Classe Audio CP-800 User manual

CP-800
STEREO PREAMPLIFIER/PROCESSOR
Technical Highlights

CP-800 Stereo Preamp/Processor
Overview
The CP-800 utilizes proprietary Classé technol-
ogy together with rigorous engineering of pow-
er supply, analog and digital audio, and control
subsystems to achieve high performance and
reliability. A wide range of input connector
formats offers compatibility with most popular
source components and digital processing
features provide exible output congura-
tion options. A dedicated subwoofer output is
provided with selectable crossover frequency
and slope. Left and Right channel outputs are
supplemented by two auxiliary channels which
may be congured for power-bi-amping. Alter-
natively, a single AUX channel may be used to
provide a second subwoofer output.
The architecture of the preamp/processor
allows for the future addition of network con-
nectivity and an optional phono module.
Power Supply
High-performance audio circuits require clean
and stable power to achieve their true potential.
The Classé Design team has developed a new
Switch Mode Power Supply (SMPS) to meet
the CP-800 performance requirements. In ad-
dition to potential audio performance benets,
SMPS technology offers many advantages for
audio components including smaller size, lower
weight, improved efciency, high power factor
and lower cost. With the very high dynamic
range of the best audio sources, the benets
of SMPS technology justify the effort required
to implement it optimally.
The linear power supplies found in high-end
audio components typically use a large trans-
former with a full-wave bridge rectier followed
by banks of ltering capacitors. For circuits
to draw power as needed, the energy stored
in the power supply must be sufcient
to last through the relatively slow refresh rate
of the AC Mains. For 50/60 Hz AC power, when
full-wave rectied, the capacitors are recharged
100/120 times per second. The components
are physically large because they are attempt-
ing to deliver clean and stable power to audio
circuits that are constantly demanding differing
amounts of power. These demands may occur
in rapid succession—before the capacitors can
fully recharge—so the capacity has to be large
enough to account for this. Countless great
sounding high-end ampliers and preampliers
attest to the fact that this can be done effec-
tively, but the size and cost of these parts are
substantial and there is now a better way.
Switch Mode Power Supplies are the most
commonly used type of power supply in
consumer electronics because of their high
efciency, low heat dissipation, light weight and
lower cost. These benets are derived from the
fact that the components used switch power at
a high frequency, which means that transform-
ers and ltering coils and capacitors can be
comparatively small. SMPS is a solid state
technology which uses transistors to switch
power on and off in a fashion that delivers
precisely the power required as it is needed.
Fig.1 Mains Voltage and Current drawn without PFC Fig. 2 Mains Voltage and Current drawn w/ PFC (CP-800)

From an objective point of view, anyone
with the right equipment can measure noise.
So making the claim that the SMPS Classé has
designed for the CP-800 is our quietest power
supply ever is not a matter of opinion. It is fact.
While those familiar with other SMPS designs
will expect noise, simply put, they will  nd it
startlingly absent here.
Power factor Correction
Power supplies have an enormous in uence
on the performance of audio circuits, but it is
not generally well understood that the cleanli-
ness and stability of the supplied power is only
part of the story. The power supply itself can
distort the AC mains in ways that can compro-
mise the performance of other audio compo-
nents on the grid.
Ideally, power would be pulled from the wall
in a smoothly ef cient manner. For maximum
ef ciency, the current demands should  ow
exactly in phase with the voltage cycle. Since
power is the product of voltage and current,
it is easier (more ef cient) to pull power from
the wall by aligning current demands with the
available voltage cycle.
If the current demands are not in phase with
the voltage cycle, ef ciency is lost. From an
audio perspective, the power supply can clip or
distort the AC mains, which are usually shared
by other components. Fig.1 shows the mains
voltage and current being drawn by a surround
processor using both linear and switch mode
power supplies. Like all other components with
non-Power-Factor-Corrected power supplies,
it gulps current for short periods of each voltage
cycle. These gulps of current occur over
a relatively short time within the cycle (called
a narrow conduction angle), meaning the peak
current demand is higher than it would be if
drawn over the full cycle, and the waveform
itself contains higher frequencies and their
harmonics. The higher current peaks and their
high frequency harmonics degrade the quality
of power available to other system components.
