Pass Laboratories Inc. was founded in 1991 by Nelson Pass who seven years later in 1998 stepped down as President in order to devote greater time towards the development of products. Through my conversations with Desmond Harrington, now the company's President, I learned that Nelson Pass designs the amplifiers and electronic crossovers while Wayne Colburn (who joined the company in 1994) is responsible for the preamplifiers, phono stages and DACs. They currently work together on loudspeaker design and truth be told they seem to always wind up collaborating on everything, with lots of great conversation going back and forth between them.
Looking to the website one is amazed with the amount of knowledge located there. Searching through various tabs and you will find in depth discussions on products, descriptions of Pass Patients, numerous reprinted technical articles which cover topics from "The Sweet Spot" to "Speaker Cables: Science or Snake Oil-" and even a safety information section. Of particular note was in the technical blog section called "Leaving Class A" (at this link), which made for quite an interesting read. I will leave it to you to spend a few hours sorting through the vast wealth of information there. As for today we will undertake a careful examination of the Pass Labs XP-10 line level preamplifier and XA60.5 Mono amplifiers. Pass Labs is located in Foresthill California only a short two hour drive north of my home. Once delivered a mandatory check for physical damage plus a quick system setup ensued to make sure they survived the trip in working order. Rarely does a combination of equipment take me so much by surprise as did this preamplifier/amplifier duo from Pass Labs. After two days of casual listening with nothing particular on my mind expect the pure joy of hearing my favorite recordings it was time to separate them for their perspective reviews. First a careful examination of each piece was done and then they were brought back together to be evaluated as a system.
Physical and Technical Description
The factory recommends going the way of a balanced output to amplifiers whenever possible claiming it will "typically retain the character of the input mode, but offers less distortion, less noise, more gain, and more voltage swing, without compromising the sound. With balanced operation, the common mode rejection of the preamp reflects the intrinsic common mode rejection of the topology, the matching of the gain devices, and the matching of the attenuator channels. In this case we have been able to keep the total mismatch to about 0.1%, for a common mode rejection of approximately -60dB." For this review the quieter XLR inputs/outputs were used as my Oppo Digital BDP-95 CD player and Monarchy Audio SM70-PRO mono bloc amplifiers could accommodate this, as later did Pass Labs own XA60.5 amplifiers.
The XP-10 comes with 83 volume steps allowing
greater control over listening levels than did their previous X model
preamplifiers. After first unpacking then plugging in the unit give it
twenty-four hours before attempting any critical listening as it uses high bias
Class A topology circuits that require them to heat up to a certain temperature
before sounding at their very best. This of course necessitates that the unit be
powered up 100% of the time but you need not worry as the XP-10 is quite "Green".
It has a current draw of only 10-watts and is designed to never really be "off"
even in the power down mode. For this reason if you must unplug the XP-10 or
remove the power cord the twenty-four hour break-in period would need to start
over for the unit to again reach its sonic peak. Like all Pass Labs equipment it
too strives to minimize the number of components in the signal path. Lifting off
the top cover revealed a carefully thought out design taking up every inch of
space inside leaving no room to spare. It is easy to understand why a design
improvement on the XP-10 necessitated a second or third enclosure for their
XP-20 and XP-30 models respectfully.
