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September / October 2005
Superior Audio Equipment Review

Pass Laboratories Aleph X2.5 Preamplifier
Rich, Warm, and Pleasant.
Review By John Gatski


Pass Laboratories Aleph X2.5 Preamplifier Unit  Pass Laboratories, under the leadership of noted designer Nelson Pass, has made some of the best sounding amplifiers and preamplifiers on the audiophile market. Over the years, Pass has come up with new designs and subtle improvements to existing products. The X2.5, designed by Pass engineer Wayne Colburn, represents great audiophile value in the Pass line with a lower price than the highly regarded X.02 and the X1 preamps, but performance that belies its lower price point.


Priced at $3,900, the Pass X2.5 is a full- featured stereo preamplifier including stepped electronic volume control, the Pass Super Symmetry MOSFET design, four sets of inputs, with balanced XLRs, a tape loop, and remote control. The Super Symmetry design utilizes a very simple signal path, including JFET input and MOSFET output very carefully matched, to produce a semi-Class A topology. Having auditioned the initial X series, I found that they provided much more bass and treble accuracy than the old Aleph series. Though the initial X series sounded a bit "colder" than the Aleph Class A products, the Pass engineers have warmed up the latest generation without spoiling the accuracy.

Pass Laboratories Aleph X2.5 PreamplifierThe X2.5 is an attractive, silver finished preamp that is quite appealing in its simplicity. The front panel contains a basic blue LED display, Mode and the Select buttons for each mode, and a volume control. The control simplicity, however, is not as simple as it appears because of the numerous adjustable functions enabled by the Select and Mode buttons. The two Mode buttons toggle through a number of user function options while the Select buttons adjust those functions. The adjustable modes include: Volume, Input, Mute, Tape, Balance Display, Mono Unit, Amp Control, and Gain.

The Volume setting enables either the remote volume or the preamp volume knob. The 32-step volume is indicated via the display. The Input mode enables selection of any of the four inputs and the tape loop. (Input four is the Unity input). The Balance function allows the balance to be adjusted by the Select buttons. The Display function allows three modes of brightness: bright dim and off. The functions Mono, Tape and Mute are pretty easily understood.

The Unity function allows the X2.5 to be used with products that have their own volume control, and the preamp merely serves as a transparent connection to the amplifier. There are two Gain function settings, +4dB/+14dB, to allow the preamp to match a variety of sources, amps and speakers. Plenty of gain in this preamp. Most of the time, I used it at +4dB.

The rear panel is chock full of inputs and output jacks including two inputs with balanced and unbalanced connections, two for unbalanced RCA only (including the Unity input), balanced and unbalanced tape loop jacks, and unbalanced and balanced output jacks. Because the unbalanced and balanced jacks are in parallel, all the balanced XLR jacks come with a termination jumper between Pin 1 and Pin 3 to allow for optimum unbalanced operation. The jumper is removed when operating in balanced mode.

The Pass Laboratories X2.5 includes a set of 12V binding posts to enable remote turn-on of an amplifier via the preamp. Wired to amps, such as the Pass X series, this feature allows turn-on of both amp and preamp. Pass recommends, however, that their preamps be left on all the time. Hence, no power switch. Included is a remote control that duplicates the front panelís volume controls and Mode and Select buttons. The remote is made from billet aluminum and exudes a sense of class that you donít get from many remote-equipped Far East audio products these days.

As you would expect from Pass, the factory specs are excellent!  A wide frequency response (2Hz to 100kHz at the minus -2dB points) insures high-resolution sources such as SACD, DVD-Audio or DualDisc without compromise. Distortion is low, listed at 0.03%. Power consumption is 35 watts. Dimensions are listed at 17-inches wide, 11.5 inches deep, and 3.5-inches tall.


The Setup
Having auditioned a number of Pass products over the last ten years, including the original Aleph amps and preamps, and the initial X150 and X250 amplifiers, I knew that the X2.5 was going to be an excellent sounding preamp. My evaluation stereo system included a number of components: Pass X250 amplifier, Bryston 14B SST amplifier, Esoteric DV-50 Universal DVD Audio/SACD Player, VSE-modified Sony SCD-XA777ES SACD player, TASCAM professional DV-RA1000 DSD/high-resolution PCM stereo recorder/player, Legacy/Coda High Current preamp, Bel Canto  Pre 6 preamp,  and a Audio by Van Alstine tube/FET hybrid preamp. I used a pair of Legacy Focus 20/20 ribbon speakers for most of the listening sessions, though I did throw in a pair of Lipinski  closefield and the Westlake LC2.65Vs for a couple of listening sessions.

Interconnects included Alpha-Core, Kimber Cable, and Westlake Low PE cables. Power cords were provided by Kimber Cable, and all power was centralized through an Alpha Core balanced power unit.

