Pass Labs XA25

Discussion in 'Power Amps' started by skem, Sep 16, 2019.

  1. skem

    skem Friend

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    XA25 is a newish amp from Pass Labs that hasn’t gotten much attention here. It was released early 2017 and the reviews have been good. What caught my eye was the 50uV noise floor, which means it should be good for most headphones too. So, I finally decided to see what was all about.

    When I first heard my new XA25, I had a negative reaction. It didn’t have the bass authority of my Pass Labs XA30.8 or my Ayre MX-Rs. On top of that, the tonality was foreign. These two effects combined to nearly kill off my interest. But then…. there were these vocals. These vocals that sounded pure, delightful… and real.

    Over the next week, it became evident that my initial reaction was just me needing to adjust to a new way of hearing my music. Every track I own sounded different on this amp, and almost always in a good way. The main effect is that the timbre is much more accurate. Compared to all other amps, instruments have a natural sound. This is something I work hard to achieve when choosing DACs, but in this case it was the amplifier making the difference—and a big one at that. I could also more clearly hear the room in which things were recorded. Outdoor music sounded like it was live. Jazz felt like it was in a club. It was remarkable to experience these new sounds — and hard to believe such realism was lurking in these digital recordings all along.

    One very quickly understands that many of these benefits come from speed. The amp is really fast. Everything is rendered with precision in clarity, tone, and placement. A whole category of songs, like the Carmina Burana and Queen’s Bohemian Rhapsody — pieces of dense, complex, overloaded music that I always struggled to enjoy because at points they begin to sound more like noise than music — became pleasant to listen to. In Bohemian rhapsody, for example, there are sections with a chorus singing. With this amp, I swear you can resolve distinct voices rather than just a harmonic mélange.

    Did I say the timbre was good. The timbre is really fucking good!

    The amp does not come without limits, but these were ones I was willing to accept. First, this amp does not have bass slam when used for speakers or big drivers. Second, the consequence of all this speed and accuracy is that it dries out the music relative to other amps. Actually, I have come to appreciate this dryness. However, if you enjoy hearing harmonic colorations that give warmth or crispness, which I confess can be especially pleasant with older recordings (see note on M22 below), then it can suddenly seem like something has gone missing. I'm going to go out on a limb and guess that if your speakers cannot resolve the stage, or your source cannot provide the honest detail that makes the music seem so real with XA25—then XA25's lack of pleasant warmth and harmonious distortions may make for less enjoyable experience than other amps.

    So, let’s talk about chain and details.

    My chain is Allo DigiOne → Metrum Adagio DAC/Pre → XA25 → Transducers. I’ll note that I also tried the Antelope Zodiac Gold DAC with Voltikus PSU—but the Metrum was a clear winner in detail, timbral accuracy, stage depth, blackground, and imaging. This amp really shows the differences clearly.

    For transducers, I listened primarily with B&W 801 Series III, but I also listened to Dale Harder TLS-1 Walsh F remakes, HEK, HD800 (sdr mod), HE6 (felt mod), and Verum-1.

    Direct comparison amps: Pass Labs XA30.8, Pioneer M22, First Watt F5 Turbo, and Ayre MX-R. From memory: Benchmark AHB2 Amp, NAD M22 Class D.

    As expected, there are noticeable transducer-amp interactions

    XA25 + B&W 801: Performance of the amp is excellent except far too soft in the bass. The even tonal response also makes the bright 801s seem… bright. I recall the the Benchmark AHB2 had control but really sucked on imaging and timbre was not accurate; the music was dead. Ayre MX-R has authoritative control, but is less detailed and is less realistic than either the 30.8 or XA25.

    XA25 + Walsh F: These speakers are just far too heavy for a measly 25 watt (or technically 80 watt @ 1% THD) rating of the XA25. The Ayre MX-Rs do a much better job controlling these cones, but you definitely hear a loss of tonal purity with the MX-R. Interestingly, the XA25 does better with these enormously heavy drivers than the XA30.8 did. The XA25 was only a small step below the Ayre MX-Rs in performance.

    XA25 + HEK: [This section has been edited to include F5 Turbo comparisons.] HEK is my primary headphone and I listen to it mainly with this Pioneer M22. The XA25 has a low-enough noise floor but... something isn’t happy here. Tonality of all three amps are different. Note, however, that neither the F5 nor the M22 contain "stock" parts, so these results may not be generalizable. For my amps, I found that the XA25 was too bright and presence was a touch overdone (this is generally true). F5 was mid-forward, with toned-down presence. M22 (with Audyn Reference caps) was too bright in the high treble, but otherwise presence-mid range were more balanced.
    Some other parameters:
    Bass depth: XA25>>F5>M22.
    Bass volume: F5>M22>XA25.
    Grain (less better): XA25<<F5<M22
    Voice quality & timbre: XA25>>M22>F5
    Imaging: XA25>>F5>M22​
    Despite the overall win on technicals, the drawback of XA25 is that it is too dry cold with HEK, so overall I think less good than M22 and F5. It has less drive and makes some music slightly less fun. F5 really rocks with its U-shaped response. M22 is more comfortable with relaxed music where its treble peakiness is a feature. I think these are valid reasons to choose something over the XA25, depending on needs.

