Pass Labs XP-32

Part 2

Evaluation protocol and design features:

The XP-32 arrived in its large box one evening. I unpacked the outer box and each of the three inner boxes. No damage. I removed the XP-22 from the rack and plugged it in at a different location to keep it warm and ready for future comparisons.

I placed the three XP-32 chassis in the rack. The controls are housed in the power supply box, so that went on the bottom shelf next to the power supply of the XP-27 phono stage. The two separate gain channel boxes were placed on the second shelf below the control/gain box of the XP-27. This arrangement keeps the gain and signal boxes furthest away from the noise of the power supply boxes. I used the same Ching Cheng power cord for the XP-32 that I had been using for the XP-22, so there was no break-in of a new stock power cord which would have been a complicating factor. I hooked up all of the connections and powered on the units.

I only listen to vinyl records in my system, but I do have an old Thule CD 150B digital player which I hooked up for break-in purposes. I ran a variety of CDs 24/7 during the entire seventeen day evaluation period. This preamp needs a lot of break-in, despite the suggestion that it simply needs to be plugged in for five days. I heard regular settling changes to the sound for two weeks. Another owner has told me that he heard changes for a couple of months until it reached its final voicing.

For the first few days, I listened only to old and familiar CDs. They had never sounded so good in this room. I had not heard digital in my system for years, and I suspect that some of the improvement in sound was due to the other recent changes I had made to my system and not to the new preamp. This was confirmed later during the evaluations when I switched back to the XP-22 and briefly listened to digital.

The XP-32 continued to break in and after a few days I began to listen to some familiar vinyl records. I did notice a few odd things. The center image that had been shifted slightly to the left with the XP-22 was now slightly to the right, both on digital and on vinyl. Strange. The shift to the left I had attributed to the wear on the SME internal arm cable because fiddling with the DIN socket does shift around the image. (That arm is due to go back to SME for maintenance and cable replacement)

Because this image shift issue could be heard on both digital and vinyl, I figured it was something other than the tonearm cable. I discovered two things. The XP-22 has an issue most probably with the volume control, and second, the resolution of the XP-32 allowed me to hear the very slight image shift to the right which I discovered was due to imprecise speaker positioning.

My house is 225 years old and has soft wide pine floor boards that, it turns out, are not precisely perpendicular to the walls. I lined the speaker footers up with the edge of one floor board but a very precise measurement with a laser and architect’s angle indicated that the left speaker was indeed 9/16[SUP]’” [/SUP]further away from a reference spot on the back wall centered in the room directly behind the listening seat. The zero toe-in was also off by fractions of an inch. After moving the left speaker forward slightly and adjusting toe angle to match the other speaker, the center images were precisely placed in the center and more solid than before. I did not hear this inaccuracy in speaker position with the XP-22 which had been getting worse over time. I had been simply adjusting the balance control to center the image thinking it was the tonearm wiring. With this mystery solved, I began more serious vinyl listening.

In addition to the higher resolution of the XP-32 allowing me to hear some minor issues with speaker positioning, I was also able to hear that the two cartridges and tone arms were not optimally set up. I made some minor adjustments to VTA which in turn led to readjusting the VTF and finally some very minor adjustments to the alignment.

The XP-32 is separated into three boxes. The controls for input switching and volume as well as display are housed in the power supply box. There are three transformers, one for each channel, and a third for the volume control. The power supply does not seem to get warm. The two gain boxes are slightly warm. By contrast, the control boxes of the XP-22 and XP-27 get pretty hot when left on 24/7.

This preamp runs much cooler but uses more energy than does the XP-22. Heat dissipation is excellent. This separation of the noisier parts of the preamp out of and away from the two independent gain channel boxes surely contributes to the extremely low noise that I am hearing which in turn leads to specific sonic improvements.

The XP-22 has 1.0 dB volume steps. The XP-32 has 0.5 dB steps making it easer to find the right volume for the music and to level match between sources. The three chassis do take up some rack space, but it is a price well worth paying in order to realize the sonic benefits, IMO.