Though "burned" in at the factory, I usually warm up preamps for about a week before I do any hard-core, analytical listening. Unlike the old, pure 'Class A' Alephs, the X2.5 does not get that warm. Almost all of my listening was done via high-resolution music including SACD or DVD-Audio. I also recorded my own acoustic guitar music in 24-bit/192kHz mode through the TASCAM and used the unit to play back the music through the Pass.

I tried the both the 4dB and +14dB gain settings with the later being way too hot with most of my gear (except for the low-level output of the VSE-modified Sony SACD playerís unbalanced jacks). A couple of notches on the volume and the decibels were way too loud. I could also hear some audible switching noise when increasing the volume in both +4dB and +14dB modes. Overall, the +4dB gave me more flexibility in adding gain slowly.

Even with the ten modes and their corresponding settings, the controls were easy to figure out. In fact, I did not refer to the manual until I started writing the review. My initial listening impressions revealed that the Pass X2.5 had a very extended top-end and accurate, tight bass. The old Aleph preamp had a warm and friendly sound with plenty of image presence, but it was not as accurate as the new X series. Compared to the bipolar output Legacy/Coda or the Bel Canto Pre6, the X2.5 is a bit smoother sounding, but not at the expense of accuracy. As Goldilocks might say, the sound was "just right."

Pass Laboratories Aleph X2.5 Preamplifier

When listening to the minimalist jazz SACD, Our Gang by the Anthony Wilson Trio [Groovenote], the warm Gibson jazz guitar tones and the thick, smoky quality of the Hammond B3 organ came through in the organic quality expected from tube amplification. The drum cymbals were tight with excellent stereo dimension ý and just the right amount of sheen. Bass drum reproduction was deep, fast and powerful.

I listened to the DMP label release of the Quality of Silence by Steve Davis. The piano and percussion is a good test of audio components. This recording has subtle nuance in its sonic layers especially with piano. Good SACD players, amps and preamps, can relay that piano's upper-register tinkle without sounding brittle, or on the other side of the spectrum, reduced to the point of not hearing the tinkleís subtle dimension. The Pass X2.5 did the recording proud, relaying the Steinway piano as about as well as I have ever heard from the recording.

On my own basement DVD-Audio recordings of my vintage Martin guitar, recorded on a TASCAM professional high resolution PCM recorder and authored on Minnetonkaís Apple version of the Bronze DVD-Audio software, the X2.5 did a great job of reproducing warmth of the solid rosewood body, spruce top and phosphor bronze strings of the guitar.

The warm yet detailed tones of Heifitz's "Beethoven Violin Concerto in D" captured on SACD in all of its analog splendor for RCAís Living Stereo series sounded incredible with the Pass. I wanted to listen to it again and again. The same was true with the Mercury Living Presence SACD Bach Solo Cello Suites by Janos Starker. As with my reference set up, the cello tones on this original analog recording and were rich and pleasant without any edge.

I tried the Pass with the Bryston 14B SST stereo amp (an excellent amp that audiophiles should take note of) and a Pass X-250. With both amps driving the Legacys, the sound was exemplary ý with the X-250 having an ever-so-slight bit of warmness and a bit wider stereo soundstage. The Bryston, however, was tighter in the bass.

Okay, so you picked up on the fact that I really liked the Pass X2.5 preamplifier. There were a few quibbles. I could hear switching noise as I adjusted the volume in either gain mode, and I would like an on/off switch. The unit is always on unless I shut off the master balanced power unit. A few other positive comments would include that Pass products continue to be built like tanks. This preamp is not that big, but its sturdy chassis and cabinet is rugged enough for professional use. Speaking of pro use, Pass should be commended for putting balanced connections on the X2.5. I am sure the preamp will make its way into mastering studios.


The Verdict
As I expected from Pass Labs, the X2.5 preamp is a first-rate audiophile product.  If you want to get that Pass pedigree and save a few dollars over its bigger brothers, buy the X2.5. If you want a Pass amp to go with it, I can heartily recommend the Pass X150.5 or X250.5 as well. But I figure just about any quality amp will work well with the X2.5.


Type: Stereo preamplifier with adjustable gain
Gain: selectable 4dB or 14dB
Frequency Response: 2Hz to 100kHz (-2dB)
Distortion: 0.003% at 2V
Output Impedance: 360 balanced (XLR), 150 single-ended (RCA)
Input Impedance: 66K balanced (XLR), 33K single-ended (RCA)
Remote Control: yes for X2.5, no for X2.2
Output Noise Floor: -125dBV ref to 10V output
Inputs: two stereo pair RCA and one stereo pair XLR
Mono Operation Setting: Yes for X2.5, no for X2.2
Unity Gain Setting: Yes
Number Of Chassis: 2 (power supply and analog stage)
Dimensions: 17 x 3.5  x 11.5 (WxHxD in inches for each of the two units)
Weight: 46lbs.
Price: $3900


Company Information
Pass Laboratories
13395 New Airport Road
Suite G
Auburn, CA 95602

Voice: (530) 878-5350
Fax: (530) 367-2193
E-mail: info@passlabs.com
Website: www.PassLabs.com














































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