Pass Labs XA 30.5 power amp

10.06.2011..

There are several ways to design and make a solid-state amplifier. For their Viola monoblocks, Tom Colangelo and Paul Jayson have chosen a no compromise, clean power supply, whereas Lars Goller (maybe Ole Lund Christensen!?), for his Gamut, has opted for a very performing and not so common amp with super mosfet. Other options are an elaborate circuitry with a wise recourse to negative feedback, as Mark Levinson did, or amplifiers with autotransformers in the transistor output stage, as traditionally chosen by McIntosh.

Then, there is Nelson Pass's way.

After the Threshold in the ’80, the first Pass Aleph and the current Pass devices, this “historical” designer has been churning out several patents and a progression of extraordinary gears.

I suggest you to have a look at his website, which I consider the most articulate and interesting in the hi-fi panorama. You can find his total credo with exhaustive descriptions of the philosophy of all products, together with the main issues and relative solutions to design an amplifier. Quite rare, isn’t it?

His everlasting goal is to obtain a stable circuit from sound design choices, without an extended use of a negative counter reaction. Even if this last one consents very good instrumental performances (at least in name only), it cannot avoid some problems, which entail, as Mr. Pass and other people - included me -emphasize, consequences not always recommendable at listening.

This is quite a lot because, if we obtain good performances by using the open loop, then we would be able to make an excellent amplifier.

If you want to know how, check the websites: www.passlabs.com, www.passdiy.com, and the new www.firstwatt.com, where you can share DIY projects, info and elucidations about Mr. Pass’s planning choices and his elegant way to solve some technical problems

about amplification.
After the splendour of the still excellent Aleph series, currently there are two lines for the power amps: for the class-AB, the X.5 line, where the digits indicate the output power of the single models, starting from the 150 watts of the X150.5 and, for the pure class -A, (this is not entirely true as I will explain later), the XA.5 line, starting from the XA30.5, object of this review.
Well, you may say, another article on the XA 30.5!

Yes, another one, but I think that this amplifier will turn out to be a small big classic which, like other analogous products, in the long run, seems to mature and deploy new virtues, maybe less explicit in the beginning, but only because it needs a deep “strong” knowledge.
Even if it weighs more than 30 kg and shows important dimensions, this amp is the “smallest” of the series.
But is it a power amp of one watt per each kilo of its weight? Definitely not.
Actually, it can outdraw from a real load that is a loudspeaker, also 200 watts with acceptable distortion rates, but somehow far from an out-and-out clipping. Therefore, is it a pure class-A power amplifier?
Yes and no.
Mr. Pass has polarized the final stage with a current adequate to drive the class-A, i.e. without interdiction of the final mosfets, up to about 30 watts into 8 ohms and 60 watts into 4 ohms. But then he has anticipated the possibility of switching to the class AB up to powers three times higher, with abridged distortion rates and, mostly, with a very positive harmonic spectrum, suchlike the one presented by the best tube power amplifiers.
In point of fact, Pass’s circuits seem thought for the tubes, but are realized with mosfets, since he considers the tubes as instable components.

Notwithstanding the available watts, the driving capabilities are very high. This is the consequence of a very good power supply stage and of the high number of final transistors for each channel, which can assure elevated output currents.
The power amp heats a lot, even if provided with some generous heat-sinks. When switched on, it has a very low consumption and, presumably, it keeps in tension only the input stage. When you are ready to listen to it, then, you have to work on the front lever switch.

When completely switched off, the Pass will sound at best only after 24 hours of working, whereas, if switched on from the standby, it requires only 15 minutes. I tested the Pass with a certain number of preamplifiers and, in particular, with the Italian Dromos Metis tube amp, which has high-quality NOS tubes, and with the Pass Aleph P preamp, in balanced connection, which I think being one of the best solid state preamp in circulation, considering its very high transparency, high tonal rigour and overall musicality.

I matched the Pass with my Martin Logan SL3 speakers that require lots of current and excellent components. I also tested other loudspeakers, with outstanding results. It matches very well with any good cable and, as Nelson Pass uses to say, his power amps are not very sensitive to power cables. Therefore, I connected my MIT 750 Shotgun bi-wire.

However, if we consider the main cables, here there is a certain sensitivity, mostly during listening tests at high volume, where it needs thicker cables. Great performances with a TDY silver cable, with White Gold cables and Kimber PK 10 cables.

When the solid-state works
This Pass amp is a real musical masterpiece. Basically neutral, with that hint of warmth common in the full production of the American designer, it competes with the best tube amps as far as the musical body and the harmonic richness that makes real the acoustic instruments and palpable the human voice, are concerned.

In comparison with the Aleph series, here there is more rigour, an improved rise time and more neatness in the releases, but also a stratospheric dynamics that livens up any musical programme by pushing away any feeling of pretence, any sensation of "plastic", as sometimes happens with some switching power amps (q.v. class D or similar).
When the pointer of the mid gauge (beautiful…) is still, testifying that the pure class-A is functioning, the liquidity of the medium range is very high, although with a neatness in the attacks and a grand detail.
By turning up the volume, you miss something, not so much, though. Only at very high levels, the Pass turns from excellent into very good.


