Accuphase DP-75V CD player
The drive's fully digital high-technology control circuitry uses "adaptive" filters to optimize servo performance for each disc. The pickup uses a very compact RF amplifier directly integrated in the photodetector pickup assembly. Accuphase says that this reduces the error rate and ensures that the signal remains free from noise interference.
The motors and actuators for the disc tray, spindle, sled, and focusing/tracking assembly are driven by two amplifiers arranged in a balanced configuration---there's no current flowing in the ground line to pollute other circuits in the player.
Synchronizing the operation of the D/A converter with what Accuphase calls the Digital Audio Interface (DAI), a phase-locked loop (PLL) circuit generates a master clock for system reference. This "Ultra Jitter-Free" PLL consists of a "preamble detector" (K-10 has one of those!) and a voltage-controlled oscillator (VCO) using a quartz-crystal element. The master clock produced by the circuit is free from pulse distortion and jitter, Accuphase says. The input auto-detects and locks with any current digital format at 32, 44.1, 48, 88.2, 96, 176.4, 192kHz, and SACD's 2.8224MHz signals. The EIAJ CP-1201-compatible input is enabled on everything above 48kHz on option boards, and a "standard" pair of RCA coax and TosLink optical inputs sits on the rear panel, ready to convey all signals up to 48kHz.
Ah, the option boards. The DP-75V features computer-like rear-panel slots that support the Accuphase Digital Bus 2 (ADB 2) interface for next-generation formats like SACD and DVD-A. The DIO-OC1 board provides The DIO-OC1 board provides two sets of optical (ST) and coaxial connectors (BNC) for digital input/output. The DI-BNC1 board provides a coax input with a 75 ohm BNC connector. The DIO-ST1 is an input/output board with ST or other optical connections. The DIO-PRO1 input/output board provides a set of balanced XLR connectors for AES/EBU operation. The HS (High Speed) Link option board can be installed for use with the DP-100 SACD transport, and the EXT-DSP board services the very impressive DG-28 Digital Equalizer (reviewed by Steven Stone in the June 1998 Stereophile).
The heart of the system is the "revolutionary" MDS (Multiple Delta Sigma) 24-bit converter array. MDS employs six parallel delta-sigma converters per channel. These combine oversampling with noiseshaping that Accuphase describes as "a kind of digital feedback to project the amplitude information of the digital signal onto a time axis for precise conversion." The block diagram shows a format converter feeding identical signals to the converter arrays, their outputs summed before the low-pass filter. Thus the "difficult to contain" noise at very low signal levels of conventional delta-sigma converters can be "drastically" reduced, Accuphase claims.
Aliasing noise in the extreme upper frequencies is removed by a three-pole linear-phase-type analog filter with what are described as "outstanding" phase characteristics. The cutoff frequency, they say, is designed to minimize phase shift within the passband.