Specifications
SWITCH
CRAFT
TYPE
128
TO
TO
LEFT
RIGHT
SPEAKER
SPEAKER
-
If,
after
the
headphones
are
installed,
it
is
found
that
the
right
and
left sides
are
incorrect
and
the
phones
are
not
of a construction which
can
be reversed
on
the
head,
this
can
be
most simply corrected
by
disconnecting
th
\
• I
resistors from
the
two
jack
lugs
and
interchanging
the
connections.
USING HEADPHONES WITH
THE
SCA-35
Headphones
made
for
high
fidelity usage
are
generally
of
the
low
impedance
type, designed
to
be connected
the
loudspeaker terminals of
the
amplifier.
These
can,
course, be
used
directly with
the
SCA-35
in
accordance
with
the
instructions of
the
headphone
manufacturer.
In
addition, for ease of
headphone
connection
and
use,
a hole for a
headphone
jack
is available on
the
back
panel
of
the
SCA-35. A
jack
of
the
Switchcraft
type
12B,
or
equivalent,
can
be
mounted
in
this
hole. A
type
290 plug,
or
equivalent, should be
used
with the 12B jack.
If
the
headphones
are
supplied with a different
type
of plug,
the
proper
jack
should
be obtained for
the
plug
used.
The
diagram
below shows
the
best
method
of connection
to
the
headphone
jack.
The
100 ohm, % watt, resistors
drop
the
signal
to
the
level which is required for head-
phones.
If
there
is
inadequate
level
after
installation, these
resistors
can
be reduced
to
47 ohms,
or
to
any
specific
value recommended
by
the
manufacturer
of
the
head-
phones. Some headphones have
the
resistors
built
in.
Then
it
is
not
necessary
to
install them,
and
straight
wires (insu-
lated
to
avoid
short
circuits) .should
be
connected
in
place
of
the
resistors shown.
If
it
is desired to
cut
out
the
loudspeakers completely
for
headphone
listening,
the
pictorial diagram shows how a
double pole switch
can
be
used
to eliminate sound from
the
loudspeakers
during
headphone
use.
This
switch
can
be
mounted
any
place along
the
loudspeaker wires so
that
it
can
be
kept
in
a convenient place if switching is required
frequently.
'\\
It
is
best
that
all
the
speakers should
be
identical types
when using
this
arrangement.
If
this is done,
the
sound
level
at
the
center
speaker
will be comparable with
that
of
the
stereo speakers.
The
volume control will reduce
the
level of
the
extra
speaker.
It
can
be used to reduce
the
level
of
this
speaker
to
zero,
and
then
the
stereo speakers will
function
in
their
normal
way.
If
the
control is
not
added,
and
it
is desired
to
cut
out
the
center
speaker
to restore
normal
stereo operation, this
can
be done
by
re-installing
the
jumper
on
the
back
panel.
This
can
also
be
done
by
adding
a switch to connect
together
the
two leads
to
the
center
loudspeaker.
This
switch
can
be
located
any
place which is convenient -
at
the
speaker
location,
or
at
the amplifier.
When
the
switch
is
closed,
there
will be
no
sound from
the
center
speaker,
and
normal
stereo reproduction will
be
obtained.
The
center
speaker
should be
phased
properly.
This
can
be done
by
listening to
the
smoothness of
transition
of
sound
between speakers while moving back
and
forth
between them.
If
there
are
sudden
jumps
in
localization of
the
sound,
the
two wires to
the
center
speaker
should
be
interchanged. Correct phasing should provide a smooth
change
in
location of
sound
from side speakers to
center
speaker.
If
the
center
speaker
is
used
remotely, phasing is
not
important.
NOTE:
At
any
time
that
the
center
speaker
is removed,
the
jumper
between
the
screw terminals must be reinstated.
If
neither
the
jumper
nor
center
speaker
is connected,
the
resulting
sound
will have no monophonic components.
There
will be
no
sound
with monophonic sources
and
unrealistic effects with stereo sources.
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RIGHT
LEFT
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Connection of
the
center
speaker is accomplished by
removing
the
wire link,
or
jumper,
which connects
the
left-
most screws
on
the
two loudspeaker
terminal
strips
and
connecting
the
two wires from
the
extra
speaker
to
these
two screws.
The
diagram below also shows how a volume,
or
level setting, control
can
be optionally
added
to control
the
level of
the
center
speaker.
The
control itself is a 4 watt,
wirewound, potentiometer
or
rheostat.
They
are
available
at
all
radio
parts
supply
stores.
The
control for
the
center
speaker
can
be connected
on
the
back
panel
of
the
SCA
using
the
hole which is avail-
able,
or
it
can
be
connected
at
the
loudspeaker
location-
this
is
particularly
convenient for a remote speaker.