Finally pulled the trigger......

heiney9

I am a planner and a researcher. Many times in my audio journey I talk for a long time about future plans. I have been talking about the Pass Labs XA25 amplifer pretty much since it was released in 2017. I recently revamped my office rig with a new integrated amp/dac. New Polk R200's and Pangea stands, and a plethora of new cables. All in about $2K or so. Then came the purely impulse purchase of Polk Audio L600's at a ridiculous discount. I had been searching for an 8' pair of bi-wire MIT Shotgun speaker cables, those came about as well.

I bought a new 2023 GTI in May of this year, took care of some house maintenance and took the girlfriend on a trip. So all the boxes are checked and next on the list was to replace my wonderful Pass Labs Aleph 30.

So I negotiated a good deal and have in transit a Pass Labs XA25 only 1 year old. In many ways an extension of the philosophy of simpler is better and in the same vein as the original Aleph 3 and then the Aleph 30 and finally the Aleph J (a Firstwatt product).

It's won many awards and accolades and uses a new type of power MosFet. 2 of these output devices per channel. 25 wpc into 8 ohms, 100 wpc into 2 ohms and stable down to 0.5 ohms. Max output is 200wpc. The biggest thing is the elimination of degenerative source resistance, which is a type of feedback that masks the output signal.

Still heavily biased in class A but has an A/B element when demand calls. It dissipates 240watts at idle and runs as warm at the Aleph.

I will be comparing it to the Aleph 30 and if it sounds better to my ears, I'll be moving the Aleph 30 along.

Such simple design = more musical purity.







H9

treitz3

Nice, Brock! Looking forward to your observations when you get it in. Best wishes for a safe delivery.

Tom

pitdogg2

Well when do the invites go out, some of us are close ya'know, some in your backyard
😉

GlennDog

that nudie shot sure is purdy . . . Congrats!

gudnoyez

Congratulations on your achievements, sounds like 2023 was a good year for you.

pearsall001

Way to go Brock!! Gorgeous piece that undoubtedly sounds sublime. Well worth the wait 👍

F1nut

Congrats Brock.

heiney9

treitz3 wrote: »

Nice, Brock! Looking forward to your observations when you get it in. Best wishes for a safe delivery.

Tom

Thanks.....I was going to wait and post the announcement after it made it safe. I hope I didn't jinx the journey...lol

Really looking forward to hearing it. I've spent a lot of time reading about it and delving into the design aspect of depletion mode Mosfets, which eliminates the "other form of negative feedback". The Aleph 30 has been a workhorse for me and I can't remember the last time I really listened to a different power amp. I've owned it for atleast 15 years and it's the piece that's been in the rig the longest.

TBH, there is nothing the Aleph 30 does that really makes me want to get rid of it. But, the XA25 comes with such glowing reviews it was time to make a change and check it out. I will admit one thing that is a little perplexing is they always seem to come up for sale. No one in their sales ad or sales conversation is going to tell you the real reason they are parting with it.

According to reviews this amp has a way of rendering the music as naked as just about anything out there. That "realism" can be a bit startling and "different" than what one might be used to.

I'm going to keep an open mind and demo all kinds of music over a long period of time. Whenever I make a major change, I take a long time to evaluate, never jumping to a quick conclusion. Because it is going to be a change in the entire presentation of the rig (unless you believe all amps sound the same). It will probably require tube rolling in the Avant as well. I have everything dialed in at the moment....lol

Pass Labs and especially First Watt doesn't have a house sound, all his amps sound a bit different and have different & subtle defining characteristics based on the circuit design he's employing. I will hang onto the the Aleph 30 until I'm sure the XA25 will be permanent. I can't remember the last time I saw an Aleph 30 for sale.

H9

DarqueKnight

You have such great taste in amplification. Congrats and enjoy.

mantis

That is one sweet amp. I love how many Capacitors it has. I gotta assume by design it has limitless dynamic range. Man I'm really digging this amp.

Congrats man.

heiney9

Here's a great, straight to the point listening review.

https://www.stereonet.com/forums/topic/259356-pass-labs-xa25-power-amp/

Stereophile really gave it accolades and I don't think Pass spends much advertising with them....lol

https://www.stereophile.com/content/pass-laboratories-xa25-power-amplifier

These (2) reviews I think give the most insight as to what to expect.

H9

GlennDog

heiney9 wrote: »

I can't remember the last time I saw an Aleph 30 for sale.

