Inovonics 230 User manual

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INSTRUCTION

MANUAL

MODEL

230

"MULTIBAND

AUDIO

PROC

E

SSOR"

_

..

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--=-

January

1977

503-B

VANDELL

WAY,

CAMPBELL,

CA

95008

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I.

GENERAL

INFORMATION

ANO

SPECIFICATIONS

General

Specifications -

8-Band

Compressor

Specifications -

Peak

Limiter Specifications

• • 3

II.

DESIGN

PHILOSOPHY

AND

FUNCTIONAL

DESCRIPTION.

• • . • 6

III.

Multiband

Compression

-

Gated

Expansion -

Peak

Limiter -Asynnetrical Modulation -

Phase

Follower -

AM

Stereo -Frequency-Selective Limiter

INSTALLATION

•

...

Unpacking

and

Inspection -

Mounting

-

RFI

-

In/Out Connection -

Polarity

-Line Considerations

. • 9

IV.

OPERATION

AND

ADJUSTMENT

.•••...•••.....••

11

Basic Adjustments -

AM

Adjustments -

FM

V.

VI.

Adjustments -

Peak

Limiter Release

Timi

ng

-

Gated

E

xpa

nsion Function -

Program

Response

Shaping

CIRCUIT

DESCRIPTIONS

.••..•

. . . . .

14

Input Amplifier -

Bandpass

Compressors

-

Gating

Circuit

- C

ombining

Amplifier/Program

Phase

Detector -

Peak

Limiter Circuits -

Output Amplifier -

Power

Supply

CALIBRATION

·

••••

•••

••

••••

••

•

General

-

Equipment

Required -

Bandpass

Com

pressor -

Program

Amplifier -

Peak

Limiter -

H.F.

Limiter Calibration -

Rectifier

Balance

...

18

VII.

APPENDIX

•.•.••••••••..

·

••....••.••

22

Parts

Lists

-Schematics -Warranty

-2-

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GENERAL

INFORMATION

ANO

SPECIFICATIONS:-

·-

-~--

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The

Inovonics

230

is

a broadcast audio orocessor

for

both

AM

and

FM

service, designed

specifically

to

enhance perceived signal loudness

and

th

us

extend the

effective

ar

ea

of

station

coverage.

When

prop-

erly

adjusted,

the

230

will

so process

the

audio

program

sfgnal as

to

increase

transmitter

modulation

density

to

a

figure

approaching

theo

ret

ical

maximum,

while

still

maintaining a high value

of

program

l

is

tenability.

General

Specifications

The

Inovonics

230

is

comprised

of

two

primary functional

sections;

the

gated

8-ba

nd

Comp

res

sor,

and

the

Peak

Limiter section

which

also

includes the Phase

Fo

l-1

ower

(AM)

.,

and

independent

Freq

uen

cy-Selective

Limiter

circuitry

{FM). Specifications

relative

to

overall ·230 per-

fonnance

,

and

data spe

cific

to

the

Compressor

and

Limiter sections

are tabulated separately.

Fre2uency

Response

(below

Compressor

thresho

ld):

-ldB,

20Hz

-

20kHz.

Noise

Level: Better than 6Sd8

below

100%

modulation.

Distortion:

<1%

THO

for

any

degree

of

compression

and

l_imiti~g

of

steady-state

signals 20Hz -20kHz.

Input: Balanced-bridging; accepts

program

levels

between

-20

and

+lOdBm.

.

Output: Balanced output feeds

600-ohm

lines

or

terminating inputs

at

levels

between

O

and

+20dBm,

corresponding

to

100%

modulation.

Stereo

Interconnection:

Two

units

may

be

interconnected

by

means

of

an

accessory cable

to

duplicate compression

on

a band-for-band

basis.

(Also

see

pg.

8,

11

AM

Stereo")

Power

Requirement:

10s

·-

130VAC

.(230V

available),

50/60Hz; l/2A.

Size

and

Weight:

7

11

X

19"

.X

9

11

;

16

lbs.

-3-

www.SteamPoweredRadio.Com

( )

_.,.

- ·

.

--

8-Bsnd

Compressor Specifica

tions

The

input

aud

io

program

signal

is

first

divided in

to

eight

frequency

bands

. each approximately

one

octave

wide

with

12

dB

-p

er

-octave

skirts.

Within

each

band

the

si

gna

l undergoes r.m.

s.

compression w

ith

full

fl

exib

ility

of

control over c

ompress

i

on

pa

rame

ters.

·

User

adjustment

of

Compression

Th

reshold

and

Compression

Ratio in each

of

the

eight

bands

pennits

program

re

spon

se

to

be

dynamica

lly

shaped in. a

manne

r

similar

to

that

afforded

by

a separate

Graphi

c Equaliz

er

to

complement

a

particular

prog

ramm

ing fonnat.

Frequency Division

(Hz):

20-60. 60-150. 150-300, 300-700, 700-1.Sk,

1.5k-3.5k, 3.Sk-7.Sk, 7.Sk-20k.

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Compr

ession Ratio: 2:1,

~:1,

8:1;

switch-selectable in each band.

Compression

Th

reshold: Variable over lS

dB

range

in

each band.

Attack

and

Release

Timing:

Optimized

for

each

band

consistent

with rapid operation, r .

m.s

. response

and

low

distortion.

