Pass Labs XA25 Pure Class A Power Amp and the HPA-1 as the Preamp

According to Pass Labs, the XA25 is not meant as an “entry-level” model but is a rather more affordable, smaller, and lighter Pass Labs Class A power amplifier, a pure Class A amplifier. According to Nelson Pass, “The new XA25 is intended to appeal to those wanting the performance without the frills in a chassis that will fit on a shelf and can be lifted without the assistance of ruffians.” This last statement about its size and weight excited me because for the last ten years my reference amp has been either the Wavac EC300B or the Pass Labs XA30.8. The Wavac weighs 65 pounds, but 85 percent of that weight is in the back and with two NOS Western Electric 300Bs in the front moving it was scary. The Pass Labs weighs 100 pounds. So, I have to admit that when I saw Pass has a new XA amp that weighs in at a mere 55 pounds and is only 17 inches deep, I thought that I had to give it a try.

Background

All of the other Pass Labs XA amplifiers are FET amplifiers with large banks of capacitors, excessive output stages, huge heat sinks and massive power supplies. They use the highest quality components in simple linear topologies, assembled and tested with care and subtlety. Yes, they measure well and are reliable, but Nelson would tell you about how they sound and not about how they measure.

The XA25 came about like so many things in audio; a designer discovers a new device and sets out to see if they can make something great from it. In this case, it was a new power FET technology that is large enough to replace banks of parallel transistors with a single pair of these industrial devices that each have a 700-watt /40-amp rating. They connect directly to the loudspeaker without ballast resistors for the lowest possible distortion and highest damping factor which makes it possible to have a greater Class A operation into low impedance and reactive loads. The XA25 is direct coupled and has no DC servos or frequency compensation.

Setting Up the XA25

When unpacking the XA25, I became aware of just how much smaller this amp is. At only 17 inches wide, 17.4 inches deep and nearly 60 pounds lighter, it is so much easier to negotiate when installing it in my system. It was much more difficult to remove my Pass Labs XA30.8 from my system than it was to install the XA25. Plugging it in and connecting the speaker cables was pretty much all there was to setting it up in my reference system which consists of a pair of Teresonic Ingenium XR speakers, an AMG V12 turntable with an AMG V12 Turbo tonearm and a DS Audio Master1 Optical Cartridge.

I used three different line stages for this review. The first one was my Emia Remote Autoformer, then the Pass Labs HPA-1 (I know it’s a headphone amp, but it’s a heck of a preamp also) and last I used the LTA MZ2-S as a preamp. With all three of these, the amp behaved well and sounded great. I started with the Emia because that’s what I use with the XA30.8 in my reference system, but I ended up with doing my final listening with the HPA-1. The two Pass Labs products had a very nice synergy.

Break-In and Warm-Up

The Pass Labs XA25 like the other Pass Labs’ amps takes a while to break-in. Now don’t get me wrong, the XA25 sounds great right out of the box, but it is slightly veiled. These veils will be lifted with time. Because of the current draw of the XA25, you will probably want to make use of that standby switch. The amp takes nearly an hour to come to life when coming out of standby, but if you turn it completely off with the switch on the back, then it’s a different story. Then it takes at least half a day of playing to come around.

A couple of other observations before I begin to talk about its sound. First as I’ve already said, I love its size and weight. Second, it doesn’t get nearly as hot the XA30.8 and not even close to as hot as any of the monoblocks. One last small but nice plus is that it doesn’t make the electric meter run as fast.

Listening

Because of the difference in its design, the XA25 is currently the only in-production amp in the “XA series” of amps from Pass Labs that’s not a Point 8 design. Still, the XA25 amp doesn’t sound like their .5 amps either; it sounds like itself. The XA25 is not quite as transparent as the 30.8, but it has a wonderful tube-like immediacy in the midrange. What I’m saying is the XA25 is transparent enough that it never reduced the musicality of my system. Its bass is not as controlled as the 30.8, but the bass is harmonically correct, full but not the least bit loose, it possesses the bass I hear from world-class tube amps but from a transistor amp.

As I listened to album after album, I could hear the textures, colors, tones, and harmonics of music in a way that was very moving. The system’s timbre realism with individual instruments and voices was as satisfying with the XA25 as it had been with any amp. All of this added up to enable my system to play music with a wonderful lifelike flow.

What the XA25 does even better than the XA30.8 is the way it involved me in a wonderful musical journey. I could hear the venue as the music is played in a hall, a club, an outdoor arena or a studio. Play one of the Mahler symphonies recorded at a live performance in Davies Hall (a hall Becky and I frequent often), and I could hear the same kind of spatial cues I’m use to when hearing a performance in the same space.

This kind of musical journey doesn’t come easily. I think part of what makes this possible is how quiet this amp is. This may explain why spatial cues are so easily experienced. The system allows me to feel the rhythm of performances. The music was very dynamic, robust, and most importantly it sounded alive. Voices were alive and musical.

