Review: Pass Labs X350.5 Amplifier

Category: Amplifiers

Since all the information has been provided about what the overall system is, I would also like to share that I predominantly listen to jazz and acoustic music.

I had the EDGE NL10 in the system for approximately two years. It had replaced Pass Labs Aleph-1 Monoblocks. There was no doubt that the NL10 was more transparent, detailed, and extended on both the top and bottom compared to my older monoblocks.

I like to use the analogy of different flavors of kinesthetic fibers or materials to describe tonal aspects or timbers of different amplifiers. The Aleph1's were smooth and "velvety" while the NL10 was smooth and "silky." However, because of the significant improvement in such areas as transparency, details, and sound staging, the NL10 was a vast improvement compared to the Alephs in my system.

Fast forward to the present:
I was not dissatisfied with the sound of my system, but I was very curious about what the new Pass Labs X350.5 amp would sound like in comparison to the NL10. I would like to mention that historically, I had auditioned the original Pass Labs X series amplifier and found it to be very detailed, transparent, and dynamic, but not as organic or musical compared to the Pass Labs Alephs. Therefore, I did not pursue purchasing a Pass Labs X amp for this reason.

However, reading what Nelson Pass was going to do in the new .5 generation of amps and talking to Kent and Peter at Pass Labs, whom I believe are quite honest about the sound of their own products, I was quite curious to see if they had really been able to take the musicality, velvety, and organic nature of the Aleph series and combine it with the transparency, dynamics and ultimate power of the original X series.

So here it is. The X350.5 amp is the best amplifier that I have ever auditioned in my own system. It truly has a tremendous ability of being transparent, detailed, and yet at the same time has the attributes of what is often called musicality and natural timbers. I want to be quite clear that I still consider the NL10 a world class amplifier which I enjoyed tremendously. However, the Pass Labs X350.5 has all the virtues that the NL10 offers but in addition, it has that special "organic sense" or offers more of a real sense of live music.

Another aspect that I found amazing about the X350.5 was that the sound stage increased in width and depth along with having more of a sense of three-dimensionality or air around each individual performer. The NL10 was no slouch in this area, but in comparison to the X350.5, the NL10 came in a distant second.

I know I have used language in this review that is somewhat subjective compared to some of the analytical statements I shared, but I hope that they made sense in trying to convey how natural, velvety, and real the timbers and the sonic signature of the X350.5 really is. The NL10 is a wonderful amplifier, but for me, it fell on the spectrum of smooth and silky versus smooth and velvety.

As a final note, the X350.5 sounded close to what it sounds now after 600 hours of burn in. Of course, I let it warm up for at least 8-10 hours before I seriously audition it. But the performance was very close to what I am experiencing now after what I would consider a total burn in. My system, including the X350.5, is never turned off so it is always operating at its ultimate level any time I choose to listen to music. There are many fine amps at this cost level. I recommend you listen to as many as you can including the Pass Labs X350.5 not just because it is competitive with the others, but you might find it as special as I do in my system.

Associated gear
The Pass Labs X350.5 amplifier is a replacement for an EDGE NL10. The total system is composed of:
1. Digital Front End - Transport and DAC both ENSEMBLE.
2. PLACETTE Active Line Stage into a Byrston Electronic Cross Over.
3. Since I Bi-Amp, the Woofer Amps are Threshold SA1 Monoblocks. The Amp is the new Pass Labs X350.5 powering the midrange and ribbon tweeters.
4. The speakers are MG20's.
5. A combination of Acoustic Zen Silver Reference II and Matrix Reference II with a double run of Satori speaker wires.
6. Digital Front End is connected to the ENSEMBLE duo isolink transformer along with Richard Gray power conditioners for the back end of the system. All power cords are Harmonic Studio Masters.

