ARP ODYSSEY User manual

ARPODYSSEY
SERVICE MANUAL
MODELS 2800 THROUGH 2823

SECTION 1
1.1 Introduction
This service manual is divided into three major
sections: А) Circuit Descriptions, B) Trim Pro-
cedures, and C) Board Test Points. The circuit
descriptions should be consulted when a problem is
suspected in a particular area of the instrument.
The trim procedures should be used to verify cali-
brations or when a component has been changed.
The board test points are a quick reference to verify
circuits with suspected problems and should be
checked whenever a problem has been identified.
1.2
Board
Identification
Three types of Odyssey models have been produced:
1) 2800, 2) 2810-2815 апа 3) 2820-2823. The model
and serial number are located at the rear or bottom
of the Odyssey chassis. Except for 2800, a typical
number might read: 2813-0490. For model 2800,
the first two digits of the serial number denote the
model,
such
as:
28490.
Listed
below
are
the
board
identification numbers for each model; they will be
referenced in the service manual by model number
for easy identification.
ODYSSEY-|
Model 2800
Board: A-1
B-1
C-1
PWR
SUP-1
ODYSSEY-II
Model
2810-2813
Model
2820-2823
Board:
A-II
Board:
A-IH
(with
PPC)
B-II B-II
C-I
С-ІІ
PWR
5ОР-ІІ
PWR
5ОР-ІІ
Note: Some Odyssey-2 models employ the older
style Board В-І.
1.3
Model
Changes
The
Odyssey
has
undergone
major
cosmetic
and
electrical
changes
since
its
original
production
in
1972,
however,
the
functional
capabilities
have
remained
virtually
unchanged.
The
following
are
the
most
noticeable
physical
differences
among
models:
PRELIMINARY INFORMATION
MODEL 2800
Black
and
white
face
panel
(some
later
models
have
black
and
gold
face
panels).
Pitch Bend knob
No Factory installed interface jacks.
Wrap
around
vinyl
bottom
cover.
MODEL 2810-2813
Black
and
gold
face
panel.
New
style
power
switch.
Factory
installed
interface
jacks:
Pitch
Bend
knob.
(Some
later
models
have
PPC.)
Wrap
around
vinyl
bottom
cover.
MODEL
2820-2823
(current
model,
Odyssey
'78)
Black
and
orange
face
panel:
Steel
chassis
Leather
endblocks
PPC
The
major
electrical
changes
found
in
the
Odyssey-ll
ὁ
as compared
to the
Odyssey-l
are:
1.
Uses
24db/octave
filter
in
place
of
12db/
octave.
2.
Improved
VCO
design
for
better
tracking;
and stability.
3.
Improved
power
supply
regulation.
4.
Improved
keyboard
current
source
for
CV
generation.
5.
Improved
S/H
memory
circuit
design.
1.4
Revisions/Changes
1.4.1
MODIFICATION
KITS
The
following
modifications
are
available
from
the
Factory
for
updating
older
style
Odysseys:
Modification For Model Kit No.
Interface
Jacks
2800
6800101
PPC
2810-2815
6800301
PPC
2800
6800501
1.4.2 KEYBOARD CONVERSION
The Odyssey-ll is designed to be used with а two bus
keyboard. When an Odyssey-ll is used with a three
bus keyboard, an interface board is inserted on the
molex pins on Board Α-ἱ to make the keyboard
compatible with the electronics. Illustrated below

are the two types of keyboards employed in the
Odyssey and their schematics.
TWO
BUS
KEYBOARD
Models
2810-2813
(Later
models
use
cat-whisker
style
shown
in
maintenance
section
6.2.
Schematic
remains
the
same.)
KYBD LO
4
99
DY,
is
“а
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HI
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E NL GATE BUS
GROUND
Р\-\
О GATE м
WEYS
085
e$
KEYS төбе $ IN
1.4.3 TYPES OF VOLTAGE CONTROLLED FILTERS
The 4023 voltage controlled filter is no longer avail-
able from the Factory. Instead, the newer 4075 filter
can be used to replace the 4023 with the following
modification (see Field Change Notice 007):
The earlier model Odyssey-lls used a 4035 voltage
controlled filter, which has since then been replaced
by the 4075. Мо modifications are necessary when
replacing
a
4035
filter
with
a
4075.
"THREE
BUS
KEYBOARD
GATE
TRIGGER
ον
KYBD LO
KYBD HI
M
cv
sus󰾰
اا
4 +15
8 XX =
1
GROUND
267 \
IIl
5
е
7
——
O
TRIG
BUS
#———
О
GATE
BUS
r
<
ш
з
v
a
°
е
9
5
a
ІМІЕНЬУСЕ ВО"
VIOLET
A change R1,2,& 3
to 680K
Change T4
to 100 ohm trimmer
Ж = Break connection

1.4.4 NOISE MODIFICATION
The newer style Odysseys use a zener diode as a noise
source instead of a noise transistor. Defective noise
transistors can be replaced with a zener diode, pro-
vided the following circuit modification is performed:
Zener diodes tend to produce a greater spectrum of
white noise with little or no noise break-up.
1.9 Specifications
Noise
Generator
Noise
spectrum
types:
White
and
Pink
Voltage
Controlled
Oscillators
Waveforms: Sawtooth, Square, Pulse, Dynamic Pulse
Frequency range: VCO 1 іп low freq. mode, .2 Hz
to
20
Hz;
VCO
1
and
VCO
2
(audio
range),
20 Hz to 20 KHz
Warm up drift: 1/30 semitone from turn on max.
Pulse width: 5096 to 596
Pulse
width
modulation:
ADSR,
+45%;
ГЕО,
+15%
Voltage controlled response: 1V/oct.
Maximum frequency shifts: LFO sine wave, +1⁄2
oct.;
LFO
square
wave,
+1.5
oct.;
ADSR
+9oct.;
S/H *2 oct.
Note: VCO 1 is a low note priority; VCO 2 is high
note
priority
Transpose
Positions:
Down
2
octaves,
normal,
up
2
octaves
Pitch Bend
Frequency
shift:
About
+
1
oct.
(exactly
1
octave
on Odyssey-2)
PPC
Frequency
shift:
About
5
semitones
+1
semitone.
Portamento
.
Maximum
speed:
About
.01
msec./oct.
Minimum speed: About 1.5 seconds/oct.
Ring Modulator
Type: Digital
Input signals: VCO 1 and VCO 2 pulse waves
ud
REMOVE
|
O.O
гмеоте
Cn
ws
Voltage
Controlled
Filter
Type: Low pass
Frequency range: 16 Hz to 16 KHz
Maximum usable Q: 30
Resonance 1⁄2 to self oscillate
Voltage
controlled
response:
1V/oct.
Voltage
Controlled
Amplifier
Dynamic
Range:
80dB
Sample and Hold
Command sources:
Sampled signals: VCO 1 square wave and sawtooth
wave,
VCO
2
square
wave
and
pink
noise
Keyboard or LFO trigger
ADSR
Envelope
Generator
Attack
time:
5
msec.
to
5
seconds
Decay
time:
10
msec.
to
8
seconds
Sustain
level:
O
to
10096
of
peak
Release
time:
15
msec.
to
10
seconds
AR Envelope Generator
Attack
time:
5
msec.
to
5
seconds
Release
time:
10
msec.
to
8
seconds
Audio Outputs
High
level:
2.5VPP
max.;
100K
impedance
Low
level:
.25VPP
max.;
10K
impedance
Interface Jacks
Keyboard
CV
IN/OUT:
1V/oct.
Gate
OUT:
+10V,
key
down;
OV
all
keys
up
Gate IN: +8V minimum
Trigger
OUT:
+10\/
pulse
on
key
depression,
10
microsec.
duration
Trigger
IN:
+8V
pulse
min.,
10
microsec.
duration
minimum
External
Audio
Input:
500
millivolts
for
full
output

