Pass XA200.8 Review - Fun measurements

Low order harmonics (up to 3rd order) and higher even order harmonics are pleasing - of this there is no doubt!

I don’t think you need a 20K x 2 monoblock power amps to achieve this. Although a Pass amp will certainly do the job eminently.

The stereophile measurements are excellent except for the IMD at 4 ohm (might not be a good fit with low impedance speakers like Magico or B&W)

My current “musical” solution is to take the Benchmark DAC3 (SOTA in measurements for low distortion and noise floor) and large ATC Active speakers (also ultra low or SOTA in all forms of distortion and Class A to 2/3 power) and place a tube preamp in between them! My current favourite flavour is McIntosh C2600 (admittedly nowhere near the same league as ARC Ref and so NOT SOTA) with Telefunken NOS in the phono stages and a combination of a 1950’s RCA long black plate with a JJ stock McIntosh tube on the line stage. It just sounds so sweet and musical and I can roll tubes whenever I want without breaking the bank. I think great musicality can be found at many price levels - even entry level - all depending on personal taste. I recommend the tube preamp route as being a great way to “cook” to your taste!

So I agree Pass designs are not SOTA for measurements but they are excellent for their musicality (SOTA for musicality). Furthermore some Pass designs are better than others (no surprise) and the XA60.5 is perhaps his best sounding ever!

@shadorne

I see where you are going. There are a number of tube pre’s I’d like to have in my system, but due to budget, and space I’m living a hyper modern lifestyle. A Myteck Brooklyn DAC to ICEpower amps via pure silver interconnects.

However, I heard a lot of Pass amps at the show in Oakland. I really did not like them at all. Mind you, you don’t have to. :) but they had a particular sonic signature prevalent in most rooms.

No one on this thread has to agree with my personal listening tastes at all. I’m mostly just asking whether you think this distortion profile is the Pass signature, and if this says something about those who like it.

My all time favorite amps, the CJ Premiere 12s, I am sure measure horribly too, but sound nothing like the Pass. Can we learn anything with this?

Best,

Erik

My passdiy amp sounds really nice, no idea about measurements but it sounds more tubey than my 300B tube amp. Warm and musical.

The measurements, as John Atkinson suggested, indicate a relatively low level and a very restricted open-loop bandwidth, which appears to be about 500 hertz.  This is unusual as a very restricted open-loop bandwidth is normally used to ensure stability where a relatively high degree of corrective feedback is used.  The loss of feedback at high frequencies results in comparatively poor high frequency distortion readings.  That said, the sound was good.  As well, the amp provides true true class A operation at its rated power (200 watts) into an eight ohm load.  The manufacturer specifies the current draw at idle at a very high 6.1 amperes, which if one applies the formula that output power is the square of the current (I) x resistance (R), means that the class A power into eight ohms is 6.1x6.1x8 or 297.8 Watts.  The manufacturer claims that it leaves class A at 430 peak watts (no impedance specified) whatever those are. Into a four ohm load, ithe amp derates (leaves class A below the rated power into that impedance of 400 Watts) at 148.8 watts, but this is still impresssive in comparative terms.  More to the point, the reviewer found it had some unique, desirable qualities in the midrange, even though the Class AB Momentum monoblocks beat it in bass slam and tightness, capture of recording venue ambience, and lack of a sonic fingerprint.  

My previous post should have said in the first line, “relatively low level of corrective feedback”.  That said, the very low measured output impedance, including cable, of 0.03 ohms suggests a very healthy degree of corrective feedback, although there may be other explanations for this.  Would explain the very limited open-loop bandwidth and consequent increase in high frequency THD to 1% at 20K into an eight ohm load.  Still, the proof of the pudding is in the eating, as the saying goes.

@erik_squires 

I think it depends on set up and taste as to what works best. My point is you don’t need to spend a fortune on power amplification to get a warm tubey sound. SS power amps that try to emulate tubes like McIntosh are going to colour everything coming through them. The beauty of a tube preamp is you can play your DAC directly or through the tube preamp - just a couple of interconnect connections....

I think that the Pass X series is their best all around amp. I have the new Pass XP-22 preamp and the Pass X350.8 amp. They produce a very detailed and somewhat tube like sound with excellent sound stage. 
While this system is expensive, you are paying for excellent sound, reliability and product support that is second to none. In fact I had Mark at Reno Hi Fi steer me away from their class A amps because of their lower power and high heat output. I run this system with an 
Allnic H 7000 phono amp (tubes) and achieved an excellent result. 
The trick with a Pas system is to have a tube phono amp like a Herron,
Audio Research or Allnic.

Finally, to me, tube power amps are a real hassle to maintain. Their reliability is far below that of a Pass which is built to last and maintain its sound level. Tubes (especially power tubes) deteriorate over time.
And they have reliability issues because of poor QC in the factories that produce them. 

 

@shadorne - Agreed. 

30 years ago I made a purchase primarily based on measurements and it turned out to be something I was not happy with. Since that time only purchase based on how it sounds, but will look at specifications for component compatibility.

