Review: Pass Labs XA60.5 monobloks Amplifier

Category: Amplifiers

Over the last twenty years I have had power amps designed and built by the audio legend Nelson Pass in my system. I still use Threshold SA-1's to power my MG-20's bass panels. I had Aleph 1's for over nine years, until I replaced it with an Edge NL-10, the only generation of Nelson Pass amps I did not like was the original X series, hence the NL-10. When Mr. Pass came out with the XA and X.5 series he won my sonic heart back. This will be my third review here on the GON of a Pass Labs amp. The progression of reviews started with the X-350.5 stereo amp, then the XA-100 monoblocks and now the XA-60.5 monoblocks. I believe that fans of Pass Labs amps come to a point were it gets harder to believe that Nelson can build that much better sounding of an amp then the last generation, but he does!

I never get into technological details because you can go to the website for that information yourself. The XA-60.5's are extremely well built, I find them to be "eye candy". Pass has made many important changes to this generation of XA.5 amps regarding parts, power conditioning/isolation, and the type of transistors used in the front end of these amps. The older AX series was class A but did not double down as speaker impedence dropped down. So, the XA amps were not a great match for very current hungry or difficult impedence load speakers. In hind sight it's amazing the XA-100's drove and sounded as wonderful with my MG-20's. My hunch is, since I biamp, that I had just enough watts/current to drive the midrange/tweeter without missing out to much on Macrodynamics on most music. The XA.5 series do double down into lower impedence loads and have much greater current ability. Since my MG-20's are a four ohms load, there is much better synergy between this amp and the 20's.

The most important part of any audio review, how did the freaking piece sound! Well, to express it in a calm way, the XA60.5's are the best amps I have ever had the pleasure to listen to in my system. Now the details why I feel this way:

1) The most natural/realistic timbres I have ever heard in my system. My all time favorite sax player is the late great Johnny Griffin the "little giant", who I had the pleasure of hearing live on more then twenty occasions, with the XA60.5's it's the closet I have heard to what he actually sounded like in my system.

2) I can't say that the soundstage got bigger with the XA60.5's compared with the XA100's, but the air around individual players and the layering became much more like the real thing.

3) These monoblocks have the lowest noise floor of any amp I have ever heard in my system. The music just floats out of a totally black background, therefore microdetails and decay trails are so much easier to hear.

4) The PRAT and dynamics of my whole system was taken to a much higher level, this is probably based on the XA60.5's having great current ability.

5) Image density and how 3-D each player sounds, yet not etched out, but intergrated with the stream of the music.

6) The last quality I want to share is also the most subjective and the most difficult to put into words. The XA60.5's are the most "musical" amps I have ever heard in the context of my system. They have an "easyness/liquidity/effortless" quality that just allows you to relax into the music and enjoy it. The XA-100's have this quality, but no were close to the level that the XA60.5's produce. Remember, this is not at the cost of microdynamics/prat or just making things sound euphonic/pretty, but the very subjective factor of "naturalness" whatever that is. Or to quote Robert Harley of the absolute sound, this from his review of the XA100.5's, " something extraordinarily beautiful about the sound. It was like slipping into a hot tub on a cold night; the music seemed warm, inviting, and enveloping. A stunning rendering of instrumental timbre,had an unparalleled sense of ease, and coupled a sense of delicacy with unfettered dynamics." I experienced the same qualities with the XA60.5's in my system.

I have said in every review I have ever written that there is no "BEST" when it comes to reference level gear because of personnal taste and system synergy. My perspective has not changed, I just would add the XA60.5's to the list of some of the most beautiful sounding amps produced today.

Finally, I would like to thank Kent of Pass Labs for always being patient with all my questions and Mark of Reno Hi-Fi for making everything so easy to get these amps in my system. Thanks, Guys.

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Hi Doug, thanks for your kind words towards my review. To address your questions:

1) Because the SA-1's have been around for almost twenty years I never felt the desire to write a review on them. They still very favorable compare to the best SS amps built today, including Pass's own designs. Smooth, rich, natural timbres,great sound staging, with great bass contol and punch. I believe they might not be quite as detailed/transparent or quick/fast as the XA-.5 series. However, if you get the full monty upgrade from Soderberg it might be very interesting which amps you might like better. I not replaced anything in my pair of SA-1's, including caps, however I'm waiting for new caps from John to install in my pair to see what these better caps will give me sonicly.

2) No, I have not switched out the XA-60.5's with the SA-1's to power my system, but will try that experiement when the new caps are installed. The SA-1's deliver terrific current so they are great bass amps on my MG-20's bass panels, so I have always used them in this way after I got the Aleph 1's for the midrange and high end which sounded better then the other way around.
Thanks for your [again informative] reply. I'll try to remember to keep tabs on your system over time to see what you find out. Haven't seen an s/500 of the later serial #s that Jon requires to enable him to do that F Monty mod [hey, a great name - you'll haveta suggest it to him] for quite some time, so maybe I'll pull the trigger on an XA30.5, since they keep showing up used.

Thanks again,

Tejay - if you want to be 'modern' check out the Spectron amps if you haven't. I believe that these, or even the nuForce amps, are perfect for driving the bass panels of actively bi-amped Maggies.

For the Spectron amp (~4k):

800 Watts at 4 Ohms
1400 Watts at 2 Ohms
Damping Factor: 500

Note that the Damping factor of a 'cheap' (1,000-ish) IcePower amp like Seymour is 2000.

NuForce says because of the way their amps work, the damping factor is basically infinite. They have, for the 8.5 (~2.3k?):

200 watts continuous at 4 and 2 ohms for cheaper 8.5 (single chassis), but max power (short time duration) is 550 and 1100, not bad!

Here is a write-up on IcePower versions (NuForce and Spectron do their own thing, and they are much better in most regards, but particularly higher frequencies which we don't care about)

However - I've looked at the frequency/noise graphs of even the IcePower amps and they are flat to around 500 Hz, so I know for the 3.7s the crossover freq is 225, so that is fine.

How does a damping factor of 2000 compare to the old Threshold?

I think these new switching amps might really be the ticket to bass panels in Maggies...

If I had to choose one the Spectron is the really special piece here, I'd love to hear your comments if you could get one into your system and compare to the Threshold...
Hi Lightminer,

You will get no arguement from me that many of the D or switching amps would do just fine driving subwoofers or the bass panels of MG-20's. However, I have on many occasions listened to amps from Nuforce, Spectron, and other highly regarded companies that offer D amps and find all of them rather unpleasant overall regarding their sonics when used to power the speaker full range.

So, I'll stick with my Threshold SA-1's that do just fine powering the bass panels and therefore not join the "modern" era for the time being.
Yeah - no - wait - I agree with you, and mentioned seeing the graph where you can see over 500 hz they start to fall apart, but you are already bi-amping? So the issue is to get that power *only* to the bass panel. At 225 Hz and lower they are flawless amps!

That is why, for example, switching amps have been used on subwoofers for 10 years while they have only been considered full range for 5 years or so.

I'll bet it makes a big difference over any Class A amp (I am a huge ClassA fan) - we're only talking about 225 Hz and lower (for 3.6s, not sure for 20.1s) - and the idea is massive watts.

I would absolutely love to hear your thoughts about the Spectron in there doing only the bass panel compared to what you have now if you could run that test.