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

for Wilson Audio Sophia 2

May be someone did face to face comparisons XA60.5 vs X350.5 or any general thoughts?
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.

I have the XA 60.5. didnt listen to the 350's. The XA60.5 has been a revelation in my system and has plenty of bass. Very tight and controlled. I think many times differences are due to interactions between amps front end and speakers. Dont make a decision from the 30.5, it was not enough class A power to run my Dynaudio speakers. The amps would go into AB. The 30.5 has plenty of power to run the speakers but the sound character changes. I would advise you to check out the 60.5.

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.

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.

thanks once again. The thing is that I'm located in Moscow, Russia where pricing for PassLabs can be killing. I like used offers at A-gon and would easily make a trip to the US for collection.

The issue is 110V used in the US while it's 220-230V in Russia. By the way, is it hard / easy to make it operational at 220V out of originally designed 110V?

A transformer could be used but I would like to avoid it, if possible.
I would go with Class A if you can afford it. Yeah, that price over there in Russia might be too tough. But, here in the US, we have much higher prices for high end European and some high end Japanese imports compared to Europe and Japan. I don't know where these distributors get those prices from, but I hope there's a logical explanation. Anyway, that's another topic for another time.

Good luck!

As far as I know and i'm also from a 220v country [Israel] the xa range can't be converted internally from 110v to 220v and I don't think you want to use a transformer which might kill dynamics. Try to look for a used one on audio-markt.de [you have a 60.5 listed there currently].
I own a pair of 60.5 and they are glorious. Good luck anyways.
Hey Sergeik,

I have owned the X-350.5, XA-100's and now use XA-60.5's in my system. For the details on each amps performance take a look at my reviews here on the GON on allof them. Their is no doubt that the XA.5 series amps are Nelson Pass's best generation yet of his designs. Have not heard his new much more expensive four box monoblocks yet, but I'm sure their something special.
Sergei - I would strongly advise you to email or call Pass Labs and ask them about the 110V/220V issue. IME, their customer service is excellent, and the information they give you will be definitive.

Also, I suggest you read Teajay's reviews of the Pass amps he's owned. They're illuminating and may help you make a decision.

Another great resource for Pass questions is Mark at Reno HiFi. You might contact him, with your question, and about demo deals, etc.
the X- AMPS are going to be a better choice for music with more dynamic
properties; the XA-0.5 AMPS would perform better on subtler material- acoustic guitar, chamber music, female vocals, solo piano. if harmonics is- or will become- the most important factor in choosing what to listen to most of the time, then the choice is obvious. OTOH, in this forum some people have clearly become disappointed with their XA-0.5 amplifiers over time due to their changing of tastes, wanting more power and control across a wider bandwidth.
So you should ask yourself which path you're on.
French_fries, Are you saying the XA.5 amps have less control at the frequency extremes than do the X.5 amps? I always thought it was more about bias into class A and the distortion at the crossover point between the positive and negative halves of the signal. (How's that for a non-technical explanation). I'm curious as I'v only heard the XA.5 in my system. Clearly some prefer one line/series over the other, and visa versa.
you didn't mention what type of pre amp you were using,
I have the Sophia 1's and the XA30.5 in an 18 X 12 X 8 room. I had the Bryston pre but it didn't work well with the higher freq. but controled the bass very well, Last year i purchased the Vac Ren. mkIII and it made all the difference in the world. The bass is still tight,but there isn't any harshness in the tweeters. I couldn't be more satisfied with my system.

There is more than enough power in the XA30.5. the amp doesn't switch to A/B until about 98db. At that volume you won't here any difference.

dear mr. peterayer,
i am going by one person who put his XA-0.5 100W mono blocks up for sale. a lot of people questioned his decision in the forums, so
he explained at length regarding his changing preference for
a different design. apparently he felt the bass was lacking something in his system even though i don't think it was a lack of power.
just for an example i have levinson amps which don't inspire much emotion-
that has to come from within. but they do reproduce bass about as well as it can be done. i would think a pass X-.5 amplifier properly matched to your speakers would do the same thing. and bass can have a dramatic effect over the sense of depth / 3-dimensionality of the stage. OTOH they might fall a bit short on reproducing textural details of acoustic instruments or sound a bit flat on a Diane Krall album.
i have only heard pass aleph amplifiers - the 30 and the 1.2 mono blocks.
they were beyond reproach to my ears, especially on piano and jazz.
but i never tried them out on Bach organ pieces where i might have been
less enthusiastic. but i am easy to please when it comes to this level of audio gear,
so i could go either way without a 2nd thought and learn to be happy.
Peterayer, I hope you and French_fries don't mind, but IMHO dollar for dollar: yes. Though there are other considerations too.

pre amp considered is Pass Labs XP-20.

