TELETRONIX LA-2A - GAIN REDUCTION FREQUENCY RESPONSE CONTROL

TELETRONIX LA-2A

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[

[.

-,

[,

A

generator

frequenc

y of

400

or

1000

cps

is

satisfactory.

Generator

output

level

should

be s et to the

average

lev

el to

be

applied

in

o

peration.

[ ,

2.

[

Place

the

meter

sele

c

tor

switches

in the +10

or

+4

position

and

adjust

the

LA-2A

"Gain"

controls

for

equal

output.

The

"

Peak

Reduction"

controls

must

be

set

to

full

counterclockwise

or

off.

3.

Mak

e

certain

that

the

screw

driver

adj

ustment

(R3)

on

the

rear

of e

ach

unit

are

[

-,

"full

on

"

(clo

c

kwise).

Place

each

meter

selector

switch

in

the

"

Gain

Reduction"

position.

[.

4.

Advance

the

"Gain

Reduction"

control

on

the

left

channel

amplifier

until

approxi-

mately

5 DB of

reduction

is

indicated

on

the

meters.

Note

which

channel

is

[

indicatin

g

the

most

gain

reduction.

Reduce

the

setting

of R3 on

this

unit

until

both

meters

show

equal

reduction.

l

5.

The

"Gain

Redu

c

tion"

controls

c

an

now

be

placed

at

any

desired

settin

g,

keepin

g

both

knob se

ttings

equal.

Gain

Reduction

will

now

be

e

qual

on

both

channels.

L' l

[

GAIN REDUCTION

FREQUENCY

RESPONSE

CONTROL

FM

broadcasting

and

TV

aural

transmission

systems

use

audio

pre-emphasis

in

the

transmitter.

The

standard

is

17

DB

increase

in

response

at 15 KC,

the

exact

curve

being

the

result

of a

75

microsecond

network.

The

program

frequencies

in

the

vicinit

y of 15

KC

will

l

modulate

the

carrier

17

DB

more

than

frequencies

below

1 KC.

Thus,

if

the

pro

g

ram

material

contains

a

large

amount

of

high

frequencies

,

over-modulation

may

occur

if

the

levels

had

been

1

previously

adjusted

for

program

material

with

less

high

frequency

co

ntent.

An

attempt

to

alleviate

this

problem

has

been

made

by

others

in

the

form

of

level

con-

[

trolled

high

frequ

e

ncy

cutoff

filters

and

high

end

peak

clippers.

Because

the

amount

of c

ontrol

over

the

remainder

of

the

spectrum

is

limited

and

because

of

the

high

distortion

creat

e d,

such

[

devices

have

found

only

limited

application.

[

The

Teletronix

Leveling

Amplifiers

are

capable

of

at

least

30 DB of

gain

reduction

or

limitin

g

with

less

than

0.5%

harm

o

nic

distortion.

For

most

applications,

su

ch

as

AM

broad-

casting

and

recording,

the

am

o

unt

of

gain

reduction

is

a

function

of

input

level

and

is

ind

e

pendent

[\

of

frequency.

By

increasing

the

gain

reduction

at

the

higher

frequencies,

the

over-modulation

caused

1 ( by

the

pre-emphasis

can

be

g

reatly

reduced

or

eliminated.

While

it

is

possible

to inc

rease

the

gain

reduction

sensitivity

on

an

inverse

of

the

pre-emphasis

curve,

this

usually

results

in

an

[ -I

insufficient

lev

e

ling

on

the

low

frequencies

. The

actual

amount

of

the

limiter

pre-emphasis

must

I

be

determined

according

to

the

amount

of high

frequency

content

in

the

program

mat

e

rial

.

L -

[L

LA-2A

(3-66)

Page

6

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