9)
Front and Back Panel Configuration
Model 2823
HC
19:9
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ASSEMBLY/DISSASSEMBLY
MODEL 2800 : 2815 MODEL 2820 - 2823
Ф
NOTE: These
two screws
MUST be
replaced in
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SECTION 2 CIRCUIT DESCRIPTIONS (Board А-1)
2.1.1 Trigger Circuit
Each key on the keyboard has its own capacitor-
resistor-diode network. The capacitors are normally
charged to +15 volts until a key is depressed at which
time the capacitor discharges through the diode
creating a trigger pulse on the trigger bus rod. Q1
through O4 are a monostable multivibrator which
delays the trigger pulses 15 milliseconds to allow
the gate and CV to stabilize.
2.1.2 PITCH BEND
P1, the pitch bend control, supplies a control voltage
to both VCOs on Board B. CR4 and СНБ create a
'dead' zone when the control is centered.
2.1.3.
CURRENT
SOURCE
Q5 supplies constant current to a resistor divider
chain made up of thirty-six 100 ohm resistors con-
nected in series, The CV contacts are located at the
junction of each of the 100 ohm resistors to supply
a specific voltage to the contro! voltage memory
when a key is depressed. There is a three volt drop
across the entire resistor chain, or one volt per octave.
T1, the Volts/Octave trimmer, adjusts the current
through the resistor chain to produce the correct
voltage
drop
across
the
keyboard.
2.1.4. TRANSPOSE SWITCH
Half of the transpose switch is connected to the
bottom end of the resistor chain to, in effect, add
two or four octaves worth of resistance (about
1200 or 2400 ohms) to the resistor chain. This raises
the control voltage level supplied to the CV memory.
The following chart summarizes the CV output for
low 'C' and high 'C' on the keyboard for each of the
transpose switch positions:
TRANSPOSE
SWITCH:
DOWN 2 OCT.
NORMAL
UP 2 OCT.
The remaining half of the transpose switch com-
pensates the second voice control voltage for the
difference in the resistor chain resistance.
2.1.5 CV Memory Circuit
Об апа АЛА are a FET input op amp which buffers
the voltage from the keyboard CV bus and supplies
it to the memory circuit through R23 and CR3.
When a key is depressed, +15 volts is supplied from
the keyboard gate through CR2 and R21 which
reverse biases CR3 and allows Q7 to conduct. The
control voltage from A1A is then allowed to charge
the memory capacitor, C8. When a key is released,
Q7 turns off to prevent СВ from discharging. О8 and
A1B are a FET op amp which buffers the control
voltage on C8 and supplies it to the control input of
VCO 1 and VCO 2 on Board B and to the VCF on
Board C.
2.1.6
Second
Voice
CV
Generator
When two or more keys are depressed, a section of
the resistor chain is effectively shorted out which
drops the voltage at the top end of the resistor chain.
This voltage drop corresponds to the ‘voltage dif-
ference’ between two held keys. A2A is a unity gain
buffer which monitors the voltage at the top of the
resistor chain and supplies it to A2B. A2B sums the
voltage from А2А with the voltage supplied by R31
and R30. These resistors are selected to produce zero
volts on the output of A2B when either no keys or
one key is depressed.
When two or more keys are depressed, the voltage at
the top end of the resistor chain drops, which, in
turn, decreases the voltage supplied to 228. 228
then supplies the difference voltage to the control
input of VCO 2 where it is summed with the
control voltage from the CV memory circuit. This
summation allows VCO 2 to be controlled by the
highest key depressed. Since VCO 1 is fed the con-
trol voltage from the CV memory only, its pitch is
controlled by the lowest key depressed.
2.1.7 Noise Generator
The noise generator circuit produces 10VPP white
and pink noise signals which are supplied to the VCF
audio input and the S/H mixer. The noise is obtained
by amplifying a reversed biased transistor junction
(Q9) in avalanche breakdown. Q9 is a transistor
selected for optimum avalanche characteristics; and
therefore, has good noise producing capability. A3
amplifies and clips the noise signal. АЗ filters the
noise to provide pink noise to the VCF and S/H.