In my present system there is ATC SCA-2 and I might as well keep it - !?
French_fries, So you haven't actually heard these amps? Why comment then?

Unsound, If you mean by "dollar for dollar: yes" one should buy the Class A Pass Labs amps, then I would tend to agree, though I'm sure there are situations where someone would prefer the A/B models. They do sell many of the X.5 amps.
Peterayer, no that's not what I meant. I was answering; "Yes, dollar for dollar" to the question: "French_fries, Are you saying the XA.5 have less control at the frequency extremes than X.5 amps?"
I believe i have a pretty good handle on what pass amps can do, and i listen closely to those who have bought (and sold) different models, as well as the reviews of those same models. based on the mere fact that Pass Labs would offer two parallel amplifier lines where one would be (IMHO) way more musical than the other, indicates that the NON-XA amplifiers have some VERY important features that certain listeners are going to prefer.
a close friend has a pair of ALEPH-1.2's (as well as an aleph preamp) and i have heard them on many occasions. i absolutely love them. but they don't have much power below 4 ohms. that has never affected the sound any time i was over there, but some people will say that is unacceptable nonetheless, and needs "fixing".
Nelson still makes First-Watt amps as well. wimpy perhaps, but very short
circuit paths. he has good reasons for making those, too. beats the heck out of me...
So Unsound, I think I now understand you. Given roughly $15,000, the XA100.5 has less control at the upper and lower frequency extremes than does the X600.5? I was not aware of that.

French_fries, I agree there certainly is a reason for having the two different lines. Both sell well, so people must prefer one over the other. Besides the power rating in Class A, I have not read a description of how they really differ sonically. I had always assumed that an XA160.5 could drive any speaker as well as an X600.5 can, it just is biased more for Class A. Perhaps someone with more experience than me directly comparing these amps can clarify this. I've never had an X or X.5 series in my system.

Regarding the Aleph series versus the XA.5 series: I have owned a few models in each line. The most similarly rated amps that I have owned are the Aleph 2 and XA100.5, both rated class A for 100 watts and both mono blocks. I used each with the Eggleston Rosa speakers (87dB, 5-6 ohm). The XA100.5 was much better in my system. More effortless, lower distortion, quieter, more control over the lower frequencies, better soundstaging. No comparison really. I much prefer the XA.5 in my system. But as I say, I've never tried the X.5 series.
Petersayer, of course your speakers, room, and listening volume levels amongst other things would have to be taken into consideration as well. As I alluded to earlier, there are other things besides control at the frequency extremes to consider too.
I've never found the XA160.5 to run out of power driving any speaker. Current capability is often more important than wattage ratings and the XA160.5 can output as much current (36 amps) as the X600.5. That's enormous.

Once you're talking about the big Pass mono blocks, the usual tradeoff of class A vs efficiency becomes more moot. The big XA.5s can drive huge loads and the big X.5s have enough bias current where the class A advantage is in a diminishing return territory. Here, personal preferences should prevail as the two lines are voiced slightly differently.

In the smaller Pass amps the tradeoff is more acute because you really can run out of power with the small XA.5s! (depending on what your drive, your music and room)
Petrushka, That seems like a good summary, though I haven't heard an X.5 amp
in my system. How would you describe the slightly different voicings? Is the
difference fairly subtle or quite noticeable? Thanks.
The XA.5s are sweeter, darker, more liquid, palpable and mellow/relaxing. The X.5s are livelier, faster/snappier, subjectively more dynamic and punchy. In terms of bass the XA is warmer and more diffuse (but not untight or lack control) and the X is leaner and tighter.

I'm speaking purely in relative terms as all Pass amps are sweet, dynamic, etc compared to the competition.

I like the XA for jazz, classic rock, etc and the X for massive orchestral or choral works, not so much because of reasons of power (the big XAs have plenty) but because that's how they are most tonally suited.
Thanks for that description, Petrushka. That makes a lot of sense. I think it would also depend in large part on the speakers and how they are voiced. Some are warmer and more relaxing and some are more dynamic and lively, etc. Also, on a listeners personal biases and types of music as you write.

I'd love to directly compare the XA160.5 to the X600.5 in my system. It's tough though with no local dealer and shipping costs for such heavy pieces.