POWER AMPLIFIER

Stereo power amplifier. Rated at 250W/8ohm
Made by: Constellation Audio, Newbury Park, CA, USA
Supplied by: Absolute Sounds LtdTelephone: 0208 971 3909
Web: www.constellationaudio.com; www.absolutesounds.com
Price: £54,998

Constellation Centaur II Stereo

LEFT: Pressing thebar on its left side
initiates a series ofself-diagnosis checks.
Once ready, the LED
switches from orange
to flashing green, toblue. The cabinet’s
dimpled finish is bothsuperb and resilient
but the limited heightof the rubber feetmakes it difficult toachieve a handhold

Available in both monoblock and stereo chassis, the Centaur II has been a mainstay of
the Constellation range for over six years. It’s clearly not broken, so why change it?
Review: Andrew Everard Lab: Paul MillerWhile some brands maintain asteady rotation – evolution– of their products, others,
including Constellation
Audio, hit on the jackpot early and feellittle inclination to change a winning
formula. So while we’ve already tested the£73,500 Centaur II 500 power amp [HFN
Dec ’19] we missed out on the £53,998
Constellation Centaur II Stereo. Until now...
The Centaur II Stereo remains themost affordable amp in the Californiancompany’s Performance Centaur lineup,
which also includes the Centaur II Mono
power amp, available at the same price permono chassis. It’s all part of Constellation’s
modular approach to amplifier design:
take the same basic chassis and juggle
with the proprietary N-type amp modules
and power supplies [see PM’s boxout, p67]
and you have a whole range of options. It
has done this not with a full-time, in-houseengineering operation, but by calling on
what it describes as ‘a “dream team” ofworld-renowned engineers and designers’[see HFN Jul ’13].

trickier by the lack of anything to get apurchase on while shifting it. The company
counsels against using the wide front
panel switch as a place to grip, insteadsuggesting it’s lifted by getting one’s hands
underneath. The feet are wide but shallow,
and the gap beneath isminimal, so you’ll also need
protective gloves before
squeezing your fingers
under the edges of thosewell-ventilated side cheeks.
Custom speaker cableconnections are included
at the rear of the dimpledcasework [see p69]. Large screw-down
inserts will clamp both cables and spadelugs in place or, if removed altogether,
reveal 4mm sockets hidden within thatwill accommodate banana-terminatedcables. For those who prefer to bi-wiretheir speakers, you’ll need to connect both

No lightweightAs Constellation puts it, ‘Instead of forcing
our engineers outside their areas ofexpertise when new technologies comealong, we seek out designers who havealready mastered those technologies.
Our team approach also prevents us frombeing mired in any one engineer’s pet
technology’. Both the Centaur II Stereo andMono models deliver well in excess of theirclaimed 250W/8ohm [see PM’s Lab Report,p69], just as the Centaur II 500 busts
through its rated 500W/8ohm ceiling.
This may be the basic model in thecurrent Performance Centaur lineup, but
in no respect is it a lightweight. At around46.7kg it’s deep into ‘two-person lift’
territory, and the job’s made somewhat
RIGHT: FETs throughout – Constellation’s J-FET
voltage gain stage [screened, far right] feeds
the eight pairs of N-channel MOSFET powerdevices in each channel’s balanced power amp
configuration [on heatsinks, top and bottom]

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sets of cables to the single pair of terminals
provided for each channel.
The Centaur II Stereo’s inputs are moreversatile with XLR and unbalanced RCA
connections and a choice of high or lowgain. The latter are designated ‘Balanced’and ‘Direct’, respectively(although in practice both
XLR inputs are balanced);the lower gain ‘Direct’connection is intended foruse with Constellation’sown Virgo, Altair orInspiration 1.0 preamps.
This connection, says thecompany, ‘forms the Constellation Direct– an audio interface that is, in essence,
perfectly balanced. The positive- andnegative-going halves of the signal will
exhibit near-zero difference except for theirpolarity’. Again, as PM notes in his boxout[p67], the Direct position’s lower gain is‘Brian May’s
celebrated Red
Special wasunleashed’

achieved by removing an input J-FET stage[pictured, below] from the signal path.
Selection between input modes is via arear-panel toggle, Constellation making it
clear that using the unbalanced RCA inputs
is a matter of ‘only if you really must’, andthat balanced connections are preferred.
An additional switch on the rear enables ordisables the front-panel mute button, while
there are also connections for 12V trigger
control, or custom installation integration
via an RS232 port or USB-B.
With all the connections in place, firing
up the Centaur II Stereo is a matter offlipping the master power switch at therear, at which point an orange LED willshow on the front-panel control bar. Press
and hold this fascia bar for around threeseconds and the LED will flash green fora minute or so while the amp warms up,then turn a solid blue. Tap the bar and theamp mutes, with a flashing blue tell-tale,
while another three-second press will shutit down into standby, after a minute or soof flashing orange in cool-down mode.