CIRCUIT
DESCRIPTIONS
(Board
B-
1)
2.2.1
Sample
&
Hold
(S/H)
The
sample
and
hold
circuit
provides
a
DC
voltage
output
by
sampling
and
storing
the
instantaneous
voltage
level
of
signals
on
its
input
each time
a
trigger
pulse
is
provided.
This
stored
voltage
is
held
until
the
next
trigger
pulse
occurs.
Signals
which
are
to
be
sampled
and
applied
to
pin
3
of
A3.
A3
is
an
op-
erational
transconductance
amplifier
(OTA),
which
is
used
as
a
gated
voltage
follower:
when
a
pulse
is
applied
to
pin
5
of
Z3,
capacitor
C7
charges
to
the
voltage
level
on
pin
3.
This
voltage
level
is held
until
another
pulse
is
applied
to
pin
5.
ОЗ
buffers
the
voltage
on
C7
and
supplies
it
to
A2B
through
the
lag
slider
(P16).
A2B
is
a
unity
gain
buffer.
The
sample
and
hold
output
is
supplied
to
the
control
inputs
of
VCO
1
and
УСО2
and
to
the
УСЕ
on
Board
С.
2.2.2
Low
Frequency
Oscillator
(LFO)
The
LFO
produces
a
triangle
and
square
wave
output
in
a
frequency
range
from
about
.1
Hz
to
25
Hz.
Z1A
and
C3
are
an
integrator
which
charges
from
current
passing
through
R11.
218
is
а
hysteretic
switch
whose
output
switches
from
-15
volts
to
+15
volts
when
the
output
of
Z1A
reaches
+5
volts.
This
then
reverses
the
direction
of
current
through
R11
and
the
rate
control
(Z5)
and
thus
the
direction
of
integration
at
the
output
of
Z1A.
When
the
output
of
Z1A
reaches
-5
volts,
the
output
of
Z1B
switches
back
to
-15
volts
and
the
cycle
repeats.
An
LFO
reset
pulse
is
supplied
from
the
keyboard
every
time
a
key
is
depressed.
O1
and
Q2
are
turned
on
momentarily
by
the
keyboard
trigger
pulse
to
discharge
the
integrating
capacitor
(C3)
thus
reini-
tializing
the
LFO
to
zero.
2.2.3
Voltage
Controlled
Oscillators
(VCO)
Oscillator circuit (VCO 1 & 2): Control voltages
from the keyboard, initial frequency and fine tune
sliders, pitch bend (2800 only) and both FM input
sliders are summed on the base of O4. O4 and Q5 are
a linear voltage to exponential current generator; for
every volt applied from the keyboard, the current
through Q5 will double. C12 is the integrating
capacitor; it is initially charged to +15 volts and
discharges through R51 and Q5 toward ground. Q5
determines the discharge time of the capacitor and
therefore the period of oscillation. Z1D is a CMOS
nand gate used as a comparator. When the voltage on
pin 12 of 210 falls below “7,5 volts, the output of
Z1 (pin 11) changes from zero volts to +15 volts
which turns on Q10, О7 and Об. Об recharges the
integrating capacitor (C12) to +15 volts to start the
cycle over again.
Q8 buffers the sawtooth wave on C12 and supplies it
to
the
sawtooth
to
pulse
converter
and
09,
the
output emitter follower. The oscillator circuit for
VCO 2 is the same as VCO 1. When the ‘SYNC’
switch is on, the reset pulse from VCO 1 is applied to
Z2D which causes VCO 2 to reset at the same time as
VCO 1, regardless of the voltage level on pin 12 of
Z2D. The waveform on the output of VCO 2 is then
synchronized with VCO 1.
Sawtooth to square wave converter: Z1A and Z1B
are a R-S flip-flop with pin 8 used as a comparator.
The reset pulse from Z1C is supplied to pin 1 and the
sawtooth wave to pin 8. Аз the sawtooth wave is
raised above the zero reference by the pulse width
trimmer and sliders (T2, P8 and P9) the flip-flop will
change state on a different point of the sawtooth
slope resulting in a different pulse width. With all
of
the
pulse
width
sliders
on
the
front
panel
at
mini-
mum, the pulse wave should be square (5096 duty
cycle). The pulse wave output is supplied to the
audio input of the VCF on Board C and to the ring
modulator circuit on Board B.
2.2.4 Ring Modulator
The ring modulator utilizes two CMOS nand gates
(218 and 228) and O18 in an exclusive ‘or’ functior.
Square
waves
from
VCO
1
and
VCO
2
are
supplied
to pin 5 of Z1 and Z2 and the output is taken from
the emitter of O18.
GATE TRUTH TABLES
AND GATE
B C
XCLUSIVE OR
VCO
2
|
|
ΠΗΓΗ ΠῚ
RING MODULATOR OUTPUT

2.3.1
Voltage
Controlled
Filter
(УСЕ)
Audio
signals
from
both
VCOs,
the
ring
modulator,
and
the
noise
generator
are
applied
to
the
audio
input
of
the
voltage
controlled
filter
(pin
1,
4023)
through
C1.
Control
voltage
from
the
S/H,
LFO,
KYBD
CV,
and
the
envelope
generators
are
summed
and
inverted
by А1. The control
input of the МСЕ accepts
negative
going
control
voltages;
as
the
voltage
on
pin
3
of
the
4023
module
is
decreased,
the
filter
cutoff
increases.
Signals
on
the
output
of
the
VCF
(pin
10)
are
fed
back
to
the
resonance
input
(pin
2)
via
the
resonance
slider, (P2).
2.3.2
Voltage
Controlled
Amplifier
(VCA)
Audio
signals
from
the
VCF
are
processed
through
the
high
pass
filter
(C3,
R13
and
P3)
and
connected
to
the
noninverting
input
of
A3.
A3
is
an
operational
transconductance
amplifier
(OTA)
whose
gain
is
a
function
of
the
current
supplied
to
pin
5.
Control
voltages
from
the
two
envelope
generators
and
the
УСА
gain
slider
are
connected
to
Q1
which
supplies
current
to
the
OTA.
T2,
the
control
reject
trimmer,
balances
the
inputs
of
the
OTA
to
minimize
the
effect
of
control
voltages
on
the
audio
output
of
the
VCA.
2.3.3 AR Envelope Generator
The
Attack-Release
envelope
generator
produces
a
control
voltage
with
variable
rise
and
fall
times.
Itis
used
to
control
the
VCF
or
the
VCA.
When
a
gate
voltage
is
supplied
by
the
keyboard
or
the
LFO
through
510,
Q4
turns
on
which
charges
capacitor
C7
through
P5,
R32
and
CR5.
The
position
of
P5
(Attack
Slider)
determines
the
time
C7
takes
to
charge
up.
When
the
gate
voltage
is
removed,
Q4
turns
off
which
allows
Q5
to
turn
on.
The
voltage
on
C7
then
discharges
through
CR6,
P6,
R31,
and Q5.
P6
(Release
slider)
sets
the
release
time.
Q6
and
Q7
buffer
the
voltage
on
C7
and
supply
it
to
the
VCA
and
VCF.
2.3.4
ADSR
Envelope
Generator
The
Attack-Decay-Sustain-Release
envelope
generator
produces
a
control
voltage
with
variable
rise
and
fall
times.
It
is
used
to
control
the
VCF
or
the
VCA
and
a
gate
and
trigger
signal
must
be
supplied
from
the
keyboard
or
LFO
to
start
the
ADSR
voltage
rising.
Attack:
When
a
gate
signal
(+10
volts)
is
supplied
through
S8,
Q8,
09
and
010
turn
on
which
then
allows
O16
to
turn
off.
With
Q16
off,
a
trigger
applied
through
C9
and
R55
will
momentarily
turn
CIRCUIT DESCRIPTIONS (Board C- 1)
TRIGGER
ATTACK
LI
AR OUTPUT
ADSR
OUTPUT
SUSTAIN
KEY DOWN
NOTE: The ADSR is initiated with a gate and trigger volt-
age, and the AR envelope requires only the gate.
оп О18 and 017. 017 then supplies +15 volts
through
CR18,
CR19,
CR17
and
R57
to
hold
Q18
on. 018 and 017 (the attack latch) now supplies
+15
volts
through
the
attack
slider
(P4),
R43,
and
CR9 and charges up the integrating capacitor, C8.
012, 013, and 014 buffer the voltage оп C8 апа
provides it to the VCA and МСЕ. Q15 is the peak
detector which monitors the output of the ADSR.
When the ADSR voltage reaches its maximum, (about
*10 volts), Q15 will turn on and provide this voltage
to the base ої Q16 through CR15. 016 then grounds
out the voltage on the base of 018 to unlatch 018
and Q17 and end the attack portion of the ADSR
cycle.
Decay & Sustain: When the attack portion of the
ADSR cycle has completed, the voltage on C8 is
allowed to discharge through CR11, R47, and the
decay slider (P15) to the emitter of Q11. The sustain
slider (P16) sets the voltage level on the base of O11.
When the voltage level on the emitter of O11 falls
below the level on the base, Q11 turns off and
prevents the voltage on O8 from discharging further.
Release: When the gate is removed, the remaining
voltage оп C8 is discharged to ground through CR 10,
R44
and
the
release
slider
(P17).

