Stereophile, Pass Integrated and personal taste

Stereophile has reviewed another Pass product, the Int-25, and again I found the distortion signatures super interesting:

I wonder if it is possible that such a signature could be something some fall in love with and some are pushed away from?


A moderator wrote this message in one of the threads on the Audioaficionado Forum. The tread was closed due to the comments from a poster. 

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"NO REAL INTEREST IN" - I think that explains the lack of responses...
I find eric's posts to be very interesting. -Certainly not 'Flame Trolling'.

Looking at the review:
       'note that the second harmonic lies at a very low –86dB (0.005%).             Higher-order harmonics are virtually absent'
This would fall into the beliefs of Ralph Karsten-Atmasphere, a person who's opinion I trust implicitly.

Going further:
      'though the low-level power supply–related spuriae can be seen in             this graph. Both high-order intermodulation products and the                     second- order difference product with the INT-25 driving an equal             mix of 19kHz and 20kHz tones at a peak level of 10W into 8 ohms             were very low in level'  
This goes a bit above my knowledge, and I would appreciate if you could break it down to my level. -If possible.
I don’t think this is a bad measuring amp, at all.

I am fascinated by how to make an amp that sounds great and is not neutral.

If an amp is not neutral, it’s going to appeal to some and not to others.

My favorite amps of all times measure super badly (CJ Premiere 8s) but if I had a pair and a room for them I’d die happy, but I can't imagine a Millennial listening to them and loving them.

I find eric's posts to be very interesting. -Certainly not 'Flame Trolling'.
Me too. Not that i always agree, but at least he posts informed comment and asks interesting, if to some provocative, questions.  Maybe if i spent more time i'd feel differently, but that's my two pence.

heck, its fact, not speculation that one part of tubes' allure is the euphoric distortion. Oh yea, same can be said about Pianos (sounding boards), Violins (cases), .....
I will admit to choosing to leave some distortions and vigorously banish others. And often, the trade off is a natural one is circuit design, so choices simply one's task.
Do we want accurate or "nice sounding".  They may be very different. I can argue either side.  Side out :-)
Nelson Pass is a Great designer . he not only builds a very good 
sounding product but takes a lot of his free time  and gives free 
schematics and helps many  other DIY on several of his amplifiers . He even sent me a pair of winged  heat sinks for free from one of his class A 25wpc amplifiers
minimal parts and very respectable specifications and very musically satisfying. Thank you Nelson Pass.
wlutke374 posts01-25-2020 1:50amGive it a rest Eric, for God’s sake
+1 and some
Ditto, Eric starts new Pass threads when he has the chance to be negative about them. This is around the 4th or 5th thread started by him that focuses on the negatives in it’s context that he pulls out of his head usually.
Someone must have drop’ed a Pass Labs amp on his foot/head at one time?
I don’t particularly like them either being Mosfet, but I don’t have this kind of unhealthy obsession with them to go out of my way to start these kinds of new threads about them.

Cheers George
@OP New here and sometimes struggling to keep up but I think I get what you're getting at.  Example.  Jitter etc aside, CD source often considered cold, clinical and uninspiring.  Too perfect perhaps? Consider too that some added noise allows for our ears/brains to resolve better (just like certain algorithms and digital processes converge better) so maybe a similar relationship exists for amp likability.  An ultimately neutral, perfect amp may end up leaving many feeling less passionate than one with "color".  Perhaps one man's natural-sounding is another's imperfection.  Perfection may actually leave one less excited (amps).  But I get it since speakers and room nuances aren't going anywhere and total system matters.  No one ever "listens" to just an amp.
Nelson was a great designer a long time ago. Now, not so much. Not surprising, since he left the refining fire that is competitive commercial products long ago.
Have you folks seen what kind of sources he uses and speakers he outputs to these days?
My criticism of Pass stuff is that NP is quite open to the idea of designing complete series of amps to have a certain "flavor" and then offering a range of flavors to the consumer. 
I don't recall if it was in that review or somewhere else but I recently read that NP now says that his .8 series of amps have a significant deficit in their circuit design resulting in inferior sound that he has now corrected with a new circuit design. How does that make the .8 owners out there feel?
mtdining, you are so far off the mark it’s not funny. :(

I am reviewing a Pass amp currently, and I was in conversation with Nelson a couple days ago about OB speakers. He is part of the industry that concern themselves with more esoteric sound in terms of speakers, not just what's popular. 

I am only going to say this at the moment; Imo Pass Labs is putting out a far superior sound now than in the recent past. Want to know more, wait for the review.  

BTW, you want to single out Pass for what kind of system is used? You would be shocked at the rigs used in the industry by many very well known companies. I have knowledge of companies that use what wouldn't even be considered high end audiophile gear in their design process. It's possible products you own have an insipid testing and development audio system.  So, I wouldn't get too fired up as though you know something important about Pass Labs. 

