Pass Labs Xs 150 Monoblock Amplifiers Review

Note that the above invites the question of how these amps differ from the very best low power direct heated triode amps that have in the past been my reference for what can be achieved outside the concert hall.  The best low powered DHT (here I am thinking of Audio Note Balanced Kegons) are ideal for small groups and solo instruments, string quartets, small jazz ensembles, vocalists (whether male or female) and most certainly acoustic music.  They are to my ear more harmonically complex, have more “bloom,” and more air around instruments; however, the image which they create lacks the edge definition of the Pass Labs. Their ability to control dynamic woofers suffers in comparison to the Xs 150.  What the direct heated triodes do is all about nuance, low level detail and micro dynamics.  In these areas, I have yet to hear a transistor amp that is comparable.

While the Pass Labs Xs 150 may have less air, they also have a somewhat more detailed top end.  These amps have superb control of the bass without being over damped, but are not quite as harmonically rich as the Kegon.  The stage created by the Pass amps is not quite as expansive but has good depth and does not narrow at the back corners.  With the Pass amps, my speakers are cleaner and more articulate.  Well recorded pianos are also a real miracle. The piano sound is very even, clean, crisp and clear all the way up and down the register.  Further, when dealing with multiple instruments, the Pass amps never seem even remotely overpowered by the breadth of a large ensemble consisting of many different timbres, whereas the Kegons will occasionally smear.  The Kegons, however, with voices and mid-range instruments, have some magic (and more so than some more recent tube designs in which the goal seems to be to come closer to transistor accuracy) that is hard to define.  The voice, or voices, saxophone, trumpet, guitar, etc., sound palpable.  They seem to exist independent of the speakers.  You can hear the slightly husky edge of the breath, or of the vocal cords vibrating.  At its best, there is a sense of presence, and intimacy, that is not as strong with the Pass amps – though it is not entirely absent either.  What I find amazing is how many of the virtues of a DHT triode the Pass possesses while also retaining the dynamics and bass control of the best solid state amps.

As a friend said, if the Balanced Kegons are a Rolls Royce, then the Pass amps are a Ferrari, equally superb but very different.

Conclusions

In a perfect world, I would keep both the Pass Labs Xs 150 and Audio Note Balanced Kegon.  They are different animals, but they are both superb.  However, that would represent a larger financial commitment to my hi fi world than I am comfortable with making, frankly.  In the end, I concluded that I had a personal preference for the simple tube approach of the Kegon; yet, I know there will be days once the Pass amps have been gone for a bit, in which I will hear things that I know would be better on the Pass amps.