Gated

Expansion

(DEFEATABLE

FUNCTION):

(See

pg.

7)

·

Peak

Limiter Specifications

Following

compression

the

input

program

is

recombined

into

broadband

fonn

.

At

this

point the

fast

Peak

Limiter

acts

.

on

the signal

to

re-

duce

program

peaks

to

the desired

ab

so

lute

value

for

100%

modulation.

The

Peak

Limiter

can

be

adjus·

tei;I

for

Phase-Followin9,

Asymmetrical

operation in

AM

service,

-0r

an

independent Frequency-Selective Limiter

enabled

for

FM

broadcast

use

.

Compression

Ratio:

:>100:1

Limiting Threshold: Variable over

25d8

range.

-

4-

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www.SteamPoweredRadio.Com

i

Attack

iime:

--=lus

for

any

degree

of

limiting:

~·:.

Release

Time:

Complex

function

of

program

peak

content; manually

adjustable over

10:l

range.

Peak

Syrr,netry

(DEFEATABLE

FUNCTION):

· Positive

peak

value can

be

adjusted

from

100%

to

150%

of

negative

peak

value.

Phase

Follower

(DEFEATABLE

FUNCTION):

(See pg.

7)

Frequency-Selective Limiter

(DEFEATABLE

FUNCTI

ON

):

Switchable

to

complement

either

75µs

or

25µs

FM

pre-emphasis

characteristics

to prevent overmodulation

from

high frequency

program

energy.

Circuit

provides

totally

independent limiting

of

high frequencies.

-5-

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F

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II.

DES

I

GN

PHILOSOPHY

ANO

FUNCT

I

ONAL

DESCRIPTION

Multiband Compression

The

Inovonics

230

Multiband

Audio

Processor represents a

significant

departure

in

design

and

operating phi losophies

from

the usual family

of

broadcast compressor/limiters.

The

most

obvious difference

is

the

individual processing

of

signals within multiple frequency bands.

The

majority

of

audio level compressors

act

on

the broadband

signal,

regulating

circuit

gain

as

a function

of

program

level. This

is

gen-

erally

accomplished

by

deriving a

DC

control voltage

from

the

audio

signal,

and

utilizing

this

voltage

to

regulate

circuit

gain.

In

order to remain unobtrusive

in

its

action,

a compressor

must

be

relatively

fast-acting;

that

is

it

must follow the envelope

of

the

audio

program

quickly

enoug

h

to

reduce sudden input

increases,

and

must

release quickly to avoid audio "holes"

and

audible fade-up

when

the input level returns to normal. Unfortunately,

this

fast

action

is

not

consistent

with

low

distortion,

particularly

at

low

frequencies,

as a necessarily

short

rectifier

filter

time constant

results

in ampli-

tude modulation

of

the

program

by

its

own

harmonic products.

The

obvious

alternative

is

to independently

compress

high

and

low

· frequencies,

tailoring

the

rectifier

filter

time constants

to

the

sub-

ject

portions

of

the spectrum.

In

this

manner,

low

frequency

distor-

tion

could remain

at

an

acceptably

low

level,

while,

at

the

same

time,

compression could

be

rapid

at

voice frequencies

and

above.

In

i

ts

utilization

of

this

multiband approach, the Inovonics

230

divides

the

au

d

io

spectrum

into

eight separate bands.

While

this

might

seem

an

unnecessary

number

of

divisions,

the

advantage

is

twofold.

First,

broadband

energy can

be

concentrated

and

maintained

at

a high

level,

as

no

loud,

single

tone or

musi

.cal note can reduce gain in any

other

than

its

own

band. Secondly,

by

providing

manual

adjus·tment over both

· the Compression Ratio

and

Compression

Threshold in each

of

the

eight

bands, the spectral

distribution

of

the

program

can

be

tailored

to

impart a

specific

''sound" to the program, almost regardless

of

the

nature

of

the

program

source. This can

be

nearly as important

an

ad-

vantage as perceived loudness

in

an

already loud, competitive market-

place.

-6-

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.l

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--

.,

Gated

Expansion

As

a

co

mpres

sor reduces the

dynamic

range

of

a program, so

it

a1so

reduces the program-to-noise

ratio.

Noises

that

wer

e

once

far

below

the average program level

(teletype

printers,

air

conditioners,

etc.)

are

now

clearly

audible

when

the average

program

level drops.

To

lessen

this

annoyance, the

230

features

an

optional

Gated

Expansi

on

mode,

which

simultaneously reduces the gain in

all

eight

bands

once

the

program

level

falls

below

a predetermined Gating Threshold value.

In

order

for

the gating

circuit

to

properly di

fferentiate

between

legitimate

program

material

and

spurious noise, frequency weighting

restricts

gating

sensitivity

to

mid-band frequencies.

Peak

Limiter

The

230

employs

a

fast,

true

p·eak

limiter

rather

than a

clipping

cir-

·

cuit.

The

apparent increase in average modulation afforded by a

clipper,

a

result

of

the

greater

r.m.s. value of the

clipper's

squared output

waveform,

is

likely

to

suffer

substantial

loss through phase

shift

and

overshoot in the

AM

transmitter

modulator or

FM

stereo generator.

The

230

preserves signal

waveshape

as

much

as possible,

consistent

with

instantaneous reduction

of

fast

program

peaks.

