Akai GX-747 dbx Service Manual page 16

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.
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15