Accuphase DP-55

The processor section uses the MMB principle to achieve outstanding conversion precision. Three specially selected 20-bit D/A converters are operating in parallel, resulting in excellent linearity, mini-mum THD, wide dynamic range, and impeccable signal-to-noise ratio. Since the DP-55 provides access to the internal converter via a set of digital inputs, its top-level sound quality and performance potential can be tapped also by external components capable of supplying a digital signal. What's more, the also provides a set of digital outputs, allowing connection of digital recorders such as DAT or MD units, for direct digital recording of supreme quality.

The CD transport section uses fully digital circuitry for control of all actuators and mechanical functions. This allows optimization of servo parameters for each individual disc as it is being played, resulting in stable operation and a drastic reduction of read-out errors. The laser pickup is an ultra-compact type with integrated RF amplifier, and all actuators are driven by balanced circuits which do not conduct any current to the ground line. A tray lock feature firmly secures the tray during playback, and the entire CD mechanism is mounted on a metal chassis of high rigidity, designed to minimize any vibrations that may arise during playback. In this way, the DP-55 covers every electrical as well as mechanical aspect to assure highly precise readout of the digital signal. A digital level control and balanced output circuitry are further advantages for optimum sound.

As can be seen from the illustration, the high-speed output of an 8-times oversampling digital filter is connected in parallel to the individual converters. Immediately after D/A conversion, the output of the converters is combined while still in high-speed form. Thus, rather than simply linking the converter elements in parallel, the MMB circuit drives each converter separately, so that it can develop its full potential. Special attention was paid to phase response at high frequencies. Parts selection, layout and wiring patterns were optimized to achieve perfect phase matching. The end result is performance which sets new standards regarding linearity and absence of distortion and noise.

An important characteristic of the MMB principle is the fact that it improves performance regardless of signal level and frequency. The converter therefore maintains excellent linearity even at extremely low levels that present insurmountable problems for conventional converter designs. The audible advantages are immediately apparent as more precise localization of sound sources and a heightened sense of space and ambiance. As illustrated by the performance chart, linearity of digital input vs. analog output is maintained from the highest signal level down to levels as low as -l10 dB.