Finally had a chance to put the MC275MKIV back into the system and spent the last few days listening to the setup. Adjusting for the gain difference between the 501s and 275, (easy to do with Bryston 10B's high pass variable level so the settings on the subs do not need to be disturbed) and getting a smooth blend between the subs and speakers with the tubes doing the driving, I did some serious listening.
In a nutshell, the 275 benefits tremendously from the active X/O setup given the right conditions. Eliminating the deep bass from it's "to do" list, the 275 comes alive. :yes: Now, I am not saying that "every" recording will sound better, those that tax the 275 are the ones that benefit the most. I had to listen to various recordings and try various x/o points from 30-90Hz and my listening sessions revealed which is pretty obvious, the higher the x/o point, the better the 275 sounded.
A good example was the first track from the Yamamoto Tsuyoshi Trio's "Midnight Sugar". The opening of the track features relatively deep and harmonically rich bass string plucking which then overlaps with a well recorded piano key strokes which always sound "icy crisp" and "startling" when driven by MC501s. The cymbals a little later in the track come across with all the sizzle and brassiness and incredible amount of air. The kick drums lead into crescendos, swelling into a combination of all instruments together, overall a very complex recording and takes quite a bit out of the amps, especially at louder than average levels. With the 501s and especially with the dual JLA F112s firing off the deep, tight, well controlled, musical bass, this recording makes the $$$$ investment into your system well justified. :yes: (Fantastic recording to show off your system! :thmbsp
Now, without the subs and the Bryston X/O, the 501s driving my SF Guarneri Memento's full range mode make child's play out of that recording, to the extent of bass my speakers are capable of.

The 275 "full range" on the other hand had always sounded a little congested during the complex parts of that particular recording. The piano notes ringing out into the room have often sounded a bit hard, edgy and brittle. The cymbals would loose some of the sparkle and air. The bass while sounding full did not have the definition and resolution of the 501s and had a bit bloat and tubbiness to it. The kick drums sound muted and did not have the same impact.
Enter the Bryston 10B active x/o and dual F112s with the 275 at the wheel and using 90Hz x/o point, WOW! I can honestly say that
in this combination the 275 smokes the 501s in sheer musicality. The harmonic texture and the midrange magic of the 275 is quite stunning. There is a good portion of added transparency and air, I've never heard the 275 quite so good before. The bass duties relegated to the F112s and the 275 responsible for 90Hz and above at 18dB/octave slope does wonders for this tube amp. The 501s are still amazing amps but the 275 in this configuration clearly edges them out to my ears and is really the best I've heard my system yet. Again I am very tempted to explore the higher end tubes in the form of MC2301s. :scratch2: There is tons of potential here and the Guarneri's really strut their musical stuff with tube juice.
