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Pass Laboratories X0.2 Preamplifier Review

A continuation of preamplification assimilation for Ed Momkus

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Pass Laboratories X0.2 Preamplifier Review

For a guy who operated without a preamp for two years, I have sure been listening to a multitude of top-of-the-line preamps in the last 18 months. In fact, I recently auditioned an MBL 1510 that I decided to purchase as my principal preamp after an extensive search process. At the time that I was completing the review on the MBL, I had also just been given a Pass Labs XO.2 preamp by a friend of mine who was building a high-end system. He had not yet selected amps, and wanted to hear what the Pass XO.2 sounded like with my Pass Labs X-600.5 monoblocks (which I purchased after I reviewed them in July 2007). As a result, I had a month in which I used his Pass XO.2 pre with my X600.5’s in my main system.

For purposes of this review, I decided to use the same discs and listening protocol that I used for my review of the Pass X600.5’s. The discs were:

James Newton Howard & Friends, Lasting Impression Music LIM-XR-004 (XRCD)

Super Analog Sound of Three Blind Mice, TBM Music, Inc. TBM-XR-9002 (XRCD)

XTC – Apple Venus Vol.1, TVT Records 3250-2

Coldplay – A Rush of Blood to the Head, Capitol, CDP 72435 40504 2 B

King Crimson – In the Wake of Poseidon (30th Anniversary Ed.), Discipline Global Mobile, DGM0502

Chicago Transit Authority-Chicago Transit Authority, Rhino R2 76171.

The listening protocol involved switching between the Pass X0.2, the MBL 1510, and no preamp, using custom-made Electronic Visionary Systems Ultimate Nude Attenuators to attenuate maximum volume. It also involved using the XO.2 with both the Pass X600.5 monoblocks and the Electrocompaniet Nemo monoblocks. Level matching between the Pass XO.2 and the MBL 1511 took some work, since the impedance, gain and volume control action of the two units are very different. However, as it turns out, the differences between the two are pretty obvious. They are obvious even though both are really superb preamps (more on this below).

Appearance, Connections & Specifications

The XO.2 consists of three machined aluminum chassis, the appearance of which matches the appearance of the Pass amplifiers. Overall, it has five sets of input connections – both single-ended and balanced, two sets of outputs – both single-ended and balanced, a tape loop and a unity gain function(for home theater pass-through).

Let’s start with the power supply control chassis.

According to Pass Labs, the analog power supply for the X0.2 consists of a toroidal power transformer whose output is actively regulated before passive filtering and powering of the current sources which bias the gain stages. Each channel has its own regulation. The relays and control systems are regulated independently. All digital circuits receive their power from a separate toroid. It has a 5-way binding post that is used for remote amplifier turn-on.

The two chassis which contain the individual gain channels connect to the power supply control chassis with four (4) DIN cables and, optionally, to each other with one optional cable. The DIN cables plug into their mating jacks and then screw into each chassis to insure a sturdy connection. The connections are simple and intuitive, and the manual lays them out clearly. I did not use the optional optical cable connection, which only applies if and when you operate the XO.2 in mono mode.

There are a total of five inputs (both XLR and RCA), a separate tape loop and two outputs (both XLR and RCA) on each of the XO.2’s two individual gain chassis. One chassis is exclusively dedicated to right channel and the other exclusively to the left channel. You may use both single-ended and balanced outputs at the same time without losing balanced operation.

The X0.2 treats all sources internally as balanced signals and converts between balanced and unbalanced inputs and outputs. Pass Labs indicates that this was a conscious effort to enhance the user’s ability to integrate source components and power amps which would otherwise be generally incompatible. Suffice it to say that you will be hard-pressed to find an input or output configuration that can’t be accommodated.

Features And Operation

The electronic features of the XO.2 address all the things that you would like a high-end preamp to do, and I found them to be quite intuitive and easy to set up.

The front panel of the power supply control chassis has two MODE buttons which, when pressed, cycle the pre-amplifier and its display through 9 different functions. These functions are as follows: Volume, Input, Mute, Tape, Balance, Display, Mono, Unity and Amp (power-amplifier turn on/off control).

Pressing the left “” MODE switch moves the function to the feature that is immediately to the virtual right. Two other buttons, labeled SELECT and designated by up “˄” and down “˅” pointing arrows, alter the displayed active function. The select arrows toggle the following functions either off or on (the up pointing arrow “˄” representing “on” and the down pointing arrow “˅” representing “off”): Mute, Tape, Mono, and Amp.