First Listen With The XP-10
My first worry was losing the wide soundstage a good tube preamplifier can produce but much to my delight that problem never arose and on "Rocky Mountain High" with the ML's it threw an immense soundstage. The female vocal on "Country Roads" could be heard with distinction correctly placed in the background singing softly behind John Denver. Ambience was also very good with the proper reproduction of the small intimate acoustic hall where this CD was recorded. To describe the XP-10 I would have to say it was more relaxed almost tube-like but without losing detail. Rather than being aggressive or bright as lesser solid state preamplifiers can sound, this one captured the essence of performances others seemed to just glaze over. During an audition of the song "Poems, Prayers & Promises" my connection to the music felt so strong I was compelled to share my experience with others. Here one could feel the true mood of the performer as he reflected back upon his life with vocals being truly transparent and clear. Switching back over to my beloved VR-35 loudspeakers for the rest of the review period I started with a favorite CD of mine, YO-YO MA & FRIENDS Songs of Joy & Peace [Sony Classical 88697-24414-2]. Here the cello in "Dona Nobis Pacem (Give Us Peace)" was heard in full detail without tipping the scale towards edgy or grainy but rather quite open, transparent and musical. The tonal character of the instrument was rightly reproduced to sound close to that of a real cello with the body of the instrument sounding alive and natural. Diana Krall's vocals on "You Couldn't Be Cuter" had a touch of midrange magic similar to what one would expect from tube good preamplifiers. Being solid-state in design it did not need one half an hour to warm up before sounding its best, just start your source component and to listen to music at its' finest. With some preamplifiers I have found it difficult to find just the right spot on the volume knob with music being either too soft or too loud. Wayne Colburn's 83 step controls found just the right spots for me and my system, a perfect match.
The Rolling Stones Let It Bleed SACD CD (abkco 90042) has many classic Stones songs, one being "Midnight Rambler". Here rapid transients were reproduced with apparent ease with images locking tightly in place. Vocals were simple to locate within a well-defined soundscape of great width. Harp, guitar, drums, percussion and bass existed separately in individual spaces distinct from one another. The layering of the choir on the opening of "You Can't Always Get What You Want" displayed great depth front to back as well as width and height. Mick Jaggers voice was powerful and full while Keith Richards' guitar located off to the side was easily recognizable and in full detail. Dynamics were strong as the ability of this preamplifier to quickly shift from soft to loud passages never posed a problem proving to be one of its stronger points.
The "earthy" quality of Tracy Chapman's vocals on
Our Bright Future [Elektra 514061-2] shown through giving an
intimate sense to her overall performance. While lacking some of that warm and
fuzzy you are there feeling found with tube preamplifiers on "I Did It
All" the solid-state XP-10 displayed an overall sense of transparency great
enough to make me sit up and take notice. Fingers gliding across strings on the
neck of the guitar were easily discernible as the texture of chords added
realism to the song. Having others over who are not audiophiles sometimes helps
to put things in perspective. When playing a demo CD distributed by Usher Audio
which was created for promotional use my non-audiophile friend commented how
real it all sounded, as if they were playing the congas right there in the room
just ten feet away. It was now time to drop in the Pass Labs XA60.5's pairing
them with my reference Aesthetix Calypso preamplifier and to put the XP10 aside.
Steps the Pass Labs XA60.5 Mono Amplifiers
The XA60.5 mono bloc amplifiers feature sixty watts of Class A power into 8 Ohms while weighing sixty-two pounds apiece or a total of one hundred twenty-four pounds for the pair. Appearance wise they sport a stylish looking billet aluminum (like with the XP-10) front faceplate with a recessed display meter, standby mode button, attractive blue lighting and some side heat dispersing fins angling upward rather than the traditional style of pointing straight out to the sides left to right. This slopping heat sink design serves the amplifier in multiply ways as it is able to hold twenty power MosFET's each ( forty total) and have the ability to dissipate a couple hundred watts efficiently. These fins also hold everything together as the top, bottom; front and real panels all bolt onto it, thereby simplifying assembly. Lastly and quite simply, they look great and that is nothing to be ashamed of. Their beauty only adds to the joy of their musical prowess and were a pleasure to openly display on the top, rather than inside, of my Salamander Audio Rack. Peering around towards the rear of each unit one finds an IEC connector, RCA/XLR inputs, a power off switch, fuse holder, a pair of handles to aide when lifting, a signal ground connection and a pair of five-way binding posts for external turn-on control.
the top cover reveals the heart of the XA60.5 with its large 1KVA toroidal
transformer. We are talking very large indeed as it takes up about one third of
the space inside the amplifier. Running in Class A allows it to draw a high
constant current even at idle which with its 180,000uF of capacitance allows for
the storage of a great deal of energy to aide in the realistic reproduction of
those demanding musical transients. Producing sixty Class A, or 120 Class
AB Watts with a low factory rated 1% distortion, the XA60.5 is able to store
sufficient current for the immediate delivery to musical peaks.
