It brings me joy to review the Quad PA-One headphone amplifier (£1299, or around $1750 USD). The Quad PA-One is a stereo vacuum tube amplifier with 24-bit/192kHz DAC and two headphone plus analog preamplifier output. Unless you have been living on the moon for the last ten years or so, chances are you own at least a pair of headphones. Worst case scenario? You have the ear buds that were included with your cellphone. Normality these days? If you are an audiophile, or should I say a head-fier, then you probably have several cans for each occasion and musical genre. Given that you have a couple of headphones, or you are about to invest in your first pair after all the buzz surrounding personal fidelity, the next logical step is a dedicated headphone amplifier. Yes, because if you want to play this game the way it was intended to be, driving your cans with nothing but a cell phone or your laptops output won’t get you to headphone nirvana.
Yes, a headphone amplifier such as the Quad PA-One as reviewed here is in the order of the day. Or maybe you already have one. A solid-state design that has enough juice to spin your cans? Are you satisfied with what you get? Is it a pleasant sound, one that has "meat" and keeps you going for many hours without listening fatigue? Or maybe after a couple of your favorite records you need a brake to set your ears back to zero?
Headphones are more than just a trend, as we
speak they rule the audio industry along with high resolution music and vinyl
renaissance. Actually headphones go all along with hi-res audio as many of the
recent amplifiers come with built in DACs. The guys over at Quad, who make the Quad PA-One,
have read the
numbers. They have seen the light of personal fidelity and decided to produce
their first ever dedicated headphone amplifier. And though Quad makes a complete
line of solid state products under the "Elite" series if you ask friends who
have been around for a while they will tell you one thing only: Quad is a legend
in tube amplification. Now the "legend" thing has lost some of its value,
everybody who has been around in the audio industry for more than a decade
considers his company a legend. Legend this, legend that, legendary performance,
you name it- it has a "legend" written somewhere on the marketing brochure. Then
there is Quad, established by Peter Walker in 1936.
In 1936, as almost 90 years ago. Originally named S.P. Fidelity Sound Systems, then Acoustical Manufacturing Co. Ltd. the company initially developed public address systems. In 1941 the factory was bombed and Walker had to move production from London to Huntingdon. Then in 1950 the launch of the first "Quality Unit Amplifier Domestic" and the acronym Quad found its place in the company's consumer products. What definitely put them on the map were the ESL 57 electrostatic speakers and a series of tube amplifiers starting with the historic model "II".
The Looks Of A Legend
Underneath the big volume knob a sliding lever manages channel balance, a feature less and less found in today's electronics. Three led illuminated buttons offer input selection (one line, one balanced and one for the three digital options: USB, TosLink Optical and S/PDIF coaxial). A toggle switch helps selecting high or low headphone impedance with high being above 100 Ohms. Also on the front plate two 1⁄4 inch headphone jacks, with the PA-One being able to drive both contemporary with no noticeable effects on the power output.
On the back you will find one balanced input (pin 3 running "hot"), one line input and the single ended pre out along with the aforementioned digital inputs. Also on the back the power switch and IEC power inlet, all clean and tidy arranged.
The tubes are positioned in front of the
transformer's casing and consist of a pair of 6SL7 driving a pair of 6SN7 in
cathode feedback topology (no global feedback for the PA-One). Though both these
double triodes look similar and pin out is identical the gain provided is
different, so make sure not to swap them! Rectification is done by a single EZ81
and this makes the PA-One an all tube design with point to point wiring for the
valve section. The five tubes are nicely covered under a protective grill fixed
with four screws on the top plate. Quad provides a special, extra-long
screwdriver for removing the grid but I would suggest doing so only in case of
tube replacement. Output transformers are double C-core type made from
high permeability steel. Power output is specified as 500mW @ 32 Ohm.
Overall built quality is nice; in fact the PA-One gives impression of a solid piece of gear that will last for years. Packaging was typical for this price range, a carton box with sufficient ethafoam making sure nothing will happen during transportation. User manual is well written with lots of images that will walk you through the driver installation for the DAC section.