H9

you are correct, sir.

I've got an Aleph sale pending to an established Polkie who's going thru a rough patch. I'm in no hurry, but we've pushed to consummate the deal after the first of the year . . .

It is a gem in the rough . . . price to performance . . . off the charts, IMHO

Rock ON!

heiney9

It arrived today safe and sound. I won't have much time tonight to get it up and running. I will leave you with the design and philosophy of this amp.

Excerpt from the Positive Feedback article:

In chatting with Nelson about the circuit of the XA25 amplifier, he told me "The initial concept dates back to 2013 when I began considering the big Ixsys power transistors (photo below) as part of a solution. Prototyping on the XA25 began in early 2016, and the first shipment of the XA25 was in 2017."

When the Pass Labs XA25 Class A 25-watt (into 8 Ohms) stereo amplifier took on the role of being the entry level amplifier in the Pass Labs product line in 2017, it diverged from the aforementioned single-ended Pass Labs Aleph 3 and First Watt SIT-3 amplifiers, instead using a relatively simple push-pull Class A circuit.

Nelson told me this about the circuit:

"There are several unique things about the amplifier that make it a departure from the rest of the Pass Labs amplifiers. It's a fundamentally very simple topology made special by new parts and a unique approach to operating them in Class A without degeneration in the circuit. Years ago, we discovered that degeneration—that is to say placing resistors in series with FET source pins (or emitter pins for bipolar transistors)—has an impact on the sonic performance."

"My late business partner Joe Sammut was adamant about the qualitative difference, and could spot it in blind testing, so I took it seriously. The difficulty comes the fact that there is a reason why people use degeneration (the "other form of feedback") in gain stages—it stabilizes the characteristics of the parts so that you don't have to do precise matching and compensation to keep circuits stable. At the same time, it acts like the feedback it is. Routinely, your "no feedback" solid-state amplifiers depend on degeneration in the gain stages to control the performance, and so it does not achieve all the goals that make SET tube amps attractive."

"For those sonic reasons there have been several efforts at operating bipolar transistors undegenerated, and while the benefits have been noted, they have been accompanied by reliability issues. No need to mention names... ."

"I set removal of degeneration from power amps as a design goal and over the course of several years came up with a couple of reliable techniques that are employed for the first time in the XA25. The result is better dynamics and more "life" to the sound, and with power FETs it turns out that there are a couple more advantages that you don't see with bipolar transistors."

"Your basic FET character is "square-law," where the current through the device is a square function of the voltage across the control pins, the gate and the source. In this regard, the FET is very much like a tube."

"It turns out that push-pull Class A operation of square law devices can result in intrinsic cancellation of distortion to literally mathematical zero. Unfortunately, degeneration in the circuit introduces distortion to that arrangement."

"The other interesting thing about square law devices is that their push-pull Class A envelope is naturally larger for a given bias current, which improves the efficiency of the circuit without recourse to special tricks. Again, degeneration spoils the party."

"And as I said, this subtle effect is not available to bipolar transistors."

When I first placed the Pass Labs into my stereo, it seemed much more powerful than its 12.5 watts into the 16 Ohms of my vintage Altec's would imply (25 watts into 8 Ohms).

I asked Nelson about the impression I had of how powerful the Pass Labs XA25 Class A stereo amplifier seemed compared to its 25 watts into 8 Ohms rating, and it turns out there was a simple answer to my perception:

"First off, it does have more power than its rating. It's not spec'd, but the last time I looked it started to clip at 80 watts into 8 ohms, which would make it about 40 watts into 16 Ohms. As I have pointed out, the other factor is a conventional Class A output stage achieved without degeneration, giving additional dynamic to the characteristic. Pretty much the only restraint on that output stage is the character of those big Mosfets, whose DC dissipation approaches 800 watts with transient current ratings up around 200 amps."

The Pass Labs XA25 Class A stereo amplifier reminds me of the classic American fairytale for children, The Little Engine That Could.

In The Little Engine That Could, there was a long train that had to be pulled over a mountain pass after its big engine broke down. Where the big engine failed, a small engine succeeded in pulling the difficult load of the long train over the mountain pass, all the while saying, "I-think-I-can".

The Pass Labs XA25 Class A stereo amplifier is The Little Engine That Could, and it is way more authoritative and powerful than its nominal 25 watt power rating would suggest.

H9

treitz3

No worries, a full and detailed review will be expected tomorrow morning at 8AM sharp. We have time to wait.