This is a problem for both linear and switch
mode power supplies (both of which are used
in the example). They draw current from the
wall in large gulps rather than smoothly fol-
lowing the cycle of voltage. The solution to
Zero Volt Switching
By using the fairly new concept of Zero Volt
Switching (ZVS), the Classé SMPS was devel-
oped to have a low noise, small RF footprint—
a requirement for the highest quality audio
rendering. The main bene ts of ZVS, re ned
by the Classé Design team during an extensive
R&D phase, are:
• The Primary Switch used in the design is
switched when the supply voltage is at a
minimum, thus greatly minimizing a ‘hard
switching’ effect which contributes to high
levels of unwanted EMI.
• EMI performance is further improved by not
adhering to a  xed switching methodology.
By instead employing a ‘valley switching’
methodology, a spread-spectrum component
further reduces EMI spectra. Instead
of artifacts being concentrated around
a single frequency, they are distributed at
lower amplitude across a wider spectrum.
• ZVS promotes higher ef ciency of the
DC-DC converter sub-system, ensuring
optimised ef ciency of the power supply.
Four Supplies in One
The CP-800 SMPS provides four separate
outputs. Techniques to capitalize on the new
power supply’s low output impedance and
perfect cross-regulation (matching for plus
and minus rails) provide a very low AC imped-
ance at local regulator input pins for optimal
performance. The outputs of all local regulators
are conditioned to have low impedance at high
audio frequencies to effectively reject noise.
USB circuitry is powered from its own galvani-
cally isolated +5 V output, ensuring unwanted
noise cannot couple into the CP-800 audio cir-
cuits from USB-connected devices. An added
bene t of this power supply design is that
fully isolated USB devices including the iPad®
(which requires a whopping 2.1 amps to charge
at full power) may charge while connected to
and playing through the CP-800.
The engineering feat to develop an audio-
friendly SMPS is considerable. The Classé
R&D focus has been to identify the key technol-
ogies and thoroughly understand how to take
advantage of all the possible advantages while
preventing or controlling unwanted side-effects.
When a transistor is on, it delivers power with
almost no resistive loss and when it is off, it’s
an open circuit so it draws no power. These
characteristics make the switcher greater than
90% ef cient. The switching occurs at a very
high frequency which, in addition to enabling
the use of smaller component parts, allows the
supply to remain perfectly stiff regardless of the
load or the  uctuations on the AC line.
So what’s the catch? Why don’t high-end audio
designers use Switch Mode Power Supplies?
The most common explanation they give is
that an SMPS inherently generates ultra-sonic
artifacts and spurious signals. In some applica-
tions these don’t present a problem but they
can seriously degrade both the perceived and
measured audio quality. Further, an electrical
engineering student could design a passable
linear power supply, but SMPS designs are
considerably more sophisticated and apply
a broader range of technology. It is this techno-
logical development applied to high-end audio
which has been lacking and has now been
addressed by the Classé Design team. Only
a team who understands both the SMPS
technology and the requirements of high-end
analog and digital audio circuitry can produce
a design that effectively deals with any gener-
ated noise while capitalizing on all of the inher-
ent bene ts of the topology.
The power supply rejection ratio of a linear pow-
er supply is determined by looking for an output
signal at the same frequency as the signal being
injected into the supply. Said another way, the
rejection ratio compares the signal you want to
amplify in the circuit to the amount of that signal
that is re ected back into the circuit through the
power supply. With SMPS, the audio signals do
not re ect back into the circuit but rather interact
with the switching frequency of the supply to
create intermodulation artifacts. For example,
if the switching frequency is 140 kHz and the
test signal is 1 kHz, intermodulation components
may show up as 139 kHz and 141 kHz signals.
