Revox B150 Service Manual

5TUDER R^OX
B250/B250-S/B150
E3/1
3.
CIRCUIT
DESCRIPTION
5.
1
AUDIO
BLOCK
DIAGRAM
Inp
uts and
outputs.
The
high-level
inputs
CD,
AUX,
TAPE
1/2
and
TUNER
are
impleniented
with
an
impedance
transT
ocmer
Ci)
and
integrates
CMOS
switches
(2).
The
phono
inputs
(3)
MM
and
MC
(option)
are
connected
to
a
separate
board
with
discrete
amplifiers.
The
input
capacitance
for the
Phono
MM
can
be
preset
on
the
slide
switch
(4)
to
50/150/450
pF.
All
inputs
are
connected
to
the
stereo
buses
(5/6).
With
the
buses
(5)
the
signals
are
connected
via
an
output
impedance
transformer
(7)
to
the
RECORD
output.
The
outputs
TAPE
1/2
are
mutually
interlocked
so
that
no
undesired
feedback
can
occur.
With
the bus
(6)
the
signals
are
connected
via
an
impedance
transformer
(8) to
the
monitor
output
and
to the
preamplifier
where
the
signal
is
tapped
for
measuring
the
input
sensitivity.
The
CMOS
switches
are
connected
with
two
8-bit
slide
switches
(9/10).
Level
controller
Power
amp
Li
—
°Mt
p.u_^^
The
signal
is
subsequently
routed
via two
different
paths.
The
first
path
leads
to
the
PREAMP
OUTPUT,
the
other
to
the
POWER
AMPLIFIER
which
delivers
a
maximum
of
200
W
into
4 ohms.
An
NTC
resistor
(23)
serves
as
sensor
(temp,
signal)
so
that the
temperature
of
the
output
stage can
be
monitored
by
the
microcomputer
control.
When
the
SEPARATED
key
is
actuated,
the
switches
(19/20)
open,
switch
(24)
closes,
thus
disabling
the
power
amplifier.
The
speaker
outputs
A/B
(26/27)
and
the
PREAMP
OUTPUT
(29)
can be
activated
via
relays
by
means
of
the
output
selector
switches.
The
headphones
output
is
activated
automatically.
Its
level is
attenuated
by
a
voltage
divider.
The
relays
are
controlled
by
the
shift
register
(25).
The
enable
of
this
shift
register
is
generated
by
the
POWER
FAIL
detector
(30)
which
ensures
that
after
power ON
the
relays
are
energized
with
a
delay
so
that the
supply
voltages
have
sufficient
time
to
stabilize.
The
relays
drop
out
immediately
in the
event
of a
power
failure.
5.2
BLO
CK
DIABRAM
OF THE
MICROCOMPUTER
SY
STEM
The
amplifier
gain
is
electronically
controlled by
a
dual
DAC
(11)
(dual
digital/analog
converter).
This
circuit
produces
a
maximum
gain
of
+22 dB
and
a
maximum
attenuation
of
—48
dB.
To
achieve
an
additional
attenuation
by
—30
dB,
a
divider
(12) is
connected
to
the
output
of
the
network.
A
continuous
gain
decrease
is
achieved
by
floating
changeover
between
DAC
and
divider.
Subsequently
the
control
range
of
the
DAC
from 0
to
—48
dB
again
becomes
effective.
Connecting
the
divider
into
the
circuit
thus
produces
a
maximum
attenuation
of
-78
dB.
This
network
is
controlled
by
two
serially
connected
B—bit
shift
registers
(13/14).
After
the
volume
control
the
signal
is
taken
to the
tone
control
stage.
Tone
control
s,t
aa,e
The tone
control
stage is
divided
into
a bass
and
treble
section
and
can be
used
as a
tone
control
or
as a
physiological
volume
control
(loudness).
It
has
been
implemented
with
one
active
band—pass
(15)
for
low
frequencies
and
one
band-pass
for
high
frequencies
(16).
Both
have
a
bell
characteristic.
The
control
is
similar
as
in
the
volume
control
except
that
two
discrete
3—
bit
DACs
are
used.
With
these
the
low
frequencies
can
be
controlled
in the
resonance
range
at
(40 Hz)
from
+/—
12
dB
while the
treble
frequencies
can
be
controlled
in the
resonance
range
(14
kHz)
from
+/-
12 dB.
The
control
is
implemented
with
two
serially
connected
shift
registers
(17/18
dB).
The
tone
control
stage
can
be
bypassed
or
activated
by
means
of
electronic
switches
(19...22).
Mijc.r_o
cjojnjm.t
The
microcomputer
system
consists of
two
different
microcomputers.
Microcomputer
(1) is
responsible
for
application-related
functions.
It
controls
the
I^C
bus. It
is
the
master
processor.
It
has
exclusive
access
to
the
memory
chip and
performs
all
control
functions.
The
Microcomputer
(2)
is
responsible
for
scanning
the
keyboard
(16)
and
for
controlling
the
fluorescence
display
(17).
Microcom
puter
.(_iJ_.
The
EEPROM
(3)
and
the LCD
driver
(4) are
selected
by
the
microcomputer
(1)
directly via
the
I^C
bus.
Various
information
that
has
been
entered
via
the
keyboard
is
subsequently
stored
in
the
EEPROM
(3).
The
serial
interface
contains
additional
chips
that
are
controlled
by
the
microcomputer
(1).
These
are
the
shift
registers
(Section
3.1:
9,
ID,
13, 14,
17,
IS,
25).
They
are
loaded
via
the
serial
interface.
With
the
strobes
(STR
VOLUME,
STR
SELECT,
BTR
INPUT)
the
data
are
read
into
the
latches.
The
microcomputer
also
monitors,
scans
and
compares
various
signals.

Revox B150 Specifications

General

Brand	Revox
Model	B150
Category	Amplifier
Language	English