With the XA25 in the system, music has an attention-grabbing effect that makes it hard not to just stop and listen. In fact, it’s one of those pieces of audio equipment that makes audio reviewers write trite things like, “It was hard to write while I was listening.” The XA25 plays music with a rich, incandescent, punchy and liquid sound. It also has an organic way with the sound that makes it more emotionally involving.

In my reviews of the  XA30.8, I said, “Both the EC 300B, a SET tube amp, and the First Watt SIT, a single-ended class A transistor amp, build the sound from the midrange out. It’s like the midrange is the main attraction, and the bass and treble are there to finish out the sound. The Pass Labs XA30.8 builds the sound on a foundation of bass, mid-bass, and power.” Well, one of the ways that the XA25 is different from the XA30.8 is that it is more like the SET and SIT amps in that it builds the sound from the midrange out. The midrange is immediate, alive and can pull off that scary real thing with voices.

Like some great vintage amps and the 30.8, the XA25 plays music with big tone. The XA25 doesn’t sound “tubey.” It just has the big, full-colored tone and immediacy of a really good SET amp. The amp was exceptional at letting me hear the layering of the music. It also did a great job of letting me hear the space and air around performers.

The XA25 has good scale and a good soundstage, but it’s not quite in the league with the XA30.8. It is, however, every bit as good as the Wavac EC300B and First Watt SIT-1; so it’s no slouch when it comes to soundstaging. The soundstage is not always big, but the size depends on the recording and the venue. It’s the kind of soundstage that when combined with good imaging and detail lets you hear the recording with a realistic, holistic soundstage.

Are there any negatives with the XA25? Well, only by comparison to the XA30.8 that I think is the best amp I have ever heard that puts out more than one-watt. What I haven’t talked about is how this amp sounds when paired with the Pass Labs HPA-1 Headphone Amplifier used as a preamp. With the HPA-1 you are basically getting a Pass Labs preamp with a world-class headphone amp thrown in for $200 less than the XP-10. This combination seems made for each other, heck maybe they were. The sound was every bit as good with the Xp-10 as it was with my more expensive linestage. I was very impressed, and stay tuned for a review of the HPA-1 as a headphone amp soon.

Conclusion

Let me close with a little on my journey with Pass Labs amps; for years I considered their XA.5 series of amps were the best transistor amps in production. Still, they were just slightly more veiled and a little too polite for my midrange taste compared to my Wavac EC-300B. Then along came the Pass Labs XA30.8, which had none of these weaknesses in my reference system. I found the XA30.8 to be a total revelation. When the XA25 came out, I couldn’t wait to hear it. In years past, some of my all-time favorite amps had been 25-watt Class A amps. The XA25 did not disappoint. The biggest difference between the 30.8 and the 25 is in how they build their sound as I mentioned above. The 30.8 from the bass up and the 25 like a SET tube amp from the midrange out.

In the end, in it’s hard for me to say if I prefer the XA30.8 or the XA25. The XA25 is exactly what Nelson Pass said in the quote I share above, “The new XA25 is intended to appeal to those wanting the performance without the frills in a chassis that will fit on a shelf and can be lifted without the assistance of ruffians.” Not only that, it cost almost two grand less than the XA30.8. The XA25 is simply an amazing amp; match with the Pass Labs HPA-1, and you have an amp and preamp that work together so well. Both are highly recommended!

And, speaking of my journey with Pass Labs amps, Becky and I visited their factory in Auburn, CA just a few weeks ago, and saw their dedication to building quality amps and taking care of their customers first-hand. You can read more about our visit here.

XA25 Specifications
Price: $4,900
Output power: 2 x 25 Watts Class A @ 8 ohms, 2x 50 Watts Class A @ 4 ohms, 2x 100 Watts Class A/AB @ 2 ohms
Distortion: 0.1% @ 25 Watts, 8 ohms, 1 KHz, 0.1% @ 50 Watts, 4 ohms, 1 KHz
Freq. Response: DC to 3dB @ 200 KHz
Gain: 20 dB gain
Noise: Output 100 uV unweighted 20 to 20 KHz
Damping Factor: 200
Slew: 100 V/uS
Input Impedance: 47 Kohm
Peak Current: 10 Amp output (200 Watts into 2 ohms) Independent of loudspeaker load phase.
Protection: Shutdown at 10 amps output
Idle Power draw: 200 watts total
Dimensions: 17″ W x 17.4″ D x 6″ H
Weight: 46 pounds

HPA-1 Headphone Amplifier Specifications
Price: $3,500
Description: Solid-state headphone amplifier/line preamplifier
Analog inputs: 2 unbalanced (RCA).
Analog outputs: 1 pair unbalanced (RCA), 1 locking ¼” headphone jack. Maximum output power: 3500mW into 20 ohms, 200mW into 300 ohms.
Frequency range: 10Hz–100kHz.
Voltage gain: 8dB.
Input impedance: 50k ohms.
Output impedance: <2 ohms, headphones.
Dimensions: 11″ W by 4.5″ H by 12.9″ D. Weight: 14 lbs

Manufacturer: Pass Laboratories Inc
www.passlabs.com