George, I just bought a pair of barely used Krell FPB 450Mcx monoblocks, upgrading from a Krell KSA-100 Mark II stereo amp. I'm using balanced interconnects to an Aragon Soundstage pre-amp, and I'm bi-wired to a pair of Krell Resolution 1 speakers.
Well, what can I say, after only a day or so of listening and comparing with rock & pop it's a big difference though I have to say the KSA-100 proved to be no slouch and is certainly a tremendous value. The FPB 450Mcx amps deliver more of everything: more and tighter bass, a more controlled and vibrant midrange, and a more extended and slightly airier top end, with the most prominent improvement being in the midrange. The music really bloomed in that area.
With rock music, the KSA-100 sounded somewhat anemic and thin with my speakers, and I surmised that the Resolution 1s needed more power to get that punch I was looking for. Now rock sounds much better, I was delighted by the added warmth and rawness in the guitars, right there in the lower midrange. Percussion took on substantially more impact and immediacy. The upper midrange also warmed up and opened considerably.
The improvement in the top end frequencies was *not* subtle, cymbal crashes had more authority and extension, the high notes on the keyboards came through better. I was pleased to note that harsh treble, a typical hallmark of poorly mastered CDs, did not hurt my ears despite the added extension. Those CDs still didn't sound good though...
Bass, well, this is kind of a strange one. With the KSA-100 much of my collection seemed to simply be lacking bass while other songs seemed to have plenty of it. With the FPB 450Mcx, the bass is significantly more amplified but the same overall characteristic remains: much of my music seems to need more bass while in other songs it's very powerful now. I've come to the conclusion that bass reproduction is largely room-dependent and my listening room, at around 10' x 14' and only 9' high and with one partially open wall, is simply not ideal for good bass reproduction. Some frequencies are "sucked out" while others are amplified. I have to live with it for now.
In addition, the soundstage opened up greatly. With some tracks the breadth and depth of the soundstage was dramatically better. When I'd upgraded to the KSA-100 from an Aragon 4004 Mark II, I'd noticed a similar improvement in the soundstage, though not as great as this time around.
I didn't notice a big difference in the imaging, but I guess that's more connected to the speakers and the physical characteristics of the room.
The system is now much more revealing and it's easy now to assess the quality of the digital mastering or re-mastering of CDs. I would now suggest that only around 10% of the CDs out there have truly been mastered properly. 50% are acceptable but could have been done better. 30% or so are poorly mastered / re-mastered. The remaining 10% is garbage and unfit to listen to. Some surprisingly big name mastering studios known for solid mastering slip up every once in a while and fall into these last two categories; I found a couple remasters by Bob Ludwig of Gateway Mastering and one by Rhino Sound that weren't up to scratch, though I have to say that most of what these guys do is really good.
Overall, "opening up" and "blooming" are the key descriptors I would use to characterize the upgrade from the KSA-100 to the FPB 450Mcx monos. The improvements in the midrange and soundstage are much more than incremental, but certainly not staggering. Like I said, the KSA-100 is no slouch and for ~$1100 used I can't think of a better value.
Now, let's compare the power consumption characteristics of the two amps. For weeks I had my KSA-100 plugged in to a Monster Power HTS 2000 MKII line conditioner, which is equipped with a current meter. Upon switching on the KSA-100 it would immediately pull about 5.5 amps (~650 watts!) and gradually taper over fifteen minutes down to about 4.2 amps (500 watts). This consumption would not change, regardless of whether or not I played music or how loud I played it. True Class A behavior I guess. Well, maybe there was a volume level where it would change but if so, it was well beyond what my poor ears can take.
Last week I had dedicated 30A outlets installed in preparation for the new amps. As an aside, I did not notice a difference in the sound when plugging the KSA-100 into the dedicated outlet vs. the Monster Power HTS 2000. Anyway, after I got the FPB 450Mcx amps, I plugged them both into the HTS 2000 just to see how much power they consume. Upon switching on the master power switches on the backs (which Krell recommend leaving on at all times), both amps together pulled about 0.6 amps (~70 watts). Then when I pushed the button on the front to turn them on, the consumption spiked to about 3.0 amps and came down within seconds to around 1.9 amps (230 watts). Then when I started playing music it would immediately increase with either volume or with more complexity or bass in the music. I took it pretty loud (but not deafening) and I saw the current usage go as high as 9.0 amps (> 1 kW). When I brought the volume down or the music became softer on its own, the amps would continue to draw high current for a few seconds before coming down. That's where the "Sustained Plateau Bias" name for the power conservation technology comes from, I suppose. Anyway, I later plugged the amps directly into the dedicated outlets, and again didn't notice an improvement in the sound. I guess the HTS 2000 would primarily manifest as a constraint during high volume playback.
During moderately loud playback, the amp gets *very* hot. The fins (particularly towards the front of the amp) and the faceplate on the fin side become too hot to touch for more than a few seconds. My KSA-100 and my friend's KSA-200 get very warm but not hot enough to burn. I think the 450Mcx fins could burn sensitive skin quite easily, if grasped for more than say ten seconds.
Physically, the amps are relatively compact but dense. Each occupies significantly less volume than the KSA-100 but weighs at least as much. There's only one handle, on the back, which makes it a bit awkward to move around but by supporting from the bottom it's acceptable. The faceplate is glossy black and looks like it would scratch easily.
Finally, note that the amp doesn't take RCA inputs, only XLR or CAST. Also, the outputs are nominally spade only but I managed to just pinch the wire directly in there and will get the spades this week.
