PREAMPLIFIER

Line preamplifier with transformer volume control
Made by: Aurorasound Inc, Japan
Supplied by: Pure Sound, UKTelephone: 01822 612449
Web: http://aurorasound.jp/english; www.puresound.info
Price: £8000

Aurorasound Preda
Strikingly individual in its approach, this meticulously-crafted, fully-balanced line
preamplifier from Japan promises pure enjoyment from digital sources
Review: Steve Harris Lab: Paul MillerOn the face of it, a line
preamplifier might seem theleast complicated componentof a hi-fi system, and of course
it should not add any character of its ownto the sound. But preamplifier design is far
from standardised and there is plenty ofscope for the ‘boutique’ builder who aims
for ultimate audio purity.
A case in point is Aurorasound, a fairly
new Japanese company with a fresh andinnovative approach. With the £8000
Preda, designer Shinobu Karaki has
included his own implementation of thetransformer volume control, a principle
that’s hitherto been associated mainly withthe most fanatically purist passive preamps.
Yet this is not Karaki’s first audiophilepreamp design. Aurorasound’s short history[see boxout] really began with his CADA
‘Control Amplifier for Digital Audio’, surely
the only commercial hi-fi product to havecombined archaic directly-heated triode
tubes (beloved of DIYers) with a modern
digital-to-analogue converter in the samechassis. Unfortunately, it proved difficult toget consistent supplies of the 3A5 tubes
used, and the CADA seems to have been
put on hold.
The Preda is quite different. It’s all
solid-state and, although it’s similarly
described as a ‘Preamplifier for Digital
Audio’, it doesn’t include a DAC. Butthe description is still logical in a sense,
because Aurorasound now caters foranalogue sources with its VIDA phono
stage [HFN Jul ’13]. Like the VIDA, the Preda
is modular in construction, and in fact uses
the same power-supply modules, one foreach channel. Another building block of
the design is a new ‘Aurora-AMP’ discrete
amplifier module, and six of these are usedin total.
But the main innovation is in the use ofa transformer attenuator for the volumecontrol, where taps on the secondary

RIGHT: Clearly a true dual-mono design, thePreda employs a ladder of relays that switch
across the 54 steps of its transformer-coupledvolume control. Inputs and outputs are buffered

Reprinted from Hi-Fi News | www.hifinews.co.uk

HFN_Oct Aurorasound Preda_Reprint.indd 58-59

winding of a transformer replace theresistors of a conventional stepped
attenuator. In the context of a passive
preamp, this approach can give a constant
input impedance and also overcome theresistor type’s disadvantage of increasing
output impedance at lower levels. A
currently-available Sowter transformer, forexample, covers a 50dB range in 2dB steps
when used with a suitable 26-position
rotary switch.

a few idiosyncracies
However, it’s far more unusual to see atransformer volume control used in an
active preamp, let alone a fully-balanced
design like the Preda. Aurorasound’s own
volume control module is apparently an
auto-transformer, where the primary andsecondary are formed by a single winding.
It offers 54 steps of 1dB, switched by UKmade Pickering glass-encapsulated relays

that are operated by external magnetic
fields. DC buffer amplifiers precede andfollow the volume control module, toprevent any interaction of source or loadcapacitance with the inductance of thetransformer. An instrumentation-typeamplifier is used for the XLR balanced
inputs, while the balanced outputs each go
through a final Aurora-AMP module.
Preda’s front panel controls are simple
enough. Two ‘endless’ rotary encoders
provide source select on the left andvolume on the right, with the settings ofeither indicated by the two-digit display inthe oval centre window.
Normally the display shows thevolume setting, nominally in dB, from 1
to a maximum of 54. When you touch
the source selector, the display shows thechosen input (1 to 4 for the unbalanced
line inputs, 5 or 6 for balanced) for a few
seconds only, before reverting. This isn’t

as convenient as a continuous display ofthe selected input, as you can find yourself
having to touch the control just to check
which one is active.
A small front-panel LED indicatesphase-invert, an option that’s provided
along with some extra facilities via thechunky, metal-bodied remote [see p61].
In a cross-shaped button
array, up and down arrow
keys control the volume
and a central button givesmuting, while the left
and right arrows alter thechannel balance.
These cause an LED tolight above the figuresin the display window, to left or right as
appropriate. When both LEDs are out, thebalance is at the centre position. Source
selection on the remote is by buttons
numbered 1 to 6, and there’s also a
display-off key.
Aurorasound isn’t the first company toplace the power switch underneath thefront panel, but there’s another switch next
to it for ‘gain select’. Pressing this cuts thepreamp’s overall gain by 6dB, while an LED
indicates this with a patch of green lightunder the unit. Most preamplifiers allow

you to fade the volume down smoothly
into silence, but with the Preda in normal
mode the lowest level, ‘1’, may still be too
loud in some circumstances. Hence theLow gain option, described as ‘convenient
for midnight listening by using highsensitivity speakers’. But some users may
still find that the volume can’t be lowered
enough for listening
quietly into the night.
On the back of theunit, reflecting the dualmono layout inside, aresets of balanced (XLR)
and unbalanced (RCAphono) inputs, plus one
unbalanced and one
balanced output socket for each channel.
Balanced and unbalanced outputs areavailable simultaneously.