These signals and their harmonics, if not dealt
with, can show up as unwanted ultrasonic noise
that ‘pours’ into the audio circuitry where it will
couple into devices, generating unwanted au-
dible artifacts. The Classé SMPS was designed
to avoid this problem.

words, the USB source is in charge and the
USB microcontroller must periodically adjust its
clock to remain synchronized. This adjustment
period is once every millisecond, which results
in jitter with signicant components at 1 kHz
and its harmonics.
This technique is known as Adaptive USB,
since the output rate adapts itself to the aver-
age rate of the incoming data. Given all the
ways in which this basic approach is suscep-
tible to noise and clock degradation, many
tweaks may be applied upstream of the USB
input that result in audible changes but do
not solve the fundamental problem.
Asynchronous USB
Improvements to the performance of the USB
subsystem are made possible by external
control options offered with certain USB micro-
controller chips. The most basic improvement
involves taking charge of the clock. In this tech-
nique, a master clock dedicated to multiples of
44.1 kHz may be employed for sources arriving
Synchronous (Adaptive) USB
(not used in the CP-800)
The problem posed by the standard USB/
DAC approach (Fig. 3) is that the USB source
(your computer or portable device) is ultimately
responsible for the jitter in the system. Further,
the USB source may degrade the performance
of DACs, power supplies and analog circuitry
by polluting the environment with noise cou-
pling through power, control, signal and electro-
magnetic pathways.
Synchronous/Adaptive USB DACs exhibit high
jitter because the clock being used by the DAC
is 1) generated in the USB microcontroller
and 2) slaved to the rate at which the USB
source is supplying the data. From an audio
perspective, this approach is backwards as it
forces the USB DAC to lock to a high jitter and
compromised clock system. As with S/PDIF,
no amount of post-processing in the USB DAC
can reverse the damage that has occurred dur-
ing data transmission.
With the USB source effectively pushing data
into the microcontroller’s buffer, the data must
be clocked out of the buffer and into the DAC
synchronous to the USB source. In other
this problem, employed in conjunction with the
SMPS used in the CP-800, is called Power
Factor Correction (PFC).
Power Factor is the ratio of real power (power
that the product’s ‘function’ uses) to the appar-
ent power (power drawn from the AC mains).
Power Factor is expressed as a ratio having
a number between 0 and 1. A non-Power Fac-
tor Corrected power supply has a PF of about
0.6, indicating a signicant reduction in the
utilization of available energy. An additional
unwanted by-product of a low PF is the distor-
tion of the AC supply that powers the entire
audio system, creating the possibility of it
rendering sub-standard audio. (Fig. 1)
For the Classé SMPS, a new R&D project
focused on developing a PFC circuit that could
achieve a Power Factor approaching unity, i.e.
>0.95 at its working load. The developed circuit
topology uses an active conguration that con-
trols the amount of power drawn by the systems’
load, such that the current waveform remains
proportional to the mains voltage waveform.
This makes the system look resistive to the AC
supply, allowing the ratio of real power to appar-
ent power to approach unity. (Fig. 2)
By pulling power from the wall in a smooth
sinusoid, the CP-800 power supply is both
more efcient and quieter than other preamps
with power supplies that lack PFC.
Classé has developed its own, designed-for-
audio-applications power supply technology
that contributes to the outstanding performance
and value of the CP-800. It is scalable and will
help yield more great sounding products for
years to come.
Digital Audio
The CP-800 accommodates a variety of digital
sources via optical, coax, AES/EBU and USB.
The upper printed circuit board handles digital
source selection and contains the USB 2.0
microcontroller chip with associated circuitry.
The USB subsystem uses galvanic isolation
to prevent noise from connected USB devices
from coupling into the audio circuitry. This
means that no direct electrical connection
exists between the USB inputs and anything
else inside the CP-800.
Most audiophile USB/DACs employ off-the-
shelf USB microcontroller chips, designed into
the system according to their application notes.
