Head-Phone; General Layout; Circuit; Vco-4 - Roland SYSTEM 100 101 Service Manual

1976-7-30
SYSTEM
lOO-TOl
GENERAL LAYOUT
CONTROL PANEL ASSEMBLY
MAIN CHASSIS
ASSEMBLY
SIDE
BOARD
NO. 5
1976-7-30 SYSTEMlOO-lOl
DESCRIPTION
of
PCB
(Printed Circuit
Board)
ASSEMBLY
1.
VCO BOARD ASSEMBLY
(VCO-4)
VCO
Board
Assembly
is
consisted of
two
main circuits:
KEYBOARD
CIRCUIT and
VCO
CIRCUIT.
In
KEYBOARD
CIRCUIT,
there are
Keyboard
CV
(Control Voltage) Circuit and Keyboard Gate
Circuit.
1-1.
Keyboard
CV
Circuit
is
the
circuit
where
the constant
DC
current
is
applied
from
the constant current source
so
as
to produce always certain voltage drop
(1
V/Oct.) on the Keyboard
resistors
when
the current
comes
across them.
The voltage therein provided then goes
to S
& H
Circuit
(Sample
&
Hold),
where
it is
so designed to be held
until
another key
is
depressed on the Keyboard
to
have another voltage thus provided
to replace the then hold
one.
The
output voltage
from
this circuit
is
then used, after another voltage produced on the Glide Circuit being
added,
as a
control voltage for VCO, VCF,
and
for
Expander
(102),
etc.
Keyboard Gate Circuit, on
the other
hand, produces
the gate voltage
by
ON/OFF
manuals
of the keys and such
voltage thus produced
is
for use
as a
gate voltage on Envelope Generator and on Expander
(102), etc.
1-2.
VCO
is
an
oscillator
having
its
frequencies controlled by
the voltage
supplied from
the
Keyboard
or other
external sources (Voltage Controlled Oscillator).
Such
control voltage
from Keyboard
or other external sources are
firstly
mixed up
in
the Control Voltage
Mixer, to
be sent afterward
to
the exponential converter
circuit
where
the voltages so far having a linear
increasing ratio receive conversion to those having exponential increasing
ratio,
thereby
to fit for use as a
control voltage for frequency oscillator.
Since the
VCO
is
fundamentally
a
sawtooth wave form
oscillator, such other triangular or square
wave
forms are
to be obtained through the
Wave Form
Converter.
And, on the square
wave form
converter
circuit,
the pulse width modulation
is also
conducted by the control
voltage supplied
from
ADSR, LFO
and
the Manual, within a variable degree of
5%
to
50%
of
its
pulse width.
VCF-VCA
BOARD ASSEMBLY
(OP-27)
Included
in
this
Assembly
are:
VCF, HPF, VCA, Envelope Generator, LFO,
Noise Generator Head-Phone
Amplifier, and Mixer Amplifier.
2-1
.
VCF
is a
voltage controlled low pass
filter
consisting of the ladder type networks with
capacitors and transistors:
connected as the
diode
strings and here the control voltages supplied from the Keyboard
or other sources
provide the variations
on
the cutoff frequencies through this
VCF.
Also, provided here such characteristic
as
to have
a
peak at around the frequency cutoff point, varied tone
colours can be
made
obtainable, and
by
further being capable of
self-oscillation in a
wide range of frequencies,
setting of musical scale here
is
also possible on following
manuals on Keyboard.
2-2.
HPF
is
a high pass filter, of a differentiation circuit
composed
of
C &
R, and here the cutoff frequencies are
made
varied
following the control variations on
the resistor values.