Similar products
Thanks for the review (the comparison to the original Alpha Series was key)! Awesome system synergy! The Placette Active is an amazingly overlooked component that is OUSTANDING! Wish I had the large room for 20.1's.. it was a hard decision before I bought my Wilson's.
Greta review. I have owned many tube and solid state amps in my time, and the X350.5 I have owned for several months now, has far exceeded my expectations. It takes a long time to burn in and come into it's won, but when it does, WOW. It truly does everything you described. I feel for the first time that an amp isn't three and I am hearing exactly what is on the software. Another upside, it doesn't seem to take much warm up to be at peak performance. Additionally, I find the midrange incredibly palpable for solid state. No grain or listener fatigue what so ever.

Now I want to try one. I had prefered the 350 to the 250 because I found it more laid back and gentle sounding. However I still felt it was a bit too clean and percise for my liking. I know that should be a good thing... but I like some extra musicality and richness instead of a lean towards sterile perfection if that makes any sense. I wonder how it compares to a accuphase A-50V which is the other amp I've been considering as a possible replacement to my beautiful tubes.

Though giving the granite 860's up might just not be possible for me. They're excellent. Just perhaps a little under powered for my rather big speaker when I run them in Triode. Plus I'd like to finish off my balanced connections instead of going single ended.

Regardless, I totally do not appreciate you making this amp sound so appealing : )

I have been an audiophile for over 35 years. My first system was a tubed receiver and through the years I have owned dozens of combinations of high end preamps and poweramps. For the last several years I have mostly owned both tube and solid-state power amps driven by An Audio Research Ref 2 mK 1. MY most recent tube amps include an Audio Research Vt-200 and a pair of BAT VK-60s. The speakers are Dunlavy SC-4a and the speaker cables are Audio Note Lexus. (They are wonderful). My last two solid-state amplifiers prior to the X350.5 were the ML-333 and the X350. I normally would switch between the two types of amplification depending on the listening material. I listened mostly to the tube amps because of their sweetness and their musicality. I found the X350 amp to be much more enjoyable than the ML-333 because of the size of the sound stage and the wonderful way it played acoustic guitar. I have now been listening my new X350 for four days ( 35 hours) after the initial 10 hour burn in driven by a Classe SSP-75. It is an amazing amp indeed. I have very varied tastes in music. I listen to everything from Wagner to the Eagles and I enjoy it all. Listening to Wagner's " Die Walkure" is an experience that could make any audiophile, even those that don't listen to opera, fall in love with their hobby all over again, The base is so deep and so rich that it makes me wish I had SC-5s instead of SC-4as. The voices are full and sweet and the instrumentation is to die for. On the "Hell Freezes Over" Eagles release, "Hotel California" shakes the room yet the vocals have no edge to them as is typical with a solid-state amp. I belong to the Bay Area Audio Asylum club and I can't wait to host a listening session. Many would consider my next comment sacreligeous, but it's it's time to stop worrying about tube rolling and replacing replacing stressed resistors and just enjoy the music.
Yours were very interesting comments, Jwin. What you are describing is similar to my, and others take on my H2O Signature amps. I am in Sacramento. I would love to have a listen, if it can be arranged. My last solid state amps were X600 monos.
I got my X350.5 on Monday. I just sold the X250.5. Before that I owned X150, X250 and X350. The X250.5 is a great amp, but just not as organic and as the X350.5, and still a bit agressive(much better than the X250) on some system. I have been playing X350.5 in my system for 3 days and my Studio has never sounded so tamed and control and beautiful ever before. I can't imagine how it would sound after it got fully broken in. This amp is truly a wonderful piece of art. Just by looking at it you'll feel contented already, let alone the incredible music it reproduces. It will stay with me for a long time.
I've had my Pass X 350.5 for a few months now. It really is incredible. It has passed the 300 hour mark and is still improving. It drives my Thiels easily.