The unity function is associated with input number 5 and has two positions selected with the up/down arrows. The up arrow toggles to a straight through function with neither attenuation nor gain. This function is useful in that it allows the pre-amplifier to function as a unity buffer for use with components that best function with their own volume controls, such as surround processors. When set at Unity, both left and right level indicators on the X0.2’s main display will have a displayed value of 54. You may also set any of the four inputs to unity (0dB gain) by manually setting the volume of that input at 54. I find the unity function to be invaluable for use with external surround sound processors.

The remote control is a very solid piece of equipment in its own right. It uses the same four-button system as the front panel controls, but in a slightly different physical configuration. The far left button is “mode” “” right. The top button is “select” “˄” up and the bottom is “select” “˅” down. Using the remote is very easy, since the XO.2’s main chassis display shows the active function and can be read at a reasonable distance. The display has two brightness levels, as well as OFF. Activation of any control reverts the display to its dimmer setting. The OFF mode shows the display for about 7 seconds and then turns off. The OFF mode worked very well for me.

Sounds Great– And It’s Not Overly Filling!

This is an extremely good preamp, and might even be considered a bargain, It is very dynamic and detailed, with a very neutral but natural presentation. Let’s review some of the results as I compared it to no preamp (using just my Ultimate Nude Attenuators) and the MBL 5011.

First, the Pass XO.2, like the MBL 5011, added dynamics and slam to the system, when compared to the system just using the EVS Ultimate Nude Attenuators. My Esoteric D-70 was designed to act as an all-in-one dac/pre, so its output is fairly high. The high output has always permitted me to use the EVS UAs and obtain a very high level of performance. Prior to the D-70 I had a Cary 306/200, which had very high output and which did not appear to benefit much at all from use of a preamp. On the other hand, I have had some lower output players which benefitted noticeably from preamplification. The dynamics and slam were evident both at low and high listening levels and significantly enhanced listening enjoyment. Improvements could be heard regardless of which amp I used.

Similarly, microdynamics benefitted significantly from the use of either of the two preamps. XTC’s Apple Venus Vol.1 has lots of stuff going on, and the XO.2 brings it out, especially when used in conjunction with the X600.5’s. The nimbleness of that combo, along with the separation of performers in the soundstage, allows you to hear every small musical hook being played without detracting from the overall presentation.

The two preamps both also improved the midrange, helping to impart a natural feeling to voices, pianos and guitars. This was evident on the Coldplay, King Crimson and XTC discs, all of which can sound very “studio”. All three felt more “real” when using the preamps. However, I would say that the Pass XO.2 does this more by use of a delicate sound which leaves air around the performers, while the MBL accomplished it more by what I would loosely describe as a “live” sounding tonal quality. (More on this below.) Suffice it to say that all recordings sounded neutral without sounding analytical, which I find to be unusual with neutral-sounding preamps.

The Pass XO.2 is very good at creating an airy soundstage with defined spaces for the performers. Let me expand – the Pass XO.2 was quite good at everything, but when used with the Pass X600.5’s, the Pass XO.2 is especially good at depth, width, separation and air. This is illustrated by the Super Analog Sound of Three Blind Mice disc, which has a fairly rich sound, and which can in turn make the performers “run into” each other on the soundstage. The XO.2 creates more space between them and creates a live feeling to the recording.

The XO.2 also feels like it’s a tad more nimble and has better PRAT than the MBL 5011, although that is less clear, and I bet I’d get an argument from other owners of the 5011. For example, the drum whacks on the James Newton Howard disc seemed even quicker and more dynamic than usual. However, the XO.2 is not as rich or weighty in the bass or lower midrange. This was illustrated by the Chicago Transit Authority disc, which is fast-paced but also has substantial mid-bass content.

What’s “The Best”?

I remember the many years in which I engaged in the search for “better” sound. These were the years in which I couldn’t afford “high-end” components or listening environments. One of the most important lessons I learned during this time was that price does not always correlate with performance. I ran into several $500 components that sounded in all respects better than $800 or $1,200 components. I’m not referring to a subjective taste issue here – I’m referring to better bass and treble extension, greater macro and micro dynamics and a more accurate rendering of certain instruments (piano, flute, etc.) I remember being astonished about how much better my smallish KEF 102.3’s sounded than the bigger and more expensive speakers I previously had. (Name withheld to prevent embarrassment.)

When I was able to afford “high mid-fi” (or was it “low high-end”?), it began to dawn on me how much I could improve my sound by, 1) improving my listening environment and started spending some money on acoustic accessories, and 2) experimenting with tweaks. Only after I made significant changes on these two fronts did I start recognizing the shortcomings of the “high mid-fi” components and really start to yearn for the high-end. The main lesson from this period was the importance of the listening room and accessory components and not to even think about truly “high-end” components until those things were addressed.

