As noted in my earlier build post, the M125s were near a threshold level of power in my 8,000 cubic foot listening room with Magneplanar 1.7s.
Also, while the amps in pentode ultralinear mode sound great, I wanted to explore using the triode mode - I listen almost exclusively to acoustic jazz at 80-90 db at my listening position, and losing half my power in triode didn't seem attractive.
In addition, I was running my PS Audio PWD II DAC output nearer the high end of its range (I don't use a separate preamp), so tried a few changes:
-Hooked up my Dynaudio Geminis, a superb MTM design that is 91db efficient compared to the Maggies' reported 86 (and I think that's reported high!)
-Since the Geminis only go down to 50 hz, connected my Sunfire sub using the sub's built-in high pass crossover (6db/octave at 70 hz) to the amps. The high pass crossover is entirely passive within the sub, so not too concerned about degrading the DAC output.
-Using the sub's high pass crossover also has provided the side benefit of unloading the amps under 70 hz. They certainly handle lows fine, but every little bit helps!
OK, here's what I'm hearing through the setup above...
In pentode mode, great dynamics, volume, and clarity - great for more powerful, dynamically demanding music. All as expected.
But, in triode mode listening to acoustic jazz.....WOW!!
Most importantly, the combination of timbral accuracy and imaging is really jaw dropping. Absolutely sounds like real instruments in my space.
Wonderful for examining each instrument's line and tone at your leisure. Choral music allows hearing each voice clearly and naturally.
In particular, the front to back "layering" of instruments in space is to die for. Recording venue acoustics, room reverb etc. all accurately portrayed.
No sibilance whatever to vocals, but no perceived loss of detail. Cymbals ring out with a metallic shimmer rather than a sandpapery hash.
I play jazz guitar on a Gibson arch top (ES-175) through a Fender tube amp, so I know how that should sound, and the M-125s get it don perfectly. Pianos as well, with a great leading, mid note and trailing edge. The M-125s nail the subtle harmonics and meat of the instrument perfectly.
Female vocals have a beautiful rounded quality, and I swear I could "see" the color of Diana Krall's lipstick !
Compared to the pentode mode, things seem a little more relaxed - like a yoga vs. a spinning class....each feels great, but different. No listening fatigue at all, but the sonics definitely change character with different recordings. Not a one note Johnny.
Even at very low late-night listening levels (around 60 db at listening chair), no loss of any of the qualities described above........this is an important difference to my SS experiences.
In summary, when you consider the power, finesse, flexibility (pentode vs. triode, 2 or four output tubes) and component quality, the M-125 is a teriffc value - Look elsewhere, and you'll pay $5K to $10K for similar performance. (Rogue M150 or 180s, C-J LM125, ARC VS 115, Quicksilver, etc)
I'm delighted with these amps!
Link to build pix - forgive me for reverse order!! > https://www.flickr.com/photos/121456711@N02/