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
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.