Easy does it
And that’s about it: there’s nothing tweaky
or fiddly about the Centaur II, but rather
an innate feeling of fuss-free operationand just getting
on with the jobQUASI-COMPLEMENTARY
All Constellation amplifiers share a novel circuit ‘concept’– a 125W/8ohm power module employing N-type
MOSFETs in a single-ended configuration. Constellation’sbalanced/bridged topology sees one set of modules
handling the negative-going portion of the audio signal,
the other the positive, both with their own power supply.
Constellation posits that these N-type FETs deliver better
symmetry than ‘matched’ N- and P-type devices mightachieve in a conventional complementary circuit. Inside
the Centaur II Stereo there are two pairs of these 125W
modules per channel, delivering rather more than therated 2x250W/8ohm [see Lab Report, p69], and driven
either directly or via a balanced J-FET input stage [see inset shot].
The latter adds a further +14dB gain to the amplifier, bringing the total to+26dB, and while it may seem counterintuitive, the subjective performance ofthe Centaur II Stereo is often preferable with this extra stage in tow. Why? The
partnering preamp will necessarily run at lower gain and the J-FET stage may
arguably provide better balanced ‘signal conditioning’ before the audio signal
hits those N-channel modules. There are measurable differences too – distortion
is 0.007-0.027% in Balanced mode but increases to 0.01-0.05% in Direct Mode(all 20Hz-20kHz at 10W/8ohm). On the other hand there’s a huge improvementin A-wtd S/N from 87.1dB (Balanced) to 99.1dB (Direct) simply as a function ofbypassing the J-FET input stage. Which will you prefer? PMat hand. It’s something the HFN team has
experienced at length while using otherCentaur amplifiers in PM’s listening room,
where they’re employed as a reference fed
from a dCS Vivaldi One APEX player/DAC,
which also acts as the system preamp.
As those Constellation Audio models
have proved over time, they fully live
up to the instruction manual’s claimthat ‘the Centaur II produces sufficient
voltage and current to drive practically
any loudspeaker made, regardless of thespeaker’s impedance, sensitivity or power
rating’. Indeed, it’s likely your speakers will
give up the fightlong before thisamplifier runs outof ability to drive
loud and clean.
And while theCentaur II Stereo
is very much thejunior model inthe range, theprodigious power
PM notes in hisLab Report [p69]means it will
deliver all thatmost users will
ever need. Evenbetter, this performance comes from a(relatively) compact design – well, at leastby comparison with some more obviously
massive super-amplifiers.
In other words, this is very much a‘rational choice’ amplifier, as it has proved
with a range of speakers over the last
few months – including DALI’s KORE [HFN
Dec ’22] and the Audiovector R 8 Arreté
floorstanders reviewed this issue [p46].
Arguably the Centaur II’s key quality is
its absence of a ‘sound’. It refrains fromwww.hifinews.co.uk | Reprinted from Hi-Fi News for global distribution

Lab
reportConstellation Centaur II

ABOVE: There are two balanced (XLR) inputs per channel – one high gain, the other‘Direct’ lower gain [see boxout, p67] – and one single-ended (RCA) input, selected by asmall toggle switch. The beefy speaker cable terminals are best suited to spades

imposing any of its own character on
the music, making it simple to hear
what the speakers are doing andletting the music breathe. Does thatmake it soulless? No, because all
the spirit and drama of what’s being
played shines through.

Iron fist, velvet glove
With one of my favourite testpieces, the Kansas City Symphony/
Michael Stern recording of Britten’s‘Young Person’s Guide...’ [Britten’sOrchestra; Reference Recordings
RR-120SACD], the Centaur II easily
conveyed the tonalities of eachsection of the ensemble. There
were delicate touches of woodwind
and riotously blaring brass, and theclosing fugue climaxed as the Purcell
theme re-emerged triumphantly.
It’s a subtle yet marvellous sound,sufficient to have the listener sittingin silence as the last note fades.
Effortlessly dramatic, yet so goodat the ‘iron fist in a velvet glove’thing, the Centaur II is at homewith the gentle jazz of the Espen
Eriksen Trio’s In The Mountains[Rune Grammofon RCD2227]. The
measured playing of piano, drums
and bass were perfectly offset by thebreathy tonality of Andy Sheppard’ssax, each instrument given real
weight and definition.
With the good-time boogie ofStatus Quo’s 2022 re-recording of‘Caroline’ [Quo’ing In – The BestOf The Noughties; Ear Music/Edel0218192EMU], the amp delivered
just the right kind of ‘turn it up
to 11’ joyous power. Meanwhile,
the acoustic version of anothertrack, ‘Down Down’, took on a real
rockabilly feel as the Centaur II
powered it out from the speakers.
Audiophile music? Why bother when
you can have this much fun!

