Doubt if anyone is going to read this after a year but here's my story on the S-275:
I had 2 amps - an LFD Integrated Zero and bridged Alner-Hambin SA400 mono blocks - each amp had its strong points. I've just completed an amplifier 'quest' to find a power amp with the best qualities of both the LFD and the Alner-Hamblin. It was successful but took several months. While my findings are obviously specific to my room, system with Harbeth Super HL5s, ears and tastes, other forum members may find my listening notes comparing amps of value. In each case I substituted the 'new' amp for the existing amp, listened for several days making notes, replaced the old amp and checked my notes. The SA400s were the prime amp for comparison. Size and ventilation constraints (amp to be placed in a cupboard with doors) ruled out class A and valve types, as well as behemoths. I chose the following short-list by reading reviews and talking to dealers. I was fortunate (in UK) to have 3 very helpful dealers who loaned me amps - I bought the last one below.
Listening Notes
Musical Fidelity M6PRX
Compared to SA400, M6PRX has excellent treble detail and tone. Conveys nuance and flow of music far better. Similar, good retrieval of low-level detail. More weighty low end with better dynamic range. 'Darker' background. Relatively poor definition of start of notes - attack seems inhibited - no 'pop' on anything but louder bass notes. Decay of notes is richer. Better coherence of sound but can tend to homogeneity in complex passages (muddy). Cannot hear the 'space' between notes as can with SA400. M6PRX has less precise stereo lateral placement, poorer depth and less recording ambience evident. Overall a lusher, lazier sound: very good class B - similar to Lentek etc - but could become boring. Not as transparent as LFD.
Leema Hydra 2
Compared to M6PRX, Hydra is very similar in terms of tone, nuance, flow of music, and coherence of sound from low to high frequencies. Treble is more transparent than M6PRX but can occasionally be fierce (violin, soprano voice). In this respect I prefer both the SA400, which does not retrieve as much detail, and the M6PRX which is never fierce. In complex passages the Hydra 2 lacks some clarity i.e. the space around each soloist or section of an orchestra, however it is much better than M6PRX but not as good as SA400. Certainly not a muddy or lazy sound. Good retrieval of detail. Drive is definitely better than M6PRX but still not as good as SA400. Ambience also not as good as SA400, but background is not as dark as M6PRX. As with M6PRX less precise stereo lateral placement and poorer depth than SA400. Overall exciting but coarse treble.
Primare i32
Large change in sound as 'run in'. Following comments are for performance after 150 hours but sound may improve further with time. Compared to SA400s, the i32 has excellent treble transparency and tone but with a little (residual?) coarseness on violin and soprano voice - overall best in this area apart from LFD(?). Voice and piano are more natural than SA400s. Richer lower treble (more body) but with occasional 'hoot' on one or 2 notes. From the bass up to the low treble there is some 'cloudiness' (much reduced from initial state) which limits soundstage cues (width, depth) and ambience retrieval. Compared to the SA400s this is particularly noticeable. Bass of the i32 is agile and reasonably well defined but not as good as the SA400s - there is a lack of 'pop' on anything but low drums. There is markedly less 'drive' than SA400s produce, although coherence and flow of music is very good with more subtle detail evident than through the SA400s. Bass is not as weighty as others (apart from LFD?). I wonder if having 2 pre-amps / volume controls in series (Bel Canto DAC and i32) may reduce transparency, and also if the (relatively) low power (headroom / current capability) of the i32 may reduce speaker control and bass definition. Perhaps both aspects might be improved if monoblock power amps based on a bridged version of the i32 power stage were available? Overall the i32 amp is the best of those I have auditioned so far (particularly in the treble) but relative to the SA400s it falls short in 3 areas that I value highly (drive, bass definition and ambience retrieval).
Bel Canto Ref500
Very large change in sound as Ref500s 'run in'. Comments for sound after Ref500s run for 150 hours; still improving perhaps, but only slowly. The combination of transparency and tonal accuracy from the Ref500s is very beguiling. Minor splashiness in treble is small compared with how sounded initially. Treble quality is now the best yet (apart from LFD?) with natural sounds on high voice, violin, etc. Well defined bass from low thro' to mid but not as weighty as MF M6PRX or SA400s. Very good micro- and macro-dynamics. Able to appreciate for the first time many nuances of performance interpretation. Micro-dynamics probably best of all amps heard. Macro-dynamics (overall dynamic range) also best due to lower noise floor(?) but may also be because can turn up volume more without onset of distortion (tonal accuracy remains fine). Drive not as good as SA400s but better than others. Similarly ambience retrieval and soundstage depth not as good as SA400s (or LFD) but close (and has improved considerably as hours built up). While Ref500s do sound agile, the attack of notes is not as defined as thro' the SA400s. Maybe in some music this is because the decay of notes is so well reproduced on Ref500s that this can mask the attack of a following note? Staccato notes sound fast and well defined. Overall very satisfying musical sound and, on balance, an advance over the SA400s. Definitely amps I could live with, however I have a slight worry that the Ref500s could be slightly too comfortable. While they are not 'lush and lazy' like the MF M6PRX they are perhaps lacking in sufficient 'presence' for my taste i.e. drive and ambience. Returning to the SA400s this was very noticeable.
Krell S-275
Harmonically rich and transparent across sound spectrum. Subtle and smooth compared with all but LFD while not being lazy like MF M6PRX. Excellent spoken and sung voice, and violin reproduction. Best amp I've auditioned as regards clarity in complex loud music passages (choir with orchestra, symphonic climaxes, words of vocals within busy, loud rock, etc). Micro- and macro-dynamics excellent; comparable with Ref500s but heavier and more substantial. Drive very evident but of a different quality to that of SA400s; on S-275 it is often nuance and emphasis within a musical line, while on SA400s it is more direct impact (leading edge of note). This is very noticeable in bass where SA400s appear to sound cleaner with better pitch and flow, however all these aspects are present with S-275 but are better integrated with rest of sound spectrum. Bass is heaviest of amps auditioned. Compared with the SA400s, the S-275 bass sometimes appears woolly on the lowest notes, but maybe this is just more volume! As with Ref500s excellent sound of decay of notes may mask some attack of subsequent notes. Soundstage size similar to Ref500s, but individual performers or sections within it better defined. Ambience retrieval not better than SA400s but more airiness around solo singers and instrumentalists. Overall the S-275 provided the most musical performances with a very involving sound. I had to play some CDs thro' to the end when I had only intended to check 1 track. Restrained, delicate and often subdued but conveying emotion, vitality as appropriate - not at all what I had expected from a Krell amp. Maybe there is a synergy between this amp and the relatively restrained Harbeth SHL5s. Returning to Ref500s from S-275 showed S-275 richer harmonically, with more natural extreme treble, more detail and better separation of performers, but less clean bass transients.
David
