TECHNICAL
DESCRIPTION
©
Cyrus
Audio
Ltd
Jun
2014
8
Cyrus
6
DAC,
Cyrus
8
DAC
service
manual
Issue
1
NOTE:
‐
Reference
numbers
in
the
text
are
for
the
left
channel.
Analogue
input
selection
and
Tape
Monitor
The
input
and
tape
monitor
selection
is
via
an
electronic
audio
selector
switch
(IC101).
The
switch
is
a
7
way
2
pole
switch
followed
by
a
buffer
(IC103)
which
then
feeds
audio
to
the
volume
control
section
of
the
circuit.
The
Zone
2/Tape
output
is
separately
selected
via
a
second
electronic
switch
(IC102).
The
signal
from
the
Zone
2/Tape
selector
is
then
sent
to
the
Zone
2/Tape
output
via
the
buffer
IC104.
Digital
inputs
In
addition
to
the
six
analogue
inputs
described
above,
the
amplifiers
include
a
digital
input
switcher
and
a
two
channel
D/A
Converter
to
enable
connection
of
an
additional
five
digital
inputs,
four
of
which
are
stereo
SPDIF
format
and
one
USB.
Digital
input
selection
is
performed
by
an
8:1
input
multiplexer
in
a
Digital
Input
Receiver
(IC701).
The
DIR
is
clocked
by
a
24.576MHz
reference
clock.
The
input
sample
rate
is
determined
by
comparing
the
incoming
frequency
to
the
reference
clock.
The
frequency
is
then
read
by
the
system
microcontroller
on
the
front
panel
PCB,
and
displayed
on
the
front
panel
LCD
display.
The
output
from
the
multiplexed
SPDIF
input
signal
is
then
synchronised
by
an
internal
PLL
and
decoded
to
I
2
S
(a
3
‐
wire
digital
audio
format)
by
IC701.
The
USB
input
is
decoded
by
IC601.
This
enables
the
amplifier
to
play
music
from
a
PC
or
similar,
but
is
not
suitable
for
connecting
Flash
drives
or
the
like.
When
a
USB
device
is
connected,
the
power
supply
for
IC601
is
powered
via
T601.
When
there
is
no
USB
master
device
connected
to
the
USB
type
socket,
the
power
supply
for
IC601
is
powered
down,
stopping
the
clock
for
IC601.
When
enabled,
and
with
a
USB
audio
signal
connected,
IC601
will
re
‐
format
the
audio
signal
to
IEC958/SPDIF
format
which
is
routed
to
IC701,
the
digital
input
switch.
The
I
2
S
audio
data
from
the
input
switch
IC701
is
fed
to
IC801,
a
stereo
D/A
Converter.
The
D/A
Converter
converts
the
digital
audio
into
an
analogue
output.
This
is
amplified
and
filtered
by
IC802
before
being
passed
to
the
DIG
input
of
IC101
(the
input
switch
on
the
main
analogue
amplifier
PCB)
via
CON100.
The
digital
audio
signals
from
IC801
are
also
fed
to
the
Qx
DAC
upgrade
connector
CON902.
If
a
Qx
upgrade
DAC
is
fitted
to
a
Cyrus
8
DAC,
a
flexfoil
cable
is
fitted
between
CON902
and
the
Qx
DAC
PCB
to
connect
digital
audio
and
power
etc
to
the
Qx
DAC.
The
audio
output
of
the
Qx
DAC
is
connected
to
CON100
on
the
main
PCB.
In
this
configuration,
the
audio
output
cable
of
the
Digital
Input
module
is
connected
to
a
spare
connector
CON905.
The
power
for
the
digital
input
PCB
is
supplied
from
a
separate
low
voltage
winding
of
the
main
power
transformer.
This
is
then
rectified
and
sub
regulated
to
a
number
of
individual
supplies,
one
3.3V
and
two
5.0V.
The
rectified
and
unregulated
supply
is
also
passed
directly
to
the
main
analogue
amplifier
PCB
to
provide
power
for
the
LCD
backlight.
The
15V
power
supplies
for
the
analogue
post
DAC
filter
are
provided
from
the
main
analogue
amplifier
PCB.
When
the
amplifier
is
set
to
standby
the
power
to
the
whole
digital
input
PCB
is
removed.
If
a
digital
input
is
not
selected
for
listening
on
the
main
amplifier
or
in
Zone
2,
the
digital
PCB
will
be
held
in
reset
to
eliminate
digital
noise
interference
coupling
to
the
main
analogue
inputs.
