about these speakers is that they are completely full range they go past the human hearing on both ends easily. The other thing is that they are incredibly fast and ruthlessly revealing, I mean take no prisoners, it's all here like it or not.

I liked the sound with my Krell Cast system but I have also heard these speaker on other equipment and amps and was amazed how good they can be but my system was not there yet for some reason? Maybe it was just system matching? A friend recently loaned me a Pass X150.5 to try out so I plugged it into my Krell KCT with balanced hook-up. WOW, the high end edginess was gone, the tone quality was much better and more even from top to bottom, the pitch definition is impeccable! Day 2, now with it more warmed up the sound stage opened up a lot and it sounds so incredibly musical! I was stunned how good this little amp is, dynamically it is a champ and does not seem to care how hard you push it, it just sounds effortless regardless of how loud I'm pushing it. A friend who's ears I trust said the 150.5 and the 600.5 are the among the best he has heard with the Apogee's, I didn't think the 150.5 would have enough power but was I wrong. Where have I been why didn't I hear this sooner? I've heard Pass amps before and always liked them but this is in a different class all together than my Krell's.

I think in the end I'm going for the 600.5's and possibly a Audio Research Ref 5 SE? Talk about bang for the buck, the X150.5 is up there in that "cost no object class". Some like the class A amps better for their systems but for the Diva Ultimate I think the X150.5 is amazing. Listening to complex music at a level that is starting to get uncomfortable the meter will swing to about the 3/4 mark with plenty left in reserve, I never heard it compress or strain at all, not even a hint! I can think of several giant expensive amps that could not keep up with this little amp, it's articulation is so precise and effortless. For example to me it can better MBL and Krell mono's and I have been a loyal krell fan for 20+ years!

Rob, I've always preffered Nelson Pass' work over Krell designs, even during Pass' Threshold years.

I have some experience with Krell, Pass labs and ARC Ref 5se.

I borrowed a friend's Pass Lab X250.5 from a friend and I compared it to my Krell FPB 450 over a period of a week. The speakers were Revel Studio 1 and preamp was a Pass Lab X-1.

The X250.5 had smoother highs and slightly warmer vocal but the Krell had much better low end and better dynamics. Overall, I preferred the 450.

Over the last 18 months I did some major upgrading to my system. I replaced the Pass X-1 preamp with an ARC REF 5 SE and the Revel Studio 1 was replaced with the Salon 2 but still kept the FPB 450. The REF 5SE really changed the sound of the 450. The vocals was much fuller and had better imaging. The highs were smoother as well and still had the Krell signature low end. The REF5SE and Krell is a good combination.

REF5SE and Pass Labs may have mismatch impedance. Pass Labs tend to have low input impedance of around 20k Ohms so it might not work well with tube preamps. You should call ARC. Krell amps have 100k and their Evolution series are 200K so they work well with the REF 5SE. My friend has since sold his X250.5. He was using a tube preamp and the X250.5 did work in his system.

Something to think about before getting the Pass Labs and REF 5SE.

I had a older Krell KSA 250 and loved until it caught on fire.
I sent it to Krell for repairs and in the interim, I bought a Pass Labs X350.5 Amp.
I ended up selling the repaired Krell.

With the Pass Labs X350.5 I tried a Cary SP-O5 Preamp and noticed there was a loss of bass and general dynamics. I ended up selling the Cary and Purchased a Pass Labs Preamp (XP-10).
So, perhaps the Pass Amp doesnt work well with Tube equipment, or maybe it was just the Cary Preamp SP-05 only.
Worth noting and looking into though.
I'm also a fan of the Pass X150.5, using it with my Magnepan 3.6 for the past 2 years. A beautiful match which bettered by far two other amps including Classe CA201 and 401, which were not in the same league. Bass extension and power, midrange and treble clarity, dynamics, were all improved. Can't comment on Krell though.

One thing about the X150.5 (and probably all other Pass amps) is the extra power and headroom above the stated power. The X150.5 was tested by one of the British mags a few years back, I think it was HiFi News, and the amp put out a surprising 280 wpc @ 8 ohms and 380 wpc at 4 ohms before clipping (I may be off a few wpc.) So, it's not surprising that you were impressed by the ease with which it drove your Apogees. For Magnepan, some like even more power, like with the X250.5 and X350.5, but the X150.5 has more than enough for me - I have rarely gotten the needle past 12:00 (perhaps because I'm in an apartment.)

I'm sold on Pass amps and have no expectation of changing.
So here's my current situation. I have the KCT which is in mint almost new condition and I do have 2 FPB750MCX amps but one is in need of repair and I have the rare transparent CAST interconnect cables from the source to preamp and to the amps. The thing is my FPB200C just never worked with the Apogee's like it did with other speakers? The sound was almost too tight really if that's possible? The Apogee's are extremely fast already and the drivers are lighter than the air they are moving so the massive control the Krell had was almost overkill with this speaker to my ears.

With the pass amp the treble is smoother the midrange is more natural and the bass is much more evenly extended. So heres the deal, do I fix and sell the FPB750MCX amps and replace them with X600.5, selling my ultra rare CAST cables too. I do love the sound of the AR 5SE but I am worried about the match like you said? I'll be using a dac8 and PH7 too with them.