The

advantage

of

true

peak

limiting in terms

of

audible signal

distortion

is

obvious, even in

casual

listening

situations.

Asyrm,etrical Modulation

In

AM

broadcast use

of

the 230, the value

of

positive modulation

peaks

may

be

continuously adjusted

to

assume

up

to

150

%

of

the negative

peak

value. Although positive modulation

is

legally

restricted

to

125%,

many

plate-modulated transmitters require drive in excess

of

+125%

to

reach the legal

maximum.

It

must

be

warned,

however,

that

transmitters

which

fall

into

th

is category

are

incapable

of

linear

operation

up

to

+125%

,

and

the very

slight

gain in perceived signal loudness must be

weighed

against probable high signal

distortion.

Phase-Follower

Asymmetrical

modulation .

of

pos

·

itive

and

negative

peaks

yields

a

modu-

lation

advantage only

when

the

program

material

is

a.symmetrical in

nature.

Most

music, because

it

is

a blend

of

complex

waveforms

which

are not phase-related,

has

a very

even

balance

of

peak

energies. Solo

instruments

and

the

human

voice,

on

the other hand, possess a

more

or

less fixed

relationship

between

the phase

of

the fundamental tone

and

-7-

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the harmonics. This leads

to

an

appreciable

and

consistent

imbalance

between

positive

and

negative peaks,

and

can

be

used

to modulation

advantage.

The

230

Phase-Follower

circuit

monitors

mean

peak

energy balance

and

instantly

inverts

program

phase

to

maintain

maximum

positive

AM

trans-

mitter modulation.

The

prog

r

am

inversion

is

effected only

at

signal

zero-crossings, however, to reduce

audibility

of

the switching action.

Nevertheless,

an

instantaneous second harmonic product

is

generated

each

time the phase

is

inverted,

and

may

be

distracting

with

some

types

of

pr

ogram

material.

Sensitivity

of

t

he

Phase

-Follower

circuit

is

adjustable so

that

a c

omprom

ise

between

advantage

and

annoyance can

usually

be

reached.

AM

Stereo

As

of

this

writing,

the subject

of

ste

reophonic

AM

broadcasting

is

receiving a

good

deal

of

attention.

Although

no

standard has

been

adopted, the

most

promising system

utilizes

a combination

of

carrier

amplitude and phase modulation.

In

this

system, a

L+R

audio signal

amplitude modulates the

transmitter

in a conventional manner, assuring

monaural

compatibility.

The

L-R

audio signal phase-modulates

the

carri

e

r,

and

is

independently demodulated

and

matrixed

by

the

AM

stereo

receiver

to

yield

Left

and

Right information.

When

interconnected

for

FM

stereo operation, the

230

Phase-Follower

circuit

is

automatically disabled. Nonetheless,

when

two

230

1s

are

interconnected,

and

the Phase-Fo·llower in

one

unit

manually enabled,

the other Phase-Follower

circuit

will

be

slaved

to

the

first.

If

the

first

230

should process the

L+R

signal

which

amplitude-modulates

the

carrier,

and

the second unit the phase-modulating

L-R

information, the

result

will

be

a

fully

modulated

AM

carrier

with the stereo matrix

phase properly maintained.

_Frequency-Selective Limiter

Standard

FM

broadcasts

utilize

a

75µ

s pre-emphasis time constant

for

signal-to-noise

improvement;

. Dolby-encoded broadcasts a

25µs

charact-

eristic.

As

a

result

of

this

signal pre-emphasis, the

amount

of

trans-

mitter input drive to achieve

100%

modulation

is

much

less

at

high than

at

low

frequencies.

An

effective

FM

limiter

mu

st

therefore

effect

greater reduction

of

high frequency

program

prak

s.

The

Inovonics

230

incorporates a separate

Pea

k Limit

er

to control the

energy

of

high frequency

program

peaks independently

of

the

normal

broadband

limiting action.

The

high frequency

limiter

can

be

switched

between

75~s

and

25µs

limiting

characteristics

.

-8-

www.SteamPoweredRadio.Com

--

...

--

~

........

.......

III.

INSTALLATION

Unpacking

and

Inspection

Upon

receipt

of

the

equipment, inspect

at

once

for

shipping

damage.

Should

any

such

damage

be

observed,

notify

the

carrier

at

once;·if

not, proceed as outlined

below.

It

is

suggested

that

the

original

shipping carton

and

materials

be

retained should future re-shipment

become

ne

cessary.

In

the event

of

return

for

Warranty

repair,

ship-

ping

damage

sustained as a

result

of

improper packing

for

return

may

invalidate the Warranty.

It

is

important

that

the Warranty Registration card

found

at

the

front

of

this

manual

be

returned; not only

does

this

assure coverage

of

the equipment

by

the

Warranty, but the user

will

automatically

receive

specific

servicing

or

modification infonnation

if

and

when

it

should

become

available.

Mounting

The

230

is

packaged

to

mount

in a standard 19-inch equipment rack,

requiring 7 inches

of

rack space per

unit.

The

230

generates

negli-

. gible heat,

and

itself

is

unaffected by

wide

variations

in

the ambient

operating temperature.

RFI

The

230

is

specifically

designed

to

operate in close proximity

to

broadcast

transmitters;

nevertheless, care should

be

exercised

in

locating the

unit

away

from

abnormally high

RF

fields.

