Block Diagram - Roland SH-1 Service Notes

JUL 20 1978 SH-1
CIRCUIT DESCRIPTION / BLOCK DIAGRAM
2.
5.
The overload indicator
(LED) lights
-when
the external signal level
is exces-
sively high.
2. 6.
The Mixer has
VCO, SUB-OSC, NOISE, and EXT SIG controls.
2. 7.
The Envelope Follover integrates external signals to make the voltage envelope.
This is used to control the
VCF,
causing vah effects.
2.
8.
The Headphones amplifier
is a Class
A
amplifier that uses an output trans-
former.
3.
VCF/VCA BOARD ASSEMBLY
(VCFHr-l)
3.
1.
The VCF
is a
voltage-controlled
low pass filter. It comprises the 4-stage
Operational Trans conductance Amplifier circuits, in which the outoff fre-
quency varies in proportion
to the bias current.
When Resonance
control
is
raised up beyond
a predetermined position,
it
provides
a
feed back necessary
to start and sustain oscillation.
,
3. 2.
The VCA
is an amplifier whose gain
is
controlled by
the control voltage from
ENY-1
or ENV-2.
3. 3.
The ENV-1 is triggered with GATE+TRIG,
GATE, and LFO signals. The ENV-1 gen-
erates the control voltage which varies with time according
to the four control
settings;
Attack Time, Decay Time, Sustain
Level, and Release Time. The result-
ing voltage envelope
is
used
to control the VCO
(PWM), VCF, and VCA.
3. 4. The ENV-2
is
triggered with GATE and LFO signals. The ENV-2 has
two control
settings: Attack
Time and Release Time. The resulting voltage envelope
is
used
to control the VCA.
4.
POWER SUPPLY BOARD
ASSEIIBLY (PSH-26, PSH-34,
PSH-27)
Provides regulated, stable +15V and -15V.
PSH-26
(AC lOOV), PSH-34
(AC 117V), or
PSH-27
(AC 220/240V)
is
used.
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