dbx 463X - Alignment Procedures; Threshold and Expansion Calibration

5
.
Alignment
Procedure:
Under
normal
conditions,
the
463X
should not
require
re-calibration
for
the life
of the
unit.
Allgment
Is
necessary
only
If
the
unit
has
bee
disturbed
mechanically
or
if
replacement
of
critical
components
has
been
necessary.
A.
RMS
Symmetry:
1.
Connect
the
audio
oscillator
to the
rear
panel
Input
jack
on
the
463X
2. Set
the
oscillator
for
50Hz,
at
-lOdBV
(0.316v
rms).
3.
Monitor
TP11
with
an
oscilloscope
and
adjust R31
for
a
100Hz
sine
wave.
The
amplitude
of
this
slnewave
should
be
15mV).
See
Photo
1.
symmetrical
70mV
p-p
(+/-
B.
RMS
Level:
l.Set
oscillator
for
1kHz
at
-lOdBv.
2.
Monitor
TP1
with
the
ac voltmeter
and
verify
-lOdBv
level
(+/-
O.lSdBv).
3.
Monitor
TP6
with
the
dc
voltmeter
and
adjust R25
for
a
readlnq
of
0 000
volts
(+/-
lOmV).
y
C.
VCA
Symmetry:
1.
Remove
oscillator
from
rear
panel
Input
Jack
and
connect
It
to
the
rear
panel
Stereo
Strapping
jack.
Use
a
tlp/rl
ng/sleeve
type
plug
with
the
signal
from
the
oscillator
connected
to
the
tip,
ground
to
the
sleeve
and
no
connection
to
the
ring
(this
Is
Important).
’
2.
Press
the
Slave
switch
on
the
rear
panel
and
verify
that
the
Slave
LED
on
the
front
panel
Is
lit.
3.
With
the
oscilloscope
connected
to
the
rear
panel
Output
jack,
adjust
Rii
for
minimum
ac
content
in
the
waveform.
The
peak
to
peak
amplitude
should
be
less
than
5mV.
See
figures
3,4.
4.
Remove
connection
from
Strapping
jack
and
return
Slave
switch
to
the
normal
(out)
position.
D.
HI
-2
Gain
Trim:
l.Set
oscillator
for
1kHz
at
-20dBv
and
connect
to
the
front
panel
Hi-2
Input
jack
with
a
standard
two
conductor
tip/sleeve
plug.
?.Set
R4
(Hi-2
trim)
fully
CCW
and
verify
a
-20dBv
reading
with
the
ac
voltmeter
at TP1
(4/-
i„5
dB).
3. Set
R4
fully
CW
and
verify
O.OdBv
at
TP1
(
4
/-
2.5dB).
Threshold
Calibration
and
Range
Check:
1. Set
front
panel
Threshold
control
to
midposition
(-30
panel
marking).
2.
Set
front
panel
More
control
full
right.
3. Set
oscillator
for
a 1kHz
sine
wave
at
-40dBv
and
connect
it
to
the
rear
panel
Key
In
jack.
4. Slowly
increase
the
oscillator
signal
level
until
yellow
Threshold
LED
turns
on.
5. Using
the
ac
voltmeter,
verify
that
oscillator
level
is
now
-30dBv
(4/-
6dB
)
.
b" 2
5
0dD
the
aC
vo1tmcter
for
ref-erenc
c,
decrease
the
oscillator
level
7.
Verify
that
the
Threshold
LED
is
now
off.
6. Locate
end
adjust R18
CCW until
all
Downward
Expansion
(DE)
LEDs
are
off.
9.
Adjust
R18
CW until
only
the
first
(-3)
DE
LED
is
lit.
30.
Increase
the
oscillator
level
until
the yellow
Threshold
LED
just
turns
on.
v