Arp instruments 2480 User manual

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tme'

OMNI

Model

2480

.~

SERVICE MANUAL

ARP INSTRUMENTS, INC.

320

Needham

Street

Newton,

MA

02164

(617) 965-9700

Document Number 90020000

ARP INSTRUMENTS, INC.

THE

INFORMATION

CONTAINED

HEREIN

IS

CONFIDENTIAL

AND

PROPRIETARY

TO

ARP

INSTRUMENTS,

INC.

IT

IS

DISCLOSED

TO

YOU

SOLEY

FOR PURPOSES OF

INSTRUCTION

AS

TO

OPERATION

OF

THE

EQUIPMENT

AND

MAINTENANCE

AS

APPROPRIATE.

IT

IS

NOT

TO

BE USED BY

YOU

FOR

ANY

OTHER

PURPOSE,

NOR

IS

IT

TO

BE

DISCLOSED

TO

OTHERS

WITHOUT

THE

EXPRESS PERMISSION OF ARP

INSTRUMENTS,

INC.

OMNI Model

2480

SERVICE MANUAL

TABLE

OF

CONTENTS

1.

INTRODUCTION

1.1

Product Description 2

1.2 Specifications 2

1.3

Function

Description 3

2.

THEORY

OF

OPERATION

5

3.

CIRCUIT

DESCRIPTIONS

3.1

Upper

Voicing

Board 5

3.2

Lower

Voicing

Board 6

3.3 String

Control

Board 8

3.4 Synthesizer

Control

Board 9

3.5 Synthesizer Board 10

3.6

Phaser

Board 10

3.7 Power Supply

11

4.

ASSEMBLy/DiSASSEMBLy

12

5.

GENERAL

INFORMATION

12

6.

CALIBRATIONS

13

7.

SCHEMATICS

&

LAYOUTS

14-33

8. PARTS

LIST

34-36

1

SECTION 1

INTRODUCTION

1.1

Product Description

The

ARP

OMNI

offers

the

unique

combination

of

polyphonic

tone

sources

and

the

versatility

of

synthe-

sizer

sound

modification.

Separate

string

and

synthesizer

sections

allow

orchestral

and

symphonic

sounds

simultaneously.

The

total

variability

of

the

synthesizer

section

permits

such

sounds

as brass,

piano,

and

clavi

net

without

single

note

limitations.

The

string

and

synthesizer

sections

may

be

separated

by

stereo

outputs

on

the

rear panel

of

the

OM

N

I.

ARP's

now-famous

systems

interface

applies

to

this

product

as well.

The

OMNI

can

accept

external

effects

or

output

its

own

signals

tv

other

instruments.

The

computer-grade

switching

mechanisms

are

fast

and

reliable.

1.2 Specifications

I.

Controls

A.

String

Section

1.

Instrument

Selection

Switches

a.

Violins

(4')

b.

Violas

(8')

c. Cellos

(8')

d.

Bass

(16')

2.

String

Envelope

Controls

a.

Attack

Time

b. Release

Time

B.

Synthesizer

Section

1.

Synthesizer

Waveform

Switches

a.

4'

and

8'

2.

Synthesizer

Bass

Switches

a.

8'

and

16'

3.

Voltage

Controlled

Filter

a.

VCF

Freq

b.

Resonance

c.

ADSR

depth

d.

LFO

depth

e. Pedal &

Acc.

depth

4.

LFO

Speed

Slider

5.

Synthesizer

Waveforms

a.

Sawtooth

b.

Dynamic

Pulse

6.

ADSR

a.

Attack

Time

b.

Decay

Time

c.

Sustain

Level

d. Release

Time

C.

General

Controls

1. Master

Volume

2. Bass

Volume

3.

String/SYnthesizer

Mix

4.

Waveform

Enhancement

Switch

5.

Synthesizer-to-Modulator

Switch

II.

Outputs

-A. Main

Outputs

1_

High Level

Cannon

XLR,

1

K,

2.5V

RMS

TYP.

2.

Low

Level

1/4"

phone

1OK,

.8V

RMS

TYP.

'--

B.

Synthesizer

Output

1.

Low

Level

1/4"

phone

10K,

.8V

RMS

TYP.

--"Can

be used

simultaneously

for

discreet

stereo

effects.

C.

Gate

Out

and

Trig

Out

1.

Gate:

Tini D

Jack;

0,

+1

OV

2. Trigger:

Tini

D

Jack;

0,

+10V

pulse,

2 microsec.

duration

D.

Foot

Switch

and

Foot

Pedal

1.

Standard

ARP

accessories

III.

Miscellaneous

A.

Keyboard

1. 4

octave

keyboard,

split

for

bass

voices

at

one

and

a

half

octaves

from

low

end

B.

Pedals

1.

Filter

control

pedal

for

foot

co~1

of

filter

brightness

.

C.

Sustain

Switch

1.

Foot

switch

works

like

sustain

pedal

on

piano

D.

Materials

1.

Aluminum

chassis

2. Rigid

high-density

particle

board

base

3.

Solid

walnut

end

blocks

4. Glass-epoxy

circuit

boards

5.

Industrial-grade

electronic

components

and

controls

E.

Weight

1.

33

pounds

2

3 2 16 17

r SYSTEM INTERFACING I r VCF CONTROL

INPU1=S

I

SUSTAIN

TRIG GATE

FOOT

SWITCH

OUT

ou'

ACCESSORY PEDAL

1.3

Function Description

1 Mix Control:

Determines

the

balance

of

the

string

voices

and

the

synthesizer

voices.

2 LFO Speed: Varies

the

frequency

of

the

Low

Frequency

Oscillator.

3 Master Volume:

Determines

overall

volume

of

the

mixed

output.

4 Waveform Enhancement:

Alters

waveforms

produced

by

the

Omni

to

a

hollow

like (square)

sound.

5 Chorus Phaser:

Routes

the

synthesizer

output

through

the

string

section's

phase

shifters

and

reduces

the

phase

shifters

speed.

(When de-

pressed

the

synthesizer

output

appears

on

the

string

output

as well.)

6

Synthesizer

8',

4':

Selects

the

synthesizer

sec·

tion's

pitch

ranges.

