Audioholics Reviews Pass Labs’ X350.5 Amp

$11K amplifier put to the test


Pass Labs is a respected audiophile brand prized for its products rugged built quality, high-quality parts and it’s smooth musicality. Audioholics tried out the new $11,000 X350.5 stereo power amplifier and came away pretty awed. Here’s what reviewer Gene DellaSala concludes: “Its pristine sonic virtues, ability to drive even the most challenging of speaker loads beyond reference levels, is even more impressive than its overall excellent bench test results.”


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The Pass Labs X350.5 350 watt/ch stereo amplifier has the appearance like it was sculpted by Cybertronians. It portrays a commanding presence that just draws your attention. The X350.5 is built like a tank, pegging the scale in the pride of ownership department and weight (132 lbs). Its pristine sonic virtues and ability to drive even the most challenging of speaker loads beyond reference levels is even more impressive than its overall excellent bench test results. But, its power hungry demeanor and luxurious pricing isn’t for the faint of wallet. However, I’m confident if Optimus Prime were an audiophile, it’s a sure bet the X350.5 would be his amplifier of choice. Audiophile & Audioholics recommended!

The X350.5 is touted as a minimalist design, which in terms of circuit complexity may be true, but the quality of craftsmanship and the layout of the components is an engineering marvel. They use very high quality output devices and tight tolerance parts to help minimize the excessive reliance on negative feedback which they claim improves transient response, bandwidth linearity and stability by not having to employ additional gain stages. The X350.5 is heavily biased into Class A operation up to 40 watts/ch peak or 20 watts/ch continuously. Pass Labs’ recommends a warm-up period of about an hour before conducting critical listening tests. At higher power levels, the X350.5 operates in Class AB for increased efficiency.

The power transformer is a hefty1.5kVA toroid, which is not visible from this picture as it’s mounted at the bottom of the chassis underneath the heatsink flanking the power supply capacitors. Each channel has 36 output devices (18 on top as pictured and 18 on the bottom). The output stage is fully differential, which if properly implemented can be a huge advantage for noise immunity and distortion reduction. Only the very best amplifiers are fully differential from input to output and the Pass Labs is in good company here.


The X350.5 was loving pumping the juice to my Status 8T speakers as I turned the volume up to lifelike SPLs. Closing my eyes, I really felt like I was in a jazz cellar in NYC listening to this sextuplet grace me with their phenomenal performance . Track #2 “Freddie Freeloader” [on the Miles Davis: Kind of Blue
] is my favorite song on the whole album. It just oozes coolness and if you’re foot isn’t tapping on this tune, someone needs to check your pulse. Bill Evan tickles the ivories with a surgeon’s precision. I got instant goose bumps when Miles’ trumpet kicked in. I just couldn’t get over how lifelike and vivacious it sounded, especially when Coltrane answered Miles in his solo. I was truly getting that “better than being there” experience found only from properly setting up and pairing the best electronics and loudspeakers in a great sounding room with exceptional source material. The X350.5 just loved showing off its sonic chops with this album.

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