Yamaha CS-50 Servicing Manual page 48

8VOL TAGE CONTROlLED AMPLIFIER CIRCUIT
~
BASIC CONSTRUCTION OF VOLTAGE CONTROLLED AMPLIFIER CIRCUIT
An amplifier of which gain can be controlled by the applied voltage is called voltage controlled amplifier (VCA).
The VCA consists of variable conductance (grn) circuit of which conductance is controlled by the voltage-to-current
conversion of externally applied control votlage. This allows modification of the amplitude of sound signal passing
through the VCA with the control voltage.
Check
Check
point
Amplitude modulation
point
From WSC
Sine wave signal
CP4
circuit and overall
CHS
Envelope level
level control
level control
r
+15
""'G VCAl
3
(!C 3 IG00151l
8
3
LP2
i
1
~ov
'V
Level lever
VCA2
(JC5 IG00151 · ,
8
LC
M!Xcrrcuit
\ \ \ (R7 sheet)
T ;:;;:
< ""
~
o
e..ro
LEVEL§"
g
~
~CTI.-.-
o"
::;
. - - - - - - - - ,
control
VCA3
3
(IC
6
IG00151)
TP2
Check point
0
>-----<>
...
ToIl terminal
of PRA circuit
board
VCF circuit
o--o$
VCF tone signal
control
VCAl
~-
;::..
CP 3 3
(]C 4 IG00151)
LP 1
\
I
l:V
VCF LEVEL lever
8
B -IOOK
+
15
/VR16[
11
SL RA
\ \ f
f
1
0VlOV
1
10V OV
!OV !OV, 0 V l!OV
A D S R Lever
Fig. 6-1 Basic Construction of VCA Circuit
The VCA consists of three circuits: VCA 1 which is statically controlled by the manual lever on the panel, VCA 2
which is controlled by the sub-oscillator modulation (AM) signal and the control voltage of preset tone, and VCA 3
which is controlled by envelope voltage.
~~~~~~~~~~~~~~~~~~~~~~~~~~~------------~--~--39
-