The same goes with the lavish
remastered set of Queen’s The
Miracle [EMI 00602508911330].
Bob Ludwig’s overhaul of thealbum sounds magnificent, fromthe drive of ‘Breakthrough’ to thefunk of ‘The Invisible Man’, and via
Constellation’s amp, Roger Taylor’s
drums sounded punchy, big and rich,John Deacon’s bass bubbled away,
and Brian May’s celebrated Red
Special was unleashed in shards of
screaming solo. As I realised having
sat through most of the boxset,
this is no analytical amplifier, eventhough it has served that purpose
well – it’s also a complete blast
when you just want to kick back andplay some favourite music.
Does that sound like the ideal
amp? I reckon so: not only can it doall the clever hi-fi stuff, it also always
remains a consistently enjoyable
listen. Even when running hard it
stays physically cool and sounds likeit’s well within its capabilities. Orto put it another way, the Centaur
II is always ready to give even moreshould you want it!

Taken at face value, the ‘250W’ Centaur II Stereo should be half
the amplifier that the Centaur II 500 [HFN Dec ’19] representsbut, in practice, the ‘little brother’ punches very close to its
slightly newer sibling. Let’s compare the figures: the ‘500W’Centaur II 500 delivers 2x585W/8ohm and 2x930W/4ohm,
boosted under dynamic conditions to 685W, 1.25kW and1.69kW into 8, 4 and 2ohm but ‘limited’ to 880W (or 29.7A)
into 1ohm. The original Centaur power amp [HFN Jul ’13] offered
2x510W/8ohm and 2x825W/4ohm with 570W, 1.06kW, 1.93kW
and a full 3.01kW (54.9A) into 8, 4, 2 and 1ohm under dynamic
conditions. The Centaur II Stereo smashes its 250W rating with2x400W/8ohm and 2x675W/4ohm, increasing to 425W, 780W,1.26kW and 856W (29.3A) into 8, 4, 2 and 1ohm under dynamicconditions [see Graph 1, below]. So, in practice, the Centaur
II loses nothing to the Centaur II 500 in its ability to drive thelowest impedance loads.
The novel N-type power amp circuit is sufficiently stable
into any likely speaker load that no Zobel, or other filter
network, is fitted to the output. Output impedance is a very
uniform 0.032ohm (20Hz-5kHz) increasing gently thereafter to0.041ohm/20kHz while the response is super-flat and extended(±0.5dB from sub-1ohm to >100kHz). Stereo separation is an
excellent 115dB (1kHz) to 88dB (20kHz) and the 0dBW-rated
A-wtd S/N is 87.1dB (Balanced) and 99.1dB (Direct) where thegain(s) are +26dB and +12dB, respectively [see boxout, p67 formore]. The enriched bias keeps distortion below ~0.01% up toaround 70W/8ohm after which it increases to 0.015%/100W,0.05%/200W and 0.085% at the rated 250W (all 1kHz/8ohm). PM

ABOVE: Dynamic power output versus distortion into
8ohm (black trace), 4ohm (red), 2ohm (blue) and1ohm (green) speaker loads. Max. current is 29.3A

HI-FI NEWS VERDICTAll the amplifier you could everwant? With its assured yet often
breathtaking sound, clean lines
and massive speaker-driving
ability, the Centaur II Stereo is as
close to ideal as most of us are
ever going to get. It has power
to challenge the pricier Centaur
II 500 model, is entirely fuss-freein use, and always has more in
reserve to meet the demands ofyour speakers or over-enthusiastic
listening levels. Magnificent!

Sound Quality: 90%0-------- 100

ABOVE: Distortion versus frequency versus power
output (1W/8ohm, black; 10W, pink; 100W, red)

HI-FI NEWS SPECIFICATIONSPower output (<1% THD, 8/4ohm)

400W / 675W

Dynamic power (<1% THD, 8/4/2/1ohm)

425W / 780W / 1.26kW / 856W

Output imp. (20Hz–20kHz/100kHz)

0.031–0.040ohm / 0.12ohm

Freq. resp. (20Hz–20kHz/100kHz)+0.00dB to –0.04dB/–0.30dB

Input sensitivity (for 0dBW/250W)

1414mV / 2290mV (Balanced)

A-wtd S/N ratio (re. 0dBW/250W)

87.1dB / 111.0dB (Balanced)

Distortion (20Hz-20kHz, 10W/8ohm)

0.007–0.027% (Balanced)

Power consumption (Idle/Rated o/p)

140W / 945W (4W standby)

Dimensions (WHD) / Weight432x280x508mm / 44.5kg

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