going Pass Labs, do I need "Class A " ?

Class A is good but A/B is better for your speakers. Pass amps have large room of class A if you prefer to listen at moderate volume levels.

I've owned two Pass amps, previously the X250.5 and currently the XA30.5. Their differences may be similar to the differences between the X350.5 and the XA60.5.

In my system, the X250.5 had somewhat better bass than the XA30.5. The XA30.5's bass is quite good, but the X250.5 controlled the bass almost like an active speaker, i.e. effortlessly dynamic and lots of headroom. On the other hand, I'm sure there are folks who would say that the XA30.5 has more *musical* bass. IMO, which amp has subjectively better bass is a matter of speaker compatibility, room size, listening volume, music preference, and taste. If you listen to symphonic music at 90+ dB in a large room with inefficient speakers... you get the idea.

In my system, the XA30.5 has somewhat better treble than the X250.5. The X250.5's treble was good, but the XA30.5 is slightly more liquid and more musical. With your speakers, I'd say that's an important consideration. Whether differences in treble are more important than differences in bass is of course subjective.

In my system, the XA30.5 has less harmonic coloration than the X250.5, though neither of them sound "colored." It's that the XA30.5 has more harmonic *variation* than the X250.5, which is perceptible mostly in acoustical instrument timbres and voices.

In my system, the XA30.5 is slightly quieter and has slightly more resolution than the X250.5, but both of those differences are subtle.

That's everything I can think of at the moment. If you mention more about your system, I might have more input.

Bryon

Bryon,
Thanks.

Ok, the room is 19x11.5 feet, ceiling 9 ft. Speakers can be placed anywhere i.e. along long or short wall.

CD dCS Puccini, PreAmp (planning Pass labs XP-20), power amps (planning XA-60.5, may be XA-100.5 or the 350-th).

Cables choosing from XLO LE or Shunyata Anaconda CX.

I listen to jazz, blues, rock, classic. No electronic and acid.

Sergei

I recently visited a Pass dealer, who explained that Pass amps are more alike than different, but are rated differently. IOW, the class A amps do indeed cross over to Class B beyond their rated class A power. A Pass class A model rated at 100 watts/channel will deliver, perhaps, 300 watts, but in class B. The rating merely tells you how many class A watts you'll get, not the amp's peak output capability. I'd speak with a Pass dealer or even Nelson himself before you decide.

Bondman is correct. Stereophile's measurements of the XA30.5 confirm this...

While the XA30.5 may give 30Wpc into 8 ohms in class-A (14.8dBW), the distortion at this power level is low, at 0.015%. The amplifier doesn't actually clip (defined as the THD reaching 1%) until a much higher power level: 130Wpc into 8 ohms (21.14dBW). Even higher powers were available into lower impedances before clipping: 195Wpc into 4 ohms with both channels driven (19.9dBW), and 332W into 2 ohms with one channel driven (19.2dBW).

Having said that, there are design differences between the XA series and the X series that go beyond biasing. IOW, the XA series isn't simply the X series with a higher bias setting. And that is reflected in the difference in sound, IMO.

Sergei - I noticed you added the XA100.5's to your list of possible amps. IMO, that would be the best of both worlds. I've heard the XA100.5's, and they are glorious sounding. They are considerably more money, but you may be able to find them used. Reno Hifi is a good place to start.

Bryon