The
Azur 851E preamp and the Azur 851W power amp from Cambridge Audio
Crossover displacement
Class A is the sledgehammer approach to
eliminating crossover distortion, which is caused by the music signal crossing
from positive to negative-going (or vice- versa) and transistors momentarily
switching off. In Class A the complementary pairs of output transistors always
have sufficient standing current to ensure they remain conducting at all times,
but the implementation is costly. Cambridge’s elegant Class XD alternative
doesn’t eliminate crossover distortion, it shifts it away from the
zero-crossing point of the waveform – hence the name ‘Crossover Displacement’
or XD. Class XD tracks the audio signal and applies a negative bias current,
offsetting the position of the crossover point without creating a DC offset. At
low signal levels the crossover point is shifted below the maximum negative
swing of the audio waveform, yielding all the benefits of pure Class A. At
higher signal levels the offset crossover point falls within the negative cycle
of the music waveform – there’s the same number of ‘transitions’ but the nature
of the distortion is more easily accommodated by negative feedback.
Cambridge
Audio Azur 851W - Front
Soundstage focus
When driving my reference Audiovector Mi 3
Signature floorstanders with a 44.1kHz/16-bit FLAC rip of Jon Strong’s Follow
Me, via my Audiolab M-DAC plumbed into the 851E’s balanced
input, I was immediately struck by the Cambridge amps’ expansive soundstage. The
opening guitar strums of ‘The Judas Kiss’ rang out from well wide of my left
speaker and really caught my ear as they resonated with such energy, before
falling away with natural decay. Likewise, as the song progressed, the way these
amps allowed the drummer’s cymbal crashes to wash across the soundstage was equally
striking, and I had the sense that the 851W was having no problems ‘opening up’
my speakers.
But it’s not just soundstage width that these
amps have the measure of, it’s how they evenly populate the sonic space they create,
well able to control the music under their command. There are many amps that
can grab your attention with their cavernous sonic landscapes, but I often find
that instruments heard at the soundstage’s boundaries can seem a little lost
and acoustically thin, with less body than those placed centre stage.
Thankfully this is not the case with the Cambridge combo, and whether presented
far afield or between the speakers, each instrument’s sound is equally
wholesome.
Stereo imaging is yet another key area
where these amps score well. Kristin Hersh’s track ‘Your Ghost’ from her Hips
And Makers CD [4AD CAD 4002] allowed the amps to really take control of
proceedings and make the speakers virtually disappear, as they brought
Kristin’s maudlin vocals to life in my room. What’s notable on this and other
material is how these amps manage to make voices sound clean and clear, without
making them too clinical or over-exposed.
Cambridge
Audio Azur 851E - Front
And the Cambridge Audio 851s impart very
little of their own character on the music and nor do they overtly favour any
particular musical genre. They pack lots of detail into the music, but they
don’t come out ‘all guns blazing’ with it: instead the amps sound confident yet
unstressed, no matter how demanding the music and its volume levels become.