7

Synthes/~er

Bass

8',

16':

Selects

the

synthe-

sizer's

bass voices

and

disables

synthesizer

8'

and

4'

voices

in

bass range

(first

octave

and

a

half).

8

ADSR

Envelope Generator:

Determines

the

attack

and

decay

characteristics

of

the

synthe-

sizer

section.

9 VCF Frequency Slider:

Sets

the

VCF's

initial

frequency

cutoff

point.

10 VCF Resonance Slider:

Sets

degree

of

VCF

resonance

("wow"

effect).

21

22

11

VCF

ADSR

Slider:

synthesizer

section.

Determines

brightness

of

12

VCF LFO Slider:

Determines

depth

of

tremelo.

13 VCF Pedal

and

Accessory Slider:

Determines

range

of

external

pedal

or

accessory.

14 Violin

ranges.

and

Viola:

Selects

the

string

pitch

15 Bass, Cello:

Selects

bass

string

pitch

(low

note

priority,

lowest

octave

and

only).

ranges

a

half

16

Attack:

Determines

attack

of

string

section.

17 Release:

Determines

the

final release

time

of

string

section

(also

effects

synthesizer

release).

18

Bass Volume:

Determines

bass

volume

synthesizer

16',8'

and

bass

and

cello.

for

19 Sustain

Foot

Switch:

Sustains

all

notes

when

foot

switch

is

depressed

(regardless

of

release

slider

settings).

20

Gate

and

Trigger

Output

Jacks:

connect

to

other

synthesizers.

Used

to

21

Accessory Jack:

Connected

to

VCF

control

input

so

that

VCF

may

be

controlled

by

ex-

ternal

sources

such

as

the

ARP

Sequencer

or

Sample

and

Hold

outputs,

etc.

for

special

effects.

22

Pedal Jack: Used

to

connect

VCF

filter

pedal.

3

~

SIMPLIFIED OMNI BLOCK

DIAGRAM

1-----------------

~

I

49

lines

1 line

..rt...rL ..rt...rL

-

MASTER

TOP

12

lines

GATE

FREOUENCY

WAVE

STRING

4'

--+--

..rt...rL

OCTAVE

PHASER

~

f-----

-

8'

OSCILLATOR

CIRCUITS

DIVIDERS

SHAPERS

VCA

2.!.J.ines

DIVIDER

t

~

tt

49

lines ,;'"

BUS

I

KEYING

r-

RODS

CIRCUITS

21 lines

STRING

AR

MIX

~

OUTPUT

0

8'

M/X

~

STRING

SECTION

,------.

BASS

L.-.t..

PRIORITY

----------------~

16'

CIRCUIT

~

-...:z::.

I

chorus

switch

BASS

I L t

r---------------~

I

~

I

L

/

VCF

r--

t I

VCA

t

ADSR

SYNTHESIZER

SECTION

I

SYNTH

ESIZER

I

OUTPUT

:

I

~

SECTION

2

THEORY

OF

OPERATION

SECTION

3

CIRCUIT

DESCRIPTIONS

The

OMN I

's

tone

generator

circuitry

consists

of

a

master

oscillator

at

500

kHz.,

which

drives a large

scale

integrated

circuit

top

octave

divider.

The

top

octave

divider

produces

the

highest

twelve

tones

in

the

instrument.

Frequency

dividers

derive

the

remaining

pitches

from

the

top

octave

divider.

The

squarewave

outputs

of

each

divider

are

waveshaped

to

a

sawtooth

form

(the

waveform

enhancement

alters

the

waveshape

to

a

differentiated

squarewave).

The

tones

from

the

waveform

generator

are fed

to

transistor

gating

arrays

which

route

the

signal

to

the

string

section

and

the

synthesizer

section.

The

transis-

tor

gating

arrays

are

'keyed'

on

by

an

RC

circuit

connected

to

each

key.

The

release

time

of

each

key

(how

long

the

note

remains

after

a

key

release)

is

determined

by

the

release

capacitor

on

each

gating

input.

The

outputs

of

all

the

gating

arrays

are

summed

and

routed

to

the

string

section

and

the

synthesizer

section.

The

string

section

consists

of

three

parallel

phase

shifters

which

modulate

the

sawtooth

waveforms

from

the

gating

circuits.

The

phaser

outputs

are

processed

through

a

Voltage

Controlled

Amplifier

to

control

the

attack

characteristics.

(The

release

is

con-

trolled

by

the

release

capacitor

on

each

gating

circuit).

The

synthesizer

section

processes

the

gate

outputs

of

the

arrays

through

a

Voltage

Controlled

Filter

and

Voltage

Controlled

Amplifier,

both

of

which

are

controlled

by an

ADSR

Envelope

Generator.

The

synthesizer

output

can

be

routed

through

the

string

section

phasers

when

the

Chorus

Phaser

Switch

is

selected.

The

speed

of

the

phasers

is

reduced

when

the

Chorus

Phaser

is

selected.

The

outputs

of

the

string

section

and

the

synthesizer

section

are

summed

together

in

the

Mix

Circuitry

and

routed

to

the

output

of

the

instrument.

A

separate

synthesizer

output

is

provided

for

stereo

effects.

3.1 Upper Voicing Board

GENERAL:

The

Upper

Voicing

Board

contains

the

Master

Oscillator,

Top

Octave

Divider I.C.,

Frequency

Dividers, Wave

Shaping

for

tones

C7

through

C4,

Keying

Circuits

for

keys

21

through

49

and

six

of

the

ten

Gate

Circuit

/.C.'s.

The

remaining

Waveshaping,

Keying

Circuits

and

Gate

I.C.'s are

located

on

the

Lower

Voicing

Board.

(Note:

There

are

two

schema-

tics

for

th

is

board.)

3.1.1

MASTER

OSCI

LLATOR

AND

TOP

OCTAVE

DIVIDER

(Refer

to

Upper

Voicing

Schematic,

sheet

1

of

2.)

L1

and

01

produce

a 0

to

-15

volt

sine

wave

at

approximately

500KHz.

The

frequency

of

the

oscilla-

tor

can

be varied

by

adjusting

the

core

of

the

coil

(externally

accessible).

Z1

buffers

and

squares

the

waveform

from

the

Master

Oscillator

and

supplies

it

to

the

Top

Octave

Divider,

Z2.

