Compact Disc Player DP-75

Front view of DP-75

The ultimate CD transport/processor system in a single body:MMB type D/A converter, ultra jitter-free PLL circuit, high-precision sampling frequency converter. Fully digital CD mechanism control allows optimization of servo performance.

The DP-75 incorporates a wealth of technology originally developed for top-of-the-line separate-type CD reproduction systems. Rather than calling it a CD player, it therefore can be justly called a CD Transport/Processor System. It offers all the advantages of separate components, conveniently housed in a single enclosure.
The D/A converter in the processor section uses the amazingly precise MMB principle which delivers performance pushing physical limits. This converter system stands at the pinnacle of the multi-bit universe. It is complemented by the Ultra Jitter-Free PLL Circuit developed by Accuphase and a high-precision Sampling Frequency Converter (SFC). Pulse distortion and jitter are virtually absentAassuring absolutely faithful conversion of the input signal. To allow use of this ultimate D/A conversion system also with external components, the DP-75 provides versatile digital input and output facilities. The unit therefore can function as a digital control center which enhances the sound quality of the entire system.
The CD transport side of the DP-75 is impressive as well. For example, it uses fully digital circuits for mechanism control. This allows optimizing servo Performance for each individual disc, assuring improved operation stability and a drastic reduction in error rate. 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 tine. The tray lock feature firmly secures the tray during playback, to maintain the high purity of the digital signal.

MMB Type D/A Converter Takes 20-Bit Linearity and Low Noise Performance to New Limits

The D/A converter uses the amazing MMB (Multiple Multi-Bit)principle which delivers performance and sound quality previously unattainable. It consists of eight strictly selected 20-bit D/A converters connected in parallel_ This revolutionary approach yields a dramatic improvement in every important performance aspect.

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. But 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 devoted 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.

The operation of the D/A converter must be Synchronized with the digital audio interface (DAI) signal. For this purpose, a phase-locked loop (PLL) circuit generates a master clock which is used as system reference. It jitter or pulse distortion are present, the master clock precision will suffer, which has a detrimental effect on the entire system.
The Ultra Jitter-Free PLL circuit in the DP-75 consists of a preamble detector and a voltage-controlled oscillator (VCO) using a quartz crystal element. Pulse distortion occurs when the signal fluctuates randomly in the intervals between "0" and "1". But the so-called preamble signal (which indicates the start of the L and R signals) occurs in regular intervals at a constant level.
It is not subject to the effects of pulse distortion. Therefore the DP-75 uses a detector which extracts the preamble component from the DAI signal and supplies it to the PLL circuit, for elimination of pulse distortion. The VCO uses a quartz crystal oscillator element with a very narrow locking range and optimized loop filter constant, to remove any jitter components from the preamble signal.

A sampling frequency converter (SFC) serves to transform the sampling frequency of a digital input signal to a different value. In the DP-75, the sampling frequency is converted to 48 kHz, resulting in a 48kHz, 20-bit, level 1 signal for decoding. The highly precise quartz oscillator used for conversion assures jitter-free performance. By transforming the sampling frequency of every input signal to the highest level, optimum D/A converter operation is always assured, allowing the outstanding D/A conversion system in the DP-75 to develop its full performance potential.

The DP-75 provides three optical and three coaxial digital inputs which can accept signals of up to 24-bit resolution The optical inputs are rated for ultra-high-speed links using the ST-format HPC (High Performance Connection) standard, which supports a data transfer rate of up to 150 megabits per second. The coaxial inputs use BNC connectors. In addition, up to two digital recorders can be connected to the DP-75. Via a set of Toslink and coaxial RCA-type input/output connectors.

The integrated SFC in the DP-75 converts all digital input signals to a 48-kHz. 20-bit, level 1 signal. This signal is available al the digital outputs- Since a digital level control is also provided, the DP-75 can be used as a digital preamplifier.

Since the 20-bit MMB D/A converter of the DP-75 has a 4-bit margin. digital noise cannot occur by principle and precise attenuation is possible down to -40 dB.

periodic codes, it can -- if allowed to enter the analog signal path -- cause noise that is c[early distinct from analog sources- The result is muddy, unclear sound. To prevent this danger a thorough separation of the digital and analog sections is necessary, in terms of static as well as induced interference. The DP-75 achieves this by using ultra high performance optoisolators manufactured by Hewlelt-Packard, rated for a transmission rate of 40 megabits per second.

The analog filter in the DP-75 is a GIC (Generalized lmmitance Converter) 3-pole Butterworth type with a gentle rolloff curve. In this discrete filter stage, the audio signal passes no active components, which assures sonic purity and total musical accuracy,

[CD Transport Section]

Fully Digital Control of CD Mechanism

The control circuitry of the mechanism section is fully digital, allowing the use of adaptive filters to optimize servo performance for each individual disc. This assures enhanced operation stability and a drastic reduction in error rate- Long-term reliability and performance uniformity are also improved, since fluctuations in ambient temperature can have no adverseinfluence.

Since the output level of a laser pickup is very low, it is highly vulnerable to externally induced noise_ To prevent such problems, the pickup used in the DP-75 employs an RF amplifier which is so compact that it can be directly integrated in the pickup assembly. This assures that the high-level output signal remains free from noise interference, which in turn reduces the error rate.

The motors and acluators which drive the disc tray, spindle, sled, and the focusing and tracking assembly require a rapidly fluctuating drive current. which can affect other circuit areas and cause sound quality degradation. In the DP-75. the drive current for each actuator is provided by two amplifiers arranged in a balanced configuration.

Strong Structural Design Effectively Absorbs Vibrations

The chassis supporting the CD mechanism uses 8-mm thick aluminum panels and the massive aluminum front panel is 15 mm thick, This effectively suppresses external vibrations and assures stable operation. Symmetrical layout and weight distribution are further advantages which help to increase mechanical stability.

If the tray is detached from the rotating mechanism during playback, it can resonate and dilute the purity of the digital signal. In the DP-75, the tray is firmly secured during playback, to eliminate any possibility of harmful resonances.