CIRCUIT DESCRIPTIONS (Board А-11)
2.4.1 Keyboard Current Source
The keyboard current source supplies constant
current through thirty-six 100 ohm resistors con-
nected in series. These resistors are a voltage divider
supplying specific voltages for each key on the key-
board. The top end of the resistor chain is connected
to J2-5 and the low end to J2-6. The current source
produces a 3 volt drop across the entire keyboard, or
1 volt per octave. The keyboard voltage is fed to
the
CV
memory
via
the
CV
bus
rod.
Pin
7
of
Z2A
(high
end
of
the
resistor
chain)
is
O
volts
when
either
no
keys
or
one
key
is
depressed
and
pin
6
of
Z2A
(low
end
of
the
resistor
chain)
is
+3
volts.
When
two
keys
are
depressed,
the
contacts
and
bus
rod
short
out
a
section
of
the
resistors
in
the
divider
chain
which
reduces
the
gain
of
Z1A
thereby
raising
the
voltage
оп
Z2A
pin
7.
This
voltage
increase
represents
the
voltage
difference
between
two
held
keys.
When
this
difference
voltage
is
sub-
sequently
added
to
the
control
voltage
at
the
control
input
of
VCO
2
(Bd.
B),
high
note
priority
control
over
the
pitch
of
VCO
2
is
produced.
2.4.2
Control
Voltage
Memory
Control
voltages
supplied
from
the
keyboard
CV
bus
are
buffered
by
a
unity
gain
amplifier,
Z4A.
This
voltage
is
then
supplied
to
the
memory
capacitor
C8
through
the
portamento
slider
(R30)
and
the
gating
FET
(Q3).
ОЗ
is
turned
on
by
the
gate
generator
circuit
only
while
a
key
is
depressed.
O4
and
Z4B
are
a
FET
follower
with
high
input
impedance
to
buffer
the
voltage
on
capacitor
C8.
J3-1
and
J3-2
аге
connected
to
the
portamento
footswitch
jack
so
that
the
portamento
slider
can
be
bypassed
while
the
foot-
switch
is
plugged
in.
2.4.3
Pitch
Bend
Pitch
Bend:
The
Pitch
Bend
control
supplies
an
off-
set
voltage
to
Z2B
to
be
summed
with
the
control
voltage
from
Z4B
(CV
memory).
СВЗ
and
CR4
create
a
'dead'
zone
when
the
control
is
centered
and
R27
calibrates
the
output
to
exactly
plus
and
minus
a volt.
2.4.4 PPC
The PPC circuit contains three resistive carbon strips,
three conductive rubber strips and various summing
resistors. Each end of the carbon strip is connected
to a designated voltage source, while each end of the
conductive rubber is making contact with the sum-
ming resistors. As the PPC button is depressed, the
conductive
rubber
makes
contact
at
various
points
on
the
carbon
strip
which,
in
turn,
provides
various
degrees
of
control
voltage
to
the
summing
resistors.
The
conductive
rubber
is
tapered
so
that
maximum
sensitivity
is
achieved
at
the
top
of
the
button.
2.4.5 Transpose Switch
Transpose: The transpose switch also supplies an
offset voltage to Z2B to be summed with the control
voltage from Z4B. R23 calibrates the output to
exactly plus and minus 2 volts.
246 Summing Circuit
Summing: The output of Z4B is +3 volts when high
"С"
is
depressed
апа
0
volts
when
low
"С"
is
depressed.
This control voltage is summed with the offset
voltages from the transpose and pitch bend circuits
on the input of Z2B. 72В is a unity gain inverter
whose output will be 0 volts with low "С" depressed
(pitch bend and transpose in the normal position)
and +3 volts with high ‘C’ depressed. This voltage is
supplied to the VCOs on Board B (pitch control) and
the VCF on Board C (filter cutoff control).
2.4.7
Gate
Generator
Each gate contact on the keyboard is connected to
a 2.2K ohm resistor to ground. When a key is de-
pressed
the
gate
bus
voltage
drops
from
+15
volts
to
about
+10
volts
which
turns
on
Q1.
Q1
supplies
two
gate signals:
SIGNAL:
CV
Memory
-15V
+15
М
Key
up:
Key
down:
Location:
Q1 coll.
Gate
out
ом
з10
М
J4-3
+15 V GATE BUS VOLTAGE
+10 V
; H +8 V
4
Key down Second key down LAU keys up
| | TRIGGER OUTPUT
2.4.8 Trigger Generator
When a key is depressed, the gate bus voltage drops
from +15 volts to about +10 volts. Additional key
depressions will drop this voltage still further. These
voltage transitions are coupled through capacitor C1
and R4 to 02. Capacitor C2 is charged to *15 volts
by Q2 when a key is depressed. 21С апа 210 are
CMOS папа gates (threshold is +7.5 volts). As C2