Z2

is

a LSI

(Large

Scale

Integrated

Circuit)

divider

which

produces

the

highest

octave

(square

waves)

of

the

instrument

(C6·C7).

3.1.2

DIVIDER

AND

WAVE

SHAPING

CIRCUITS

(Refer

to

Upper

Voicing

Schematic,

sheet

1

of

2.)

The

square

wave

outputs

from

Z2

are

supplied

to

the

clock

inputs

of

CD4520BE

divider

chips

(Z3-Zl)

which

produce

square

waves

for

each

key.

The

square

wave

outputs

of

the

CD4520BE's

are~uffered

by

inverters

Z9-Z16.

o i

Waveform

converter

and

waveform

enhancement

The

square

waves Trom

inverters

Z9·Z13

and

from

Z2

are

differentiated

by

capacitors

C17-C49

(values are

selected

for

each

frequency).

CR1

through

CR41

clip

the

negative

portion

of

the

differentiated

square

wave

resulting

in

sawtooth

shaped

waveforms.

By

altering

5

the

DC

bias (P6-7,

Waveform

Control

Bus)

some

of

as

the

inputs

to

the

devices. Five

of

the

arrays

are

the

negative

portion

of

the

differentiated

waveform

is

used

for

4'

pitches

and five

for

8'

pitches.

Therefore,

permitted

to

pass

through

diodes

CR1-41

when

the

one

key

controls

two

gate

chips

at

a

time

(4'

and

8').

Waveform

Enhancement

is

selected

resulting in a

"hollow"

type

sound.

The

Upper

Voicing Board

contains

three

4'

gate

arrays

and

three

8'

arrays;

the

remaining

arrays

are

on

3.1.3

KEYI

NG

CI

RCUITS

the

Lower

Voicing Board. All

of

the

arrays

have

the

base pin (7)

grounded.

Each

of

the

sawtooth

wave-

(Refer

to

Upper

Voicing

Schematic,

sheet

2

of

2.)

forms

are

supplied

to

an

emitter

through

a

100Kohm

resistor

(e.g.

Tone

G 4

is

supplied

through

resistor

Each

key

contact

(P7-5, P7-4,

P7-3,

etc.)

is

connected

pack

Z30

pins 5

and

6

to

12

of

Z31.).

Keying

to

a

22uf

electrolytic

capacitor

through

a

4700hm

voltages

(denoted

by KV)

are

supplied

to

the

emitters

resistor.

The

capacitor

is

normally

charged

to

0

volts

also

through

150Kohm

resistors (e.g.

KV21).

As long

(The

negative

side

of

the

capacitor

is

at

-15

volts.). as

the

keying

voltage

is

at

or

near

0 volts,

the

transis-

When a key

is

depressed,

the

capacitor

is

discharged

tor

remains

off.

When a

key

is

depressed,

the

keying

to

-15

volts.

The

time

the

capacitor

takes

to

recharge

voltage

drops

to

-15

volts,

which

turns

on

the

tran-

to

0 volts sets

the

release

time

of

each

note

and

can

sistor

in

the

array

and

permits

the

signal

to

pass

to

be varied by

the

release slider

(R31)

on

the

String

the

collector

of

the

array

and

out

to

the

mixing

cir-

Control

Board.

The

key

voltages

produced

for

each

cuitry

(e.g.

from

pin 12

of

Z31

to

14).

key

(indicated

by

letters

KV) are

supplied

to

two

gate

circuits;

one

for

8',

one

for

4'.

3.2 Lower Voicing

Board

GENERAL:

The

Lower

Voicing

Board

contains

the

OUTPUT

Bass

Low

Note

Priority

circuitry,

4'

and

8'

Mixing

circuitry,

Gate

Sensing

circuitry,

Suppression

Trigger

circuitry,

8'

and

16'

Bass

circuitry,

Keying

circuits

for

-15

470

keys 1

through

20,

Gate

circuits

for

tones

C2

through

G3,

and

Waveshaping

for

tones

C2

through

G3.

ohm

150K

3.2.1

WAVESHAPING,

KEYING

AND

GATE

KEY

CI

RCUITS

CONTACT

(Refer

to

Upper

Voicing

Schematic,

sheet

2

of

2.)

,

~-------

-

----

TDA470

TRANSISTOR

ARRAY

100K

,

~~WmJi

SAWTOOTH

WAVE

(TONE)

_IL

SUPPRESSION

TRIGGER

AND

STRING

RELEASE

CONTROL

3.3K

Keying

and

Gating circuit

BUS

ROD

-15V

3.1.4

GATE

CI

RCUITS

There

are

a

total

of

10

gate

transistor

arrays

(TDA470)

in

the

OMNI

which

gate

signals

from

the

tone

generator

sections

to

the

output

section.

Each

Gate

has

ten

transistors

(on

a

common

substrate)

with

common

collectors

and

bases.

The

emitters

serve

(Refer

to

Lower

Voicing

Schematic,

sheet

2

of

3.)

3.2.2

BASS LOW

NOTE

PRIORITY

CIRCUIT

(Refer

to

Lower

Voicing

Schematic,

sheet

1

of

3.)

The

Waveshaping,

Gating

and

Keying

circuits

on

this

board

are

a

continuation

of

the

circuits

on

the

Upper

Voicing

Board. See

sections

3

1.2,

3.1.3

and

3.1.4

for

detailed

descriptions.

The

8'

and

16'

Bass

section

of

the

OMN I

is

single

note,

low

note

priority.

The

Bass

section

covers

the

lowest

octave

and

a half

of

the

keyboard

(Keys

1

through

20).

The

release

time

of

the

Bass

section

is

fixed,

the

release

control

on

the

front

panel

has no

control

over

the

Bass

section.

Unlike

the

4'

and

8'

polyphonic

tones,

the

Bass

Priority

Circuit

receives

and

generates

only

square

waves.

The

function

of

the

Bass

Low

Note

Priority

circuit

is

to

route

the

square

wave

of

the

lowest

note

depressed

(only) in

the

Bass

section

to

the

8'

and

16'

Bass Wave-

shaping

circuits

(through

CR41-60)

for

processing.

6 I

The

Bass

Waveshaping

circuits

are

monophonic;

they

may

only

accept

one

waveform

at

a

time.

