Inhaltsverzeichnis
Werbung
INSTALLATION DETAILS
when
inslallingthe
stereo power
amplifier
Revox
B74O
into
furniture
etc.
make sure
that sufficient
air
can circu late
to
prevent overheating.
A
minimum
spacing
of
3/16
inch
between the
heat sinks and any side panels plus
a
ventilating
slot,
3/4
inch wide, on the amplifier's
top
side.
will
ensure adequate
convection cooling.
lmportant:
lf
various
equipments
are
to
be
installed
on
top
of
each
other,
place those
which
give
off
the
least
amount
of
heat towards the
bottom.
SWITCHING
ON
Prior
to
connecting
the
amplif
ier
to
the
electric
current supply,
make sure the voltage selector
is
set
to
a
voltage reading
which
corresponds
to that
of
your
electric
current supply. Should
a
change
of thevoltage
selector's
setting
be
required,
please
consultyour
nearest
Revox
service
dealet
to
have
this
change
effected.
Connect
the
stereo
power amplifier 8740 to
the
current
supplV
and
rnove
the switch
POWER
to
position ON. With the electric current
switched
on, the
peak
program
meters
will
be
illuminated.
With the electric current
switched
off,
the
peak
program
meters
will
indicate
0
dB.
INPUTS
Phono sockets
The
Cinch-sockets
are provided
to
connect the
incoming
signal lines
f
rom the
tuner/preamplifier
8739
or
the
receiver
8780.
Connecr
the
right
channel 1o
socket RIGHT and the
left
channel
to
socket LEFT.
XLR-type
receptacles
Alternatively, the
signal
lines
feeding
the
right
and left
channels
may
be
connected
to
the
XLR-
tvpe
receptacles
F
IGHT and
LEFT
respectively.
Pin
connections:
l
Chassis
2
0
volt
3
Signal
INPUT SELECTOR
The input
selector INPUT permits the
insertion
of
a
high-pass
filter
when
using
input
A
(phono
sockets
LE
FTlR
I
G
HT)
by switch ing
it
to position
SUBSONIC
Fl.
This
filter
attenuates substantial-
ly all
f
requencies
below
20
Hz. In
switch
position
A
DIRECT and
B
DIRECT
the
inputs
A
or
B
are
.
connected
directly
to
the
first amplifying
stage.
OUTPUTS
The
speaker
outputs
are
divided into
the
groups
SPEAKEFS
A
and
SPEAKERS
3.
Each group
output
accepts speaker systems
with
a minimum
impedance
of
4
ohms.
lf it
is intended
to
oper-
ate
groups
A
and
B
simultaneously, the individual
speaker
systems
must
have
an
impedance
of
not
less
than
B
ohms.
SPEAKEhS
A
The DIN
sockets
(Speaker
group
A)
should
be
used
only
when operating
at
moderate
output
leve
ls.
SPEAKERS
B
The
two
pairs
of
brnding posts
(Loudspeaker
group B)
are
to
be
used,
when operating with
high
power
output.
The black binding
posts
are
wired
to
0
volts
and the
red posts are carrylnq
the
signal.
To
avoid
excessive
losses
when
installing
long
speaker lines,
do not
use
wires smaller than
gau
ge
19.
LOUDSPEAKER GROUP
SE
LECTORS
Loudspeakers
connected
to
the
outputs
A
and
the outputs
B
may be switched
on
and
off
by
means
of
togg e switches marked SPEAKERS
A
and SPEAKERS
B.
OVERLOAD
PROTECTION
The
stereo power
amplifier 8740 protects
itself
against
thermal
overload.
The
fail-safe circuit
operates
in
two
stages
in the
following
manner:
First temperature threshold
:
Excessive
temperature rise
in
the
power supply
or
at
the
heat
sinks
of
the
output
trans
stors
will
cause
the
stabilized supply voltage
to
becorne
disconnected. There
will
be no longer
any
signal
at the
speaker
outputs and
the illumination
of
the
peak program
meters
gets
turned
off.
Since
quiescent
current
will
no
longer
flow
through
the
output
devices,
rapid
cooling
is
achieved. As
soon
as
the
temperature
has
dropped
to
a
safe
level,
the
supply
voltages
to
the amplifier
and
meter
iliumination
become
activated
automati-
cally.
Second
temperature
threshold
:
Should
rhe
temperaiure
conlinup
to
liqe,
ä
so-
called
crowbar
circuit
becomes
activated.
A
sili-
cone-controlled
rectifier (thyristor) short-circuits
the
filter
capacitor in the power
supply section,
and
this
causes
the amplifier's
fuse
to
blow. The
amplif
ier
has
to
cool
off
and
a new
fuse must
be
inserted, before
it
can be
operated
again.
The fuse must
be
replaced
with
one
of
the correct
rype and
spec,ried currenL rating.
LOUDSPEAKER PROTECTION
lf
an
output
signal
in
excess
of
B
volts
and
with
a
frequency
of
less
than
3
Hz
remains
present
for
1
to
1.5
seconds,
the
earlier described crowbar
circuit
becomes
activated
also.
Thus
the
loud-
speaker systems connected
to
the amplifier
are
protected
from
quasi
DC
overload.
INPUT
ATTENUATORS
The attenuators
LEFT
LEVEL and
BIGHT
LE-
VEL
permit
accurate evel
adjustment
for
each
channel over
the
range
from
0 to
21
dB
in
steps
of
3 dB.
ln
the position
O
dB
and
with
a
signal
input
of
1
volt
the
amplifier
will
deliver
175
watts
into
a
4
ohms
load. (Output
voltage.
26.5
volts
across
4
ohms.)
HEADPHONE JACK
The jack
marked
PHONES
is provided
for
the
connection
of
stereophonic
headphones.
lf
the
Revox
tuner/preamplifier
8739
or
the
receiver
BTBO is used
as
a
signal source,
then the
voltage
appearing
on the jack
PHONES
will
be
identical
with that
on the
headphone
output
of
31391180
when the input
attenuators
are
set
to
their
15
dB position.
PEAK PROGRAM METERS
l-he
peak program meters
LEFT CHANNEL
and
RIGHT
CHANNEL
fully
conform
to
the
appli-
cable specifications
for
peak program
meters.
Their
linear
scale ranges
from
40
dB up
to
+5
dB.
The
O
dB
mark corresponds
to
a power
output
of
100
watts
into 4
ohms.
The
absolute
power
levels
for
a
4 ohms load
are
marked in
red
on the
meter
scales.
When
switching on the
elec-
tric
current
to
the
amplif
ier, the
meters become
internally illuminated
and
-
provided there
is
no
signal appearing
at
the
amplifier's inputs
-
the
pointerswill
drop
from 0dB to
the
-40
dB
mark.
Werbung
Inhaltsverzeichnis