In

some

installation

situations,

an

RF

ground

loop

may

.be

formed

be-

~

tween

~he

input

or

output cable

shield

grounds

and

the

AC

power

cord

ground.

Use

of

a "ground-lifting"

AC

adapter should

remedy

any

problem.

hfOut

Connection

The

230

input

and

output.connections

are

brought out to a

rear

panel

screw-terminal

barrier

strip.

Both

the input

and

output are balanced

(transformer-isolated), with

ground

terminals provided

for

cable shields.

•

-9-

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The

input

and

output

of

the

230

are

each

marked

with+

and

-desig-

nations

to

aid

in

maintaining prope·r phase in stereo

applications,

or

proper asyrrmetrical modulation

of

program

peaks. In the

latter

case,

the+

output tenninal will

be

positive-9oing with positive modulation

peaks.

Line

Considerations

Should

the equipment

which

feeds the

230

require output loading,

an

external

600

ohm

resistor

should

be

placed across the

230

input tenni-

nals; otherwise

the

input is "balanced-bridging" with a

characteristic

input

impedance

of

lOK

or

gre

ater

.

The

source

impedance

of

the

230

output amplifier (ahead

of

the

line

output transfonner)

is

virtually

zero

. .

However,

as

the

output

trans-

former

has

some

reactan

ce,

it

is

important

that

the

230

output be

terminated in

600

ohms

to

minimize

output overshoot.

..

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www.SteamPoweredRadio.Com

----

-----

-

--

,

--

----,--.~-----·----

---

-·

-~-·-

·~-

..

--

IV.

OPERATION

AND

ADJUSTMENT

The

Inovonics

230

is

a f

undamen

tally

more

complex

device than most

other broadcast audio processors, a

nd

hosts a

full

complement

of

ac-

cessible controls

whi

ch

materially

aff

ect both

the

technical composition

and

the subjective audio quality

of

the transmitted

program

s

ignal.

The

various adjustments are

identified

on

the inside

of

the removable

front a

ti

justment cover. Despite

the

seemingly obvious

mean

ings

of

the

control function descriptions,

it

is

highly

recommended

that

the out-

lined

procedu

re

be

carefully

followed

for

initial

setup. Subsequent

readjust

men

t

to

secure a desired

effect

should

be

made

only

after

it

has

been

est

ablished

that

the 230 functions properly

and

predi

ct

ably

in accordance with the

initial

setup procedure.

All

adjusune

nts

are

made

"on

the

air..,"

utilizing

a typical program feed .

and

the

station

Modulation Monitor.

Basic Adjustments

1.

Preset controls as follows:

COMPRESS

ION

THRESHOLD

(a

11

8) -

fully

"up"

(

OdB)

COMPRESSION

RATIO

(all

8) -4:1

FUNCTION

- Ungat

ed

LIMITER

MODE

-Flat

PEAK

LIMITER

RELEASE

-

fully

counterclockwise

2.

With

a n

onn

al

program

feed

from

the console,

adjust

the

INPUT

GAIN

(CO

MPRE

SSION)

control

for

10 -

lSdB

of

.compression in the

most

active

bands.

3. Adjust

PEAK

LIMITER

DRIVE

for

5 -

lOdB

Peak

Limiting.

4. Adjust

OUTPUT

LEVEL

control

for

100%

modulation

on

peaks as

indicated

by

the Modulation Monitor.

5. Proceed with

specific

AM

or

FM

adjustment~.

~~

Adjustments

(Asymmet'.ical

Modulation)

1. Set the

LIMITER

MODE

switch

to

Asymmetrical,

and

adjust

the

POS.

PEAK

AMPLITUDE

(ASYMMETRY)

control

for

desired

positive

peak

modulation per the Modulation Monitor.

_2.