Square

wave

tones

C2-G3

are

routed

from

the

Upper

Voicing

Board

frequency

dividers

to

one

input

of

a

three

input

nor

gate

for

each

key

(Z33-Z39).

The

outputs

of

these

nor

gates

are

inverted

square

waves

only

when

the

other

two

inputs

are a logic 0 (e.g.

Z33B

6

is

a

square

wave

only

if

pin 4

and

pin 3

are

at

logic

0.).

NOTE:

All

logic gates in the Bass

Low

Note

Priority

section are COSMOS (Complimentary

Symmetry

Metal Oxide Semiconductor) devices. For this

particular application,

they

are operated

between

ground

and

-15

volts. Therefore, a logic 1

is

any

voltage

between

ground

and

-7.5

volts, logic 0

is

any

voltage

between

-7.5

volts

and

-15

volts.

~

LJLJ

(Z33-Z47)

to

transmit

serially a logic 1

state

to

all

keys

higher

than

the

one

depressed.

ENABLE

)-------e

(A)

(C)

0-------------,

KEYING

VOLTAGE

(B)

0------1

Enable (A) is a logic 0

only

when Enable

(C)

and

the

Keying voltage is less than

-7.5V

(logic 0). -

The

release

time

(decay

time

after

keys

are

released)

is

fixed

at

about

2.5

seconds,

however,

an

additional

charge

path

is

provided

through

01-20

for

those

keys

not

depressed

to

shorten

the

release

time.

When

no

keys are

depressed,

01-20

are

off.

The

base

voltage

of

01-20

is

always

held

a full

diode

drop

above

the

keying

(bus rod)

voltage

in

the

reference

generator.

------I~

!

(C)

~~I-----i-

--0

6

,

(A)

~

<)

I

ENABLE

6

(B)

KEYING

VOLTAGE

The

output

(C)

of

the

NOR

gate will

be

a square wave

only

when the Enable (A)

input

is a logic 0 (-15V)

and

when

the Keying voltage is less than -7.5V.

The

"enable"

input

of

the

three

input

nor

gates

(e.g.

Z33B,

3)

will

always

be

a logic 0

(-15

volts)

provided

no

keys

are

depressed

to

the

left

of

the

circuit

under

examination.

When

a

key

is

depressed,

-15

volts

from

the

bus

rod

discharges

a 1

uf

sustain

capacitor

through

keying

transistors

(01-020).

(e.g. Key

2,

Pl-12

discharges

C42

through

R7,

02

and

CR63

to

-15

volts

on

key

depression.)

When

a

key

is

released,

the

voltage

on

the

capacitor

is

allowed

to

charge

back

to

0 volts

through

a

3.3Mohm

resistor

(e.g.

R5).

This

keying

voltage

is

routed

to

an

input

of

the

three

input

nor

gates

(e.g.

Z33B,

4).

Thus

the

keying

voltage

permits

the

square

wave

to

be

transmitted

from

the

input

of

the

three

input

nor

gate

to

the

output

provided

that

A)

the

keying

voltage

is

less

than

-7.5

volts

and

B)

the

enable

input

is

a logic 0

(indicating

no

lower

keys

are being

played).

The

keying

voltage

is

also

processed

through

a

COSMOS

inverter

(Z45-Z47)

and

a

nor

gate

3.2.3

BASS

KEYING

VOLTAGE

(Refer

to

Lower

Voicing

Schematic,

sheet

3

of

3.)

The

T

point

of

the

Bass Keying

Reference

Generator

supplies

a

voltage

to

the

bass

of

01-20

of

the

Bass

Low

Note

Priority

Circuit

which

is

at

least

three

diode

drops

higher

than

the

keying

voltage

supplied

to

the

Lower

keyboard

bus

rod

(P1·14).

The

diode

drops

are

created

using CR

114,

030

and

CR

113.

Th

is

insures

that

01-20

will be biased ON regardless

of

the

bus

voltage

wh

ich

decreases

as

more

keys

are

depressed.

3.2.4

GATE

DETECTOR

CIRCUITS

(Refer

to

Lower

Voicing

Schematic,

sheet

3

of

3.)

There

are

two

bus

rods

in

the

OMN

I,

one

for

the

lowest

20

keys,

one

for

the

upper

29

keys. Splitting

the

bus

rod

in

this

manner

permits

a bass

envelope

(Bass

AR)

to

be

developed

separately

from

the

higher

keys.

CR107

(Upper

Bass

Gate

Detector)

is

the

voltage

source

for

the

upper

bus

rod.

-15

volts

is

suppl

ied

through

CR107

and

R130

to

the

bus

rod.

When

a

key

is

depressed,

comparator

Z52B

switches

from

-15

volts

to

ground

(Gate).

The

current

drawn

through

R130

on

key

depression

results

in

a

voltage

drop

across R

130.

The

voltage

change

across R

130

is

differentiated

by

C86

so

that

the

output

of

comparator

Z52A

momentarily

switches

from

+15

volts

to

-15

volts

and

back

again

(10ms.

typical

duration,

longer

for

multi-key

depressions).

This

7

pulse

is

used

for

triggering

the

Envelope

Generator

(ADSR)

and

to

discharge

sustain

capacitors

on

keys

not

bei

ng

played.

3.2.5

8'

AND

16'

BASS

WAVESHAPING

(Refer

to

Lower

Voicing

Schematic,

sheet

3

of

3.)

The

single

square

wave

from

the

Bass

Low

Note

Priority

Circuit

(U2)

is

buffered

through

Z51A

and

gated

through

a

"VCA"

made

up

of

CR1

05,

R

112

and

cn.

The

Bass AR

voltage

(J11-8)

is

0 volts

when

no

keys

are

depressed

and

drops

to

-15

volts

when

a

key

is

depressed.

This

voltage

sets

the

bias

of

CR1

05

to

clip

the

square

wave

on

the

output

of

Z51 A.

As

the

AR

voltage

drops

from

ground,

the

amplitude

of

the

square

wave

increases.

C77

AC

couples

the

square

wave

to

an

emitter

follower

(021)

and

the

8'

Bass Waveshaping (R

116,

C78,

R

117,

C79,

022).

The

base

and

emitter

of

021

are biased

the

same

(+

7V).

