 Compact Disc Player 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
absentAassuring 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. |
|
[ Digital Processor Section]
MMB Type D/A Converter Takes 20-Bit Linearity and Low Noise Performance
to NewLimits
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.
Ultra Jitter-Free PLL Circuit
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.
High-Precision Sampling Frequency Converter
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.
Versatile Digital Input Configuration PermitsUse 8S Digital Control Center
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.
Digital Output Supports 48-kHz 20-bit Data Width
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.
Digital Level Control Prevents Sound Quality DeteriorationSince 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.Thorough
Separation of Digital and Analog Sections Shuts Out interference Because
a digital signal consists of regular.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.
GIC 3-Pole Analog Filter With Selected Components
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.
Laser Pickup With Integrated RF Amplifier for Error-Free Operation
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.
Balanced Drive Circuitry for Servo Motors
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.Because there is no circuit flowing
in the ground line, the operation of other circuits in the player remains
entirely unaffected.
Strong Structural Design Effectively AbsorbsVibrations
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.
Tray Lock Prevents Resonances
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.
|
|
|
|
|
|
|
|
|
