Art Audio PX-25 SE
Stereo Power Amplifier
Pleasing the audio G-ds.
Review By Dick Olsher
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As the name implies, the Art
Audio PX25 amplifier is all about the PX25 directly-heated triode - a
British tube that was originally designed and manufactured in the mid 20s
by GEC. The tube stayed in production until the end of WW II when it
became a casualty of a new breed of beam power tubes (e.g., KT-66) which
were capable of more bang for the buck. The KR version is a copy of the
original, but it cannot comfortably handle in excess of 370 V plate
voltage versus the original's 450 V. Art Audio runs this tube at a bit
less than it's maximum (around 360v) where the distortion level is at it's
best. So what's the attraction here? According to Art Audio's Joe Fratus,
this tube measures more linearly than most other "single ended"
triodes (SET) and better than any new production tube that Art Audio has
tested. The PX25 tube is said to feature a midrange sound similar to that
of 2A3 but with more extension at the frequency extremes, and of course
more power. The slightly higher plate resistance, relative to a 300B,
allowed Art Audio to design an output transformer with an extended
bandwidth - beyond what is typical for 300B or 2A3 based amplifiers. Throw
in tube rectification and a 12BH7 driver stage and you've surely got a
tasty tube concoction.
The Sound
Is
a PX25 simply a 2A3 on steroids? While I think that there's some truth in
such a portrayal, the whole truth is not so simple. A good 2A3 is capable
of astounding midrange clarity. There's an unmistakable you-are-there
directness about its sound that is quite startling. No experienced
triodephile is, however, likely to confuse the sound of the PX25 for that
of a 2A3. For starters, its midrange clarity approaches, but does not
equal the benchmark of the 2A3. In contrast, the PX25 is a warmer, more
luxurious sounding tube. This tube gets much closer to my ideal of
"velvet in a bottle" than either the 300B or the 2A3. It is the
sonic equivalent of a rich milk shake. The PX25 baths the midrange with a
lavish tapestry of harmonic textures, and it does this without sounding
overly thick or by sacrificing detail. Here's an amp that satisfies my
sonic sensibilities: a glorious blend of harmonic rightness and detail.
Because subjective tonality is affected by the amplifier's
bandwidth, it's difficult to make comparative tube judgments without also
taking the output transformers into account. Some SET designs currently on
the market have hard time exceeding a power bandwidth of 20 kHz. As the
bandwidth shrinks, stage lights turn more mellow yellow. Midrange tonality
is emphasized and textures are perceived as softer, more liquid. This is
the trap many other SET amps fall into, trading transient speed for an
overly soft and sweet sound. This was not at all the case with the Art
Audio PX25/Lowther BassZilla coupling. The combination of Art Audio's
extended bandwidth (60 kHz) and the Lowther BassZilla's DX4 full range
produced exemplary transient speed and control. The remarkable point, that
bears emphasis, is that even with all this inherent speed and treble
extension, the PX25's midrange sounded gloriously lush and natural.
The other hugely enjoyable aspect of this amplifier is its
rendition of spatial perspectives and image outlines. It paints a truly
believable 3-D soundstage. The depth and width perspectives are especially
noteworthy, and are responsible for the soundstage's breathtaking vista.
In this regard, the PX25 sets a new standard, at least in the context of
driving the BassZilla loudspeaker. Acoustic signatures of various halls,
and even artificial reverb added to individual channels in a multi-channel
mix were clearly resolvable, down to the noise floor of the recording. No
other amplifier to date, regardless of cost, has equaled the PX25 in
fleshing out a believable soundstage. Image outlines were palpably
resolved with exceptional resolution. It was easy to delineate the spatial
coordinates of individual instruments in a mix or to isolate a particular
voice in a chorus. In contrast, lesser amps homogenize massed voices, in
effect causing spatial cues to bleed together as in a runny watercolor.
The PX25 snaps image outlines into focus for a 20/20 view of the
orchestra. In addition, image size was more realistically proportioned
than with say the Volksamp Aleph 30. The dipole mounting of the Lowther
DX4 with its large open baffle provides for more realism with regard to
the emulating the wave launch of individual instruments, and the PX25
pushed the BassZilla to the limit. The chest, sounding board, body, or
whatever resonant structure you can think of was effortlessly resolved.
Volume and pitch nuances, the domain where microdynamics
and emotions reside, is given full bloom by the PX25. Taken in
combination, its virtues of harmonic integrity, emotional intensity, and
spatial incisiveness breath life into the soundstage. In the process, my
favorite instrument - voice - benefited dramatically. Over the years, I
have struggled mightily in all of my designs and audio system integration
to get one thing right; namely, my spouse Lesley's voice. Her 1992
recording session in the old VTL studio (sadly, now defunct) by David
Manley (Lesley Olsher: Jazz Me, Black Dahlia Music BDM 78003) gave
me a lasting reference. The live-to-two-track recording session, the
analog master playback in Manley's listening room, the digital master, and
ultimately the production CD - my ears were in the loop every step of the
way. It's fair to say that I have a excellent idea of what this CD should
sound like.
After auditioning numerous systems using the Jazz Me
CD, both at trade shows and elsewhere, I'm flabbergasted (and depressed)
at how rarely expensive audiophile systems do it any justice. Dynamics are
typically compressed, which is equivalent to letting the air out of a
tire; the drama gets sucked right out of the soundstage. Spatial
resolution may also suffer, but I can deal with it, as long as rhythmic
drive and emotions are present and accounted for. Finally, the timbre of
Lesley's voice is usually pummeled by multi-way speakers, whose disparate
sounding dome tweeters and midranges, and inevitable crossovers in the
range of 2 kHz to 4 kHz harm coherency and harmonic purity. It's actually
an amazing experience to walk away from a $100K system, that failed to
resurrect Lesley, shaking your head in disbelief. How can something so
simple, be so difficult to reproduce?