At the heart of Quad PA-One lays the well-known
Cirrus Logic CS4398 DAC chip capable of 24-bit/192kHz conversion as found on Quad's
Platinum player and guess what? The company promises minimum jitter and absolute
accuracy! In order to squeeze out as much performance as possible from the DAC
they have engineered the power supply section using four stages of regulator
circuit which should help to minimize the ripple of the DC line. High quality
capacitor such as Wima and Nichicon complete the promising package.
The Closest Approach To The Original
From the Canadian Cohen to the Irish artist Hozier and his single "Take Me To Church" [Columbia]. Dramatic interpretation expressed in an equally dramatic manner from the PA-One/ Audeze LCD-X combination despite the track being compressed. The Quad had no problem in resolution with Hozier's guitar always being well focused and providing the typical electroacoustic timbre. At the same time the PA-One managed to hide some of the nastier passages, taking away the edges from the recording but leaving all the "air" intact. For comparison reasons I used the similarly priced Burson Conductor (headphone amplifier and 24-bit/192kHz DAC) in the latest iteration with the CMedia receiver connected with a second identical USB cable to my PC. Switching the necessary drivers from Foobar's interface was rather fast and provided excellent ground for comparisons. The guitar sounded better through the Quad amplifier, maybe because of the instruments inherent distortion which matches the tube harmonics? Perceived soundstage was also wider and overall playback gave the impression of being alive, it simply sounded right to my ears.
For something more complex let me talk to you
about Ole Bull's Concerto Fantastico [2L -067-SABD]. Written in the middle of
the romantic era by this Norwegian Paganini and performed here by Annar Follesø
with Ole Kristian Ruud conducting the Norwegian Radio Orchestra, this is a
masterpiece of intimacy reflecting the Scandinavian character of the composer
with elements of lyric expression mixed with demanding technical passages.
Despite this recording being little to no compressed at all the PA-One managed
to drive the Audeze LCD-X cans with ease with the volume knob comfortably set
around 11 o'clock. Power output should be enough for all but the most demanding
headphones and even during bursts of energy coming from the Norwegian Radio
Orchestra there were no particular signs of stress coming from the tube
amplifier. The Burson provided a tighter grip on certain passages but this was
to be expected from the beefier solid state design. Macrodynamics were also
wider with the Aussie amplifier but the Quad performed in a more intimate and
touching manner, closely connecting the listener to the performers.
The "Serious" Audiophiles Do A
Couple Of Things
Besides tube rolling I remember reading that serious audiophiles use their headphone setups for vinyl playback too. Not sure if I candidate as one but resisting the way that balanced input was staring at me was beyond my forces. After plugging the ASR Basis Exclusive phono stage to the PA-One via Synergistic Research Element Copper balanced cables I reached for one of the latest entries in my collection, Liszt's Dante Symphony [HMV/MelodiyaSXLP 30234] with Boris Khaikin directing the Bolshoi Theater Orchestra and Chorus. This massive, earth shaking work will wreak havoc with many systems but the PA-One showed its full potential with no particular signs of congestion or hazy sound. Part of the merit should go to the LCD-Xs, the most capable headphone in the Audeze range when it comes down to transient response, treble and bass extension. Liszt demands a complete set of woodwind, string and percussion instruments in order to create the "Inferno" and the PA-One transmits this thunderous performance in a convincing way. The match exceeded my expectations as the tube warmth was palpable without ending up being too syrupy. Articulation was good rather than excellent with a slight coloration of the 3rd and 4th octave, still nothing major.
Last but not least among the PA-One's features is
the possibility of using it as a pre-amplifier and drive a power amplifier or
maybe a couple of active speakers directly. This is more of an added bonus for
potential buyers who are only now entering the high fidelity universe or maybe
for those who would like to taste what tube preamplification sounds like in
their systems. The headphone and 24-bit/192kHz DAC section alone are worth the
£1299 ticket and the wide connectivity options can only make this package even
Instead Of The Typical Conclusions
Equipment During Review
*The Self Noise category would easily become a 3.5 if the potential buyer substitutes the provided tubes with higher quality after market or NOS ones. An additional touch would be to use silicone tube damping rings. The votes reflect the PA-One's performance with stock tubes, half note should be added in bass, mid, high frequency, attack and inner resolution with the NOS tubes described in the review. Soundscape does not apply for headphone amplifiers.
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