‘“The Sad Cafe”
was infusedwith a timelessmelancholy’little details revealed
For the listening sessions I settled downon my usual sofa [see www.hifinews.
co.uk/news/article/meet-the-team;-steveharris/9911], but with some different
components. I used a Bryston 4BSST
balanced stereo power amplifier kindly
loaned by Unilet, with balanced cables byVan Damme. For unbalanced operation,a rising AURora
Osaka-born but now based in Yokohama, Shinobu Karaki played guitar in rockbands at high school and university and built his own first RIAA phono equaliser
at the age of 15. He joined Texas Instruments Japan in 1980, eventually
becoming Digital Audio Group business director. Taking early retirement fromTI in 2009, he then pursued his interest in audio, initially building power amps,
DACs and switching boxes for local audiophiles and shops. Then in 2011 camehis unusual Aurorasound CADA, a tube preamp with built-in DAC, and theAurorasound HiFace Pro D/D converter, a ‘tuned up’ version of M2Tech’s HiFace.
For 2012, Shinobu added BusPower-Pro, a clean power supply for USB devices,
and introduced the VIDA phono stage. In 2013, he established Aurorasound Inc
as a limited company. Shinobu now runs the business out of a new workshop andlistening room, helped by his wife and two engineers working on contract.

ABOVE: With rotary controls for source selectand volume, both power-on and high/low gain
switches are tucked away underneath the unit.
The display shows selected settings and gain

I used Vertere Pulse B interconnects.
Speakers were the B&W CM10s.
I decided that the balanced connection
was better, but it was a very close-run
thing. On Wynton Marsalis’s Selections
From The Village Vanguard Box [Columbia
CK62191], when the trumpeter banteringly
asks the time, you could hear just a bit
more clearly the audience members’
replies. On ‘Easy To Love,’ the opener from
Patricia Barber’s The Cole Porter Mix [BlueNote 50999 5 01468 2 6], there was just abit more texture to the voice, and a slightlyclearer perspective to all the instruments.
After this, I continued listening using
the balanced format. On track after track
and with CD after CD, I was arrested by
the preamp’s ability to reveal little details
that had gone unnoticed before. One
example was the subtler bits of percussionin Gwyneth Herbert’s ‘Perfect Fit (Original)’from Clangers And Mash [NaimEdge naim
CD137]. While the handclaps soundednotably fleshy and real, the little rhythmic
finger taps now also had shape and reality,
instead of disappearing in the mix.
An indicator of the quality of acomponent is how well it can reveal thesubtleties of the production on a CD track.
June Tabor’s wonderful rendition of ‘TheLads In Their Hundreds’ from Quercus [ECM372 4555] was recorded live at The Anvil inBasingstoke in early 2006. But it was mixed
for release at the Rainbow Studio in Oslo by
Jan Erik Kongshaug and label boss Manfred
Eicher, and with the Preda I felt I could
almost see the way they had overlaid The
Anvil’s ambience with the ‘ECM sound’.
With a very different kind of threesome,the Tori Freestone Trio and In The ChopHouse [Whirlwind Recordings WR4648],
www.hifinews.co.uk | Reprinted from Hi-Fi News

10/9/14 14:47:41

Labreport
PREAMPLIFIER

Aurorasound Preda

ABOVE: Rear panel reflects its dual-mono internal layout. Each channel has twobalanced and four unbalanced inputs, with one balanced and one unbalanced output

the music really came alive in all its
rhythmic complexity and precision.
Freestone’s brilliant harmonic sensemeans that you never feel theabsence of a chordal instrument,
and with the Preda the sheer beautyand honesty of her saxophone soundwas more compelling than ever.
Listening to some archetypal
1970s rock recordings showedthat the Preda could convey great
dynamics while remaining poised
and unruffled, never sounding edgy
or untidy. On Dylan’s Blood On The
Tracks [Columbia 512350 6] itsclarity allowed you to appreciate
every instrumental contribution as
the band maintained that oom-pahrhythm throughout ‘Lily, Rosemary
And The Jack Of Hearts.’ On ‘Simple
Twist Of Fate’ the acoustic guitars
had body, feeling and dynamic
subtlety as they ebbed and surged
to accompany the twists of the tale.