Tom

heiney9

Not happening, never has happened....lol. I'll post some impressions, but a full evaluation will take months. I may need to reinforce the area the amp is going to sit....lol.

H9

treitz3

Hehe....just razzin' ya' is all.

Glad to hear it made it safe.

Tom

audioluvr

heiney9 wrote: »

Not happening, never has happened....lol. I'll post some impressions, but a full evaluation will take months. I may need to reinforce the area the amp is going to sit....lol.

H9

Months???!!! You'd make a good government employee. ☹️

VR3

Pics? Congrats!

heiney9

VR3 wrote: »

Pics? Congrats!

1st post has pics. Mine looks the same....lol.

H9

Clipdat

Does it have a suggested break in time?

heiney9

Clipdat wrote: »

Does it have a suggested break in time?

Yes, about 600 hours. It's about a year and half old, so it should be broken in. It does take about 1 hour of operation to sound 100% as it stabilizes . Same with the Alpeh 30. At first power up, it sounds closed in and slightly veiled until about 60 minutes in and the magic happens.

pitdogg2

It's closing in on winter just leave that sucker on 24/7, I'm sure your van down by the river could use the extra heat

stangman67

Pics!!!!!

VR3

Ummm... We need pics of your unit bro

Preferably the amplifier

Clipdat

Without photos how do we know he actually purchased it?

Also we're going to need you to hold a sign next to it with your username and today's date so we can make sure you actually own it.

pitdogg2

Clipdat wrote: »

Without photos how do we know he actually purchased it?

Also we're going to need you to hold a sign next to it with your username and today's date so we can make sure you actually own it.

Right because daily papers are so yester-year

heiney9

It's like you don't believe me. I had dinner with my Dad and brother tonight after work. I did manage to get the amp out and working tonight. The handles on the back are life savers.

Couple quick snaps......




I'll leave you with this final reviewer's comments - this was the one that really hit me, as this is exactly what I'm looking for and started my obsession with this specific amplifier.

There is an old platitude often used in high-end audio: the perfect amplifier would have the best of both worlds--the beautiful colors, lack of grain, and space/imaging of a great tube amplifier and the dead quiet nature, rock-bottom/tight bass, and transient speed of a great solid-state amplifier. In my 30 years of listening to great amplifiers from Threshold/Pass Labs, I believe that Nelson Pass and his team have come closest to this utopian ideal with the new XA25 amplifier than ever before in their long and illustrious history.

The XA25's performance in my system is still somewhat shocking to me. I thought I would never hear a solid-state amplifier that could create the gorgeous timbres/tonality/color of the finest tube-based amplifiers, yet that's what you get with the XA25. Another quality that distinguishes the XA25 from other solid-state amplifiers is its amazing liquidity. It's not just that this amp has a lot less grain and dryness. Rather, it's the XA25's total absence of grain and dryness. The XA25 also creates a soundstage with three-dimensional space and air between players, with realistic depth/width/height, and "meat on the bones" image palpability. Then add in the fact that the XA25 has virtually has no noise floor, leading to amazing transparency, and is also fast and dynamic, with a simmering sweet top end and full bass extension with control and grip on the bottom frequencies. The Pass Labs XA25 amplifier will not be leaving my system; it is definitely my new reference solid-state amplifier.


H9

heiney9

My first impression is startling transparency & liquidity, blackest background I've ever encountered. Holy cow! This will take some getting used to.

Tom, that's all you're going to get out of me until I spend a lot more time with it.

H9

P.S. the seller rated this a 7 and I almost passed because of it. This thing is like brand spanking new can't even see the 7/32" scratch he states is on the top of the face plate. I'd rate it a 9.

audioluvr

heiney9 wrote: »

I suppose that works.

stangman67

Beautiful!

treitz3

heiney9 wrote: »

My first impression is startling transparency & liquidity, blackest background I've ever encountered. Holy cow! This will take some getting used to.

Tom, that's all you're going to get out of me until I spend a lot more time with it.

If your description of a black background mimics mine? You are in for a treat! It makes a big huge difference and you will get used to it quicker than you think.....and then you won't ever be able to go back to grey. It spoils you and draws you closer into the music. Sounds like it really did make it to you safe and sound. That's great!

BTW, I love the photos. It's reading/seeing something like that first thing in the morning lets one know that they are gonna have a great day. Quite the chuckle out of me on that one. Thanks for that.

Tom