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k)
Repeat steps ( h) through ( j) for the right channel.
1)
Observe
the junction of R669 and R670 with a high- impedance ( 10 megohm
or
greater) DC DVM. Adjust R671 (OVERSHOOT COMPENSATION THRESHOLD)
until the DVM reads + 4.50VDC.
m)
Return Card # 6 to its slot.
7: CARDS #0
This
procedure
is
performed twice:
once
for
Card # 0 and
once
for
Card # 1.
AND #1
Only Card # 0 will be referenced.
a)
Extend Card // 0.
b)
Place
the
COMPRESSOR
PROOF/OPERATE
switch
in
PROOF,
and
the
LIMITER PROOF/OPERATE switch in OPERATE. Switch the Loudness Controller
to DEFEAT.
c)
Connect
the oscillator to the left OPTIMOD-TV input, and set its frequency
to
lkHz.
Connect the AC VTVM to pin Z ( HF OUT) of Card # 0. Increase the
output
level
of
the
oscillator
until
the
level
observed
on
the
VTVM
stops
increasing, indicating that the limiting threshold of the Hilbert- Transform Clipper
has been reached. Vary the oscillator level between the threshold of limiting and
roughly
5dB
above
threshold
while
observing
the
VTVM
for
changes
in
level.
Adjust
R69 ( RATIO) to achieve no change in output level as the input level is
varied over a 5dB range. Note that each time R69 is readjusted, the level at pin
Z will change. To achieve a correct adjustment, you therefore have to readjust
R69 slightly and then test by varying the input level through its 5dB range while
watching to see if the output level changes.
When
you are finished, reduce the oscillator level until you are exactly at the
threshold of limiting. Measure the level at pin X of Card # 0, and verify that it
is + 6.2dBm + 0.5dBm 21kHz.
d)
Switch
the
LIMITER
PROOF/OPERATE
switch
to
PROOF.
Adjust
the
oscillator output level to produce + 6dBm at pin X ( the Hilbert- Transform Clipper
input). Observe pin Z with the THD analyzer, and adjust R25 ( HF DIST NULL) to
minimize the THD. Then adjust R50 ( GAIN TRIM) to produce + 7.0dBm at pin Z.
Observe
pin
Y with
the
THD
analyzer,
and
adjust
R44 ( LF
DIST
NULL)
to
minimize the THD. Then adjust R52 ( LF RESPONSE) to produce + 11.4dBm at pin
Y.
e)
Disconnect the oscillator from the OPTIMOD-TV input, and connect it to the
side of R56 closest to R61 ( RIPPLE NULL). Adjust the oscillator output level to
produce 1V rms @ 100Hz. Then observe pin Z with the AC VTVM and adjust R18
(HF
THUMP NULL) to minimize the 100Hz observed. Move the AC VTVM to pin
Y,
and
adjust
R38 ( LF
THUMP
NULL)
to
minimize
the
100Hz
observed.
f)
Set
the
LIMITER
PROOF/OPERATE
switch
to
OPERATE.
Reconnect
the
oscillator to the left OPTIMOD-TV input. Set the oscillator frequency to 2kHz,
and
adjust the oscillator level approximately 5dB above the threshold of limiting
of
the
Hilbert- Transform
Clipper.
Observe
the
THD
at
pin
Z and
adjust
R61
(RIPPLE NULL) to minimize the THD. ( 0.6% is a typical reading). When you are
done,
measure
the
level
at
pin
Z and
verify
that
it
is + 7.2dBm + 0.5dBm.
g)
Return Card # 0 to its slot.
h)
Repeat steps ( a) through ( g) for the right channel ( Card # 1).
E-6
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