If you have heard the X350 but not the X350.5 hold your opinions until you hear the new version. Words you will hear are sweet, musical, fluid etc... This amp will be in my system for the long haul.
Has anyone tried any isolation tweaks under their amp? What results did you get?
hi Teajay,
Excellent review. I see you also own SA/1 monos so you are familiar with the SA series sound. I have an SA/3 and am looking to make the move up to the 350.5. I have not moved until now as I did not want to lose the richness of the pure class A SA/3, but I would like more slam, dynamics and a larger soundstage that a higher powered amp should give. Can you give me an impression of how large a difference I will see making this switch, and if there might be any drawbacks? Speakers are Dynaudio Contour S3.4.
Hello Page12, thanks for your kind words regarding my review. The answer to yourquestion is that you would keep the warmth and richness of your SA/3, but gain wonderful details, more natural timbers, more "air" around the individual players in the soundstage along with the slam and dynamics you are looking for. Nelson Pass is a true genuis! Let me know if this helps you out
I personally have heard the evolution of Teajay's system since he is a very good audiophile friend and my "brother-in-law". His review is very accurate and I agree to everything he says about 350.5. Teajay doesn't make a move in his system unless it truly does improve his system. Not just to have the latest and greatest. I was amazed myself how much the .5 improved his already incredibly sounding system because it improved in all aspects. I heard all the virtues of the NL 10 and then some. More air, transparency, details, improved timbres & dynamics. All with a hint of that "tube magic" people search for. I hate to say it since the NL 10 is a world class amp, but the .5 made the NL 10 sound dry, lacking warmth, wimpy and "boring". If you were to ask me if I would like to own a NL 10, the answer is yes in a heart beat, but I know I would have that itch to upgrade to the .5.

Everything I've said about the .5 may not sit well with some people, but I personally think it all comes down to personal taste and system matching. I do think you owe it to yourself to audtion the .5 if you are considering the NL 10 or an amp in that price range.
Anyone compared X350.5 with Rowland 3.02? 302 is 60% more expensive, but that may not imply necessarily better sound.
I have just posted a brief update on the development of the upcoming Pass X600.5. Please see:
Hi Teejay,
Great review!!! It has certainly helped me shortlist my next amp upgrade to the X350.5 or the CJ Premier 350. BTW have you tried the X350.5 with a passive pre and if you did what was your experience? I having plenty of success with my Passion passive pre mating with Ayre V-3 amp driving my Platinum Solos speakers (Sensitivity of 84dB/m) in my smallish room.
My main concern here is the passive pre/X350.5 combo may not drive the Solos to reasonable sound levels but I think it might be ok.
Thanks for any insight you might have.
Hello Ipy, thanks for liking my review of the 350.5. As you know from the review, I use a Placette dual mono active line stage in my system. However, as far as I know, there should be no difficulty in matching most passive preamps, regarding volume, with the Pass Labs X-350.5. I am not familiar with your specific passive preamp but if it is similar to a Placette, which is a transistor based passive, you should have no difficulty in my opinion. Hope you audition the 350.5 because it really is a wonderful sounding amp and I think you would enjoy it. Hope this helps.
I now have 650 hours on my 350.5 and it has continued to improve its musicality. Base extension and the tubelike warmth have now matured and the amplifier I was so impressed with has gotten even better. The 650 hours hours I refer to is actual music playing. I do not count warm up or down time in between listening.
Jwin, with out hopefully causing emotional distress or interfering with your pleasure regarding the 350.5, which is a great sounding amp indeed, I have just replaced mine with a pair of Pass Labs XA-100 monoblocks. I know you love the sonic virtues of the 350.5, if you ever have a chance to try the XA's you would find them to take those virtues to another qualitative level.

Your speakers are an easy load to drive, so even the XA-60's would probably drive them with no difficulties regarding D/B levels or dynamics. My XA-100's drive the midrange panels and ribbon tweeters of my MG-20's with no problems at all. The MG-20's are not highly efficient and are somewhat of a reactive load to drive yet the XA-100's just cruise when driving them. So, the smaller and less expensive XA-60's would probably work beautifully in your setup. The sonics of all the XA amps is exactly the same the only differences are in power output, unlike some of the X-.5 amps that do sound somewhat different. I believe that the 350.5 is the gem of the .5 series and the only way to better its performance is a pair of 600.5's, but at that point money wise, the XA-160's are priced right there and if the shear power is not needed, then the XA's would be my choice.