charges up, 210 pin 11 will produce a 10 millisecond
pulse (the pulse width is determined by C2) which
is supplied to Q8. О8 will conduct during the fall of
the pulse from Z1D to provide a +10 volt trigger
pulse (20 microsecond duration) to Board C and B.
Trigger pulses from external sources are coupled
through C20, 21А and Z1B to O8. Z1A and 218
are connected in parallel to increase drive.
2.4.9 Noise Generator
The noise generator circuit produces 10VPP white
and pink noise signals which are supplied to the VCF
audio input and the S/H mixer. The noise is obtained
by amplifying a reversed biased transistor junction
(ОБ) in avalanche break down. ОБ is a transistor
selected for optimum avalanche characteristics and
therefore
has
good
noise
producing
capability.
Об
is a buffer and 25 amplifies and clips the noise signal.
Z3 filters the noise to provide pink noise to the VCF
and S/H.
NOTE: The more recent model Odysseys employ a
zener diode instead of a noise transistor. See the re-
visions section 1.4.4 for the circuit change.
CIRCUIT
DESCRIPTIONS
(Board
B-II)
2.5.1 Sample δι Hold (S/H)
The sample and hold circuit provides a DC voltage
output by sampling and storing the instantaneous
voltage level of signals on its input each time a trigger
pulse is provided. This stored voltage is held until
the next trigger pulse occurs. Signals which are to be
sampled are applied to pin 3 of Z1A. Z1A amplifies
and buffers the signal and supplies it to O1. When a
trigger
from
either
the
LFO
or
the
keyboard
is
received through СЗ, О1 conducts just long enough
for the memory capacitor (C1) to assume the new
voltage level. Then O1 turns off until another trigger
is supplied. 02 and 22А аге а FET op amp follower
which buffers the voltage on C1 and provides it to the
lag circuit (R15 and C2) and the output buffer (Z2B).
Noise
Generator
LFO
Trigger
(LFO Trig. off)
———_h b
S/H
Output
2.5.2 Low Frequency Oscillator (LFO)
The LFO produces a triangle and a square wave out-
put in a frequency range from about .1 Hz to 25 Hz.
25А and C7 are ап integrator which charges from cur-
rent passing through R33. Z5B із а hysteretic switch
whose output switches from -15 volts to +15 volts
when the output of Z5A reaches +5 volts. This
change in output polarity then reverses the direction
of current through R33 and the rate control (R34)
and thus the direction of integration of the output
ої
ZbA.
When
the
output
of
Z5A
reaches
-5
volts,
the
output
of
Z5B
switches
back
to
-15
volts
and
the
cycle
repeats.
An
LFO
reset
pulse
is
supplied
from
04
every
time
a
key
is
depressed.
ОБ
is
turned
on
momentarily
by
the
LFO
reset
pulse
and
discharges
the
integrating
capacitor
(C7)
thus
reinitializing
the
LFO
output
to
zero.
2.5.3
Voltage
Controlled
Oscillators
(VCO)
Control
voltages
from
the
keyboard,
initial
fre-
quency
and
fine
tune
sliders,
the
sample
and
hold
circuit,
LFO
square
wave
and
sine
wave,
and
the
ADSR
are
summed
on
the
base
of
Q6.
Q6
and
O7
are
a
linear
voltage
to
exponential
current
generator;
for
every
volt
applied
to
the
control
input
of
the
VCO
from
the
keyboard,
Q6
will
conduct
twice
as
much
current.
C11
is
the
integrating
capacitor;
it
is
initially
charged
to
15
volts
and
discharges
through
R61
and
O7
towards
ground.
Q7
determines
the
discharge
current
of
the
capacitor
and
therefore
the
period
of
oscillation.
09
buffers
the
voltage
on
C11
and
supplies
it
to
a
comparator,
Z3B
and
Z3A.
Pin
2
of
Z3A
is
fixed
at
about
+7.5
volts.
When
the
voltage
on
pin
4
of
Z3B
decreases
to
below
+7.5
volts,
Z3A
turns
оп
Q11
which
supplies
+15
volts
to
the
gate
ої
Q8.
О8
then
charges
capacitor
C11
back
to
+15
volts
to
start
the
cycle
over
again.
R63.
C10
and
R59
supply
current
to
Q7
as
the
frequency
of
the
oscillator
is
increased
to
prevent
the
oscillator
from
going
flat
due
to
the
recovery
time
of
the
circuit.
O12
is
a
phase
splitter
which
takes
the
sawtooth
from
pin
3
of
Z3
and
supplies
it
to
the
oscillator
output
and
the
pulse
converter.
The
wave-
form
on
the
emitter
of
012
is
7.5VPP
negative
going
(*7.5
volts
offset),
and
the
collecter
is
about
БУРР
positive
going
(zero
referenced).
Sawtooth
To
Pulse
Converter:
Z3C
and
Z3D
is
a
11

12
Sawtooth
output
VCO
Square
Wave
output
comparator with R86 and R87 setting the switch
point at +7.5 volts. The sawtooth wave from the
oscillator is supplied to the comparator through R75
and C12. Z3E supplies an offset current to raise or
lower the DC level of the sawtooth wave to change
vco
CIRCUIT
DESCRIPTIONS
(Board
С-П)
2.6.1 Voltage Controlled Filter (VCF)
Audio signals from both VCOs, the ring modulator,
and the noise generator are applied to the audio
input of the voltage controlled filter (pin 1, M1)
through C1 and C13. Control voltages from S/H,
LFO, KYBD CV, and the envelope generators (ADSR
and AR) are summed and inverted by Z1. The con-
trol input of the VCF accepts negative going control
voltages; as the voltage on TP-1 is decreased, the filter
cutoff increases. Signals on the output of the VCF
(pin 10) are fed back to the resonance input (pin 2)
via the resonance slider (R73).
2.6.2 Voltage Controlled Amplifier (VCA)
Audio signals from the VCF are processed by the
high pass filter (C8, R13 and R74) and connected to
the noninverting input of Z2. Z2 is an operational
transconductance amplifier (OTA) whose gain is a
function of the current supplied to pin 5. Control
voltages from the two envelope generators and the
МСА gain slider are connected to Q1 which supplies
current to the OTA. R70, the control reject trimmer,
balances the inputs of the OTA to minimize the
effect of control voltages on the audio output of the
VCA.
2.6.3 AR Envelope Generator
The Attack-Release envelope generator produces a
control voltage with variable rise and fall times. It is
used to control the VCF or the VCA. When a gate
voltage is supplied by the keyboard or the LFO
through S10, O4 turns on. which charges capacitor
C7
through
R76,
R32
and
СВ5.
The
position
of
R76
(attack
slider)
determines
the
time
C7
takes
to
charge up. When the gate voltage is removed, 04
the
point
at
which
the
comparator
switches.
When
the
pulse
width
sliders
on
the
front
panel
are
at
mini-
mum,
the
comparator
will
switch
exactly
in
the
middle
of
the
sawtooth
slope,
producing
a
square
wave
(5096
duty
cycle).
The
output
of
the
compara-
tor
(Z3,
pin
8)
is
processed
through
24А
which
inverts
the
shapes
of
the
pulse
output.
2.5.4
Ring
Modulator
The
ring
modulator
utilizes
two
CMOS
nand
gates
(Z4B
and
24С)
and
Q20
in
an
'exclusive
or'
function.
Square
waves
from
VCO
1
and
VCO
2
are
supplied
to
pin
5
and
pin
8
of
Z4
and
the
output
is
taken
from
the
emitter
of
Q20.
turns
off
which
allows
Q5
to
turn
on.
The
voltage
on
C7
then
discharges
through
CR6,
R77,
R31,
and
ОБ.
R77
(release
slider)
sets
the
release
time.
Q6
and
O7
buffer
the
voltage
on
C7
and
supply
it
to
the
VCA
and
VCF.
2.6.4 ADSR Envelope Generator
The Attack-Decay-Sustain-Release envelope generator
produces a control voltage with variable rise and fall
times. It is used to control the МСЕ or the VCA. A
gate and trigger signal must be supplied from the key-
board or LFO to start the ADSR voltage rising.
Attack: When a gate signal (+10 volts) is supplied
through S8, Q8, O9 and O10 turns on which then
allows Q16 to turn off. With Q16 off, a trigger
applied through C9 and R55 will momentarily turn
оп 018 and O17. 017 then supplies +15 volts
through CR18, CR19, CR17 and R57 to hold 018
on. O18 апа 017 (the attack latch) now supplies
*15 volts through the attack slider (R85), R43, and
CR9 and charges up the integrating capacitor, C8.
012, 013 and 014 buffer the voltage on СВ and
provides it to the МСА and МСЕ. О15 is the peak
detector which monitors the output of the ADSR.
When
the
ADSR
voltage
reaches
its
maximum,
(about
*10 volts), Q15 will turn on and provide this voltage
to
the
base
ої
016
through
CR
15.
O16
then
grounds
out
the
voltage
on
the
base
of
Q18
to
unlatch
O18
and 017 and end the attack portion of the ADSR
cycle.
Decay & Sustain: When the attack portion of the
ADSR cycle has completed, the voltage on C8 is
allowed to discharge through CR11, R47 and the
decay slider (R86) to the emitter of Q11. The sustain