To add value, designers rely on using high
quality DACs and making the power supply
and analog output stages as good as possible.
This approach dates back to the eighties when
audiophile companies began to tweak CD
players made by leading consumer electron-
ics manufacturers like Philips and Sony. It was
understandable at that time, since digital audio
was new and high-end audio designers didn’t
fully understand it.
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Fig. 3 Synchronous (Adaptive) USB
Fig. 4 Non-Optimal Asynchronous USB

The solution developed for the CP-800 was
to place a Field Programmable Gate Array
(FPGA) near the DACs and master clock
oscillators. USB microcontrollers are general
purpose devices and cannot manage signals
or clocks with the precision of an FPGA, which
is its specialty. The CP-800 employs a 300
MHz video-grade FPGA to manage audio
clocks running at less that 25MHz.
Although two clocks are interfaced to the
FPGA, only one is enabled at a time, as deter-
mined by the sample rate of the received music
data, hence the term Single Clock Substrate.
Data from the USB microcontroller on the
digital input board is received and buffered
by the FPGA located adjacent to the DACs on
the motherboard below. Data are transferred to
the DACs synchronous to the CP-800 master
audio clock. This topology ensures the greatest
isolation of clocks and data from all upstream
artifacts. Analysis shows better clock purity
and signal-to-noise at the critical instant digital
audio is converted into the analogue domain in
comparison to a topology where audio clocks
are derived from the USB microcontroller.
iPod®, iPhone® and iPad® Connectivity
USB DACs—even those employing asynchro-
nous techniques—do not typically offer support
for high quality audio from USB devices such
as Apple’s popular range of portables. This
is unfortunate, as these devices can play the
same lossless les as stored on a Mac or
PC, with the same level of audio quality. It is
understandable why support for these portable
devices in high-end USB DACs is so rare
when one considers the additional complexity
involved:
• The product must “host” the device, which
is considerably more complex than simply
acting as a USB “device” hosted by a Mac
or PC.
• For best performance, asynchronous tech-
niques must be developed for pulling data
from the device.
• Apple’s qualication process is rigorous.
Only after passing their certication program
can a product be certied “Made for iPod®,
iPhone® and iPad®.”
Using the knowledge and experience gained
from the B&W Zeppelin design project, the
Classé Design team addressed all of these
points, allowing a remarkable level of audio
performance to be realized from Apple portable
devices, Fig. 6.
Single Clock Substrate
There are several ways in which the perfor-
mance of the master clock may be degraded.
The CP-800 employs a technique we call
Single Clock Substrate to isolate them and
ensure the best possible performance.
For data to be “clocked” out of the USB micro-
controller’s buffer, the master clock is used to
create other clocks called bit clock and word
clock. The word clock running at the sampling
frequency divides data into left and right chan-
nels, the bit clock synchronizing each data bit.
The master clock, which is controlling the
timing of the D-to-A Converter, is connected
inside the microcontroller, which is a CMOS
device. For microcontrollers, CMOS is the most
commonly used semiconductor technology be-
cause it is low cost yet performs well for most
applications. The limitation for our application
is that CMOS cannot provide the isolation from
other clocks that we require for our master
clock. You can partition functions on the silicon
but you cannot isolate them.
at that frequency or its multiples, and a different
clock may be used for sources at 48 kHz and
its multiples. By controlling the clock locally in
the USB/DAC, we make it asynchronous to the
clock in the computer or portable USB device.
When the master clock for 44.1 kHz sources
is being used, the clock for 48 kHz sources is
switched off. The master clock is used by the
USB microcontroller to generate bit and word
clocks, and to clock data out of the buffer and
into the DAC. The USB microcontroller now
controls the ow of data from the source rather
than the other way around (Fig. 4).