With

the

LIMITER

MODE

switch in

the

Phase-Following

position,

-11-

www.SteamPoweredRadio.Com

-----

·- -

---

~

-~

:->

•

··

:1;;;.

~~~

-

~

=-

..

. ' .

the

230

will

invert

the signal

at

zero-crossings

to

maintain

maximum

positive

modulation.

The

PHASE-FOLLO

WE

R

SENSITIVITY

control

can

be

left

fully

clockwise

to

enable inversion with

the

least

amount

of

signal asymmetry,

or

rotated counterclock-

wise

to

invert

with correspondingly

greater

asynmetry, thereby

reducing inversion incidence.

(See

wa

rning

on

pg. 8)

FM

Adjustments (Fr

equ

ency-Selective Limiting)

With

the

LI

M

ITER

MOD

E switch in

either

the

75µs

(n

ormal

FM)

or

25ps

(Dolby

FM)

positions,

high

frequency program

peaks

will

be

inde-

pendently attenuated

to

prevent o

vermodul

ation

due

to

transmit

ter

pre-emphasis.

The

OUTPUT

LEVEL

control

will

require readjus

tme

nt

from

the

initial

setting

made

under Basic Adjustments

to

insu

re

full

FM

carr

ier modulation.

S

UB

JECTIVE

ADJUSTMENTS

Peak

Limiter Release

Timing

As

preset under Basic Adjustments, the

Peak

Limiter release

time

is

at

maximum,

resulting

in

s

low

est

recovery

from

program

peak

s.

Average

modulation can be increased

significantly

by

turning the

PEAK

L

IM

ITER

RELEASE

contol clockwise

from

its

present

full

CCW

position, thus operating with a

shorter

re-

lease time.

The

final

setting

must

·

be

based

on

a judgement

of

program

quality,

compromising

between

a

sound

that's

just

"loud,"

and

one

that

can

be

listened

to

for

an

extended period

without fatigue.

Gated

Expansion

Function

With

the

FUNCTION

switch

in the

Gated

Expansion

position,

Com-

pressor gain will reduce

by

a

nominal

lOdB

figure

when

no

legit-

i

mat

e input signal is present. This serves

to

reduce background

noise

by

the

same

lOdB

•.

The

GATING

THRESHOLD

contral

sets

the

point

at

which

an

·input signal will

open

the gate

and

return

Compresscr

gain

to

maximum.

The

control should

be

advanced

suf-

ficiently

clockwise to

keep

the

GATE

OPEN

indicator illuminated

constantly during music, but not so

far

as to prevent gating

action during pauses in speech.

-12-

www.SteamPoweredRadio.Com

--

-

------

Program

Response

Shaping

Since the

230

has independent control over both Compression

Threshold

and

Compression

Ratio in each band, frequency char-

acteristics

may

be

tailored

to

complement

a

specific

program-

ming

format in

much

the

same

manne

r as with a Graphic Eq~alizer.

Regardless

of

THRESHOLD

and

RATIO

setting,

230

response·

at

low

levels

(below

Compression

Threshold) will remain

flat.

The

control

settings

will,

however,

directly

influence the

amoun

t

of

energy in e

ac

h

band

at

normal

program

levels.

When

all

eight

bands

are adjusted

similarly,

the

230

will impart a "bright"

sound

to

the

program;

this

is

due

to

spectral energy

distribution

in typical

music

and

speech

signals,

and

the tendency

of

the

230

to bring

up

the higher frequency

bands

which

are

by

nature lower

in energy

level.

If

it

is

desired

to

maintain spectral balance

and

prevent response

coloration

by

the 230, the

COMPRESSION

RATIO

switches should

be

set

identically,

and

the

THRESHOLD

controls adjusted

for

approxi-

mately equal compression in

all

bands

with typical

program

material.

Response

may

be

tailored

by

adjusting

either

the

RATI

O switch

or

the

THRESHOLD

control (or both),

to

yield

the desired "sound."

It

is

advis~d,

however,

that

the following precautions

be

observed:

1.

Make

all

changes in small

steps,

listening

carefully

to

the

results

each time.

2.

If

it

is

desired

to

e

mphasi

ze

certain

bands,

keep

the

THRES-

HOLD

controls

of

these

bands

at

OdB,

and

the Compression Ratio

lower than in the others.

3.

Avoid

differences

of

more

than

SdB

in the

THRESHOLD

settings

of

adjacent bands. Violation of

this

warning.

can

lead

to

very

undesirable "phasing"

or

"swishing"

effects

.

..

www.SteamPoweredRadio.Com

-

......

·"'!"..::- -

...

--

--~

-..

V.

CIRCUIT

DESCRIPTIONS

--

Input

Ampli

fier

The

230

program

input

is

transf

ormer-iso

lated

by

Tl

on

the "mother"

circuit

board

and

routed

to

the P

rogram

Amplifier assembly

and

-Input

Amp

lifier

!Cl. Current gain stages

Ql

and

2 provide additional output

drive to feed

all

eight

Bandpass

Compressor

assemblies, the inputs

of

which

are

paralleled

at

the

Compressor

Input

Bus

.

Gain

of

the Input

Amplifier

can

be

adjusted over a

30d8

range

by

the

INPUT

GAIN

(COMPRES-

SION)

cont't

ol

R4

to

accommodate

different

input

line

levels.

Bandpass

Compressors

In

each

of

these

assemb

1i

es,

si

gna

1s from the

Compress

.

or

Input

Bus

.are

fed

to

ICl, a voltage-variable gain

stage.

Th

is

circuit,

the

•santana•

configuration,

utilizes

FET

Ql

as

an

active

variable

resistance

across

the inv