So I am curious if anyone has actually heard the Int 25, and how they felt it compared to other Pass amps, and other amps in general.

Is there something to match up between the distortion profile and listener impressions??
Last year I went on a turbo mission to find the best amplification that makes the most music to my ears; I purchased and lived with top Luxman solid state: 509x, m900/c900 combo; numerous ancillary equipment swaps in the process so I could best discern the signatures of the amplification;

I also purchased and lived with Pass Labs x150.8, x250.8, xp12, xp20;

I have settled with a Pass Int 250;
In my book, Nelson Pass is, was, and will be an analog designer of epic stature; Pass Labs is a super company that defines customer service.
I will never understand members that bash gear, either passive aggressively, or full flame, on a public forum. It’s just kind of pitiful in a way;  

It’s my understanding that jealousy is something like: ’I want what you have’, but envy is something worse and different: ’I don’t want you to have what you have’; It’s really sad to see adults that carry on in this manner.

Anyway psychology 101 off, and back to audio: To thine own ears be true!

Erik interesting observation.  I remember reading a recent article / interview with Nelson Pass.  He stated that he was trying to create a type of distortion and use it to positive effect in the sound. 
These measurements might show the results of that effort.   
Hi @dpac996

I'm very happy that you are a true Pass fanboy.  However, what I'm asking here is if we can get to specifics of one amp.

Have you heard this particular integrated and can you tell anyone how it sounds compared to other Pass amps, or other amps you've heard?
Pro or anti Pass comments don't really move this question forward.


Hi @erik_squires thanks. I keep what I like and sell what I don't; In this case Pass won me over compared to the best Luxman had to offer; Pass Fan boy? Absolutely!! and thank you for the compliment :)

Good luck on your quest of trying to understand the sonic virtues and character of a Pass amp, (or any amp) via input from other people's ear/brains/memories. 

Recent interviews with Uncle Nelson indicate that he certainly is currently on top of the designer heap in just about every way, and has explained (and shared things including giving away his "distortion generator" at Burning Amp) at length his ever evolving design theories...note the term "evolving" which doesn’t seem to apply to many of the neanderthals around here, but has resulted in his amps receiving near unanimous rave reviews...both Pass Labs items and his First Watt designs are considered by many as representing the state of the transistor amp art. There may be some that don’t like the sound of his new stuff, but those are likely to be people who haven’t heard it in the first place (as noted above) as otherwise you’d be hard pressed to find many dissatisfied Pass gear owners.
I’d love to hear an INT 25; I really like the approach they took with the output stage topology; reminds me of Gamut or Dartzeel;
My speakers are probably not best load for that amp, but I have to admit I was shocked by how great my XA 30.5 sounded through them; on paper many would say don’t bother, but reality was far different;
The m900 is a beast and has bipolar devices but the Int 250, (all MOSFET ) digs deeper with notably better bass; 

I wonder now many of us really are qualified to judge which designer is at the top of the heap or not. The Berning designs are light years better than the Pass products I have heard or owned to my ears. And yes I have owned designs from both. Rave reviews mean less and less as this industry gets smaller. Nelson is an interesting cat and a great designer, which means nothing if you dont like the sound of his products as much as the designs from some neanderthal designer. 
This is an interesting thread from both sides. 

There is no denying that Nelson Pass is a legend in audio design along with the other famous circuit jockeys, Bob Carver, John Curl. 

There are a couple of disturbing points if Nelson sent out a series of products that he knew were under performing that is pretty poor that he rushed the product to market when he knew the product could and should be better. 

As per Dpac prefering Pass, that is his opinion with his matching gear, the Pass signature tends to be a bit laid back the Luxman is a more neutral sound, so it would all depend on cables, dac, speakers, room acoustics.

Pass is but one excellent choice if you like their sound, styling, size, Class of operation, and in the case of his Class A designs the heat output. 

Dave and Troy
Audio Doctor NJ

jsautter, what is your system; what speakers are you running and which Berning? I can certainly see how/why you might select another amp as preferred over the past Pass designs. No secret that people have strong preferences as to make and sound signature. 

How do you think the Berning would do with my Kingsound King III electrostatic speakers? My initial reaction to looking at the specs is that I think it would choke. Perhaps that is mistaken, but I am open to being corrected if Ihave missed something about the Berning amp's in relation to driving something let's say a bit different than a Sadurni. So, what if it could not drive the King III anywhere near as well as the Pass? Does that make the Pass light years better? 

In other words, generalizations about which amp/manufacturer is better would be more helpful if speakers were included to give some perspective. I use a variety of speakers along the spectrum, so an amp that can drive all with authority is very important to me. In many cases amps with robust power can drive all the speakers well enough, but lack the erudite nature of the finer amps. On the other hand, several along the lines of the Berning, at about 100 or so Watts have been utterly incapable of driving the King III well. 
Holy smokes; why are people jumping to conclusions that Pass knowingly rushed an inferior design to market? Fsonicsmith please list your sources otherwise we might conclude your summary may be based on phrases taken out of context.
 I read the article listed here on OP’s link and there is no discussion of input circuit topology; There is a brief conversation about degeneration in output stages and their known trade offs, but nothing that suggests Pass Labs pushed bad designs into production. Again, please list a link to this material!

