What Difference between Pass X150.5 and X250.5?

Is it just power?
What else would I hear?
Eril, this can be a little confusing unless we define which generation of X-amps we are talking about. In the original X series the X-150 became the X-150.5 when Pass decided to add the blue meter to the front of the amp, which the X-150 lacked. Otherwise, the amp was exactly the same. I'm assuming your question is regarding the new generation of X-.5 series, which is a major revamp of all the X-series amps. All the new x-.5 amps sound terrific in their price range. What you get as you go up in the series is not just more power, but higher initial single-ended class A biasing for certain amount of watts. This is followed by a number of regular class A watts untill the amps go over to class A/B. Because of this the 250.5 will give much more of the taste of the Pass Labs X/A series amps. The dynamics, slam, transparency of the old X-series with the warmth of timbres and organic/liquidity often heard in tube amps. I have the 350.5 in my system and enjoy its virtues on a daily basis. The 250.5 will give much more of the above stated sonics then the 150.5, even though the 150.5 is terrific at its $ point the 250.5 is just that much better. Hope this helps.
Thanks Teajay.
I am currently using a Cairn Integrated Amp (first 10 watts in class A) with my Jean-Marie Reynaud Evolution 3 speakers. 88db sensitivity - easy to drive but do better with high current and high damping factor.
The speakers are well banced but a tad soft/warm.
I like the Class A sound better than any AB or valve sound I have yet heard and I thought the new Pass X-5 series was a good potential match.
I assume the new Pass ".5" series of amps was only from the X250 and up, i.e. the current X150.5 untouched correct?
Teajay, you say: "X-150 became the X-150.5 when Pass decided to add the blue meter to the front of the amp, which the X-150 lacked. Otherwise, the amp was exactly the same." The Pass site seems mostly to confirm this, but they do give one measurement which is significantly different from X150 to X150.5: something called "Balanced CMRR" is given as " -85 dB @ 1 kHz" for the X150, but "approx. -70 dB @ 1 kHz" for the X150.5. This suggests that the amps do in fact have some significant internal differences, not just a meter on the front...unless you have heard otherwise from Pass themselves?
Calanctus, I have no information that would put in doubt what you stated on the Pass Labs website. I remember a long time ago that I talked to someone in Pass's office who said their was no sonic difference between the 150 without the meter compared to the 150.5 with the meter. The new 150.5, along with the whole new X-.5 series, is a different matter entirely. Remember, Eril, its not just class A biasing in the new series, like your Cairn amp, but single-ended class A biasing for certain amount of watts before going into regular class A. This gives some of the sonic virtues normally associated with tube SET amps. The 250.5 lives in a different sonic world than your Cairn Intergrated amp, which is great for its cost, but is not is not really competitive with the 250.5. But remember your comparing amps that are a least $4000.00 different in their prices. In this case more $ really brings a much higher level of performance, often more $ doesnot = better.
Thanks again Teajay.

Yeah I sort of appreciate the difference in the Class A stuff. I live in New Zealand. We get stuff all here so I import. The Cairn Fog 2 CDP and 4808A were my first venture into good audio. Loved it so now moving up. Started with Combak Reimyo CDP-777 - which is outa-this-world-wonderful - I don't want valves in a power amp and can't afford XA series. But I am also wanting a great valve pre-amp . Any thoughts on what works well with Pass X -5 series?

Two different Pass dealers say internals are the same between X150.5 and X250.5 - power and Class A bias are only real diffs - X150.5 goes over at 15 watts - X250.5 at 25 watts.
Nelson Pass himself says "authority and control are only big difference. The other audible differences are subtle."
Eril, you live in a beautiful country! The closet I have gotten to New Zealand was a trip I did to Tasmania two years ago. If the MAN himself, Mr. Nelson, says that's the major differences between his amps, who am I to argue. I would just add that as you go up in the X-5. series you get more and more of that special "organic" sense because of the higher single-ended class A biasing. I wrote a review here on the Gon about my experience which lead to me replacing an Edge-NL10 with the PassX-350.5 in my system. You might want to take a look at it. This "organic" sense is subtle in the Pass amps but after you hear it, its hard not to want it in your system. I think its time for you to have a home audtion and let your ear's decide what you like. Please share what your experience/decision is after you listen with us. Thanks.
Eril, in my last reponse I forgot to address your question concerning Pre-amps that are good matchs with the X.5-amps. I'm not an individual who is to enamored with tube Pre-amps, but let me share what I have heard with my own ears regarding the matching with the 350.5 in my own system. I replaced my highly regarded ML-32reference pre-amp with a Placette dual mono active line stage. It blew away the 32 on every factor(dynamics,transparency,soundstage,timbres,extenstion of bass,etc.). Not inexpensive, but a bargain at 4,500.00 dollars. You buy it factory direct with a full month audtion period with a full money back guarantee. Mr. Placette,Guy Hammel, is a great guy and a real gentleman along with being a genius regarding his Pre-amps. The other Pre-amp which sounds gorgeous with the X-.5 series is the highly rated, rightly so, Lamm reference pre-amp which is a hybrid tube/ss two box piece. However, it sales for over 12,000.00 dollars. The combination of the Placette active linestage and the Pass LabsX-350.5 is just exceptional in my system and I'm totally happy with this duo. Finally, someone I know has just changed his Pre-amp to the Herron tube linestage with his 250.5 and loves this combination. All three Pre-amps would really sing with any of the X-.5 amps along with many other brands/types of other amps. Hope this helps.
Info just in from Pass.
Per channel continuous:
X150.5 10 watts
X250.5 40 watts
X350.5 50 watts
With higher instantaneous peaks.

teajay - thanks for your thoughts. Auditions are impossible for Pass, Herron and Placette here in N.Z. I have heard several passives and they don't "do it" for me.
The Pass pre-amps are considered a little on the dry side by the Australian importer - I will buy from him, great dealer.
So I will continue my research on suitable pre-amps.
Latest in from Nelson Pass:
"The X250.5 and 150.5 differ in power supplies, output stage size, and bias. In these amplifiers
the first few watts are single-end Class A, and they leave push pull Class A at something like
20 watts and 40 watts peak respectively."
Eril, If you live in NZ, I would give Paul a call at PQ imports and see if you can have a listen to a VTL pre-amp if you are not against tube pre's.
Pass Labs are wonderful designed amplifiers, Pass Labs offer a substantial range of amplifiers to match most loudspeakers manufactured today.
If you are looking for a Pass Labs amplifier in New Zealand please contact Parmenter Sound.
Thanks Jason Parmenter.
^Agree. Lack of class. Resurrect an 8 year old thread in a discussion forum for an "ad" ?????
I know this thread is old, but felt compelled to respond as I have experience with both of these amps. My previous amps have been Anthem, Proceed, Bryston, Classe, Cary, and Krell. My affinity with Pass Labs amps started with the X3, and then onto the X150.5. After living with the excellent X150.5 for a few years the upgrade bug bit again. Pass labs amps don't come up for sale often on Audiogon as they are a great value for the money. A X250.5 showed up and I jumped on it. I did an A/B comparison between the X150.5 and X250.5 after allowing each to warm up and the source playing for several hours. Me being the somewhat cheap bastard that I am tried not to tell any difference in sound quality, to justify the difference in price. I was using CD's playing through a tube pre amp with NOS tubes and Dynaudio C1 monitors. Although the X150.5 had provided many hours of listening pleasure, the X250.5 had just a bit more in some ways. Same clear presentation, but a little more slam. The clincher was the small nuances that I had never heard before. It allows me to connect to the music closer to a live event. The build quality and design are also superb.