erting

input

of

the operational amplifier.

Q2,

a

similar

11

durrmy

11

FET,

is

placed across the non-inverting amplifier input

and

cancels the

c

hann

el

non-linearities

of

Ql.

Th

is permits control

of

the

aud

io

signal

at

levels

which

would

otherwise

be

above

the

low-distortion operating

range

of

the

FET's

•

.

Q3

and

associated .

components

form

the high-pass section

of

the bandpass

filter,

Q4

the low-pass section.

Both

sections are second-order

active

filters

with 12d8-per-octave

rolloff.

The

output

of

the

filter

circuit

is

fed to the

common

Combining

Bus

through

the

BAND

GAIN

calibration

control

R25

. Amplitude

and

phase

characteristics

of

the

eight

individual

filters

are

such

that

the

combined

outputs

yield

a

flat

signal with

min-

imum

ph

ase

distortion.

A portion

of

the bandpass

filter

output

also

passes through

THRESHOLD

control

R13

to

IC2,

a voltage gain stage.

QS

and

6 comprise a "Baxandall"

full-wave

rectifier.

The

positive-going portion

of

the input

waveform

is

,amplified

by

corrnnon-emitte

r stage

QS,

the negative

by

co!llTion-base

stage

Q6.

Thus

equal positive

and

negative information cause

similar

currents

at

the junction

of

the

Q5

and

6

collectors.

Q7

is

a non-linear

current-

source

collector

load

for

Q$

and

6,

and

imparts a logarithmic character-

istic

to the

resultant

DC

voltage. This log

tr

·ansfer function

creates

the desired

linear

compression

of

signals exceeding the

preset

Compression

Threshold. · .

Further

DC

amplification

of

the

rectified

bandpass signal

is

performed

by

Q8

and

IC3.

The

combined

gain

of

these stages establishes overall

Compression

Ratio

which

can

be

varied with

COMPRESSION

RATIO

switch

S1

and

calibration

pot

R22

.

Compression

is

inhibited

for

test

purposes

..

-14-

www.SteamPoweredRadio.Com

-.

•

when

the

Program

Amplifier

FUNCTION

switch

is

placed in the

11

Proof"

position. This

clamps

the

anode

of

CRl

slightly

negative, shunting

Q8

collector

current

to

ground. .

A positive current

is

fed through

R27

to

the inverting input

of

IC3,

generating a negative

DC

offset

at

the output

of

this

stage.

It

is

-

--

this

off

set

which

ultimately appears across

R36

and

is

adjusted

by

this

calibration

control

to

"pinch

off"

FET

Ql.

As

rectified

signal

reaches the non-inverting input

of

IC3,

the

DC

offset

is

reduced, thus

causing signal compression.

The

offset

current through

R27

can

be

varied

by

the Gating

circuit

to

simultaneously reduce gain in

all

eight

channels, lowering

background

noise

when

no

input signal

is

present.

The

components

between

the output

of

IC3

and

the base

of

Q9

filter

the

DC

control voltage.

Compressor

Attack

and

Release timing are a function

of

these

component

values,

which

are

optimized

for

the range

of

fre-

quencies

specific

to

each

band

to

insure rapid operation,

low

distortion

and

minimum

audibility

of

Compressor

action.

Complementary

emitter-

followers

Q9

and

10

isolate

the

filter

from

metering

and

other loads.

Gating Circuit

A portion

of

the "raw

11

230

program

input signal present

on

the

Program

Amplifier assembly

is

routed through

GATING

THRESHOLD

control

Rl

to

. voltage amplifier .

IC2.

This stage

is

bandwidth-limited, with -3d8

points

at

300Hz

and

3kHz.

This insures

that

the signal

at

the

output

will consist mostly

of

legitimate

program

material,

rather

than ~purious

noises.

IC3,

a unity-gain

inverter,

and

diodes

CRl

and

2

provide

full-

wave

rectification

of

the weighted

signal.

With

FUNCTION

switch

S1

in the

Gated

position,

capacitor

C8

charges

to

the

positive supply through

R12.

When

the weighted

and

rectified

input

signal reaches the predetermined threshold value,

Q3

begins

to

conduct,

discharging

C8.

IC4

adds

DC

gain

and

hysteresis to the

circuit,

and

its

output toggles negative

when

program

is

present, positive

when

the

pro-

,

gram

level

falls

below

the threshold

level.

Transistors

Q4

and

5

and

the

RC

combination

of

R18

a

nd

ClO

integrate

the gating logic

to

provide

a

smooth

level

transition

between

the gated

and

ungated,

or

"gate

open"

states

.

Combining

Amplifier (

Program

Phase Detector

The

outputs

of

the eight

Bandpass

Compressors

are

combined

by

the

oper-

ational

summing

amplifier

!CS

on

the

Program

Amplifier assembly.

Drive

to

the

Peak

Limiter

(and

thus the

amount

of

program

peak

limiting

em-

ployed)

is

set

by the gain

of

this

stage,

variable over a

25dB

range by

...

-15-

www.SteamPoweredRadio.Com

l

'

,·

(

.I

-·-

·

·--

-

. .

....

PEAK

LIMITER

DRIVE

control

R26.

Positive

and

negative output excursions

of

JCS

are also independent

ly

rectified

by

diodes

CR8

and

7,

respectively;

the

peak

values held

by

capacitors

C16

and

15.

Pol

arity

of

the

DC

voltage across

Cl?

indicates

