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Lexicon LXP-5 Service Manual

Lexicon LXP-5
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Circuit
Description
Lexicon
Converter
Circutry
w/c
SAMP
j
CCLK1
DEGQ
iru
mLwwmum
y
DEG1
^
A/D
CONVERSION
J
„
RIGHT
CHNL
D/A
CONVERSION
_
_
LEFT
CHNL
D/A
CONVERSION
A/D
SAR
Conversion
Timing
SAH
The
sample
and
hold
(SAH)
circuitry
consists
of
op
amp
1)39,
an
SPDT
analog
switch
U38
and
capacitor
089.
The
SAH
is
controlled
by
the
SAMP
signal
command
from
the
Lexichip,
which
terminates
at
pin
11
of
U38.
WhenSAMP
is
high,
pins
13
and
14
of
switch
U9
are
shorted,
which
performs
the
sample
function.
At
this
time,
an
output
level
from
pin
6
of
U39
is
used
to
charge
C89.
The
hold
function
takes
place
when
SAMP
goes
low,
which
shorts
pins
12
and
14
of
switch
U38.
The
charge
across
C89
keeps
the
audio
signal
level
constant
during
the
analog
to
digital
conversion.
The
output
of
the
SAH
passes
through
an
AC
coupling
capacitor
(C92)
and
a
pulldown
resistor
(R62)
to
prevent
DC
offsets
from
affecting
system
performance.
DAC
The
analog
to
digital
conversion
involves
use
of
a
comparator
(U32),
the
Lexichip
(U21),
and
a
16
bit
digital
to
analog
converter
(DAC,
U31).
The
SAH
output
is
applied
to
pin
3
of
the
comparator.
The
output
of
the
DAC
feeds
pin
2
of
the
comparator.
During
the
analog
to
digital
conversion
cycle,
the
internal
successive
approximation
register
(SAR)
of
the
Lexichip
is
used
in
conjunc¬
tion
with
the
DAC
to
output
different
voltage
levels.
These
voltages
are
compared
with
the
audio
signal
level.
The
conversion
is
completed
when
the
two
voltage
levels
are
equal.
After
the
conversion,
the
L+R
signal
is
proc¬
essed
digitally.
After
the
signal
has
undergone
digital
processing,
separate
left
and
right
analog
signals
reappear
after
the
digital
to
analog
conversion.
At
this
time,
the
Lexichip
sends
16-bit
data
to
the
DAC,
which
converts
it
into
analog
voltage
levels
(see
Data
to
Voltage
chart
below).
These
voltage
levels
are
applied
to
the
output
hold
circuitry.
Digital
input
Code
Analog
Output
OOOOh
+2.99991
V
7FFFh
0.0000V
8000h
-91.6uV
DAC
Data
to
Voltage
FFFFh
-3.0000V

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Lexicon LXP-5 Specifications

General IconGeneral
BrandLexicon
ModelLXP-5
CategoryRecording Equipment
LanguageEnglish

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