    XA25 + HD800: Wow! This is the first time I have actually liked the HD800. Noise floor is also low enough for these cans. I didn’t spend a lot of time doing careful listening, so these impressions are not authoritative, but from what I did hear: detail out the ass and none of the sibilance or ugliness that I heard from these cans when paired with Cayin IH6, Dragon Inspire IHA-1, and Eddie Current Zana Deux. I am one of the few that think HD800 are actually weak in mid-range detail (others will disagree) but with this amp behind them, I had no complaints. From my quick listen, seemed like a perfect pairing. (Note: I agree with @bozebuttons comment here)

    XA25 + HE6: Actually, this was a disappointment. I used to love HE6 off the F5 turbo. The HE6 from XA25 seemed oddly dark and muddy. I didn’t listen long. By this time I had listened to so much great music made possible by this amp paired with other transducers that there was nothing here to listen to. Maybe the HE6 as a transducer is just not be up to the task. Sad this didn’t work out.

    XA25 + Verum: Another disappointment. Verum does not scale to the detail level XA25 provided to all other systems. Also, Verum is too sensitive: the noise is clearly audible. It’s a bad match. I’m a fan of Verum and like it out of my portable—but XA25 is not the way to go.

    Overall, I heard so much fantastic music from XA25 that it became my new main-system amplifier. I think it ranks as the best overall amp I’ve heard—which obviously depends on your transducers (seems not to like planar magnetics?)—but it is just all around remarkable. That said, it clearly has a weakness with driving heavy drivers with low bass. To solve this, I will be bi-amping with some clean class D to see what happens.

    Some references to comments about XA25 on SBAF

    @purr1n doesn't like XA25 with JBL 4698b.

    @bozebuttons likes XA25 for headphones, especially HD800.

    @JoshMorr is using XA25 with his Klipsch Forte, and learned something about tubes in the process.
     
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    Last edited: Jan 8, 2020
  2. purr1n

    purr1n Finding his inner redneck

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    I actually thought the XA25 with the RAAL SR1a was pretty good. The criticisms I offered were in the context of me being nitpicky. Maybe the second best after the Dartzeel. And after that mono Aegirs, and then the Vidar and Crest CA2 in a toss-up (just different). Definitely synergy there in terms of tone and very good bass heft. The last three amps requiring EQ, the first two less so.

    However, I thought the XA25 sounded like butt with the JBL 4698b, hence my comment on the XA25 being a better amp after the first watt (the JBLs are super-efficient, per spec 103db, but in reality probably more like 98db). Muddy mushy bass with no dynamics and with veil going up to the mids. Like a smear of poo. Middle-mids on to upper mids were good and crisp. Top-end was gentle. I actually felt the lows were disjointed with the mids/highs a bit. Microdynamics were also lackluster with the JBLs, a bit on the sleepy side. Yes, it's better than the Benchmark AHB2 which really didn't do anything wrong, a bit on the lean side is OK, other than sounding soulless.
     
    Last edited: Sep 16, 2019
  3. Thenewerguy009

    Thenewerguy009 Friend

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    Was your primary preamp for the Pass the Nano Patch?
     
  4. purr1n

    purr1n Finding his inner redneck

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    Yup. Ran passive for every combination.
     
  5. skem

    skem Friend

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    I’d be curious to hear a Dartzeel vs. XA25 comparison.
     
  6. JoshMorr

    JoshMorr Friend

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    $$$ vs. $$ - shout out to Dartz magnetic ghost busting capabilities.

    As far as XA25 - I haven't really written much about it here as I've pretty much exclusively used it as a speaker amp, a bit above the price range of most items discussed here. Plus I have a complex about bragging about working hard and buying nice things.

    Anyway here is probably where I wrote about it most - in comparison to the single Aegir loaner. https://www.superbestaudiofriends.o...ower-amp-impressions.6953/page-15#post-262441

    I've owned XA25 for close to a year (Black Friday purchase) and it continues to be best solid state amp I've used. Maybe has something to do with being a Pass fan before owning this amp (via Firstwatt, DIY projects, articles, etc). With the Klipsch Forte, I can find the speakers horns a bit bright. Like you would do with a HD800, I feel the subtle turn down at both ends is favorable. I agree with Skem on most points - highlight reel of this amp is mids, speed, spooky real fine detail, reproduction of live recordings, timbre. Most of these attributes I grew to love with tube amps, and was surprised to find a SS amp that matched and even surpassed. I use a transformer based passive pre amp - I have plenty of gain with Soekris 1541 DAC or phono preamp (which has 55 db of gain).

    XA25 is rated at 25W class A (.1% THD), but can deliver 80W @ 8 ohms before it hits 1% THD (via stereophile article https://www.stereophile.com/content/pass-laboratories-xa25-power-amplifier). I think this still may be a stretch for the B&W speakers you are using Skem - they like serious power. 30.8 will be more authoritative on the low end, bit sharper on the top end, and deliver 20W or so more juice. I bet a bigger amp from the .8 series would flesh out the speaker even more.

    Glad to see others are enjoying this amp, and what it pairs well with (or not) for headphones and speakers.
     
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    Last edited: Sep 17, 2019
  7. zonto

    zonto Friend

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    Maybe others knew about this, but I just found out that Pass released an integrated amp called the INT-25 ($7,250): https://www.passlabs.com/amplifier/int-25. Looks like it's an XA25 amplifier with a single-ended version of the INT-60's preamp included. Stereophile (Herb Reichert, so treat with grain of salt) reviewed in the February issue, and the review includes quite a bit about the XA25 topology as well.

    6/9/20 edit: added link to Stereophile review above.
     
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    Last edited: Jun 9, 2020

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