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.

Associated gear
Click to view my Virtual System
When I read that you upgraded to the XA60.5, I knew it was just a matter of time until I would see a review posted by you. Ha… finally I get to read it! As always thank you for the post, I always enjoy reading what you have to say as I do with other members of Audiogon.
Thank you for sharing…
Nice review, Teajay. I went from the XA160 to the XA100.5. I also noticed a remarkable improvement, especially with the timbre and ability to better drive the lower frequencies. The bass became much more accurate - deep and full with great micro detail. I can't say I identified the PRAT per se, but the black background and spacial cues are better and the sense of ease/effortlessness is spot on. I agree with you about Kent and Mark @ Reno HIFI. They are very good about answering questions. If you're interested, you can check out my review. Thanks for sharing your experience with the various amps.
Thanks guys, for your kind words towards my review. Peterayer, I was the first to post on your review on the XA100.5 and thought your review was very well written and informative.

About the prat issue, I find the XA60.5's to be a much more dynamic and faster amp then the XA100's, therefore the amount of prat increased in my system. I totally agree about the bottom end being much more accurate both in speed and harmonic presentation. Since I biamp, I'm mainly talking about the middle or upper bass region and the lower end of the midrange. The good old Threshold SA-1's take care of the deepest bass frequencies.

Congrats Teajay and nice review. I drive my 3.6's with their XA100.5's. They are my favorite amp on them.

Are you at all interested in trying your 60.5's full range on your Maggies? If you ever do, I would be interested in how it sounds to you compared to the bi-amp way.

Besides being happy with the amp, the whole package of Company/Dealer/Product is at the top of all my experiences in this hobby. Rare that you get all three. Nelson and Kent at Pass were excellent as well as Mark at Renohifi. Enjoy.
Onemug, it's been my experience that biamped MG-20's or 20.1's always sound/perform on a higher sonic level mainly because of using an active x-over vs. the passive stock one. Many owners of 3.6's have gone this way also, active x-crossover and a pair of amps.

I believe that the XA-60.5's would have enough current/watts to drive the 20's full range very well indeed, however for the above stated reasons I would not get the best performance because of that rather mediocre passive x-crossover. In my system I still have not found a better amp then the Threshold SA-1's for driving the bass panels of the 20's because of the hugh amuont of current that these amps can deliver.

I agree that it is really is great that starting with Nelson Pass himself and his co-workers for years, Kent and Peter, and now Mark at Reno Hi-Fi are all great guys who know there stuff, are totally honest and are great to do business with.

I wonder how do 60.5s handle microdynamics. I have had X-350.5, and although it was a nice sounding amp, what finally made me sell it, was the fact that it was just dead microdynamics wise.
Teajay, The reason I am curious is I am experimenting, in another system, with an active x/o driving 2 different amps driving my 2 way speakers.

I love the active x/o way, it makes amps happy. No doubt a powerful amp for the bass and something sweet and musical for the mid on up is a great way to go.

For my 2 way, I cross over around 3k so the experiment is with the "blend" of the 2 amps at that x/o and the octave above and below of course. I had good results with ss on the bottom and tubes on the top but I get a better blend with tubes top and bottom. Probably would work with ss top and bottom also but these speakers are great with tubes. It seems logical in that ss and tubes each have their own characteristics and asking them to shake hands from 2k to 6k might not give the best feel where tube to tube or ss to ss might be better. Remember the old saying, "better is enemy of good." It's a great hobby :-)

You may well have the best of the best. I used to listen to the SA-1's driving Apogee Duetta Sigs at my dealers way back when. I loved that sound. The X series didn't seem to have that "magic" but the XA.5's sure do so I'm sure your "blend" is fantastic and going back thru the old passive would not be a fair fight.

BTW, I agree with you on the "mediocre" stock x/o. The stock Maggie still remains a phenominal value but anyone interested in the next level should address the x/o. In my case, a friend (he used to be an authorised Maggie tech) sent me a pair of his customised x/o's. He believes in the active route but said this would get me close if I had enough power. With the XA100.5's, I'm pretty happy with it.
Elberoth2, since I had the 350.5 in my system at one time I can objectively tell you that the XA-60.5's are in a totally different sonic league and that would include microdynamics. The 60.5's have the lowest noise floor I have ever experienced in my system so you hear the smallest details emerging/floating from blackness. These details emerge with speed/quickness, these amps are the most dynamic I have yet had in my system.
Teajay, I just bought a s/h 30.5 to evaluate it in the context of my system. So far, no transistor amp I have tried (and I owned such an exotic amps as Lamm M1.2 Reference among others) could match the microdynamics and sonic purity of a good SET amp. The closest one I found so far is Dartzeel NHB-108. We will see how does the Pass XA.5 compare to the Dart.
Elberoth2, I'm very curious what your opinion will be regarding the performance of the XA30.5 with your Wilson speakers. I have heard the Dartzeel, not in my own system, and thought it was quite good, my hunch is the 30.5 will give you more of the warmth and liquidity of a SET tube amp. Please post your impressions, it will be fun to hear what you think.
Hi guys,

Sorry for my english, but I'm writing from Brussels. So, 2 days ago I listened a XA60.5 with a Wilson Sasha and it was Great. Has anybody made the comparison between the XA60.5 and the XA100.5?

