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Review in AUDIO magazine (Germany), March 2006
Accuphase Integrated Amplifier E-550

Precision Job by Joachim Pfeiffer

The biggest and dearest integrated amplifier by Accuphase tested exclusively in AUDIO.
Not really a big surprise on the first sight. The new integrated flagship from
Accuphase, the E-550, comes just slightly higher and a tad less wider than its already legendary predecessor E-530. The formerly rather matt side-cheeks are showing high-gloss now, and - I'm sure you'll be pleased to read this - its retail price has come down by an enjoyable margin! Well, the new model does not look really new and the old one not really old. So, what? Just a barely noticeable facelift?
You've done the wrong pools! This Accuphase-flagship operating in Class-A
mode boasts - to stay in the picture - of its new "engine" of which the key feature is without doubt the highly elaborate volume control circuitry dubbed AAVA (Accuphase
Analogue Vari-gain Amplifier). This is something that to this date had been reserved exclusively for the top-of-the-line and much more expensive preamplifiers from the same maker. Now, what's behind and how can the user take benefit of all this?
In conventional amplifiers, i.e. in the E-530 also, potentiometers are taking care of the volume control. Evidently, by turning the knob clockwise the music becomes louder and likewise is attenuated if the knob is turned to the left. And no matter how elaborate a potentiometer has been constructed and built there are nevertheless inherent weaknesses by principle. To wit: impedance is always increasing when the output level is increased which in turn is causing a higher noise floor. And even worse: channel imbalances as well as crosstalk between channels may spoil the listening pleasure, in particular when the potentiometer is in a position between 8 and 9 o'clock respectively beyond 11 o'clock and therefore in ranges below and distinctly above the average room volume level.
AAVA - the electronic trick
Fighting this root of all evil has ever since been put on top of the agenda by the Accuphase engineers: they simply made use of the best potentiometers on the market and consciously refrained from employing digital regulators which are (rightly so) said to rob the sound colour and resolution.
The analogue AAVA circuitry was designed to regulate the signal from soft to loud with absolutely no losses. The input signal first meets an array of 16 parallel voltage/current converters which are transforming the signal voltage into differently sized "current-figures" whereby from one to the next the transformation ratio is downsized by one half. The resulting current portions can be combined in any way, yet the switching operation is controlled by a CPU according to the position of the volume control knob. Altogether there are 216 or 65,365 combinations possible.

At first the voltage of the input signal is via AAVA converted into a signal current whereupon gain is set by a turn of the volume knob. Finally, the combined current is converted back into a signal voltage. This elaborate measure is to alter neither frequency response nor impedance and therefore has also no influence on the noise.
That AAVA makes sense indeed could be confirmed in the many listening sessions in which the E-550 had to mount the boxing ring versus it predecessor.
Albeit not so clearly in the classic test configuration, in which both candidates could