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PCB &
CIRCUri DESCRIPTION
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RS-505 CIRCUIT DESCRIPTION
PCB AND CIRCUIT DESCRIPTION
1.
Mother Board OPH-28
1-1.
Master VCO
This
is
basically an
IC
oscillator whose frequency
is
variable by changing the
voltage applied
to
varicap
diode.
Maximum pitch
shift range
is
1
octave.
Frequency stability
is
within
15
cents at normal working
temperattire
.
1-2.
Top Octave Divider
The
VCO
output
is
divided
to
create
12
notes by
IC6.
The notes are octave downed
several times
by
the tone dividers at the next stage and routed to the corresponding
tone gates.
The top octave notes themselves are not supplied to the
tone gates.
2
SEP.10 1978
1-3.
Tone Divider, Tone Gate
(GTH-9,
10,
11)
Pressing
a
keyswitch applies negative voltage
to the
transistor keying circuit
Ql
Q7
....).
This negative voltage
is
applied
to the collectors of
Q2,
Q3
(Q5,
Q6
)
where they are chopped
by
the signal outputs from the dividers
TC-4024's applied
to the bases.
The negative voltage from a keyswitch also charges
C2
(C5,
C8
)
which discharges
upon releasing
a
key
and holds Ql
on.
The discharge rate
of this
capacitor
is
controlled by
the
frequency
of the
pulse that comes from Release Pulse Generator
via terminal
No.
4.
1-4.
Bass Priority
Three 8-bit priority encoders TC-4532 generate 6-bit codes by the on/off action
of the bass keyswitches.
These coded signals are fed
to the two IC's (TC4042)
and
latched.
At
the same time, the output of TC-4042
is
sent to the 8-bit priority
decoders
at the next stage
and
one out of 24 bass
notes
is
selected. The latched
signals are held until a next bass key signal
is
given.
The bass gate signals for the bass
AR
envelope generator are also generated by this
priority
circuit.
2.
String Voicing & Synthesizer VCFH-2
The
VCF
of the
synthesizer section
is
an LPF
of 24dB/oct. Its control
voltage
is
supplied through an Anti-log circuit. The control voltage
of the
VGA
is
also
supplied through an Anti-log circuit. The level adjusting trimmer pot
is
mounted
on each circuit.
3.
Bass Voicing LFO LPOH-2
3-1. Bass
Tone Gate
The output signals
of the
Bass
AR
Env
(Ql,
Q2) are
chopped by the bass tones at
Q5,
Q6,
and
Q7.
The output
is
sent to the tone filters and
the
VCF
of
synthesizer
section.
3-2.
LFO
This
is
an R-C sine wave oscillator whose frequency
is
varied from about
IHz to 15Hz
by the RATE
control. Its
oscillation
is
once stopped by the gate signal
which
is
generated by depressing
a key,
then
it starts
again and
the
amplitude
is
gradually
increased. The oscillation
stop time until
the start of
oscillation
is
adjusted
by the
DELAY TIME
control.
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