real transparencyAnd the Preda was reallyimperturbable on more modern
recordings too. When I cranked up
the volume and put on Kings Of Leon
with ‘The End’ from Come Around
Sundown [Sony 88697782412], thedrum sound was truly gigantic andCaleb Followill’s groaning vocal wasmonolithic, with the fractured pianothat winds things down at the end a
perfect contrast.
Turning to classical music, thePreda could maintain clarity andsparkle even with the heaviest oforchestral textures. On the LSO’s
2003 Barbican recording of Brahms
Symphony No 1 with Bernard Haitink[LSO Live LSO0045], the huge soundof the opening movement was freeof that deadening opacity thatcomes in many systems from a lackof detail, and moved forward likethe sea.
Moving on to hi-res sources, I
used the Preda with a Chord Hugo
DAC to replay files from a MacBook
via iTunes and Pure Music. Here it
offered a real transparency, withthe feeling that you really werehearing the source unsullied anduncompromised. On Tim Hugh’srecording of the Kodály solo Cello
Sonata, from Hands On Heart [Naim],
there was nothing to get in the wayof the intensity of the music, thecello sounding superbly rich andsonorous in the supportive acousticof Wigmore Hall.
With Rimsky-Korsakov’s ‘Danceof the Tumblers’, the Minnesota
orchestra sited comfortably in theacoustic of the hall, the percussion
had a truly live and free breathing
quality. Among other tracks fromthe same HDtracks sampler, Bach’s
Violin Concerto BWV1041, playedby Anne Akiko Meyers, had a lovely,
unforced delicacy to the stringsounds, while J D Souther’s ‘The Sad
Cafe’ was grippingly infused withtimeless melancholy and regret. Atruly communicative sound.

Aurorasound’s proprietary 54-step transformer-coupled volumecontrol operates over a (limited) 50dB dynamic range inrough 1dB steps although the usable scope of the control issupplemented by the Preda’s ‘Standard’ and ‘Low’ gain setting.
Tested in balanced mode and switched via the green button
under the fascia, ‘Standard’ offers a maximum +13.4dB gain(a volume range of –36.5dB to +13.4dB) and ‘Low’ –0.5dB (arange of –52.1dB to –0.5dB). The Preda offers substantial input
and output overload margins – in excess of 10Vrms and 25Vrms
respectively via the balanced XLRs, the latter via a 46ohm
source impedance – so it has the headroom to cope with anyline level source with the output swing to drive any likely
power amplifier.
Importantly, because the stepped-transformer volume
control is correctly buffered, the Preda’s input and output
impedance remains constant as does its frequency (andphase) response [see Graph 1], the former gently tailored to–0.38dB/20kHz rising to show a hint of presence emphasis(+0.03dB/1kHz-10kHz). Distortion is very low indeed above500Hz, falling to a consistent 0.0008% right up to 20kHz. The
transformer causes an increase in THD at bass frequencies –from 0.01%/100Hz and 0.1%/20Hz to 1.9%/5Hz [see Graph 2,below], in line with the tailored LF response [Graph 1]. Noise,
too, is a little higher than with competing preamps as a very
low-level carpet of 50Hz harmonics spreads through midrange
and treble. However, an A-wtd S/N ratio of 95dB (re. 0dBV) is
still perfectly acceptable (105dB+ is state-of-the-art). Readers
are invited to view a comprehensive QC Suite test report for
the Aurorasound Preda preamplifier by navigating to www.
hifinews.co.uk and clicking on the red ‘download’ button. PMABOVE: Extended frequency response (1Hz-100kHz)
at 0dBV/60kohm via balanced input/output

HI-FI NEWS VERDICTNo ordinary preamp, to say theleast, the Preda seems to reflect
its designer’s long experience inmodern commercial electronics
as well as his lifelong audiophilequest. It’s somewhat idiosyncratic
in styling and ergonomics, and so
it may not be for everyone. But
sonically, it can be revelatory,excelling at portraying therealism of vocal textures, forexample, which makes the music
expressive. It must be heard.

Sound Quality: 86%0-------- 100

ABOVE: Distortion versus extended frequency from
5Hz-40kHz at 0dBV (left, black; right, red)

HI-FI NEWS SPECIFICATIONS
Maximum output (<1% THD, 47kohm)>25Vrms (Balanced)

Maximum input level (<1% THD)

>10Vrms (Balanced)

Output impedance (20Hz–20kHz)

46ohm (Balanced)

Frequency response (20Hz–100kHz)–0.38dB to –1.27dB

Input sensitivity

213mV (Standard gain setting)A-wtd S/N ratio (re. 0dBV)

94.9dB

Distortion (20Hz-20kHz re. 0dBV)

0.00078–0.093%

Power consumption

28W

Dimensions (WHD) / Weight

420x90x330mm / 10.8kg

www.hifinews.co.uk | Reprinted from Hi-Fi NewsHFN_Oct Aurorasound Preda_Reprint.indd 61

10/9/14 14:47:42