This

means

that

only

the

differentiated

rising edge

of

the

squarewave

will bias

021

on,

thus

clipping

off

the

falling edge

of

the

squarewave.

The

sawtooth

waveform

on

the

emitter

of

021

is

divided

down

by R

114

and

R

174

and

used

for

the

synthesizer

Bass signal.

The

sawtooth

is

also

altered

and

resonated

by

022

and

used

for

the

string

bass

signal.

The

16'

Bass

Waveshaping

accepts

the

buffered

8'

square

wave

from

Z51 A

and

divides

the

frequency

in

half

(Z49).

CR

106,

R

119

and

C80

are

the

"VCA"

for

the

16'

Bass

circuit.

Buffer

and

filtering

are

provided

as

with

the

8'

Bass

(023

and

024).

3.2.6

WAVEFORM

CONTROL

(Refer

to

Lower

Voicing

Schematic,

sheet

3

of

3.)

The

Waveform

Control

sets

the

bias

point

of

the

clipping

diodes

in

the

Waveshaping

circuits

for

each

key.

When

the

output

of

Z53

is

0

volts,

sawtooth

waveforms

are

produced.

When

the

output

of

Z53

is

+15

volts,

the

"hollow"

sound

is

produced.

J11-9

is

ground

when

the

Waveform

Enhancement

switch

is

off,

+15

volts

when

the

switch

is

on.

CR1

07

provides

a

little

extra

voltage

to

the

output

when

the

input

is

+15

volts since

the

op

amp

cannot

supply

more

than

about

+13.5

volts

by

itself.

NOTE: The CA339E (Z52)

is

an

open collector

output

comparator. When the inverting

input

(-)

is

more

negative in voltage than the noninverting

(+)

input, the

output

is

open; the voltage

is

determined

bV external "pull

up"

resistor circuits or networks.

This device

is

not

a standard

op

amp;

it

is a

specialized comparator (no feedback).

The

Lower

Bus

Trigger

Detector

circuit

and

Lower

Bus

Gate

Detector

circuit

are

equivalent

to

the

Upper

Bus

circuitry.

CR

112

is

the

lower

bus

voltage

source,

R

150

creates

the

voltage

difference

for

the

lower

bus

trigger

on

key

depression.

The

Upper

and

Lower

Bus Triggers

are

combined

on

the

base

of

027

and

supplied

via

026

to

the

pulse

drive

circuit

and

sustain

bus.

The

sustain

bus

is

the

common

discharge

path

for

the

keying

capacitors

for

each

key.

The

trigger

pulse

rapidly

discharges

any

keying

capacitor

not

being

played

to

prevent

notes

from

running

together

when

the

release slider

is

at

maximum.

3.2.7

4'

AN

D

8'

SUM

(Refer

to

Lower

Voicing

Schematic,

sheet

3

of

3.)

The

outputs

of

the

five

4'

and

8'

gating

transistor

arrays

(TDA470)

are

summed

in

the

4'

and

8'

Sum

circuits.

Formant

filtering

is

provided

to

voice

the

instrument.

CR101,

CR102,

CR103

and

CR104

are

blocking

diodes

which

disable

the

outputs

of

the

bass

section

(first

20

notes)

when

the

8'

or

16'

Synthesizer

Bass

switches

are

on.

Z48

supplies

+

15

volts

when

the

Bass

controls

are

on

which

reverse biases

the

blocking

diodes.

The

4'

Poly

Sum

(J11-16)

and

8'

Poly

Sum

(J11-2)

are

routed

to

the

String

and

Synthesizer

sections

of

the

OMNI.

3.3 String Control Board

GENERAL:

The

String

Control

Board

contains

the

String

AR

Envelope

Generator,

AR

Suppression,

AR

Squelch

and

String

Voice

Selection

circuits.

The

AR

Suppression

forces

the

AR

to

release

fully

between

key

depressions,

yielding

the

proper

stf{()g

attack

times.

The

AR

Squelch

forces

the

release

time

of

the

AR

to

be

the

same

as

the

release

time

of

all

the

key

capacitors

by

tracking

the

audio

level

from

the

String

Voice

Selection.

3.3.1

STRING

VOICE

SELECTION

(Refer

to

String

Control

Board

Schematic.)

Z1

is

a

COSMOS

Ouad

Switch

which

selects

the

four

pitch

ranges:

4'

and

8'

polyphonic

and

8'

and

16'

bass.

Z3A

sums

the

four

pitch

ranges

and

routes

them

to

the

Phaser

Board.

Z2

(pins

3,

4

and

5)

permits

the

Synthesizer

section

to

be

summed

with

the

Stri

ng

signals

and

for

processing

through

the

Phaser

Board.

Pins 1, 2 and

13

disable

the

String

AR

when

no

string

voices

are

selected.

8

3.3.2

STRING

AR

AND

AR

SUPPRESSION

(Refer

to

String

Control

Board

Schematic)

The

String

AR

Envelope

Generator

produces

a

control

voltage

which

controls

the

gain

of

the

String

VCA

on

the

Synthesizer

Control

Board.

C15

is

the

integrating

capacitor

and

is

normally

at

0

volts

when

no

keys

are

depressed.

When

a

key

is

depressed,

the

gate

signal

on

Z4A

pin 6

changes

from

-15

volts

to

o

volts.

Comparator

Z4A's

output

changes

to

-15

volts

which

charges

C15

down

toward

-15

volts

at

a

rate

determined

by

the

attack

slider.

When

a

key

is

released,

the

-15

volts

is

allowed

to

discharge

through

R37,

38,

39.

When

a

key

is

depressed,

Q3

momentarily

turns

on

to

partially

discharge

C15

to

0

volts

if

any

voltage

remains

from

depressions.

3.3.3

AR

SQUELCH

(Refer

to

String

Control

Board

Schematic.)

Z4B

monitors

the

audio

signal

from

Z3A

in

the

String

Voice

Selection

circuit.

C10

integrates

the

output

of

Z4B

and

supplies

it

to

Z4C.

The

output

of

Z4C

is

low

(-15V)

as

long

as

an

audio

signal

is

present

which

reverse

biases

CR

11

and

prevents

the

AR

from

dis-

charging

faster

than

the

decay

of

the

audio

signal.