slider
(R87)
sets
the
voltage
level
on
the
base
ої
O11.
When
the
voltage
level
on
the
emitter
of
011
falls
below
the
level
on
the
base,
O11
turns
off
and
pre-
vents
the
voltage
on
Q8
from
discharging
further.
CIRCUIT
DESCRIPTIONS
(Power
Supply)
-15
Volt
Supply:
The
-15
volt
supply
derives
its
regulation
from
the
+15
volt
supply
through
R8.
When
the
output
of
the
-15
volt
supply
is
at
the
correct
voltage,
the
junction
of
R8
and
R12
is
zero
volts.
The
base
of
O2
is
referenced
to
zero
volts
through
R9. Should
the output
of the minus supply
increase,
the
voltage
on
the
base
of
ОЗ
will
also
increase
which
begins
to
turn
off
ОЗ.
Q2
conducts
more
current
which
requires
O4
to
conduct
more.
O4
drives
the
pass
transistor
(Q5)
which
then
con-
ducts
more
current
thereby
lowering
the
output
to
-15 volts.
*15
Volt
Supply:
Z1
contains
a
voltage
reference
which
supplies
+7.4
volts
to
pin
б
of
Z1.
This
voltage
Release:
When
the
gate
is
removed,
the
remaining
voltage
оп
C8
is
discharged
to
ground
through
CR
10,
R44
and
the
release
slider
(R88).
is
connected
through
pin
5
to
the
noninverting
input
of
an
op
amp.
The
output
of
the
op
amp
is
con-
nected
to
an
emitter
follower,
also
located
in
Z1,
which
controls
the
pass
transistor
(Q1).
Should
the
output
of
the
power
supply
change,
the
voltage
at
the junction
of R3 and R6 will supply
the inverting
input
of
the
op
amp
in
Z1
with
the
voltage
differ-
ence.
The
op
amp
will
then
supply
a
correction
voltage
to
the
emitter
follower
and
pass
transistor
and
bring
the
power
supply's
voltage
to
normal.
Short
circuit
protection:
R2
and
the
transistor
in
Z1
connects
to
pins
2
and
З
limit
the
+15
supply's
current
to
a
maximum
of
180
milliamps.
Q6
and
R16
limit
the
-15
supply's
current
to
a
maximum
of
150 milliamps.
NOTE:
Although
the
circuit
description
above
is
for
the
Power
Supply
-
11
Board,
the
information
applies
to
the
the
Power
Supply
-
|
Board
as
well.
The
schematics
and
reference
numbers
for
the
two
supplies
are
different,
but
the
circuits
are
the
same.

SECTION
З
TRIM
PROCEDURES
NOTE:
The
following
procedures
must
be
performed
in
the
order
presented.
Power
Supply-!
Trim
Procedure
МОТЕ:
Always
execute
Power
Supply
trims
first.
REF.
TRIMMER
TRIM
PROCEDURE
*15 VOLT SET
-15
VOLT
SET
3.2 Board А-І Trim Procedures
V/OCT
UP 2 OCT
2ND VOICE
3.3
Board
B-I
(&
B-II)
Trim
Procedures
NOTE:
The
reference
numbers
for
the
B-II
boards
are
in
parenthesis.
1.
Monitor
the
power
supply's
+15
volt
output
with
a
digital
voltmeter.
2. Adjust T2 for exactly “15.00 volts.
1. Set T2 (+15 volts) first.
2.
Put
the
digital
voltmeter's
ground
lead
on
the
power
supply's
-15
volt
output
and
put
the
meter's
plus
lead
on
the
power
supply's
ground
output.
3.
Adjust
Т1
for
exactly
415.00
volts
(reversed
polarity).
=
Monitor
pin
8
on
Board
A
(CV-1
on
the
interconnecting
board)
with
a
digital
volt
meter.
Put
the
TRANSPOSE
switch
in
the
DOWN
2
OCTAVES
position.
Pin low "С" on the keyboard.
Measure the voltage on pin 8 (CV-1).
Pin high ‘C’ on the keyboard.
Adjust
the
V/OCT
trimmer
on
Board
A
(T1)
for
exactly
3
volts
higher
than
the
voltage
measured
in
step
4.
AARWN
ч
Pin low "С" on the keyboard.
Put
the
TRANSPOSE
switch
in
the
NORMAL
position.
9.
Adjust
the
NORM
trimmer
(T3)
for
exactly
2
volts
higher
than
step
4.
со
10.
Put
the
TRANSPOSE
trimmer
in
the
UP
2
OCTAVES
position.
11.
Adjust
the
UP
2
OCT
trimmer
on
Board
A
(T4)
for
exactly
4
volts
higher
than
step
4.
12.
Put
the
TRANSPOSE
switch
in
the
NORMAL
position.
13.
Monitor
pin
6
on
Board
A
(CV-2
on
the
interconnection
board)
and
measure
the
exact
voltage
with
a
DVM
(should
be
about
15
millivolts).
14.
Put
the
TRANSPOSE
switch
in
the
UP
2
OCTAVES
position.
15.
Adjust
the
2ND
VOICE
trimmer
on
Board
A
(T2)
for
exactly
the
same
voltage
as
measured
in
step
13.
VCO1&2
50% PULSE
WIDTH
Put
the
TRANSPOSE
switch
in
the
normal
position.
Depress
a
key
in
the
middle
of
the
keyboard.
Monitor
TP-5
(square
wave
output)
with
an
oscilloscope.
Adjust
the
VCO
1
(or
VCO
2)
COARSE
FREQUENCY
slider
to
display
exactly
one
complete
cycle.
5.
Adjust
the
50%
PULSE
WIDTH
trimmer
until
the
duty
cycle
of
the
waveform
is
exactly
50%
(exactly
square).
P ° N >
VCO1&2
CALIBRATE
-
Monitor
TP-5
іп
VCO
1
(ог
VCO
2)
with
either
ап
oscilloscope
ог
a
frequency
counter.
Put
the
VCO
1
(or
VCO
2)
COARSE
FREQUENCY
slider
DOWN
fully.
Put
the
VCO
1
(or
VCO
2)
FINE
TUNE
slider
exactly
in
the
MIDDLE.
Pin
low
“С”
on
the
keyboard
(transpose
switch
midposition).
Adjust
the
VCO
CAL
trimmer
for
a
50
msec.
period,
or
20
Hz.
ором
14