Each gain chassis also has a secondary volume knob with for a linked secondary output. If I ever get around to experimenting with powered subwoofers, these may be very useful.

Near the end of the evaluation, I reinstalled the XP-22 and listened to three LPs. I then removed it again and reinstalled the XP-32 which had been plugged in staying warm. I listened to the same three LPs and confirmed my earlier impressions. The differences were indeed significant. I had heard all I needed to hear to decide which preamp to keep.

For the evaluation, I listened to acoustic music, mostly large and small scale classical, some choral music, some solo vocal music, and some jazz. Here is a list of some of the recordings:

1. Beethoven, Violin Concerto, Arthur Grumiaux, Philips
2. Holst, The Planets, Los Angeles Phil., Mehta, Decca
3. Cantata Domino, Proprius
4. Schubert, Death and the Maiden, Quartetto Italiano, Philips
5. Hindemith, Crumb, Solo Cello, Frans Helmerson, Bis
6. Bach, Sonatas and Partitas for Violin, Kuijken, Harmonia Mundi
7. Bach’s Trumpet, Don Smithers, Philips
8. Schubert, Winterreise, Schreier/Richter, Melodia
9. The King Singers, A French Collection, EMI
10. Holst, Savitri, Argo
11. Brown & Almeida, Moonlight Serenade, Jeton
12. Johnny Hartman, Once in Every Life, Beehive
13. Art Pepper+Eleven, Contemporary
 
​Part 3

Listening Impressions:

I often tell people that the one overwhelming impression I get when listening to the Boston Symphony Orchestra is one of “clarity”. Every instrument sounds so clean, so immediate, so present. The connection with the energy of the sounds produced by the musicians in command of their instruments is profound. One just absorbs the sounds and becomes lost in the music.

Here is a long list of specific words I can use to describe the differences between the two preamps, but more importantly, how the XP-32 brings me closer to the real thing: clarity, energy, natural resolution and dynamics, low noise, ambiance, texture, weight, body, harmonic content, tonal density, layering, decays, space, air, nuance. These attributes are all better with the XP-32 in the system, but it is the gestalt, the whole presentation, the sum of the experience which is meaningful, not the individual attributes making up parts. I only mention the parts for specificity in an attempt to explain differences. Were I not writing a report for others to understand what I was experiencing, I would simply describe the XP-32 as having greater “clarity” and presenting the sound more naturally. That is the essence for me.

For others, to whom such a description is too vague, here is more: the tonal balance and voicing of the XP-32 is very similar to that of the XP-22. From there, the differences become more pronounced. With larger scale recordings of orchestra and choir, there is a greater scale and cleanness to the sound. Individual instruments and voices are more distinct. There is less homogenization of the sound. It is more grand. There is more air between, around, and above the players. The sounds decay and reflect off of the stage boundaries more realistically. My listening room disappears more and the speakers disappear more, as the musicians take on more presence. On smaller scale music, if the solo instrument is on a large stage, that space around the instrument is more defined because decays hang in the air longer and move away more audibly toward the boundaries. Both the stage and the cello, or piano, or voice, is more present. The setting is more clearly audible.

String texture is better, and its contrast to the instrument’s hollow wooden body is more clear. With instruments that have complex harmonics like viola de gamba, harpsichord, or French horn, the sheer harmonic content is intense. It is more complex, more colorful, more nuanced. It is also more accurate in terms of distinct timbre. Separate sounds are more easily heard, but they are also richer tonally, instruments and voices are more timbrally distinct and identifiable. Energy is released more easily. The sound is freer. There is less strain, more relaxation. The listener does less work.

Cymbals are less splashy, less white, more colored, more metallic, more defined. Wooden string instruments are more hollow, more resonant, more “woody”. Clarinet and saxophone are more “reedy”. Drums have more impact and are more defined by skin, size, and extension. Dynamics were always excellent with the XP-22, but with the XP-32, they are less stark, and less bold, more nuanced and realistic.

