4-1-5 LEVEL SENSOR FILTER
OR
BAND
PASS FILTER (Figs. 6-17 and 6-18)
H.P.F
L.F.F
r-----~r----------7
I
C9
CIO
I I
Rl7
Rl8 I
I NP
UT
~
10,1/63
0,1/63
I
I
I
I
Q.
0
<D
IO
I I I I
I
11
I
I
11
I
L-----J
1...
___________
J
+B
(+ll,6Vl
TR2
2SC2320
---
0
0UTPUT
-B
Hl.6Vl
Fig.
6-1
7 Level Sensor Filter Circuit
(dB)
0
~
- IO
J----12_d_B_/_O_C_T
___
.,.....
__
z
0
g;
-20
w
o::
-30
I I
I I
I I
I I
I I
1
fL=
17,5Hz
I
fH
=
20KHz
-40-1--L----~--.,........L----
IO
100
IK
IOK
IOOK
(Hz)
FREQ
Fig. 6-18 Level Sensor Filter Characteristic
This filter circuit
is
a
BPF
(Band
Pass
Filter) in which
the third order LPF (Low
Pass
Filter) and the second
order HPF (High
Pass
Filter)
are
combined.
the level sensor
in
the region where the frequency
response
of
the tape deck
is
not
flat. (Misoperation
prevention).
The purpose
of
this filter circuit
is
to prevent gain
error occurrence by attenuating the characteristic
of
4-1-6 WEIGHTING
NETWORK
(Figs. 6-19 and 6-20)
Cl4
R20
R21
INPUT
o--t
I-I
-c-....w,•8,--__.,
_
_,
3
•w.,\K•,,-------O
OUTPUT
0.1/63
27K
Cl~
0,0033/100
Fig. 6-19 Weighting Network Circuit
If signals in which the high frequency band
is
emphasized by the pre-emphasis circuit, are directly
recorded by the tape deck, the high frequency band
saturation level
of
the tape might be exceeded.
The weighting network prevents this by lowering the
amplification
of
the
VCA
(Voltage Controlled Ampli-
fier) by a corresponding amount
in
the case
of
As
shown, in the GX-747 dbx, fL=17.5
Hzmd
fH=20
kHz.
{dB)
+15
-10
100
IK
FREQ
IOK
(Hz)
Fig. 6-20 Weighting Network Cha1a.cteristic
signals containing many high frequency baod
com-
ponents. For this reason, a weighting
nitVJ"Ork
as
shown in Fig. 6-19 which has the
charac:e:J'.'istic
as
shown in Fig. 6-20
is
provided before
th.-e
RMS
sensor circuit. The weighting network rai-ses the
sensitivity
of
the level sensor for signals
With
a
high
content
of
high frequency band compo1er:,.ts,
and
lowers the amplification
of
the
VCA.
----------------SERVICEMANUALGX-747dbx----------------
15
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