With this technique, we can also isolate the
USB/DAC from noise propagated from the
source. The CP-800 uses complete galvanic
isolation, severing all electrical pathways from
the source to ensure unwanted noise is kept
out of the audio system. The asynchronous
technique also provides a means to control the
quality of the clock by using local clocks dedi-
cated to specic digital audio frequencies. This
is where most others stop. The Classé Design
team, however, went further.
Fig. 5 Optimal Asynchronous USB with SCS
Fig. 6 Optimal Asynchronous USB with SCS for Host
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A few words about execution…
An often overlooked but vital part of any
electronic circuit is the printed circuit board
(PCB). It is natural to consider key components
in an audio design; using quality components
is very important, but just as important is what
the engineer does with them as component
selection alone does not guarantee the highest
performance.
The layout of Classé-designed PCBs is always
done by hand. No computer programmed auto-
routing scheme could approach the results
possible when each part, pad, plane and trace
is painstakingly considered and located for
optimal performance. This time-consuming
approach is costly, but there is no substitute.
Literally thousands of decisions are made that,
taken in isolation, may or may not be audible.
Taken as a whole, these decisions make all
the difference.
Most boards in the CP-800 are six-layer circuit
boards. (Fig. 6)
User Interface and Control
Classé brought touchscreen control to high-end
audio in 2004. The CP-800 represents the rst
substantial upgrade of that interface. A 16x9
aspect ratio allows more room for controls,
which results in fewer menu pages and an
even better user experience. New graphics
give the CP-800 a more polished and updated
appearance.
The CP-800 comes with a basic backlit
handheld remote which can be used to control
most aspects of the CP-800’s daily operation.
Additional commands such as discrete input
and conguration commands can be taught
to a learning remote by using the IR transmitter
located in the same window as the IR receiver
on the front of the unit.
The CP-800 also supports automation systems
with a bi-directional RS-232 control capability.
DC triggers are provided to enable simple
automation schemes, triggered by events that
are chosen in the setup menu. The triggers are
12V and may be congured for inverse logic
if required.
Summary
The CP-800 introduces a new architecture
for high-end preampliers. By combining the
functions of a USB DAC, digital processor
and analog stereo preamplier in a way that
optimizes the performance of every source, it
offers a unique solution for the most demand-
ing audiophile. Capitalizing on the potential for
computer-based audio and employing powerful
processing tools, the CP-800 offers compelling
performance, features and value
Note: if Analog Bypass is chosen the analog
audio remains in the analog domain regardless
of the speaker conguration or EQ/Tone set-
tings, which will be ignored. It is however pos-
sible to run analog signals through full range
in bypass mode while simultaneously generat-
ing a subwoofer output.
Processing is performed in 56-bit, double preci-
sion mode, offering good low level resolution
and audio performance.
Analog Audio
Balanced signals remain balanced from input
to output and single-ended sources are con-
verted to balanced immediately upon arriving
inside the chassis. Signal pathways and power
distribution are optimized for isolation and over-
all performance.
The L&R channels never share the same sili-
con, so the volume controls are kept separate.
Stereo volume controls (BB PGA3310) are
used as differential volume controls, one for
each channel.
A headphone output on the front panel is a no-
compromise feature, offering the same quality
of analog output as the main output channels.
Analog inputs may be routed through the ADC
and processed for EQ, tone control and bass
management (high pass ltering). Alternatively,
sources may be identied as Analog Bypass,
in which case they remain analog and full
range throughout. Selecting sources identi-
ed as Analog Bypass (without subwoofer)
results in the clocks used for digital audio being
switched off. Note that one pair of analog con-
nectors may have two or more source buttons
associated with it. This allows automatic selec-
tion of Analog Bypass or ADC paths, along with
other convenience and customization benets.
D-to-A Conversion
Two stereo D-to-A Converters (Wolfson
WM8741) produce differential outputs for both
Left and Right channels. Their power supply
is regulated locally using techniques to ensure
nearly zero output impedance for supply rails
and tuned specically to lter noise generated
by the DAC at its modulator frequency.