I used to think of the distinction between the source of the sound up on stage and the sound that is created and moves outward into space. The XP-32 so clearly and naturally conveys the two that paradoxically, they sound more as one and not distinct. They are more complete. They are more whole. The instrument or singer has more weight, more body, and is spatially better defined. It is more present. And yet, the sound produced is more nuanced, more atmospheric, more energized. It is a part of the presence, intimately related to the source, and it leaves or explodes away moving to fill the space. This sense of completeness is so well conveyed that I often lost the impression that I was listening to reproduced music. It was pure energy naturally thrust into the room.
 
Part 4

Conclusions:

After more than two weeks of continual playing, I reinstalled the warm XP-22 and played music through it for a couple of hours before comparing its sound to the XP-32. I played three LPs: Beethoven’s Violin Concerto, Cantata Domino, Solo Cello. My first impression was that the XP-22 sounded considerably better than I remember it sounding. Then it occurred to me: the slight improvements to speaker position and cartridge set up. That explains the better sound than what I remember. The XP-22’s resolution level prevented me from hearing those setup issues before.

In direct comparison to the XP-32, Grumiaux’s violin was not as present, not as emotional, not as convincing. The massed strings did not soar as high, or fill the listening room with quite the same energy. The sound was flatter, and a bit greyer. The chorus on Cantata Domino actually sounded excellent and pretty similar to the XP-32. That recording has an incredible ambiance and could probably sound fantastic on most systems. Here it sounded grand and quite beautiful, but not quite as natural or quite as sublime. Decays were shorter. The images were similar, but the hall was less defined. The individual voices were not quite as distinct.

The solo cello as portrayed by the two preamps sounded perhaps the most different. I find solo instruments make it easier to focus on one or two particular attributes of sound because one is not distracted by other instruments. I was taken back to Vienna where my mentor told me to pay attention to the “energy” from that solo cello in the pit. In my room, years later, it was clear that the XP-22 simply could not convey the same energy, weight, nuance, string texture, hollow body, or ambient hall information - all the things that made that cello come alive in my room with the XP-32.

We often hear people say that one does not know what he is missing until he hears it for the first time. Putting the XP-32 back into my system has made this comment more relevant. I knew what I was missing because of my reference to the real thing, real music in a real space. I heard that live cello sound years ago in Vienna and again a few times in the Boston chamber setting. I am now, for the first time, hearing something much, much closer to the real thing, right in my listening room. The increased clarity, and the lower noise and distortion, allows me to increase the volume which goes a very long way towards making it sound more convincing. The system and room changes, including the new arm and cartridge leading up to this evaluation, certainly helped to create a setting in which the XP-32 could more clearly demonstrate its capabilities.

Wayne Colburn should be commended for this fine achievement. The XP-32 is all about clarity and presenting the music in a more natural and convincing way. It brings me much closer to the music embedded in my precious vinyl LPs, and it more often enables me to forget that I am actually listening to an audio system. What more could one want? The XP-32 has made me realize how much a really good preamp can improve the sound of one’s system and bring him closer to the music.
 
Peter, excellent write up. Thank you for sharing. The XP32 is a wonderful preamp from a great American company.
 
A very thorough approach and excellent write up Peter. Congratulations on the XP32 and all of the changes you’ve made in the room and system.
 
Peter, outstanding write-up (as usual!). Your meticulous ways with the setup and evolution of your system over the years are fascinating to me.
 
Thank you everyone for the kind words. I find it is easy to write when I know what to say. This was a pleasure, and I hope that others get a change to hear this excellent preamp.
 
Does anyone know if the XP-32 modules can be stacked on top of each other? I’m sure they are better separated but is there any sound penalty for stacking?
 
I am sure they can be stacked up on each other without any problem. I have them stacked up and the control unit at the bottom.
 
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