When I did my review of the Pass Labs XA60.8 Class A mono-block amplifier, which I purchased for my reference system, I shared the numerous reasons why Nelson Pass has legendary status throughout the high-end community. I also gave the details of my long history (more than 30 years now) of owning his amplifiers and enjoying every musical moment that his designs have provided for me. When I was offered the chance to review the new Pass Labs X250.8 Class AB stereo amplifier, which retails for $9,600 [editor's note, 12/14/15: Pass Labs has raised the price of this amp to $10,000], I thought it would be a fascinating experience to hear it in comparison with the more expensive XA60.8 mono blocks, which cost $12,800/pair, in the exact same system.
The specific differences between the new X250.8 and its predecessor, the X250.5, are summed up by this statement by Nelson: "Technically, the new X250.8 has a slightly larger power supply (more capacitance), more output stage (56 output devices versus 40), larger heat sinks, and more bias on the front end and the output stage. There is also a larger percentage of its output stage single-ended bias. The Class A output is larger."
The X250.8 weighs 100 pounds and measures nine inches high by 19 inches wide by 21 deep. Located in the center of the front plate is the large blue light meter, which shows you that the amplifier is running in Class A bias, unless the needle starts to move higher. In my system, no matter how high the volume levels were, the X250.8 never let Class A bias. Underneath, the meter is the on/standby button.
The back panel is where you will find the master power switch, a pair of handles, a pair of single-ended (RCA) and a pair of balanced (XLR) inputs, the IEC power input, and (just like the XA60.8 mono blocks) the finest and easiest-to-use speaker wire terminals. These terminals have large wing nuts that allow you to tighten your speaker wire spades until you hear a clicking sound that lets you know that the connection is secure.
The X250.8 is rated 250 Class AB watts into eight ohms and 500 Class AB watts into four ohms. The first 25 watts are Class A into either ohm rating. Like all Pass Labs gear, the X250.8 is built to a high standard, and its understated but beautiful appearance would produce pride of ownership for anyone who would purchase it.
I placed the X250.8 stereo amplifier in my large reference system as a direct replacement for my Pass Labs XA60.8 mono blocks. The system is composed of the following equipment: the Lawrence Audio Cello speakers on speaker platforms from Star Sound Technology, a pair of MartinLogan Depth i subwoofers, the Concert Fidelity reference preamplifier and DAC-040, the MBL reference 1621 CD transport, the Running Springs Dimitri power conditioner, a Krolo Tomo Audio Rack, Harmonix Studio masters power cords, MG Audio silver reference interconnects, and reference copper speaker ribbons. I did not start any of my serious listening sessions until I put about 100 hours on the X250.8 amplifier because it was a new unit that had been shipped to me for review.
Click over to Page Two for Performance, The Downside, Comparison & Competition, and Conclusion...