Amp/Preamp Asylum: REVIEW: Pass Laboratories X150.5 Amplifier (SS) by the analog kid

Model:	X150.5
Category:	Amplifier (SS)
Suggested Retail Price:	$4,500.00
Description:	150 Watt Solid State Amplifier w/Blue Meter
Manufacturer URL:	Pass Laboratories
Manufacturer URL:	Pass Laboratories

Review by the analog kid ( A ) on June 12, 2003 at 19:58:34
IP Address: 35.12.26.246

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For many years now, the biggest audio dilemma I've faced is proper amp/speaker matching. There has been a near-constant rotation of both speakers and amplifiers through my "reference" system, with none staying longer than 3-4 months. As far as amplifiers go, I've owned the following: Adcom GFA-555, Musical Fidelity XA-1, Classe CAP-80, Creek 4330, Sonic Frontiers Power 1 & SFC-1, SF Anthem Amp 1 and Integrated 1, Classe DR-25 and 25, Wavelength Cardinal XS monoblocks, Pass Aleph 3, Aleph 5, Aleph 30, and Aleph 60 monoblocks. I THINK that's it....!
A brief digression regarding tubes versus solid state. I've personally come to the conclusion that although I LOVE the liquidity that tube amplifiers provide, they do NOT sound like reality. This has been hard for me to admit, because I do love that dripping rich liquid tone of tubes. But having been to several concerts - symphonies, Broadway productions, and most recently CSN - and listening with eyes closed only to run home and listen to "the system," I'm convinced that "real" music in a real space sounds warm, natural, and clean, but NOT cloyingly liquid the way that tubes (re)produce music. Consequently, I've been solid state for the last two years (although I do run a tubed front-end - CAN'T let go completely).
For the last three years, I've been through a series of Pass amps - ast listed above, the Aleph 3, 5, 30, and 60 monoblocks. I've found them - of all the amps I've owned - to sound the most like natural, warm, music as it hits my ears in a concert hall.
I recently (six months ago) purchased speakers that are now my "finally found them" references - speakers that I find truly satisfying in all regards: the Totem Forests (see my archived review). However, pairing them with my Aleph 3 was impossible, and even with the Aleph 5 they were underpowered (the Forests rate fairly high sensitivity, but REALLY come into their own with more than 100 watts pumping through them). Consequently, I decided to "take the plunge" and return to big watt solid state.
I have to admit, this was a hard decision for me to make - I have long been a devotee of Nelson Pass's Aleph designs, and find them phenomenally liquid (there's that word again!), natural, and warm. The X150.5 represents a fairly strong departure from this - Class A up until a certain point, then class AB. Supersymmetry circuit rather than single-ended. I've read on various posts that the X series sounds "more sterile" and "leaner" etc., but I decided to try it out anyways.
The X150.5 is basically the 150 with the addition of the "blue meter" on the front panel - pretty cool aesthetic, although I don't know if it's worth the extra $500 you'll pay for it (depends on the value you put on eye candy). For me it's worth it. Upon arrival, I was EXTREMELY impressed with the appearance - the website photos don't do the industrial beauty of these amps justice.
I ran the X150.5 for over 100 hundreds solid (using a tuner) before any listening. Hard to do, being as impatient as I am! Then I plugged in my Art Audio Vinyl 1 (with volume control - run directly into the amp - I only listen to vinyl in my reference system), and sat down to listen.
This is an EXTREMELY impressive amplifier, and overall it bests the Alephs in almost every way imaginable. MOST noticeable in terms of improvement is the utter transparency. I now hear all kinds of low-level information that was muffled by the warmth of the Alephs. For example, listening to the MoFi Beatles White Album side 1, I was startled by the soundstage prominence of the tamborine in the mix - and for the first time could hear the tamborine jingles clearly as small metallic disks (rather than some kind of blurring jingling). Album after album: Radiohead, Rush, Sarah McLachlan, Dave Brubeck, Vaughn Williams, Emerson Lake & Palmer, the effect was the same - this is THE most transparent amplifier I have yet owned (see list above).
A second dominant, noticeable attribute is the power and extension at the frequency extremes. Bass is prodigious, and completely redefines what my Forests are capable of. And to think I was pondering a sub - HAH!! Plugging in PJ Harvey "To Bring You My Love," the bass literally rattled shelves throughout the house. Yet at the same time, it's tuneful and balanced. The highs seem to extend forever, without a hint of brightness or edge.
The final characteristic of this amp that merits mention is the naturalness of tone. It is an EXTREMELY realistic and natural sounding amp - warm, clean, clear, and transparent. But it is NOT high on the liquidity scale. For those seeking that "drip from the walls" sound, this amp will strike you as comparatively sterile. However, I find it the closest sound to "the real thing" I've yet experienced, and it is the PERFECT mate for the Forests, which perform SO far beyond the envelope now it's frightening.
All in all, I can't say enough good things about the X150.5. An incredible sonic accomplishment. Well done Nelson!! For the first time in ten years, I've had an amp/speaker combination remain stable for six months, with NO desire for "upgrade," and each time I listen all I can think is "how can it sound this great!!??"

Product Weakness: will disappoint those hoping for the same degree of warmth and liquidity as the Aleph series
Product Strengths: beautifully built; incredible dynamic punch, transparency, natural tone, and warmth; phenomenal extension

Associated Equipment for this Review:
Amplifier:	Pass X150.5
Preamplifier (or None if Integrated):	Art Audio Vinyl 1
Sources (CDP/Turntable):	Basis 1400/OL Silver 250/Grado Statement
Speakers:	Totem Forest
Cables/Interconnects:	Silversmith Pure Silver
Music Used (Genre/Selections):	Rock, Female Vocal, Jazz, Classical
Room Size (LxWxH):	22 x 11 x 9
Room Comments/Treatments:	RPG Diffusors
Time Period/Length of Audition:	6 months
Other (Power Conditioner etc.):	Monster HTS2000
Type of Audition/Review:	Product Owner

Product Weakness:	will disappoint those hoping for the same degree of warmth and liquidity as the Aleph series
Product Strengths:	beautifully built; incredible dynamic punch, transparency, natural tone, and warmth; phenomenal extension