Advertisement
VCA (Voltage Controlled Ampllfler)
In accordance with breath strength, the VCA changes the sound volume.
VAD (+5V)
To VCF
HighPass Filter
To VCF
I p - : -
-
In accordance with pressed keys, CPU generates pitch signal PC6 which enters transistorT6. As the collector
of T6 is connected to T5 emitter, amplitude of T6 depends on T5 base voltage. Thus, DAC1 output voltage
(i.e. breath strength) determines the volume of pitch signal.
VCA atso consists of high pass and tow pass filters. According to the set tone, CPU provides signal PF4, PF6,
or PF7 which SEtect the fitters' cutoff frequency.
The following shows an equivalent block diagram of VCA Circuit.
Equivalent Circuit
52, S3
:.:,:
i , : , . r , ' .
i ; l ; i ; i :
l :
;|.. .
l: i: i':
i
t:-t !.'.
il;c'
iiii,
l:';';.
:, "-.
{
i
.
' l ' . ,
i
;
PA7-PAO
t"t
TL
Low Pas
Pitch signal
+5V
- 1 5 -
Advertisement
