Full review in Stereoplay magazine (Germany), Issue March 2007

Accuphase Class-A Stereo Power Amplifier A-45

Gentle Giantby Dalibor Beric

When Accuphase is about to launch a new power amplifier, be sure the entire
hi-fi world will be all ears! Stereoplay however was the first to audition thismajestic machine.
Accuphase: this name is certainly commanding everybody's respect as it stands formodel consistency, longevity and an always recognisable, very good sound. Yet it
may sometimes be overlooked that there is nevertheless innovative engineering tooin far Japan, where new ideas are masterly combined with tried and tested circuitdesigns. A nice example is the sophisticated Class-A technology in the recently
launched power amplifier A-45.
In this mode of operation a permanently flowing high bias current is taking
care that the transistors are always working in an optimum temperature range. The
advantage is, by nature, that much less distortions can be achieved if compared toother amplifiers operating in conventional AB mode, for instance, in which distortions
have to be compensated or reduced by the rather rigid means of negative feedback.
There is no denying the disadvantage of Class-A though, namely the fairly highenergy consumption and hence enhanced dissipation of heat, which eventuallyrequires a much more solid amplifier construction at comparable output power.
Since with any Accuphase solidity can be taken for granted, we were moreinterested in circuitry details, like for example the automatic function for controllingthe bias current in order to keep it totally stable and constant even when thesurrounding temperature is changing or the amplifier running hot.
This measure is said to improve the signal-to-noise ratio and with the same
goal in mind Accuphase also provided the A-45 with its proprietary "Multiple CircuitSumming" technology (MCS+). By employing fully balanced input stages Accuphasehas managed to kill two birds with one stone: firstly, MCS+ yields a substantiallybetter signal-to-noise ratio because the uncorrelated (random) noise of the parallel
circuits are partly deleting each other whereupon the (correlated) music signals arecleanly added in the end. Secondly, MCS+ is leading to perfect conditions for anyconnections. It's because in the A-45 there is not merely a balanced (XLR) input
behind which things are going the normal, i.e. unbalanced, way again. No, the twobalanced signals do encounter each their own circuitry up to the drivers for the MOSFET power transistors. This measure ensures that noise can be greatly reduced not
only in the input section but along the entire amplifying stages. Evidently, Accuphaseconsidered this worth the efforts including the doubled quantity of parts andcomponents required.
Very nice and practical is the input sensitivity selector on the front panel where
gain can be adjusted in four steps. This feature can be very useful indeed if the A-45

is to be combined with power amplifiers from other makers, or if an individual soundtuning is required when used for bi-amping. Provided a speaker system comes withthe possibility of having the midrange-tweeter frequencies and basses separated, twoA-45 amps could be employed and gain accordingly adapted for each range, as toyour liking.
An additional mode selector switch on the rear panel allows, among otheroptions, dual-mono operation (again with two A-45) whereupon both channels are
switched to the amp's left input jack (balanced or RCA). This configuration is ideal for
vertical bi-amping because any sound-deteriorating adapters can thus be avoided. In
this mode of operation each A-45 can drive the mid-high frequency and bass sections
separately, at each speaker that is. Horizontal bi-amping, for which one A-45 isdriving the mid-high frequency section of both speakers while the other A-45 is taking
care of the basses, is also possible yet this configuration would require altogether
four connection leads to the pre-amplifier.
The A-45 will enlighten you with an abundance of true sound colours
In our listening room the A-45 was hooked up to our "workhorse" Thiel
CS 2.4, yet in spite of it's not so voluptuous power rating at higher speaker
impedances, it was immediately clear that this amp does certainly not need any
backing whatsoever. Even at hefty dynamic attacks, like with Tosca's "Every Day And
Every Night" (Dehli 9, !K7), it was never forced to its knees.
Nevertheless, the A-45 really excelled when it came to painting sound colours
in all shadings you could think of. It was a real treat to have the Auryn Quartet playing"Beethoven's String Quartets op. 18, Nr. 1-6" (Tacet) bewitching us through this amp!
Eventually, the A-45 managed to convey this recording with a marvellously smooth
string sound whilst the instruments were positioned on a particularly large
soundstage.
In this respect the Accuphase even gave our tried and tested AMP mono
amplifiers a run for their money. Although the latter seemed a tad more powerful here
and there, they certainly could not compete with the sovereign, elegant and smooth
performance of the A-45. All this thanks to the sophisticated Class-A circuitry which isin fact offering the Accuphase-sound by square.