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
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teajay
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.