The DACs are run at either 176.4 or 192 kHz,
depending on whether the input is a multiple
of 44.1 or 48 kHz respectively. Both measured
and sonic evaluations conrmed this as the
preferred rates for the Delta Sigma DACs
used in the CP-800.
The WM8741 is a voltage-output DAC, so no
I-V Converter stage is required. A fourth-order
reconstruction lter with a 100 kHz pass band
nishes the job of converting audio from digital
to analog.
Processing
All inputs have access to powerful, perfor-
mance-enhancing Digital Signal Processing.
Two Analog Devices Sigma DSPs are used
as follows:
DSP 1 – Used to set Parametric EQ and tone
control functions of front left and right Main
and Aux channels.
DSP 2 – Used to set Subwoofer crossover
frequency of SUB output and Aux 1 (if cong-
ured as a Subwoofer output).
If a DSP mode is selected for an analog audio
input, the analog audio is routed to a Cirrus
Logic CS5381 ADC to convert the audio into
the digital domain prior to processing. If no
DSP is required, the analog signal remains
in the analog domain.
Fig. 6 Signal Routing (showing only 3 of 6 layers) CP-800 Motherboard

Frequency response 8 Hz - 200 kHz < 1 dB,
stereo analog bypass
8 Hz - 20 kHz < 0.5 dB,
all other sources
Channel Matching better than 0.05 dB
(left to right)
Distortion (THD+noise) .0005%, digital source/bypassed
analog source
.004%, processed analog source
Maximum input level 2 Vrms (DSP), 4.5 Vrms (bypass)
(single-ended)
Maximum input level 4 Vrms (DSP), 9 Vrms (bypass)
(balanced)
Maximum output level 9 Vrms
(single-ended)
Maximum output level 18 Vrms
(balanced)
Gain Range -100 dB to +14 dB
Input impedance 50 kΩ (balanced)
100 kΩ (single-ended)
Output impedance 300 Ω (balanced),
(main output) 100 Ω (single-ended)
Signal-to-noise ratio 104 dB, bypassed analog source
(ref. Bal. 4 Vrms input, 101 dB, processed analog source
unweighted) 105 dB, digital source (ref. full-scale
input, unweighted)
Channel separation better than 100 dB
Crosstalk better than -130 dB @ 1 kHz
(any input to any output)
Standby power <1 W
consumption
Rated power 31 W
consumption
Mains Voltage 90-264 V, 50/60 Hz
Overall dimensions Width: 17.5” (445 mm)
Depth: 17.5” (445 mm)
(excluding connectors)
Height: 4.78” (121 mm)
Net weight 23 lbs (10.43 kg)
Shipping weight 33 lbs (15 kg)
Made for
iPod touch (4th generation) iPod nano (6th generation)
iPod touch (3rd generation) iPod nano (5th generation)
iPod touch (2nd generation) iPod nano (4th generation)
iPod touch (1st generation) iPod nano (3rd generation)
iPod classic iPod nano (2nd generation)
Made for
iPhone 4 iPhone 3G
iPhone 3GS iPhone
Made for iPad
Specications
Classé and the Classé logo are trademarks of Classé Audio Inc.
of Lachine, Canada. All rights reserved.
“Made for iPod,” “Made for iPhone,” and “Made for iPad” mean that
an electronic accessory has been designed to connect specically to
iPod, iPhone, or iPad, respectively, and has been certied by the developer
to meet Apple performance standards. Apple is not responsible for the
operation of this device or its compliance with safety and regulatory
standards. Please note that the use of this accessory with iPod, iPhone,
or iPad may affect wireless performance.
iPhone, iPod, iPod classic, iPod nano, and iPod touch are trademarks of
Apple Inc., registered in the U.S. and other countries. iPad is a trademark
of Apple Inc.

5070 François Cusson
Lachine • Quèbec
Canada • H8T 1B3
Tel [phone]
Fax [phone]
www.classeaudio.com
email: [email protected]