3.3.4

ADSR

BLANKING

The

ADSR

blanking

provides

a

pulse

to

the

ADSR

circuit

on

the

Synthesizer

Control

board

which

prevents

the

ADSR

from

triggering

when

the

foot

pedal

is

released.

3.4 Synthesizer Control Board

GENERAL:

The

Synthesizer

Control

Board

contains

the

Synthesizer

Voice

Selection,

Low

Frequency

Oscillator,

Synthesizer

Voltage

Controlled

Amplifier,

String

Voltage

Controlled

Ampi

ifier,

final

Output

Mix

and

Bass

AR

Envelope

Generator.

3.4.1

LOW

FREQUENCY

OSCILLATOR

(R

efer

to

Synthesizer

Control

Board

Schematic.)

The

LFO

produces

a

triangle

and

a

square

wave

output

in a

frequency

range

from

about

.1

Hz

to

20Hz.

Z4B

and

Cll

are

an

integrator

which

charges

from

current

passing

th

rough

R45.

Z4A

is

a

hysteretic

switch

whose

output

switches

from

-15

volts

to

+15

volts

when

the

output

of

Z4B

reaches

+5

volts.

This

then

reverses

the

direction

of

current

through

R45

and

the

rate

control

(R44)

and

thus

the

direction

of

integration

at

the

output

of

Z4B.

When

the

output

of

Z4B

reaches

-5

volts,

the

output

of

Z4A

switches

back

to

-15

vo:ts

and

the

cycle

repeats.

3.4.2

SYNTHESIZER

VOLTAGE

COI\JTROLLED

AMPLIFIER

(Refer

to

Synthesizer

Control

Board

Schematic)

The

Synthesizer

Voltage

Controlled

Amplifier

attenuates

signals

from

the

output

of

the

VCF.

The

gain

of

the

VCA

is

determined

by

the

amount

of

current

supplied

to

the

differential

pair

Z2A,

B.

The

ADSR

output

is

connected

to

the

control

input

(pin

3,

Z2)

via

P12

10.

The

control

rejection

trimmer

(R

14)

minimizes

the

effect

of

control

voltage

changes

on

the

output

of

the

VCA

by

balancing

the

current

through

Z2A

and

Z2B.

CR7,

C R8

and

R

17

provide

output

protection

to

prevent

external

voltages

from

entering

the

OMN I

circuits

through

the

output

jack.

3.4.3

STRING

VOLTAGE

CONTROLLED

AMPLIFIER

(Refer

to

Synthesizer

Control

Board

Schematic.)

The

String

Voltage

Controlled

Amplifier

is

the

same

circuit

as

the

Synthesizer

VCA

except

that

it

is

controlled

by

the

String

AR

Envelope

Generator

instead

of

the

ADSR.

3.4.4

OUTPUT

MIX

(Refer

to

Synthesizer

Control

Board

Schematic.)

The

output

of

the

Synthesizer

VCA

and

String

VCA

are

mixed

by

Z5A.

R23,

the

Mix

slider,

controls

the

volume

of

the

two

signals.

3.4.5

SYNTHESIZER

VOICE

SELECTION

(Refer

to

Synthesizer

Control

Board

Schematic.)

The

four

pitch

range

push

buttons,

4',8'

Synthesizer

Polyphonic

and

8',

16'

Synthesizer

Bass

route

the

audio

through

Z1

to

the

VCF

input

on

the

Synthe-

sizer

Control

Board.

CR5

and

CR6

disable

the

audio

output

of

the

first

20

notes

of

the

polyphonic

tone

gates

(TDA470s)

when

the

8'

and

16'

pitch

ranges

are

selected.

9

3.5

Synthesizer Board

GENERAL:

The

Synthesizer

Board

contains

the

Voltage

Controlled

Filter,

ADSR

Envelope

Generator,

ADSR

Gating

and

the

Gate

and

Trigger

Output

Processing

circuits.

3.5.1

VOLTAGE

CONTROLLED

FILTER

(Refer

to

Synthesizer

Board

Schematic.)

The

four

pitch

ranges,

4'

and

8'

Polyphonic

and

8'

and

16'

Bass, are

summed

and

voiced

on

the

audio

input

of

the

VCF

(pin

1,

M1).

M1

is

a

4075

Low

Pass

Voltage

Controlled

Filter.

It has a

cutoff

of

24

dB/

Octave

and

has a

manually

variable

0

(resonance).

The

filter

accepts

negative

control

voltages

(-1

volts/

octave)

on

pin 4

to

control

the

filter

cutoff

point.

ZlB

sums

and

inverts

external

voltages

which

control

the

VCF.

R22,

the

CVR

(Control

Voltage

Reset)

trimmer,

prevents

control

voltages

from

affecting

the

audio

output

(pin

10).

The

output

of

the

VCF

is

routed

to

the

Synthesizer

VCA

via J

12,

5.

3.5.2

ADSR

GATING

(Refer

to

Synthesizer

Board

Schematic.)

To

"start"

the

ADSR

Envelope

Generator,

the

output

of

Z3A

must

change

from

0

volts

to

-15

volts

(Logic

1

to

Logic

0).

Two

signals

must

be

sent

to

the

ADSR

Gating

to

set

up

this

condition:

the

Gate

and

Pulse Drive.

The

Gate

(J12-7)

is

-15

volts

(Logic

0)

with

no

keys

depressed,

and

0 volts

with

one

or

more

keys

depressed.

The

Gate

is

supplied

to

the

Reset

input

(Z4D

13)

of

R·S

flip

flop

made

up

of

Z4C

and

Z4D.

The

first

negative

transition

on

Z4C

8

will

cause

Z4C

10

to

change

from

-15

volts

(logic

O)

to

0

volts

(logic

1).

Pin 10 will

remain

at

0

volts

for

as long as

the

Gate

on

J12-7

is

at

0

volts.

The

Pulse Drive

is

normally

logic 0

(about

-13

volts)

and

pulses

to

logic 1

(about

-1

volt)

every

time

a

key

is

depressed.

The

ADS R

blanking

is

normally

logic 1,

but

drops

to

logic 0

when

the

sustain

footswitch

is

released

to

prevent

the

ADSR

from

triggering.

The

output

of

Z4A

is,

therefore,

normally

logic 1

(0 volts)

but

drops

to

logic 0

(-15

volts)

during

the

Pulse Drive pulse

or

the

ADSR

blanking

pulse.