the predominant

polarity

of

program

peaks

and

controls the automatic

program

phase reversal feature

to

maintain

maximum

positive

AM

carrier

modulation.

IC7

adds

DC

gain and

hysteresis

to

the switching signal .

FET

Q8,

normally

off,

prevents

IC7

from

changing

state

except

when

m

om

entarily

turned

on

at

signal zero-crossings. A zero-crossing de-

tector

is

com

prised

of

amplifier

st

ages

IC6

and

Q7,

and

diodes

CR9

and

10.

PHA

SE

FOLLOWER

SENSITIVITY

adjustment

R34

selects

the degree

of

peak

po

larity

imbalance required

to

effect

a

program

phase

reversal.

Peak

l

im

iter

Circuits

Input signals to

the

Peak

Limiter assembly

are

fed

to

ICl,

a variable

gain stage

of

the Santana configuration (See pg.14). ICl,

acting

as

the

br

o

adband

peak-controlling

ele

m

ent,

drives

IC2,

a second Santana

circuit.

In

this

instance, however,

capacitors

C3

and

4

are

introduced

in

series

with the

variable-resistance

FET

Q4

to

im

part

a frequency-

selective

nature

to

the gain reduction

characteristic.

This

totally

independent control

of

high frequencies

is

utilized

in

the

75µs

and

-

~5µs

FM

limiting

mqdes

.

In

AM

use,

IC2

functions only as a unity-gain

.inver

ter.

.

A broadband peak-reducing

DC

control voltage

is

derived

from

the

output

signal

of

the

Peak

Li

miter assembly. In

AM

processing

applications

this

can

be

either

the output

of

ICl,

or

the inverted output

of

IC2.

In

the Phase-Following

mode,

the

two

switching

FET

1

s

Q5

and

6

are

controlled

by

logic

from

the

Program

Amplifier assembly,

selecting

the

program

phase

which

results

in

maximum

positive

modulation. In

the

ot

her operating

situations,

Q6

is

kept

on

to

maintain overall

230

phase

integrity

and

to

permit frequency-selective limiting

for

FM

by

the

high frequency limiting

circuit

of

IC2.

Transistors

Q9

and

10

comprise a Baxandall full-wave

rectifier

config-

uration (See

pg.

14) driven

by

buffer stage

IC3.

Q9

and

10

can

be

balanced

for

symmetrical

pe~k

rectification

wit~ a variable

DC

offset

from

calibration

control

R25.

When

asymmetrical

rectification

is

desired,

the

sensitivity

of

the

rectifier

to

negative-going program

peaks

is

decreased by biasing the base

of

QlO

negative with

POSITIVE

PEAK

AMPLITUDE

control

R30.

Since buffer stage

IC3

inverts,

this

decreased

sensitivity

of

the

rectifier

to

negative

peaks

corresponds

to

an

increase in the ievel

of

positive

program

peaks

at

the

230

out-

put.

The

value

of

positive

peaks

can

be

varied

from

10

0%

to

150%

of

the negative

peak

value. Transistor Qll multiplies the gain

of

the

..

-

16

-

www.SteamPoweredRadio.Com

.

_,,.,,;___·-----=---

......

Baxandall

rectifier,

resulting

in

a very high

com

pr

ession

ratio

(on

the order

of

50:1

or

more)

above

the peak

limiting

threshold.

The

time constant

of

the

peak

rectifier

filter

is

a function

of

peak

incidence

and

duration.

The

first

half-cycle

of

a

program

peak,

or

isolated

single

peaks

in

excess

of

the

mean

peak

reduction value, pass

through

CR3

to

the

gate

of

QI

and

effect

instantaneous peak reduction.

Repetitive peaks,

on

the other hand, cause

CB

to charge through-

R39

and

CR4,

introducing a longer-term gain reduction. This longer-term

re-

duction

of

repetitive

peaks

prevents the audible

distortion

attendant

to

peak

"clipping."

The

Peak Reduction meter

is

driven

by

a sample-and-hold

circuit

consist

-

ing

of

!C's 4

and

5

and

transistor

Q13.

Peak

holding time

of

the

metering

circuit

is

fixed

by

the time constant

of

Cll

and

R44,

and

at

about

two

seconds permits

an

accurate display

of

even

the

fastest

pro-

gram

peaks.

The

independent high frequency

limiter

f

un

ctions

similarly

to

the broad-

band

peak

reduction

circuit

just

discussed.

The

output

of

IC2

is

equ

al-

ized

to

the 75µs

or

25µs

characteristic

by

C12

and

R48

and

49.

IC6

is

a gain stage driving

the

Baxandall

rectifier

comprised

of

Q14,

15,

16

and

17.

The

resultant

DC

is

applied

to

Q4

tc

reduce the higher

fre-

quencies. CRll, Cl4

and

R61

and

62

form

a dual

release

filter

similar

to

that

used

in

the broadband

circuit.

Output Amplifier

The

Output Amplifier

is

part

of

the

Program

Amplifier assembly

and

consists

of

IC8, with

Q9

and

10

as current-gain

stages.

Gain

is

set

by

OUTPUT

LEVEL

control

R43.

The

230

line output

is

isolated

by

the

chassis-mounted transformer

T2.

Power

Supply ·

'

Power

transformer T3,

rectifier

diodes

CRl-4

and

filter

capacitors

Cl

and 2

deliver

"raw"

DC

to the

two

"three-terminal" voltage

regulators,

IC's 1

and

2.

Dua

l operational

amplifier

1C3

is

connected

to

provide

additional

AC

feedback around the

two

regulators,

further

reducing

ripple

and

noise

on

the ±18-volt regula·ted supplies.

-17-

..

www.SteamPoweredRadio.Com

VI.