Many thanks for your help
Hi Teajay,

nice review on the Pass amps, good to see that you are enjoying. Did you ever get around to putting other fuses in your MBL 1521 transport? I currently replaced the original ones with the HiFi-Tuning SilverStar ones in my 1621A and very pleased with the over all improvements. When referring to the manual says only one fuse being active but found you have to have two fuses in the unit to actually work, not sure how it actually works but decided to just put two in.
Hi Dev, it's good to hear from you. I have called you at least a couple of times in the the last 3 to 4 months to get your opinion regarding a few things audio, but was not able to get of hold of you. I have not replaced the fuses in my MBL transport. Please share what sonic benefits you heard when you did. Talk to you in the future.
I have XA-30.5 driving JM Labs Electra. It's a very musical sounding amp. Bass handling is just phenomenal. It excels in macro dynamics, but not a slouch in micro dynamics. But I think my previous Pass amp, First Watt F5 was better in micro dynamics and delicacy. F5 has a lot of similar qualities of good SET amps. They both sound warm and liquid. In fact I think XA-30.5 sounds warmer and F5 sounds more neutral. They are both great amps.

Thank you for the excellent review. I use four Quicksilver V4 tube amps to power the mids and highs of my custom 3-way active Magnepan 3.6s. They are wonderful amps--pure beauty in the midrange--but I feel like I'm missing out on the last word in top-end extension and dynamics.

It seems like I could get away with two XA 30.5 amps, seeing as I'd need a channel for each driver. However, I wonder if there would be any sonic detriment to going with a non-monoblock configuration.

-- Nils (neuro on the Planar Asylum)
Hi Teajay,

Great review on the XA60.5, it certainly help me in my decision for getting a pair.
i just received the pair from the local deal and I am enjoying it very much like what you described. Breaking in seems a long time for now.

I have a concern though as my audio room is not huge which is about 4mx3m and I am sitting about 2m from where the XA60.5 are placed.
on one of the mono block, I could hear humming sound when switched on and when the no music is played. The room is quiet but it seems one of the mono block has a louder hum than the other. Thinking this should not be normal.

Have you had experiences with your pair of XA60.5?
I am thinking hard how this can be rectified, does connecting the gounding pin at the back of the humming amp solve this?

Hi Elmerpoh, my assumption regarding the hum is that it's the transformer that you are hearing. I'm a little confused regarding what you refer to as the grounding pin, if your running RCA's single ended IC's the grounding pin on the XLR's has to be in place. So, if you are running single ended cables by all means put the grounding pin in place.

Otherwise I would call Pass and talk to Kent about the noise you are hearing. If I put my ear right above the chassis of my amps I can hear a very slight hum from the transformer, but I mean very/very slight hum. So, check the pin and if its in place and you still get a noticable hum give Pass a call.

I hope you are enjoying the sound of your 60's as much as I do and congrats on your new babies!
to test to see if its ground related, simply run a thin piece of wire from one chassis to the other (ie, use chassis screws, NOT the speaker binding posts). if they're on diff AC circuits, i would expect this to be the problem.

if thats not it, you prob have DC on the line (most homes do). transformers object to this. get some sort of DC blocker and it will fix it.
Hi Teajay/Rhyno,

Thanks for all the advise and suggestions. Well appreciated.
I will give a call to my local dealer who sold the XA60.5 to me and see what they could suggest.

The hum was slightly obvious few feet from the humming mono block especially in a quiet room before i start the music.

Only one of the mono block has this hum,the other one was almost dead quiet. I tried to narrow the cause by using the same wall socket supplying electricity and the same power cord which powers the dead quiet mono block to test on the mono block which hums.
After plugging in and power up, the humming still persist.
Noting that no other cables were connected to the mono blocks when i did this test. With this test, it seems the supply line should be clean and should not be the cause of the hum since both using the same power cord and same wall supply socket, but the hum persist.

Maybe the transformer of the humming mono block is having issues/problems and should be replace in order rectify this hum.
But I just received this brand new mono blocks yesterday and would be a big hassle if i have to wait for it to be repaired.
Unfortunately this pair that i received is the last pair the dealer have.

Hope it get solve soon since I've heard lots of good things regarding Pass Labs services.

just b/c the amps act differently when plugged into same outlet does not mean that DC isn't the problem. could simply be one amp is more susceptible to DC. get a multimeter and check if you're getting DC out of the outlet.

if no DC and you'd like to try self service, try tightening the mounting bolt of the tranny (prob need to remove top cover of amp, though might be able to from the bottom without removing anything). another option, more invasive (and your dealer should handle) is to take the bolt out of the tranny, raise it up a tad and put some damping material b/w the tranny and the bottom of the chassis--this is mechanical decoupling, and usually effective).

very unlikely anything is wrong w/ the amp. buzzing trannys are a very common problem IME.
I have the XA160.5. Like Teajay, I hear a VERY slight hum from each amp if I put my ear directly on the top plate above the transformer. I assume this is normal. It was slightly louder with my old XA160. I'd talk to the dealer and then Kent at Pass Labs.
Wonderfully informative review; wonder if you plan ever to review your pair of SA/1s? I'm thinking about a Soderberg-ed s/500 (his modification to Class A channels, if I ken him right, is the one-chassis equivalent to an SA/1 pair). I'm thinking of this, vs just getting an XA30.5, since both would come to about the same total on the 'Gon. I'm assuming similarity other than raw power between 30.5 and your 60.5, which is why I'm interested in your own assessment of the SA/1s. And just out of curiosity, have you ever switched the SA/1s for the XA30.5s on your MG20s?

Thanks, Doug
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.