NEW! Read this great review of the COPLAND CDA 825 CD player from ULTRA AUDIO
As
a result of our quest for refining the musical capabilities
of the CD-media, and our constant efforts to understand and
taget the underlying technological requirements, we believe
that the introduction of the CDA825 is offering significant
improvements of sound reproduction from CD-media.
Obviously
the CD-media is a digital representation of an initially analog
event, and the design of the CDA825 is therefore determent
by an ambition to reconstruct the complex and delicate harmonic
structure of the original analog waveform. This objective
adheres to all details of the design, as well as their integration
into the whole.
Starting
with the power supply, the following paragraphs offers some
insight into the various design considerations.
Power
supplies
The
routing and grounding scheme of the CDA825 power supply provides
effective isolation between the digital- and analog- parts
of the CD-player. Furthermore, the power supply has been designed
to ensure constant low output impedance towards the power
consuming electrical circuits. The numerous individual power
supplies in CDA825 are designed to operate with a constant
power, thereby eliminating reverse modulation towards the
transformers and the AC supply grid.
Error
correcting capability
The
servo/error correction circuit is a prime source of ensuring
error-free extraction of the data from the disc. These circuits
are designed by a few select semiconductor manufacturers.
Extensive testing was performed in order to select the best
chip-set available, and then to provide optimum operation
conditions for these devices.
Inherently
to the red-book CD standard, is an 8 -14 modulation, interleaving
and Reed- Solomon error correction. Due to cost reasons, not
all available decoder chip-sets include a full implementation
of these powerful error- correcting capabilities.
The
Philips chip-set used in the CDA825 provides full implementation
of all error-correcting schemes of red-book CD and hence,
guarantees that the extracted data from the CD-Pro2LF mechanism
are recreated correctly.
Buffer
circuitry
In
order to provide further isolation between the data-extraction
parts (drive, servo and error correction) and the reproduction
parts (DAC, analog and output filtering), a digital buffer
containing two seconds of musical data has been included in
the signal path between the drive mechanism and the DAC’s.
The purpose of this digital buffer is to
isolate the drive from the DAC’s.
The
data, as they are extracted from the drive, are not completely
equidistant in time; there are slight variations (jitter)
imposed in the time domain. By absorbing these slight time
variations at the input side of the buffer, the memory of
the buffer is used as a data-pool from which the extracted
data are clocked out towards the DAC’s at an absolutely
constant rate (completely equidistant in time) - and
consequently the jitter in the data is eliminated.
The
DAC’s are feed digital data arising from the registers
of the memory device and so the modulations in time and electrical
energy (drive variations in power consumption) are completely
eliminated; the DAC’s are fed data from an environment
that do not comprise any moving parts.
Digital
filter
In
the field of psychoacoustics it is a well known fact, that
when modelling the human hearing, the perception of sound
exhibit masking effects - both in the time- and frequency
domain. The time domain masking effect (temporary masking)
can roughly be explained as, the ear being less sensitive
to noise immediately after an impulse than before. This fact
has been exploited in the design of the digital up sampling
filter for the CDA825.
As
the bandwidth of CD replay is limited to approx. 20 KHz, the
low pass filters used to up sample the CD data exhibit a pass
band up to this frequency. A conventional linear phase up
sampling filter has an impulse response that is symmetrical
in time - i.e. equally much 20 KHz “ringing” before
and after an impulse. The up sampling filters for the CDA825
has been designed in such a manner that the pre-”ringing”,
the “noise” prior to an impulse is reduced under
consideration of the temporal masking of the human hearing.
This filter design yields a stable and “quietness”
to the sound of the CDA825; transients arise out of a silent
background and transients are perceived to be very clean and
well defined. These sorts of filters have lately become known
as
apodizing filters.
Clock
circuit
The
clock circuit is responsible for providing the correct data
for conversion into analog voltage at the correct instant
in time. If the clock phase has variations in time (phase
modulation: the phenomena known as jitter) the data will not
be converted into analog voltages at the correct instant in
time. The net-effect of these timing errors correspond to
the introduction of amplitude errors - i.e. that the analog
voltages are not the correct analog voltages for recreating
the analog waveform with high signal integrity and high fidelity.
For this reason the jitter performance of the clock circuit
as well as the layout of the clock-distribution lines are
very critical. The clock oscillator of the CDA285 is meticulously
designed for optimal jitter performance. The clock oscillator
has its own regulated power supply.
Digital
to analog converters
The
CDA825 uses the Wolfson WM8741 24bit, 192 KHz DAC. Two of
these devices are used - one for each channel. Each DAC consist
of two Digital to Analog converters each providing an in-phase
signal and an opposite phase signal. By combining two in-phase
and two opposite-phase signals per channel, the statistical
properties of the signals are taken to advantage; the signal
power of the phases correlate and add-up in constructive addition,
whereas the noise power of the phases are decorrelated in
a manner that improves on the signal to noise ratio of the
resulting analog waveform.
Analog
circuitry and post filtering
Due
to the high degree of over sampling, the undesirable aliasing
energy at the output of the DA converters is minimized. This
has allowed a design of a high bandwidth analog output stage
and a lower order analog filtering.
Sound
quality
The
hallmark of the Copland sound philosophy, the deep, tight
and free flowing bass reproduction, seamless mobility of musical
energy and authentic recreation of the time dimension from
the original recording session, are inherent virtues of the
CDA825.
The
dynamic resolution of the CDA825 is extraordinary in the sense
that musical energies related to complex amplitude modulations
appears to flow with an unconstrained mobility and acceleration.
Whether
it’s a small acoustical trio or a large orchestral outburst,
the complexity of the harmonics and the fidelity of the time-dimensions
remain intact. Everything remains in place and with exceptional
resolution. The individual instruments are reproduced with
absolute unconstrained musical flow. In fact, it could be
a challenge for other components in the reproduction chain
to reveal these aspects of the CDA825’s capabilities.