Board
В-І
δι
B-II
Trim
Procedures
(Continued)
TRIMMER
TRIM
PROCEDURE
ы
T4
VCO
V/OCT
EM
R44,
R56)
9
Set
the
following
sliders
on
the
front
panel
at
maximum:
VCO
1
(square
wave)
to
AUDIO
MIXER,
VCF
FREQUENCY,
VCA
GAIN.
Put
all
other
sliders
on
the
front
panel
down.
Put
the
TRANSPOSE
and
PITCH
BEND
controls
in
the
NORMAL
position.
Put
the
VCO
1
range
slide
switch
in
the
KYBD
ON
position.
Put
the
VCO
2
SYNC
switch
in
the
OFF
position.
Monitor
the
HIGH
OUTPUT
of
the
Odyssey
with
a
frequency
counter
or
strobe
tuner.
7.
Pin
low
“С”
on
the
keyboard.
8.
Adjust
VCO
1
COARSE
FREQUENCY
slider
for
exactly
100
Hz
(or
'C'
on
the
strobe
tuner).
.
Pin
high
‘C’
on
the
keyboard.
10.
Using
the
VCO
1
V/OCT
trimmer
on
Board
B,
adjust
the
frequency
of
VCO
1
to
exactly
800
Hz
(or
‘C’
three
octaves
higher
on
a
strobe
tuner).
11.
Repeat
steps
7
through
10
until
the
frequency
of
VCO
1
is
correct
on
low
"С"
and
high
"С".
12.
Pin
low
‘C’
on
the
keyboard.
13.
Raise
the
VCO
2
(square
wave)
slider
to
the
AUDIO
MIXER.
14.
Adjust
the
VCO
2
COARSE
and
FINE
TUNE
sliders
until
VCO
2
is
exactly
in
tune
with
VCO
1.
15.
Pin
high
‘C’
on
the
keyboard.
16.
Using
the
VCO
2
V/OCT
trimmer
on
Board
B,
adjust
the
frequency
of
VCO
2
until
it
is
exactly
the
same
as
VCO
1.
17.
Repeat
steps
12
through
16
until
the
frequency
of
VCO
2
is
the
same
as
VCO
1 on
low
"С"
and
high
"С".
19.
Pin
high
‘C’
on
the
keyboard.
20.
Depress
and
release
low
‘C’
(while
high
‘C’
is
pinned).
21.
Adjust
the
VCO
2ND
VOICE
V/OCT
trimmer
on
Board
B
until
the
pitch
of
oscillator
does
not
change
in
step
20.
AAR WN
THE
FOLLOWING
ADJUSTMENT
IS
FOR
THE
MODEL
2800
ONLY.
22. Pin
low
‘C’
on
the
keyboard.
23.
Raise
the
VCO
1
(square
wave)
slider
in
the
AUDIO
MIXER.
24.
Adjust
VCO
1
&
2
FINE
TUNE
sliders
so
that
VCO
1
&
2
are
in
unison.
25.
Set
the
TRANSPOSE
switch
to
the
UP
2
OCTAVES
position.
26.
If
the
two
oscillators
are
not
exactly
in
tune
with
each
other, adjust
the
2nd
VOICE
TRIMMER
on
BOARD
A
until
the
two
oscillators
are
zero
beating.
TUNING SET-UP
15

3.4 Board C-l Trim Procedures
й I
T4
T3
VCF
CUTOFF
T5 VCF
V/OCT
i
|
TRIMMER
TRIM
PROCEDURE
E m > бо N >
-
ол о m > ο N
-
m 2 wN
9
Put
the
VCF
RESONANCE
slider
at
MAXIMUM.
Monitor pin 10 of the 4023 module with an oscilloscope.
Put all other sliders on the front panel DOWN.
Adjust
the
VCF
FREQUENCY
slider
for
a
sine
wave
of
about
1000
Hz.
Measure
the
peak
to
peak
amplitude
of
the
sine
wave
on
pin
10.
Measure
the
peak
to
peak
amplitude
of
the
sine
wave
on
pin
9
of
the
4023
(should
be
about
half
the
amplitude
of
pin
10).
Adjust
the
BAL
trimmer
on
Board
C
until
the
sine
wave
on
pin
9
is
exactly
half the amplitude of the sine wave on pin 20.
Put the VCF RESONANCE slider at MAXIMUM.
Put all other sliders on the front panel DOWN.
Monitor pin 10 of the 4023 module with an oscilloscope or frequency
counter.
Adjust the VCF CUTOFF trimmer for a 62.5 msec. period, or, 16 Hz.
Put
the
following
sliders
at
MAXIMUM:
VCF
RESONANCE,
VCA
GAIN,
and VCF KYBD CV.
Put all other sliders on the front panel DOWN.
Pin low 'C' on the keyboard.
Monitor
the
HIGH
OUTPUT
of
the
Odyssey
with
a
frequency
counter.
Adjust
the
VCF
FREQUENCY
slider
for
100
Hz.
Pin high 'C' on the keyboard.
Adjust the VCF V/OCT trimmer on Board C for 800 Hz.
Repeat
steps
3
through
7
until
the
frequency
of
the
VCF
is
correct
on
low
"С" and high "С".
Put
the
following
sliders
at
MAXIMUM:
VCO
2
‘SQUARE
WAVE’
to
the
AUDIO MIXER, VCF FREQUENCY , and VCA GAIN.
Put all other sliders on the front panel DOWN.
Measure the peak to peak amplitude of the waveform on pin 10 of the 4023
module with an oscilloscope.
Monitor the HIGH OUTPUT of the Odyssey with an oscilloscope.
Adjust
the
VCA
GAIN
trimmer
on
Board
C
so
that
the
amplitude
of
the
waveform on the output of the Odyssey is that same as the amplitude
measured in step 3.
Put
the
following
sliders
at
MAXIMUM:
МСА
'ADSR',
апа
LFO
FRE-
QUENCY.
Put the ADSR ‘DECAY’ slider at ONE-FOURTH.
Put all other sliders on the front panel DOWN.
Put the three slide switches under the ADSR sliders DOWN.
Monitor the HIGH OUTPUT of the Odyssey with an oscilloscope (set to
about .5 volts per division).
Adjust
the
VCA
CVR
trimmer
on
Board
C
for
the
minimum
amplitude
signal on the output of the Odyssey.