Strong points
A lot, indeed.
The low range is extremely controlled and articulate, even though warm at the same time: one of the best you can listen to nowadays. The mid-bass is very well aligned, never out of control. From the mid range up, the frequencies are remarkably linear and rather controlled, but so dynamic to appear sometimes quite nasty. The Music flow is overwhelming and grants a pushed dynamic treatment very close to the live performance although underpinned by an excellent harmonic body for a solid state amp. Is that enough, isn’t?

Let us go on.

The perspective is clear, very clear and the sound subjects are never too big or too small, always well represented. Deepness and wideness are extended. Furthermore, what helps a lot is the ability of making heard the resonances and echoes of the recording studio that put the instruments into an imaginary world. A world that your mind can recreate without any effort, automatically.

But there is something else

The XA 30.5 holds that sense of truth capable of representing the reality in front of you, the sensation of the real illusion. Its reactivity, its micro and macro contrast, jointly with its harmonic richness, make the sound subjects often very real, concretely of matter and undeniably three-dimensional.
All these are merits, regardless the price. Substantially, nothing is missing.
 
Weak points
The only weak point, for me, is a behaviour at high volume that I find less homogenous than with low output powers. The distortion is never audible and the clipping is smooth. Nevertheless, when the power supply stage has to deliver more current to the final stage, which starts to function in class-AB (only on the peaks, though), the extraordinary refinement and fine-grain of the XA 30.5 starts to diminish. The quality remains high with no doubt, but from the magic… we are down to earth. Maybe we can turn to the major models for the high powers, but the minor amp has a sort of grace and can touch your feelings as no other competitors can do (although if much more expensive).


Conclusions
Compared with the Alephs, this new XA series has more rigour and offers a faster performance together with a masterful control of the low range. Maybe the only incomparable thing -someone says – of the Alephs’ devices, is a characterization that here is not so remarkable, but that I deem sometimes like a crack in the imaginary wall of the perfect neutrality.

The XAs, and in particular the 30.5, have absolute rigour, balance and coherence, accompanied by a harmonic body, rather than a timbric body, very appreciable in the mid range for whatever power amp, and especially for a solid state amp.

If you want more, then you have to pay at least three times the price. For sure, you can get more refinement in louder listening levels whereas the 30.5 loses some tone refinement and cleanness, but nothing else, because in some parameters the Pass approaches the maximum you can obtain from an amplifier. In sum, it is a power amp that poses the boundary quality/price beyond which the madness harbours.

It interfaces with any kind of loudspeaker: horn or electrostatic, tall, low or chubby, better with an efficiency equal or higher than 90/91 db/w/mt, and with every preamplifier. My suggestion, however, is to choose a tube partner for its neutrality and dynamics.
These, are Mr. Pass’s watts.


P.S. Musical insert
Sviatoslav Richter was a great piano player, Herbert Von Karajan a great conductor, Deutsche Grammophon a great record company. Moreover, if we add one of the most popular concerts in the history of Music, written by one of the most famous romantic classical musician, we can only achieve a surprising outcome.
The Piano concert No.1 in B-flat minor, Op. 23 by Tchaikovsky is well-known indeed, at least in the first impetuous movement, and can be considered as one of the most intimately popular classical compositions. The Russian artist can be considered intimately popular too, in the best sense of the word, of course.

This recording dates back to 1962 and represents the successful cooperation between two great and young artists, a pianist and a conductor at the top of their career. They gave a new and inspiring key to the reading of this concert, maybe too performed and too much known, to result somehow predictable.
At that time, some critics said that Richter sought after a too personal and less fast mark to the concert, as he had to deal with Schumann’s work. On the contrary, the union with Von Karajan produced a performance rich in contrasts, articulate and original. The musical tension arrives at high levels, remarked by a masterly played soloist instrument, in an opera that many consider the anthem of the piano virtuosos.

The standard of the recording is very good, with a precise focus and positioning of the instruments, appropriately rearward but completely to the fore regarding the orchestra, which is set at the back, although vivid and detailed.
The Pass, differently from the most part of the solid-state power amps, gives back a lucid sound, even though solid, harmonic, personable.

It is the sound of a solid state that does not want to imitate the best tubes (as the Aleph series maybe does), trying to emulate their harmonic content, going down on their field, where the medium range is absolutely rich, concrete, present and material.

The piano has a genuinely correct tone and you can catch all the notes and intonations. There is no coloration and the harmonic scales are very fast and never incoherent.
The strings are fine, never vacuous and aseptic. There is always that harmonic fullness capable of reproducing truthfully the authentic violins.
With classical music, the Pass can show all its tone pleasantness, but also its rigour in defining properly the instruments and a very rare euphonic musicality together with detail and fine grain.
In the second movement, there is no perspective aberration in the spatial relation between Richter’s piano and the orchestra. The start with the pizzicato is very fine, full of echoes and extraordinary detailed. At the end of the third movement, the piano is very percussive, but also provided with a concrete, vital, full-bodied soundboard, nurtured by the unequivocal talent of the artist.
This is the additional value of an amp that can tell you not only the Music, but also its protagonists and their artistic genius. To do this what is required is balance, dynamics, refinement and most of all soul.
The Pass, as the protagonists of this great recording, has a real musical soul.

 

 

RIGHT OF REPLY | MANUFACTURER'S FEEDBACK

Dear ReMusic,
Thanks for the very nice review. We don't need to comment.
Best regards,
Desmond.
from passlabs.com

20/09/2011

by Paolo Di Marcoberardino
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