Yamaha CS-50 Servicing Manual page 41

75%
pulse
Wide rectangular wave shape (pulse wave)
It has even-numbered harmonics in contrast to the square waveshape and is useful in producing brass-like
sounds like those of trumpets.
Ju
rv
Sine waveshape
It has only basic wave and is useful in producing flute-like sounds.
(NOISE SOURCE CIRCUIT)
This circuit produces the white noise used as source signal, and the pink noise used for modulation signal.
+
15
1M
ZD
22K N
,-----------"'-~--r~----0 ~
0-
il
To function switch as
VR!O
B·JOOK
I
flf-,
. st.b-oscillator si;snal
Low pass filter
NOISE source+
Pick-up amplitler
+Limiter amplifier
• Noise Generator
When the POWER switch is turned ON, the zener diode ZD is counter-biased to produce irregular current,
which constitutes the white noise with amplitude and frequency varied randomly: The noise is detected and
amplified by a pickup amplifier OP
1
and further amplified by a limiter amplifier OP
2
up to the saturation level
(30Vp-p) to give the white noise of constant amplitude.
• level Control Circuit
The level control circuit is a voltage-controlled amplifier (VCA) with the gain controlled by the voltage. The
voltage 0 to 1 OV serving as control voltage is applied to PIN 3 as input by the NOISE levervia the C terminal,
and controls the level of white noise coming from PIN 8 as output.
The gain is adjusted by VRJ 0 (B-1 OOk) so that the output level of white noise is 3Vp-p when the voltage at C
terminal is lOV.
The level-controlled white noise passes through the buffer amplifier and is output from the NO terminal to be
fed into the Nl terminal of oscillator circuit for the sound source signal.
G
low Pass FiittJr
The low pass filter cut off the high frequency components of white noise produced by the noise generator to
make the pink noise, which is output from the N terminal to be used as one of the modulation signal for the
sub-oscillator.
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