CALIBRATION

Genera

l

The

Inovonics

230

has

been

carefully

calibrated

at

the factory

and

"burned-in"

to

verify

circuit

stability

prior

to

shipment. There

is

no

requirement

for

routine instrument

calibration,

and

the only reason

which

might

necessitate

adjustment

of

the various

calibratio

n controls

would

be

a catastrophic

failure

and

subsequent replacement

of

critica

l

components. A

calibration

procedure

is

nonethele

ss

given, but should

be

attempted only

by

qualified individuals

who

have

read the C

ir

cuit

Descriptions

and

who

understand the various

circuit

functions.

Equipment

.Required

1. Printed

circuit

Extender Card: Inovonics

A/N

137300

(Available

from

Inovonics, $20, postpaid)

2.

Audio

Oscillator:

Hewlett-Packard

200CD

or equivalent.

3.

AC

Voltmeter: Hewlett-Packard

400H

or

equivalent.

Bandpass

Compressor

Preliminary

1. T

he

Bandpass

Compressor

assemblies -are adjusted one-at-a-time

in

their

own

respective sockets, with

all

other

Bandpass

Com-

pressor

assemb

lies

removed.

2.

AC

voltmeter access to the

Compressor

Input

Bus

and

the

output

of

the

Combini

ng Amplifier

is

made

by

temporarily soldering

sh

ort

"pigtail"

leads

to

the

INPUT

GAIN

(COMPRESSION)

and

PEAK

LIMITER

DRIVE

controls

on

the

Program

Amplifier assembly.

In

both cases connection

is

made

to the control pin nearest the front

edge

of

the board. .·Hereafter, these monitor

poi

nts

are

referred

to

as

11

input

11

and

"output," respectively.

3. Set the

Program

Amplifier

FUNCTION

switch

to

Ungated,

and

rotate

the

PEAK

LIM!TER

D~IV

E control

fully

CCW.

Settings

of

other

controls are unimportant.

4.

Connect

the

oscillator

to

the

230

input.

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FET

Balance/

Threshold

Cal.

1.

Insert

the assembly

to

be

calibrated

into the Extender Card,

and

the Extender

Card

into the proper socket.

-----

2. Set the

oscillator

to

the

midband

frequency

for

the assembly

under

test.

Adjust the

oscillator

output level

for

a reading

of

-lOdBm

at

the "input" monitor point. ·

3.

Connect

the voltmeter

to

the

"output" monitor point.

Turn

R36

and

RlS

fully

CCW,

and

set

the

THRESHOLD

control

fully

"up

.

11

Adjust

R2

for

a

minimum

reading

(null)

on

the

AC

voltmeter.

4.

Turn

R36

fully

CW.

Adjust the

BAND

GAIN

control

for

a

volt-

meter reading

of

-19.

6dBm.

5. Slowly

rotate

R36

CCW

until

the

voltmeter drops

0.2dB.

to

-19

.

SdBm.

~

·

-·

· .

6.

Turn

Rl5

slowly

CCW,

setting

for

an

additional drop

of

0.2dB,

to

-20dBm.

At

this

point

set

R37

for a front-panel

Compression

me

ter

reading

of

zero.

Ratio Cal.

1. Set the

RATIO

switch to

2:1.

With

the

AC

voltmeter connected

to the "input" monitor

point,

increase the

oscillator

output

level

for

a reading

of

+6d8m.

2.

Reconnect

the

AC

voltmeter

to

the

"output"

mo

nitor

point.

Ad-

just

R22

for

a voltmeter reading

of

-12dBm.

3. Set the

RATIO

switch

to

4:1; the output should

fall

to

-16dBm

.

At

8:1 the reading should

fall

to

-18dBm.

Repeat

this

procedure for each

Bandpass

Compr

essor assembly.

It

is

suggested

that

the

calibration

pots

be

resealed with a small

amount

of

white

glue

(Elmer's,

etc.).

When

all

assemblies

have

been

adjusted,

remove

the

two

monitor access leads

from

the Pro

gram

Ampli

fier

assembly.

Program

Amplifier

There

are

no

calibration

ad

ju

stments

on

this

assembly.

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Peak

Limiter

Preliminary

1. Plug

the

Peak

Limiter assembly

into

the Extender Card,

and

the

Extender

Card

into the

Peak

Limiter assembly socket.

2. This assembly

is

calibrated

with

all

other

assemblies

installed,

the

Program Amplifier

FUNCTIO

N

switch

in

the

11

Proof

11

position

and

the

OUTPUT

LEVEL

control

fully

CCW.

3.

The

oscillator

should

be

connected to the

230

in

pu

t,

the

AC

voltmeter

to

the 230 output.

4.

Turn

both the

POS.

PEAK

AMPLITUDE

(ASYMMETRY)

and

PEAK

LIMITER

RELEASE

controls

fully

CCW.

01/,Qg_

Balance/

R34

Adjustment

1.

Set the

Peak

Limiter

MODE

switch

to

Flat.

Set the

oscillator

to

a frequency

of

500Hz

and

adjust

the

oscillator

output level

for

a reading

of

-lOdBm

on

the

AC

voltmeter.

2. Rotate

R34

fully

CCW.

Adjust

RI

for

a

minimum

reading

(null)

on

the

AC

voltmeter.

3.

Turn

R34

fully

CW

and

note the output reading. Slowly

rotate

R34

CCW

until

the output decreases

by

O.ldB.

4. Set

R45

for

a front-panel

Peak

Reduction meter reading

of

zero.

mfM

Balance/

R58

Adjustment

1. Increase the osci

11

a

tor

·frequency

to

20kHz.

2. Rotate

R58

fully

CCW.

Adjust

RS

for

a

minimum

reading

(null)

on

the

AC

voltmeter.

3.

Turn

R58

fully

CW

and

note the output reading. Sl

owly

rotate

R58

CCW

until

the

output

decreases

by

O.ldB.

_

,,.,_

7

Inovonics 230 User manual

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