Meters Don't Go To Zero"
"The meters on our amplifiers are different. They reflect the current consumption of the amplifier, and when the amplifier is operating, they don't go down to zero like the meters on other amplifiers. This is because the electrical current consumption of our circuits has a fairly high value at all times, a property called the bias. The bias current runs through the amplifiers at a minimum value, determining the class of operation – Class B, Class AB, or Class A.
Class B has no bias current, Class AB has a moderate bias current, and Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias.
For several years Pass Labs has specified the nominal wattage's at which our amplifiers leave push-pull Class A operation into an eight ohm load."
"Like all bias decisions, the amount of single-ended bias and push-pull bias is a balance between performance and efficiency. The bias is generally set at a level suited to the heat dissipation capacity of the hardware. At Pass Labs the bias is set to the value which raises the heat sinks 25 to 30 degrees C. above ambient temperature. The result is a heat sink which you can put your hand on for about 10 seconds or so.
As a practical matter, this means that our X (Class AB) amplifiers are biased to dissipate roughly half of their rated output power. The XA (Class A) amplifiers are biased to dissipate roughly three times their rated output power.
The whole point of going to this trouble is to build an amplifier which sounds as good as possible. We find that this is achieved by building a simple amplifier which is intrinsically distortion-free. Getting that depends on a high bias.
Measurements are helpful at illustrating the differences between design approaches, but they are certainly not the last word in audio. If they were, then numerous other approaches would sound as good or better.
You can certainly imagine an amplifier which operates with a low bias current but has the necessary amount of negative feedback and/or circuit complexity to insure that it measures as well. Actually, you don't have to imagine it – such amplifiers are for sale.
Do they sound better? We don't think so. Our meters don't go to zero"
If you want to experience this amplifier at its
best turn it on and wait until it gets hot to the touch as it sounds better when
warm. Leaving it on for somewhere close to an hour should do the trick. Once
again it is now time to leave the technical and physical discussions to move
onto some real world listening evaluations.
the Amplifiers Through Their Paces
The opening guitar sequence on "Free Fallin' "
from Tom Petty's Anthology Through The Years CD
[M-C-A 088 170 177-2] had a magical sparkle to it sounding high pitched but
never shallow or thin, a positive testament to these great amplifiers. The
classic Joni Mitchell CD, Blue
(Reprise 2038-2) in HDCD format was another pleasure to revisit. Here on
"Carey" the soundscape was neatly laid out before me with clearly
defined space defining musicians and singers both lead and background. There
is nothing like a good Joni Mitchell performance. It was indeed a great pleasure
hearing her unique voice filling the open space between my loudspeakers, yet
sounding as if emanating center stage directly in front of me. The range of her
vocal talents was vividly displayed as the XA60.5's had no trouble quickly
recovering from the many fluctuations of her vocal prowess. Notes from the piano
fell upon my ears appearing to be just the right distance beneath her voice
giving this instrument a sense of its appropriate height. She really hits
those high notes with a tonal quality unique to her singing style and these
amplifiers never let me down with their ability to create the illusion of her
performing live right there in the room. This CD was enhanced by the
performance of these Nelson Pass designed amplifiers with their ability to play
music with a beautiful sense of ease and naturalism. As much fun as it was
listening to them it was time to give a serious audition to both XA60.5's and
XP-10 as a system setup which is really where this review was headed from the
very beginning. Besides after those first few days of casual listening with the
both of them, my mind keep racing forward to the time when a more serious
endeavor would be undertaken to evaluate their sonic merits in greater detail.
So why wait any longer, lets us now begin.