When I first started to be able to afford consensus “high-end” components, I began seeking out the “best” components. However, I found myself regularly confused. Often times these components didn’t seem to sound better than my old mid-fi components. It’s not that they didn’t go deeper or sound more detailed or image better – they just didn’t necessarily sound much better in an overall sense. They didn’t really give more musical satisfaction. I slowly started to learn about the importance of synergy and component-matching and the role they play in overall musical satisfaction. I was also introduced to the idea that there may be several components which can all be called the “best” in their functional category. I was even introduced to the idea that when choosing among “statement” components, system synergy and (gasp!) personal taste become the most important factors.

Why did I include the prior three paragraphs in this review? Because I believe that the Pass X.O2 is one of those preamps which is the “best” in its category. In fact, it might even be called a “best buy” among statement preamps, since at $10,000 it is actually significantly cheaper than most of its direct competitors, the bulk of which exceed $13,000, and some of which exceed $20,000. That’s one reason my friend chose it (remember – this is not a review sample but a unit loaned to me by a friend).

He purchased a very high-end component for a (comparatively) real-world price. Of course, he has the luxury of starting from scratch. He doesn’t have to think how this preamp will fit into an existing system. He will still be choosing a front-end, speakers and cabling – all of which will be more determinative of his ultimate system sound. He will then do his final tweaking with power cords, IC’s, speaker cables, stands and isolation devices. This is not the only way to build a high-end system, but it is one very logical way.

My friend was particularly interested in how the XO.2 sounds with the Pass X600.5’s because he expected that the two are synergistic. Well, he was certainly right about the synergy.

All the strong points I described about the Pass X600.5s in Dagogo July 2007 Issue were enhanced by their pairing with the XO.2. The resulting dynamics were world-class, both on a micro and macro level. PRAT was also world-class. Together the two could sound as delicate as the most nimble of low power amps, while also sounding incredibly dynamic on room-filling musical crescendos. Anyone who owns the X600.5s should definitely hear them driven by the XO.2. (Conversely, anyone who owns the XO.2 should probably also hear it with a pair of the X.5 series monoblocks.)

Individually, the XO.2 does everything extremely well. Run through the litany of audiophile qualities and you can clearly discern them in the XO.2. However, like most other top amps, it exudes a character that reflects the values of the designer.

In the XO.2’s case, its character leans more to the quick, detailed, dynamic and (when appropriate) delicate. What does this mean in practical terms? First, it means that if you feel that your system is a bit lacking in PRAT or liveliness, the XO.2 will work to offset that. Second, if your soundstage seems too thick or congested, the XO.2 will definitely help sort things out, improve imaging and performer placement. Third, if delicate music rarely sounds delicate in your system, the XO.2 will help restore that.

I think that the only system that would not benefit from the Pass XO.2 would be one that is already very fast and delicate with a well-developed soundstage, but which is lacking bass weight. The XO.2 will articulate every note of the bass in every piece of music. If the weight of a note gets in the way and obscures the note’s beginning and end, or if it risks blending that note into the next, the Pass errs on the side of articulation. You might say it “lightens” a “heavy” note so that articulation is preserved. Certain rock which is dominated by a weighty (sometimes even muddy) mid and upper bass may feel too “light” to some through the Pass XO.2. However, for my taste, this characteristic of the Pass XO.2 makes it spectacular with classical and jazz and very good with blues and most rock.

“So Ed, you’re saying it all comes down to taste?!?!” Well, no – not exactly. You may prefer the Ferrari 369 Spyder to a Corvette Z06, but you’re still dealing with elite sports cars, which already puts you into a small class of people. The taste factor only comes in after you’ve taken things down to a few alternatives. Moreover, and unlike the Ferrari vs. Corvette example, you absolutely must take into account your existing system. Putting a rich tube amp into an overly rich-sounding system will not help improve the definition of bass notes if that’s your problem. Pass Labs helps you address these taste and matching issues by making the X series and XA series amps, but obviously believes that the XO.2 preamp should remain as neutral as possible.


The Pass XO.2 is a statement preamp with neutral tonality, tremendous dynamics, PRAT, articulation and soundstaging. Is the Pass XO.2 “better” than other statement preamps? I can’t say, because I have only heard a handful of “statement” preamps. However, there is no doubt that it will significantly enhance musical enjoyment in almost any type of system. My friend selected a great preamp to build his system around.

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