Z3A

will

change

from

logic 1

to

logic 0

then

when

Z4C

has

changed

to

logic 1

and

after

Z4A

changes

to

logic 1

as

well.

Thus

Z4A

delays

the

ADSR

"starting"

until

after

the

Pulse Drive pulse has

occurred,

A

second

Pulse Drive will

momentarily

force

Z3A's

output

to

logic 0

to

restart

the

ADSR.

3.5.3

ADSR

The

ADSR

Envelope

Generator

circuit

provides

a

negative

going

DC

voltage

to

control

the

VCF

cutoff

and

the

VCA.

ATTACK:

When

the

output

of

Z3A

changes

from

high

to

low,

-15

volts

is

appl

ied

through

C

R2

and

R46

to

the

non

inverting

input

of

follower

Z2.

During

the

attack

mode,

04

is

off

and

R45

is

disconnected

from

ground.

Z2

directly

follows

the

voltage

on

3

and

applies

-15

volts

through

CR6,

R52

to

charge

integrating

capacitor

C13

down.

DECAY

AND

SUSTAIN:

ZlA

is

a

buffer

amplifier

following

the

voltage

on

capacitor

C13.

The

output

of

ADSR

voltage

approaches

-10

volts,

02

begins

to

turn

off

and

R35

lowers

the

voltage

on

13

of

Z3D.

Z3C

and

Z3D

is

a

bistable

latch.

When

13

falls

below

the'

threshold

of

the

nand

gate

(about

-7.5

volts)

the

output

of

Z3C

changes

from

high

to

low

applying

-15

volts

from

10

of

Z3

through

CR4,

R38

and

CR3

thus

holding

02

off.

04

now

turns

on

and

the

voltage

divider

consisting

of

R45

and

R46

establishes

the

Sustain

Level.

CR6

is

now

reverse biased

and

capacitor

C13

discharges

through

R51

and

CR5

to

the

level

at

Z2

3.

RELEASE:

When

the

gate

voltage

is

removed,

Z3B

goes

low

which

turns

on

06.

The

remaining

voltage

on

capacitor

C13

discharges

through

R53,

R50

and

06

to

ground.

The

output

of

ZlA

is

applied

to

the

input

of

follower

Z2

through

R59

thereby

preventing

the

sustain

and

decay

charge

paths

from

affecting

the

release

time.

05

and

07

permit

the

release

slider

setting

on

the

front

panel

to

be

overridden

~n

the

sustain

footswitch

is

depressed.

Pulse

Drive

input

is

disabled

by

ADSR

Release

Control

pulse

which

occurs

whenever

the

footswitch

is

released.

3.6

Phaser Board

GENERAL:

The

Phaser

Board

contains

three

identical

parallel

Phase

Shifters

each

modulated

by

Low

Frequency

Oscillators.

The

Phasers

are

chiefly

responsible

for

the

orchestral

string

effects

of

the

OMNI.

3.6.1

LFO

(See

Section

3.4.1

for

details

of

the

Low

Frequency

Oscillator

circuit.)

10

LFO

CONTROL

HFO

OUTPUT

DELAY

LINE

OUTPUT

SUMMMING

AMP

OUTPUT

-llUlJlJ1JIJ

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The

three

Low

Frequency

Oscillators

are used

to

modulate

the

Phase

Shifters

varying

the

delay

time

up

to

.8msec.

Pin 1 of Z1

05A

is

a

triangle

waveform

wh

ich

is

clipped

to

approximate

a

sinewave.

Z106B

connects

R

128

in parallel

with

R

127

when

the

chorus

switch

is

depressed,

which

slows

down

the

LFO.

3.6.2

HIGH

FREOUENCY

OSCILLATOR

(Refer

to

Phaser

Board

Schematic)

Voltage

controlled

High

Frequency

Oscillators

are

used

to

control

delay

time

of

each phase

shifter.

Z1

04B

is

a COSMOS

one

shot

wh

ich uses

the

inherent

capacitance

of

COSMOS

gates

(typically

5 pf) as

the

timing

capacitor

on

T2.

The

"capacitor"

is

charged

by

0101.

Once

the

"capacitor"

is

charged

to

maximum,

the

0

output

(pin 10)

changes

to

logic

o

wh

ich resets

the

one

shot.

Z104A

is

used

to

maintain

oscillation

in

Z104B:

should

Z104B

cease

oscillation,

or

not

begin

to

oscillate

after

power

up,

the

0

output

of

Z104

discharges

Z1

04B

14

to

start

Z104B

oscillating.

The

0

output

of

Z104A

is

a logic 1 as long as

Z104B

oscillates.

0102

and

0101

are a Iinear voltage

to

exponential

current

converter

which

determines

the

frequency

of

the

H.F.O.

R

116

(calibrate)

sets

the

initial

frequency

of

the

H.F.O.

The

sinewave

from

the

LFO

controls

0101,102

to

vary

the

H.F.O.

exponentially.

R119

is

placed

in

parallel

with

R118

to

increase

the

depth

of

modulation

when

the

chorus

switch

is

selected

by

varying

the

depth

of

frequency

change

produced

by

0102-0101.

3.6.3

DELAY

CIRCUITS

(Refer

to

Phaser

Board

Schematic.)

Z102

is

an

analog

delay

line

whose

delay

time

is

controlled

by

the

frequency

of

the

square

wave

on

pins

2

and

12

(typically

50KHz.).

Pin 2

and

12

must

be

square

waves

of

the

same

exact

frequency,

180

out

of

phase.

The

audio

input

of

the

device

is

3,

the

outputs

are Pin

13

and

14.

Z103

is

a

latching

flip

flop

which

converts

the

high

frequency

pulses

from

Z104B

to

square

waves

(0

and

0).

3.6.4

FINAL

MIX

(Refer

to

Phaser

Board

Schematic.)

The

outputs

of

the

three

Phase

Shifters

are

summed

by

Z1

and

supplied

to

the

string

VCA

on

the

Synthesizer

Board.

3.7

Power Supply

3.7.1

+15VOLTSUPPLY

Z1

contains

a voltage

reference

which

supplies

approximately

+7

volts

to

pin 6

of

Z1.