The Beatles Song Says, "All Together Now" (A System Review)
As for the preamplifier my only suggestion would be that if you are looking for that last drop of musical detail and will settle for nothing but the very best then by all means look into their other two preamplifiers (XP-20 @ $8600 or the XP-30 @ $16,000) which sell for considerably more. These are indeed a great value considering the performance they deliver and I must consider them a bargain in the realm of high-end audio. At listening levels normal for me when not in the process of reviewing but rather just enjoying the music these amplifiers were all that was needed and then some. When I mentioned smooth it was not in reference to a sound that was rolled off at the top and bottom frequencies but meaning instead very natural sounding. Often were the times when a listening session lasted well into the night five and six hours at a stretch where not even the slightest fatigue from digital madness set in, a definite testament to this pair of audio gear from Pass Labs. Read a few of my reviews and you will quickly discover my love for the various CD's from the Norwegian company 2L. The CD Nidaros Domkor [2L 72] is a visit to the Nidaros Cathedral located in Trandeim Norway with its choir performance under the direction of Vivianne Sydnes, Organ performances by Torbjorn Dyrud with the String Quartet from the Trandheim Soloists. The layering of images of rows of choir singers was first rate as one could hear individuals within a row perform from a slightly separate space but clearly close by to the singer located on either side of them. There was ample power from the XA60.5's to recreate this event being held back only by the confines of my rooms own boundaries rather than any constraints put upon it by amplifier power. While it is true that it was possible to get the needles to move the sound was still first rate no matter what was played.
Playing rock and roll with the XA60.5/ XP-10
combo proved equally satisfying as demonstrated by Queens
Greatest Hits [Hollywood Records 2061-62465-20 CD]. Crank up the
volume, let the meters a bit then sit back to enjoy some rock solid bass equally
appropriate for the occasion. While it is tough to pick a favorite from such a
good company of songs I must profess a fondness for "Fat Bottom Girls"
the song and maybe well you know. The important point here though is this was no
wimpy setup where you get enjoyment out of only less complex soundscapes of
Baroque music, small ensembles, vocals etc. but a combination of equipment that
drew the best out of whatever you care to throw at it complex musical passages
or not. It was enjoyable hearing everything from Willie Nelson to Prince played
back through this duo from Pass Labs. My days and nights both started and ended
with songs heard through them thereby enhancing my overall mood throughout the
day to finish with a sense of peace just before sleep. Speaking of Prince
if you are a fan the three disc CD Lotusflow3R (NPG Records) is worth checking
out. On "I like It When You Danced for Me" it was difficult to sit
still. Played back through this electronic combination of designs from
Nelson Pass and Wayne Colburn the music gave me great enjoyment at a gut level
as this dance song seemingly was intended to do. PRAT was obviously incredibly
and made it impossible for me not to enjoy the music heard on the song
"Chocolate Box", starting with the opening drum sequence later to be
joined by the sounds of a synthesizer and of course Prince on vocals. Try as I
might it was just not possible for me to find a style of music that was not
enjoyable to hear through this amplifier/preamplifier combination. If you have
the funds available and music is important in your life you owe it to yourself
to consider either or both of these when you are ready for your next purchase.
This pair of preamplifier/amplifiers sounded close to a tube setup without having to actually use tubes in your system. An extended vast soundscape, holographic imaging, precise placement of musicians in the soundstage, instruments heard with excellent truth of timbre and vocal reproduction to die for, please how much more do you really need? If the answer is well maybe just a little my suggestion is to look upwards in the Pass Labs lineup to some more powerful amplifiers and perhaps even a step or two upwards in their preamplifier position to see what might be possible. For my money though these hit a comfortable price point while giving back an incredible amount of sonic pleasure. To top it all off this was my first review where only the factory supplied power cords were used instead of expensive aftermarket ones. During the review it never even dawned on me to try upgrading the sound by experimenting with ultra-expensive power cords as they sounded so good without. This one is a definite no brainer and both come HIGHLY RECOMMENDED whether purchased separately or better yet together as a system. Do not pass over these two creations of Wayne Colburn and Nelson Pass without so much as an audition for they seemed destined to become classics in their own right to fly off the production lines as fast as they are produced.
Pass Labs XA60.5 Mono Amplifier Specifications