These Apogee's are just a different deal, I have not heard the FPB750MCX with them yet but I have a bad feeling about the match-up given the experience with the FPB200C. One thing I did notice recently was on some high sustained notes like a power soprano the amp meter on the X150.5 will swing far to the right showing a very high current draw into those high notes. The FPB200C never compressed on me but I have owned these amps for so long now I know it was working pretty hard driving the Apogee's, too hot to touch.

Not to go on and on about them but the Apogees are a little different like I said before, the bass is very full and insanely articulate, I don't even know how low it really goes but they can generate a temporary nausea at times so I'm guess like 10 hertz or something? The midrange and treble are effortless. I have heard them sound so damn real before, goosebumps all over real, and that's what I'm looking for. The AR 5SE and Magnus 300 is a stunning combo, the only way to describe the Magnus sound is REAL and completely unrestrained but I have my concerns about the Magnus and Id like MONO amps, at least in my experience I always get the best sound-stage that way. I'm not surprised by the power you stated Dne for the X150.5 it really is a little power house of an amp.

You should have the FPB 750 repaired and try it out with the Apogee. I had the FPB200 many years ago and it sounded so different from my FPB 450 that it was not even close. There is probably a bigger gap compare to the 750.

As for the X600.5, you might call Reno Hifi and see if you can do a 10 day trial. If you can borrow a REF 5SE that might be a good option to try it out with the FPB 750 and maybe even the X609.5.
I agree about repairing the 750mcx and trying these with your speakers. Those amps are among the best in class and are quite further evolved from the topology in the FPB200C. I would be very surprised if they didn't warm up the Apogees to your satisfaction.

I too have purchased Ultimate Diva's from Rich. They are still in production. I think he is painting them next week.

I am really interested in how you choose to proceed. I have a Halcro DM-10 preamp and Pass X350.5. I would like to use tubes somewhere and was thinking about the ARC Ref 5SE to replace my Halcro.

I am actually sending my Halcro to Rich so he can plug it into his various systems. I trust his opinion. He is a straight shooter.

What I like about the Halcro is that it includes a great phono stage and is considered by many to be top class overall.

Also, I will be looking at the Magnus 300 as Rich seems to like it.

Ultimately, I would like to go all tubes. Maybe when ARC Ref 250 used prices come way down.

I'm curious to hear how the ARC250's handle the Diva's? Mine draw a lot of power in the top end, I had to use the X150.5 for a while before I correlated what was going on. The sound of the Magnus is very impressive and real sounding, I have no fault with the sound at all, emotionally real sounding.

I hooked up the Krells again to my PS Audio P-1200 to see more of what was going on, while listening to Adele (vinyl) the amp was drawing in excess of 1400 watts during her whaling. Rich told me the Diva's need more power than the full range and he as usual, is right on. I think the X150.5 was maxing out although it didn't sound like it during the same songs, the needle did bury itself during those same passages. I think it's impossible to beat the ARC Ref 5 SE right now as preamps go and on these speakers you can hear everything as naked as it can be.

Rich is also recommending I fix the FPB750MCX amps and try them but I'm kind of formulating an opinion now, maybe prematurely? I want to try the Pass X600.5 mono's with the ARC Ref 5 SE, Rich did have this combo with the ARC Ref3 and said it was stunning.

You are going to love the Diva's, they do cause other issues because they sound so neutral and nakedly transparent but once broken in they are the most amazing speaker I have ever heard in my life next to the full range. I don't feel like I'm missing anything, anywhere. Mine are 5ft from the rear wall which sounds the best to me. If you have never had one of Rich's speakers in your house before it will be a shock at first, once they break in they are just jaw dropping amazing, I don't think there is a cone woofer on the planet that can produce limitless sub-bass that way?

I know the Pass X350.5 is pretty damn good. Once you get the preamp and amp combo figured then it's sources and cables. Like I said they are so transparent you can just throw any previous experience out the door, kinda jealous you are starting out with a X350.5 already, that's got to be sweet. I'm running a ARC PH7 (Updated) for my Phono preamp, you might have seen it at Rich's house I left it there for a couple months and just got it back a week ago.

Rob, if you considering to spend that amount of money on pass x600.5 monos, you should also consider latest Evo (E) series Krell amplifiers, nobody in this thread mentioned about comparing them with the Pass. Based on my dealer advise, I compared the krell 402E with pass XA160.5 monos using ARC ref 3, and in my system I liked the krell 402E more, it was more refined and more neutral with better defined bass. Krell made a really significant improvement with latest E series all across the models range. Ideally I would like to own Krell 400E or 600e monos, but it is a lot of money.
I have been a loyal Krell owner for 20+ years. I currently own a FPB200c, FPB 750 MCX (2) and Krell KCT with Transparent CAST cables. I'm not sure about spending more on Krell and so far with these speakers I'm not finding a lot of synergy? I'm also not a fan of the XA 160.5 amps, the pass class A amps just don't have the sound I'm looking for with these speakers however the class A/AB amps like the X600.5 sound a lot better. With Krell now trying to get out of servicing older equipment and kicking Dan out I wonder where all that is going? The ARC service seems to be first class. I have always owned Krell, I have not heard the newest stuff with my speakers so I'm not really sure how good they really are but they also seem far more expensive than ARC or Pass? I sure would like to try them but kind of skeptical too.