I’d love to hear an INT 25; I really like the approach they took with the output stage topology; reminds me of Gamut or Dartzeel;

Me too, honestly.  I have no idea how this sounds, but very curious as to how those measurements will translate into sound for me.



What part of the distortion signatures concern you?    From what I see you might hear a slight 60 cycle hum at -76 dB's but everything else is under 90dBs.   And there is some kind of harmonics in the noise signature (it is not random) so my guess it is intentional. 

The 50 Hz chart looks OK too.  There is a first order harmonic of -85 dBs at 100 Hz but everything else is under -100 dBs.    You think you can hear that?

I am using Ascendo Model M speakers with a Zesto Deluxe phono stage, Berning ZOTL One preamp, VAC Phi 200 amp and Zesto stereo amp. I use a Merrill-Williams turntable with a modest arm for the time being. I have just ordered  a Mu-Tech Hyabusa cartridge. Cabling from Analysis Plus, Bionics and Inakustik.  

Berning used to make a Quadrature amplifier that some have used with the older Apogees with supposed great success. But I dont think this amp is in production any longer. Having just heard the Kings at shows I am not familiar with this load. What I have heard has impressed me a great deal and under different circumstances I would consider this speaker line as a possible for my room. There are several European S.S. amps that I think better the Pass in every conceivable way. Apples to oranges though as these are much more expensive. 

My favorite amps under the right circumstances are OTLs, but it is hard to let the amp dictate the speaker design.

What part of the distortion signatures concern you?  

Please reread my entire original post.

jsautter, fair points, good comments. I wish I could get my hands on more overseas components, but it’s hard to review, recommend a product that does not have a distributor in N. America.

Ha, I was presuming initially that you were discussing Berning amps, not preamps. Now, I see that you were probably referring to preamp. Yes, there can be very wide differences between preamp designs. I have heard shocking differences between brands and models of preamps. So, I get your strong preference in that regard.

If you attempted to pair the Pass preamp with the VAC Phi200 I very much understand if you did not care for it. I would not think the two would be ideal. Manufacturer’s house sound plays a huge role in matching gear, and some combinations are simply not ideal, whereas others are seen as heavenly.

Nice looking speaker; I presume you mean the M5 passive. Well, that’s 8 Ohm, 91dB, so yeah, 110 watts is plenty. It’s been several years since I worked with the VAC Phi200, and having been through many more amps, there is more in terms of resolving power and depth that can be achieved if you wish, and you could go either with a second unit in mono or move up the line if you chose. Moving to another brand of amp would open up the "can of worms", however, another amp I can recommend that would provide some variety with similar tonal palate would be the Wells Audio Innamorata. If you adore the sound, getting a second Phi200 and going mono would be a big bonus. You have room to roam in terms of improvements. It would make your speakers seem more formidable and refined at the same time. It’s also important to try different power cords with the Phi200. :)

You have a very fine system, and it is at a level where the changes will reveal very strong, distinct characteristics. No wonder you feel strongly about the matching. I get that. We tend to anchor to our "prime component" and work off of it. The direction one takes with a different brand is either going to be horrid or heavenly. So much depends upon synergy between brands/models, cables and speakers. I have had a few preamps, amps, etc. that were not impressive with one speaker work stunningly with a different speaker. If you heard it with the first, you would say it is overrated, while hearing it with the second you would say it is sublime.
Let me try again.


I glad you found what you liked, but can you be specific as to the speakers, the Pass amp and what tonal qualities won you over? Any specific recordings which you feel made your choice clear?

What was done better than your Luxman combo??


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Thanks so much for the description of your personal experiences, @dpac996

I have the 507ux, so I know what you mean about them being amazing values. I think it is interesting you have moved towards the Dynaudio and Focal range, a range I've moved away FROM. :) Like now I pretty much only drink IPAs while in the past I drank only lagers.


Thank you;
Hilarious about the beer; I WAS purely an IPA guy but have been gravitating towards sweeter lagers but I still like Bells Two Hearted Ale;

Horses for courses, they say :)

I’ve been listening to Dynaudio ever since 2005 when I first heard the S3.4 model powered by a McCormack DNA 225 and Cary SLP-98 with a Marantz SACD player, at my bosses place; I never heard a sound like that; I was a Thiel guy but when I heard singers sound alive and truly present in front of me, I finally understood just what in the heck people were talking about when they said the word "organic" when describing loudspeakers, LOL;

I use the Focal Aria 906 in my HT area with the matching center; Focal Chorus 7 somethings for the rears;

Cheers and enjoy the music!

I think Nelson's listening room is awesome and I would trade gear with him in a heartbeat.