Power Amplifiers

Pass Labs X1000.5 Monoblock Power Amplifier


The Pass Labs X1000.5 Power Amplifiers In Use

For the listening tests, I used an OPPO BDP-95 universal player (stereo XLR analog outputs), BAT Vk-5i preamplifier (XLR inputs), and Magnepan 1.7 planar speakers. Cables were Wireworld.

What I was really after here was a comparison of the X1000.5's with the XA100.5's which I reviewed in April, 2011. Those monoblocks are Pure Class A, but output 100 watts instead of 1,000. The X1000.5's are biased Class A for the first 80 watts. So, I wanted to see if dynamic range would be affected by transient peaks that might require more than the XA100.5's capability, at moderate listening levels.

Guitars, especially when you have a quartet of them, have leading edge transient peaks when the strings are plucked. I did find that, at moderately loud levels, there seemed to be more snap to the leading edge of the sound with the X1000.5's, indicating that those transient peaks were requiring a very short period of more than 100 watts, even though the overall sound averaged about 50 watts or so. This does not surprise me. I just wanted to confirm it. So now that we have that question answered, let's just talk about the musicality of the sound.

At modest listening levels, I heard no difference between the XA100.5's and X1000.5's. This is because both were playing in Class A. However, when I really cranked things up, having those extra 900 watts made a huge difference, which could be summarized by saying the entire room was moving in time with the musical rhythm. I did notice that there was a slight difference in the detail during certain musical passages, due probably to the Class AB operation of the X1000.5's above 80 watts. However, one has to decide on a preference for detail or high power. You get the detail with the Class A and the power with Class AB. You want a 1,000 watt Class A monoblock? You had better have room for two refrigerator-sized amplifiers.

I prefer power, and with the X1000.5's in the system, I never ran out. Never felt that the amplfiers were straining. Never felt the music had hit a wall. And the transients were always there regardless of the volume, due most likely to the reserve power storage in the power supply.


Piano is another instrument that is very transient-oriented. The strings are not plucked, but they are struck, and a lot of power goes a long way in making the piano sound like it is across the room in front of you. The low notes were full bodied, the high notes were crystal clear and clean, and the tonality was completely natural.



For this Fleetwood Mac DVD-A album, I switched out my two front channel power amplifiers for the Pass X1000.5's, driving two full-range electrostatic speakers. This is my stress test, as the speakers dip to about 1 ohm in the high frequencies. I had the entire system cranked, and there was no problem with the Pass amplifiers at all (my other amplifiers will sometimes shut down with intense high frequencies). So, if your speakers have low impedance (and/or low sensitivity as do the electrostatics), a pair of the X1000.5's will fix you up just fine.

For this test by the way, I had to move my SSP and electrostatic speakers from downstairs into the room with the Pass amplifiers because the amps are too heavy for me to lift by myself. I didn't bother moving the side or rear channel speakers because I was only interested in how the X1000.5's would drive the electrostatics. As a second test, I used the dance scene from House of Flying Daggers. The trouble with my other amplifier comes when all the crystals are tossed onto the floor. The X1000.5 didn't dial 911.


It would probably an understatement to say that Fleetwood Mac is legendary, but it is, and the music soared with the X1000.5's. Perhaps that is because when a rock band performs, they use amplifiers with thousands of watts of power on stage. So, it seems logical to play the music with thousands of watts of power to get a feeling of the live performance. I got that feeling. I don't know if my cats did or not. I couldn't find them for two hours after playing this album. I was in a garage band in the 1960's and we played LOUD. The X1000.5's play LOUD too. One of my neighbors called and asked me if I had finally found some people to jam with (I play drums now and then), and I said, "Thanks for the complement. Even if I had found some friends to jam with, I don't think we would have sounded quite this good in musicianship."

Anyway, enough said. The X1000.5's are extreme high fidelity, and are killer amplifiers when it comes to transients and volume capability.