To the OP's question, I think there is undeniable distortion in the amplifier's output. This appears to be by design. In the review of the 200.8, Pass is quoted: 

"The lesson of the Xs and SIT amplifiers was that a small amount of second harmonic of a particular phase character gives a desirable sonic result. To get that effect, we altered the arrangement of the constant-current sources in the output stage to better duplicate the sound of the Xs output stage. While the .8 amplifiers still have low distortion, they do not suppress second harmonic as much as the .5 series, giving a mostly second-harmonic character at ordinary listening levels and segueing into third harmonic at higher power."

Also: 

"I don't think the audiophile wants technical perfection. He wants to be happy.—Nelson Pass"

Read more at https://www.stereophile.com/content/pass-laboratories-xa2008-monoblock-power-amplifier#EuGPmgvtCD4uc...

Great points about the distortion though. I own a Pass amp and am extremely happy with the euphonic distortion. I personlly appreciate Pass's approach to amplifier design. 

yes, it is, and they say so themselves, but a bit in a disguised way. They built amps for what one hears, not for measurements. If one likes the sound, who cares of measurements?? which even excellent sounding tube amp measures well... none!!
either you buy on sound quality/performance, or on specs/measurements. My Benchmark AHB2 are good amps and measure brilliantly well, but in performance against the Pass, not many will choose the Benchmark!

shadorne,
i have nearly all from Benchmark, all dac models and amps. Used the AHB2 in mono on Tannoy GRF90 through very good tube preamp. Very nice sound, fast and dynamic, which to me are the strong points of these little marvels. Tried the XA160.8 on same: so much better in just about every aspect of sound; especially tones, bass, coherence, soundstage and overall musicality. No comparison. But i still love my Benchmark gear. They are better adapted to other speaker types, and Pass is very well suited to Tannoy in general. Nelson Pass does lots of evaluation on Tannoy, and Desmond Harrington, president of Pass has Tannoy at home!! As much as I think we can say Pass XA are not adapted to the Wilson.

hddg :

I very much care about measurements. That is part of how I enjoy this hobby is learning what measurements mean to perceived sound quality. That doesn’t mean I buy based on . specs. The point of this thread is very much to help illuminate this aspect of our hobby. Whether distortion is a selling point.

I also wonder how much of this is learned or trendy. I’ve lived with Parasound and Class D amps that have much lower distortion figures than Pass. I also loved old CJ tube amps. I simply do not like the Pass sound at all. The point is not that you should agree with me, but rather, I wonder if this is in fact a learned or acquired taste? Does our ear / brain mechanism change according to what we spend time listening to?

And how much of this is driven by reviewers and price? I’ve seen plenty of evidence of this in speaker land. 

Kind of related to this, I really would have liked to have seen what Carver did when he attempted to match the CJ Premiere amps. Did he add more harmonics? 

Best,

Erik

I read the measurements and they are quite respectable and aren't pejorative in substance or assessment.  I'm not sure of the point of this post, other than an axe to grind with the concept of Pass?  These amps are massive, heavy, and there are two of them. Adjusted for inflation, the XA100.8 pair would have been about 6.5K in the mid 80s, back when a Levinson 200W, unbalanced, stereo ML-3 was 5K. A pair of ML-9 amps was 6K which would be about 18-20K today.

Want to spend less? Choose the X60.8.  I have a pair of XA100.8 which replaced the XA60.5 which replaced Classe MA-600 and Luxman M800a, which replaced a pair of Bi-Amped Accuphase A50s, all of which were excellent.

I read the measurements and they are quite respectable and aren’t pejorative in substance or assessment.

I disagree. That’s quite a bit of distortion in the 21st century.

I’m not trying to grind an ax here so much as talk about whether it is exactly that distortion which people are paying money for, and it seems it is.

That’s fine, it adds to our understanding of what people like to listen to. 


Best,

E

Erik,

I think i did catch the sense of your post, and i have responded to it my way, cannot do otherwise. I do not own any Pass amps at this stage. Heard them several times and I cannot objectively say that they are bad sounding amps, on the contrary. In my thread I also said that they bettered by far my beloved Benchmark AHB2 amps on the Tannoy GRF90, but these are efficient speakers. This assessment was without appeal before a panel of over 10 experienced audiophile, with only one of them actually owning Pass. I cannot say neither that they measure badly, but they certainly have drawbacks. I don't think that it is neither a learnt or acquired taste, except maybe for a few beginners or marketing influenced few. At this level of price, I think that many buyers are well advised audiophiles. From my continuous observations, I have come to conclusion that Pass try to achieve the good sound that good tube amps provide, so it seems logical to me that the measurements correlate in some way, although the Pass actually do measure far better...but they are not tubes, so they'd better!! And, from my various experiments with them, I also think that in most cases they must/should be associated with quite efficient speakers, especially as concerns XA.8 models, due to their lack of dynamics (for my taste). They have beautiful tones and other qualities, they are easy listening amps and maybe this is a large part of what attracts people to them, but in my view, dynamics and attack are essential to perfectly reproduced music, and this is maybe where the measurements are at fault !!...slew rate, damping, available current, type of fets used, whatever, but it must correlate to measurements at some point. The distortion certainly makes for the nice tones, but some energy is missing for the dynamics, and for such power consuming, heat producing, price of amps, I think it is an issue that Pass should address ASAP. 

by the way this is a nice and intelligent post Erik.