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Low
level peak
lamp
lights
High level peak famp lights
NEW
CIRCUIT
DESCRIPTION
+7
2.
Point Peak Indicators
Since VU meter cannot follow,
indicated
level
is lower
than
actual.
—_
e@
Peak indicator circuit diagram
B
+3
>
®
®
od
ao
a
TRi
METER
"
:
Time
—>
.
af
a
.
< Fig. 15>
e@
Recording
Level Settings According to Tape
4—+
Distortion
can
be
suppressed
to below
3%
and
optimum
LED(L)
LEDIM)
recording
performed
by
setting
the
recording
levels
as
®
ry
-
14 Bi
follows.
HIGH
;
F
cae
Ri
LOW
LH Tape:
Lights occasionally at +3dB; does not light at
TRS
Re
|
+7dB
TR
,
Fe-Cr Tape:
Lights often
at +3dB;
lights occasionally at
©
=
+70B
a \
wy
ss
i
6
CrO2 Tape:
Does not light at either +3dB or +7dB
i
T
I
P r
|seRe
Zo i
Ra
|
Input and output level distortion characteristics
< Fig. 14 >
Presently
employed
VU
meters
are capable
of indicating
continuous
wave
signals of approximately
300msec. They
are incapable of following faster pulse type signals however,
resulting
in an indicated value considerably
lower than the
actual!
jevel. Thus
if the recording level is set in reference to
the VU meters, an instantaneous high level input can cause
an over level, resulting in distortion.
Peak
indicators
are provided for preventing this situation
and are capable
of indicating to about Imsec instantaneous
inputs.
Earlier
single point designs
(a single peak indicator
which
lights
at
+6VU)
however,
were
ambiguous
and
difficult
to
interpret.
The
indicator
was
not
supposed
to
light,
but
if
it
did
not
light,
the
level
could
not
be
determined.
The
2
point
peak
indicator
system
employed
in
the
AD-1800
represents
an
improvement
over
earlier systems.
Two
peak indicators are used with different lighting levels
(42.5~3VU
and
+6~7VU),
allowing
more
accurate
peak
indication.
Output
level
(dBm)
Distortion
(%)
20
3
5
7
.
gy
|
Input signal (1) is amplified approximately
10dB by TRt.
Dput level (dB)
< Fig. 16>
Previously,
it passed
from
(2) through
the SFR
and was
rectified
and
connected
to the meter.
However,
since the
meter
load is heavy, TR1
output voltage became
varied by
SFR
adjustment,
preventing
connection
to the peak
indi-
cator circuit.
TR2
is therefore
inserted
at
that
point
as
an
emitter
follower,
reducing
meter
amplifier
output
impedance
in
order not to influence meter and peak indicators.
The signal to the meter amplifier is divided at (3). The peak
indicator signal is rectified at (4) and the voltage is applied
to SFR2.
At this point the signal from the other channel is
mixed, while the peak indicator lighting level is determined
by adjusting SFR2.
When
(6)
reaches
a specified
voltage,
TR3
and
TR4
Darlingtons become on, and LED
(L) lights. C1 is inserted
at this point to
provide
a certain
degree
of lighting time,
since instantaneous
lighting with a pulse signal input would
be difficult to observe.
The
voltage at (6) is divided at R3 & R4. By a higher level
than
TR3
on
level, TR5
and TR6
become
on. R1 and R2
are
inserted
as
protector
resistors
to control
the current
flow through the LED.
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