Th

is

voltage

is

connected

through

pin 5

to

the

noninverting

input

of

an

op

amp.

The

output

of

the

op

amp

is

connected

to

an

emitter

follower,

also

located

in

Z1,

which

controls

the

pass

transistor

(01).

Should

the

output

of

the

power

supply

change,

the

voltage

at

the

junc-

tion

of

R

11

and

R

12

will

supply

the

inverting

input

of

the

op

amp

in Z1

with

the

voltage

difference.

The

op

amp

will

then

supply

a

correction

voltage

to

the

emitter

follower

and

pass

transistor

(01)

and

bring

the

power

supply's

voltage

to

normal.

3.7.2

-15

VOLT

SUPPLY

The

-15

volt

supply

derives its

regulation

from

the

+15

volt

supply

through

R14.

When

the

output

of

the

-15

volt

supply

is

at

the

correct

voltage,

the

junction

of

R14

and

R15

is

0

volts.

Z2

is

referenced

to

0

volts

through

R2.

Should

the

output

of

the

minus

supply

increase,

the

voltage

on

pin 2

of

Z2 also increase.

Z2

then

forces

02

to

supply

more

current,

thereby

lowering

the

output

to

-15

volts.

3.7.3

SHORT

CIRCUIT

PRODUCTION

R7

and

the

transistor

in Z1

connected

to

pins

2

and

3

limit

the

+15

supply's

current

to

a

maximum

of

800

milliamps.

03

and

R5

limit

the

-15

supply's

current

to

a

maximum

of

1000

milliamps.

11

C. Pull

forward

2-3

inches.

D.

Lift

chassis

straight

up.

SECTION 5

GENERAL

INFORMATION

~

..

5.1

LM339 Comparator

The

LM339

contains

four

independent

precIsion

voltage

comparators.

With

an

open

collector

output.

the

LM339

is

compatible

with

TTL

and CMOS.

OUTPUT

4

INPUT

4+

OUTPUT

3 GJ\ID

14

12

In

the

OMN I, pin

12

of

LM

339s

are

connected

to

-15V.

Thus

the

ouput

states

of

the

device

are

open

(voltage

determined

by

external

circuitry)

or

·15V.

V+

08

INPUT

,-

SECTION

4

ASSEMBLY/DISASSEMBLY

,r

.

1,1

,

TUNE

CONTROL

B.

Lift

rear

of

instrument

3-4

inches

(high

enough

to

clear

Tune

Control).

A.

Remove

all

10

screws

as

indicated.

12

SECTION

6

CALIBRATIOI\lS

6.1 Synthesizer Board

Trim

Procedure

TRIMMER

TRIM

PROCEDURE

REF.

1.

Monitor

pin 10

of

filter

module

Ml

with

an

oscilloscope.

VCF

CVR

R22

0

2.

Put the

VCF

FREQ

slider and

VCF

RESONANCE

slider

fully

DOWN.

3. Put the

VCF

"ADSR"

slider

fully

UP.

4. Set the

ADSR

sliders

as

follows:

ATTACK

DOWN,

DECAY

3/4

UP,

SUSTAIN

DOWN,

RELEASE

DOWN.

5.

Adjust

R22

for

minimum

amplitude

when

keys are depressed.

1.

Monitor

pin 10

of

filter

module

Ml

with

an

oscilloscope.

R16

VCF

CAL

0 2.

CI

ip

a

33K

ohm

resistor

from

pin 10

of

M1

to

pin 2.

3.

Put the

VCF

FREQ

slider

fully

DOWN and the

VCF

RESONANCE

slider

fully

UP;

put

all

other

sliders DOWN.

4.

Adjust

R16

for

a

16Hz

sinewave.

6.2 Synthesizer Control Board

Trim

Procedure

SYNTH

R14 1.

Monitor

the

high level

output

of

the

Omni

with

an

oscilloscope.

VCA

CVR

2. Set all

VOICE

SELECTION

switches

OFF

(out).

0

3.

Put the

MIX

slider

fully

LEFT

(synthesizer).

4. Put the

MASTER

VOLUME

fully

RIGHT

(maximum).

5.

Set

ADSR

sliders

as

follows:

ATTACK

DOWN,

DECAY

3/4

UP,

SUSTAIN

DOWN,

RELEASE

DOWN.

6.

Put all

other

sliders at

minimum.

7.

Adjust

R14

for

minimum

deflection

of

the

oscilloscope trace

while

repeatedly

depressing keys.

STRING

0 1.

Perform

the

synth.

VCA

CVR

trim

procedure.

VCA

CVR

R33 2. Move

the

MIX

slider

to

fully

RIGHT

(string).

3.

Depress

(turn

on) the

STRING

BASS voice selection switch

(only).

. 4.

Adjust

R33

for

minimum

deflection

of

the

oscilloscope trace

while

repeatedly

depressing keys in the highest octave.

6.3

Phaser Board

Trim

Procedure

R

116

HFO

CAL

1 1.

Monitor

TP7

(Z102)

with

a

frequency

counter.

0 2.

Attach

a

lOOK

ohm

resistor

from

+15V

supply

to

TP6.

3.

Adjust

R

116

for

an

11

microsecond period square wave (+O.l-{}1icroseconds).

R216

HFO

CAL

2 1.

Monitor

TP9

with

a

frequency

counter.

0 2.

Attach

a

lOOK

ohm

resistor

from

the

+15V

supply

to

TP8.

3.

Adjust

R216

for

a

20.4

microsecond period squarewave (+0.1 microseconds).

HFO

CAL

3 1.

Monitor

TPll

with

a

frequency

counter.

R316

0 2.

Attach

a

lOOK

ohm

resistor

from

the

+15V

supply

to

TP10.

3.

Adjust

R316

for

a

11.3

microsecond period squarewave (+0.1 microseconds).

6.4

Power supply

Trim

Procedure

+15

VOLT

SET

R19 1.

Monitor

the

power supply's

+15

volt

output

with

a

digital

voltmeter.

0 2.

Adjust

R19

for

exactly

+15.00

volts.

-15

VOLT

SET

1. Set R5

(+15

volts)

first.

R20

0 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

R20

for

exactly

+15.00

volts

(reversed

polarity).

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ARP Instruments 2480 User manual

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