3.5 Power Supply-ll Trim Procedures
TRIMMER TRIM PROCEDURE
+15
VOLT
SET
.
Monitor
the
power
supply's
+15
volt
output
with
a
digital
voltmeter.
. Adjust R5 for exactly 15.00 volts.
-15 VOLT SET . Set R5 (*15 volts) first.
. Put the digital voltmeter's ground lead on the power supply's -15 volt
output and put the meter's plus lead on the power supply's ground output.
. Adjust R11 for exactly 15.00 volts (reversed polarity).
THE FOLLOWING PROCEDURE RECALIBRATES THE +15 VOLT SUPPLY SO THAT THE CV
OUTPUT JACK WILL PROVIDE EXACTLY 1 V/OCT. THIS TRIM PROCEDURE MUST BE PER-
FORMED WHEN THE ODYSSEY IS TO BE USED AS A 'MASTER' SYNTHESIZER.
+3V CV SET . Connect a digital voltmeter to the CV OUTPUT jack on the rear of the
Odyssey.
Pin low 'C' on the
keyboard (transpose and pitch bend normal).
Measure the exact voltage on the CV output (millivolt range).
Pin high 'C' on the keyboard.
Re-adjust the +15 volt trimmer (ΒΒ) for EXACTLY +3.00 volts higher than
the voltage measured in step 3.
Perform
the
А-И
trim
procedure
and
the
В-11
(or
В-1)
trim
procedure.
3.6 Board А-ІІ Trim Procedures
TRANSPOSE
.
Perform
the
PWR
SUP-II
trim
procedure.
Perform
the
V/OCT
section
of
the
Board
В-І
(or
В-11)
trim
procedure.
Put
the
following
sliders
at
MAXIMUM:
VCO
1
(square
wave)
to
the
AUDIO
MIXER,
VCF
FREQUENCY,
and
VCA
GAIN.
Put
all
other
sliders
on
the
front
panel
DOWN.
Put
the
TRANSPOSE
switch
in
the
NORMAL
position.
Pin low 'C' on the keyboard.
Connect
a
frequency
counter
or
strobe
tuner
to
the
HIGH
OUTPUT
of
the
Odyssey.
Adjust
the
VCO
1
COARSE
FREQUENCY
and
FINE
TUNE
sliders
to
100
Hz or ('C' on a strobe tuner).
. Putthe TRANSPOSE switch in the UP 2 OCT position.
.
Adjust
the
TRANSPOSE
trimmer
(R23)
for
exactly
400
Hz
(or
'C'
two
octaves higher than step 8).
R26
PITCH
BEND
.
Perform
the
PWR
SUP-II
trim
procedure.
.
Perform
the
V/OCT
section
of
the
Board
В-І
(or
В-11)
trim
procedure.
. Put the following sliders at MAXIMUM: VCO 1 (square wave) to the AUDIO
MIXER, VCF FREQUENCY, and VCA GAIN.
.
Put
all
other
sliders
on
the
front
panel
DOWN.
. Put the PITCH BEND control in the CENTER.
. Pin low "С" on the keyboard.
. Connect а frequency counter or strobe tuner to the HIGH OUTPUT of the
Odyssey.
. Adjust the VCO 1 COARSE FREQUENCY and FINE TUNE sliders to 100
Hz (or 'C' on a strobe tuner).
. Put the PITCH BEND control fully CLOCKWISE.
. Adjust the PITCH BEND trimmer (R26) for exactly 200 Hz (or ‘C’ one
octave higher than step 8).
17

3.7
Board
B-II
Trim
Procedures
(See
Section
3.3
on
page
14)
3.8 Board
С-ІІ Trim Procedures
TRIMMER
TRIM
PROCEDURE
R67 VCF BAL . Put the following sliders at MAXIMUM: VCA GAIN, and LFO FRE-
QUENCY.
. Putthe ADSR 'DECAY' slider at ONE-FOURTH.
.
Put
all
other
sliders
on
the
front
panel
DOWN.
. Put the three slide switches under the ADSR sliders DOWN.
.
Monitor
the
HIGH
OUTPUT
of
the
Odyssey
with
an
oscilloscope
(set
to
about
.5
volts
per
division).
.
Adjust
the
VCF
BAL
trimmer
on
Board
C
for
the
minimum
amplitude
signal
|
оп
the
output
of
the
Odyssey.
R71 VCF . Put the МСЕ RESONANCE slider at MAXIMUM.
CUTOFF . Putall other sliders on the front panel DOWN.
.
Monitor
pin
10
of
M1
with
an
oscilloscope
or
frequency
counter.
.
Adjust
the
УСЕ
CUTOFF
trimmer
for
a
62.5
msec.
period,
ог,
16
Hz.
R68 VCF . Putthe following sliders at MAXIMUM: VCF RESONANCE, VCA GAIN,
V/OCT and VCF KYBD CV.
. Put all other sliders on the front panel DOWN.
. Pinlow 'C' on the keyboard.
. Monitor the HIGH OUTPUT of the Odyssey with a frequency counter.
. Adjust the VCF FREQUENCY slider for 100 Hz.
. Pin high “С” on the keyboard.
. Adjust the МСЕ V/OCT trimmer on Board C for 800 Hz.
. Repeat steps 3 through 7 until the frequency of the VCF is correct on low
'C' and high 'C'.
VCA GAIN . Putthe following sliders at MAXIMUM: VCO 1 'SQUARE WAVE' to the
AUDIO MIXER, VCF FREQUENCY, and VCA GAIN.
. Put all other sliders on the front panel DOWN.
.
Monitor
the
HIGH
OUTPUT
of
the
Odyssey
with
an
oscilloscope.
.
Adjust
the
VCA
GAIN
trimmer
on
Board
C
so
that
the
amplitude
of
the
waveform
on
the
output
of
the
Odyssey
is
2VPP.
VCA CVR . Put the following sliders at MAXIMUM: VCA 'ADSR', апа ГЕО FRE-
QUENCY.
. Putthe ADSR 'DECAY' slider at ONE-FOURTH.
. Put all other sliders on the front panel DOWN.
. Put the three slide switches under the ADSR DOWN.
. Monitor the HIGH OUTPUT of the Odyssey with an oscilloscope (set to
about .5 volts per division).
.
Adjust
the
VCA
CVR
trimmer
on
Board
C
for
the
minimum
amplitude
signal
on the output of the Odyssey.
18

SECTION 4 BOARD TEST POINTS
4.1 Board А- І Test Points
TEST
POINT
FUNCTION
SET
UP
SPECIFICATIONS
1.
No
keys
depressed
ον
2ND
VOICE
CV OUTPUT
2.
High
'C'
and
low
'C'
both
depressed.
+3V
1. Transpose switch: Down 2 octaves
(no keys depressed). ταν
CURRENT
SOURCE 2. Transpose switch: Normal position. +5V
3. Transpose switch: Up 2 octaves.
1. Depress and hold low 'C' (transpose
switch in the normal position).
CV BUFFER
2.
Depress
and
hold
high
'C'.
+5V
1. Depress and release low “С” (transpose *2V (Should not change more than 20
switch in the normal position). millivolts in one minute.)
CV OUTPUT
T
2.
Depress
and
release
high
'C'.
ay
(Should
not
change
more:
than:
20
millivolts
in
one
minute.)
1.
No
keys
depressed.
ον
САТЕ
OUTPUT
2. Depress any key.
GATE
BUS
2. Depress any key.
TRIGGER
1. Depress any key.
TRIGGER D k
OUTPUT ; epress any key.
WHITE NOISE
OUTPUT
PINK
NOISE
OUTPUT
19