This should give you a rational basis for my current love
affair with full range drivers such as the Fostex FE208 sigma and the
Lowther DX4, and my current minimalist design approach. Driving the
Lowther BassZilla, the PX25 did Lesley justice. David Manley was so
convinced that Lesley could not overload his Gold reference mic. Nobody,
especially a diminutive soprano was going to do that to his mic. Well, he
was wrong. Therefore, there's no close miking on the Jazz Me album.
Lesley was deliberately positioned about a meter away. Still, in spots she
still challenged the recording electronics. These dynamic peaks were
easily handled by the PX25. Take Bill Ebanks' "Lay All Your Love on
Me," which absolutely rocked during the recording session. Listening
to the live feed, this track left me breathless, yet over the years it
proved elusive to recapture the magic of the moment. Joy at last!
Male voice was also given full scope for expression. Let
me mention just one example. Keb' Mo' (aka Kevin Moore) with a slightly
raspy take on original blues, is crisply recorded on his 1999 self-named
album (Okeh/epic EK57863). Performing triple duty on guitars, harmonica,
and banjo he lets loose with lightening fast transients and benefits from
excellent rhythm and bass support. Timbre accuracy with plenty of natural
detail was how the PX25 facilitated the music. I certainly have not
enjoyed reproduced music at this level before. That sense of anticipation
that accompanies a live concert is back in my listening room.
All of the above gets me to the business of system
considerations and synergy. Occasionally, perhaps a handful of times in an
audio career, there comes together an assemblage of components that
transcends ordinary HiFi. This is just such a happening. To tout an
amplifier out of context makes about as much sense as an engine review
without reference to a particular car. So let me sort through the
compatibility issues. The PX25 is not a bright sounding amp. In fact,
based on auditions with both the Diva M7 and Air Tight ATC-2 line stages,
I inferred that the PX25's voicing is slightly laid back, and benefits
from a lively sounding preamp. The Air Tight, itself being organic and
very relaxed, did not complement the PX25. Instead, the Diva M7, a purist
reworking of the Marantz 7, proved to be an ideal match for the PX25,
filling in the upper octaves and stepping up the sensation of presence.
It's true that only a handful of amps mate well with the Lowther's
propensity for excess presence region. So getting the right mix of spices
is not an easy thing at all. In general, I would expect the PX25 to work
well with bright sounding speakers, since it has some cushion to soak up
excess energy through the upper octaves. From my perspective, the question
isn't so much about the PX25 being the perfect amplifier, but rather it is
about nailing down the perfect system.
To be sure, the PX25 is not a perfect amplifier. If
falters a bit in negotiating the bass range. The deep bass lacks the
extension and punch afforded by the Volksamp Aleph 30. Performance
relative to the Aleph 30 improves as we climb the frequency ladder though
the mid and upper bass bands. Still, the PX25 lacks the Aleph's iron hand
control in dishing out bass detail. Bass territory is Aleph country. With
its current drive it simply bulldozes over the PX25. Yet, relative to
other SET amps, the PX25 rates highly. It is especially adept in
reproducing the full majesty of a cello.
Note that a majority of my listening is based on substituting the Philips Bugle Boy 6922 for the stock
Tungsram NOS provided by the factory. In all honesty, the Tungsram is not
the cleanest sounding 6922 to grace this planet. The Philips Bugle Boy
really does bridge the gap between the PX25 and the sound of a good 2A3 in
terms of midrange clarity and incisiveness.
Conclusion
Would you like to look and feel 10 to 20 years younger?
Would you be interested in increasing energy levels by 84%? How about
Increasing Sexual Potency Frequency by 75%? Would you like to increase
your Muscle Strength by 88% while... at the same time... reducing Body Fat
by 72% and Wrinkles by 51%? Well, guess what, the Art Audio PX25 can't do
all that for you (try Human Growth Hormone instead). But it can absolutely
transform your musical experience in the home - providing you choose a
mating loudspeaker carefully. Life is presently good: I'm having the time
of my life driving it into the Lowther BassZilla. In the realm of
low-power SET amps, it represents an essential audition for anyone with
access to a high-efficiency loudspeaker.
Kudos to the Art Audio design team, Joe Fratus, Tom Willis
and David Gill, who invested 17 months in perfecting this design. The
audio G-ds are very pleased. At last, a sublime auditory delight without
sticker shock! And finally, a word of thanks is also appropriate to KR
Enterprise's Riccardo Kron for keeping the flame and spirit of the PX25
alive.
Specifications
Power Output: 6 wpc
THD: less than 1%
S/N Ratio: >85dB
Output Impedance taps: 4 and 8 Ohm
Input Sensitivity : 400mV
Input Impedance: 180 kOhm
Frequency Response: 10Hz to 20kHz (+/- 0.5dB)
Weight : 60 lbs.
US Retail: $6,500 ($6,000 w/black chassis & chrome
plated accents; $200 additional w/volume control)
Company Information
Art Audio
34 Briarwood Road
Cranston, Rhode Island 02920
Voice: (401) 826-8286
E-mail: vze572mh@verizon.net
Website: www.artaudio.com