Brenell MINI 8 - Page 13

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7.

RECORD

BIAS

ADJUSTMENT

7.1

Mount

a

reel

of

blank

tape

on

the

recorder

7.2

Connect

an

audio

signal

generator

to

the

input

of

channel

one

7.3

Set

the

generator

to

a

frequency

of

1kHz

at

a

level

of

approximately

OdBm.

7.4

Set

the

line-in

level

control,

with

the

monitor

switch

set

to

INPUT

to

give

an

indicated

record

level,

on

the

VU

meter,

of

-IDdB.

7.5

Connect

an

AC

millivoltmeter

to

the

output

of

channel

one

7.6

Start

the

deck

in

RECORD

mode

and

switch

the

channel

unit

to

RECORD

ON

and

the

monitor

switch

to

REPLAY

7.7

Adjust

the

output

level

control

to

provide

any

convenient

level

on

the

millivoltmeter

(e.g.

-IDdBm)

ADJUSTING

THE

RECORD

BIAS

7.8

Set

the

audio

signal

generator

to

10kHz

at

-IDdBm

7.9

Turn

the

BIAS

adjustment

fully

anti-clockwise

and

then

slowly

turn

it

clockwise.

The

output

(observed

on

the

millivoltmeter)

will

rise

to

a

maximum

and

slowly

start

to

fall.

Note

the

maximum

value

and

continue

increasing

the

bias

until

the

output

level

has

dropped

by

the

correct

amount

for

the

particular

tape

used

-

e.g.

BASF

SPR

50

3.5dB

below

maximum

Scotch

206

3.0dB

below

maximum

7.10

Repeat

7.2

to

7.9

for

remaining

channels.

8.

RECORD/

r

EPLAY

TOP

FREQUENCY

ADJUSTMENT

8.1

Set

the

input

signal

as

in

sections

7.2

to

7.7

of

the

record

bias

adjustment.

8.2

Sweep

the

audio

signal

generator

from

30Hz

to

20kHz

in

steps

of,

say

100Hz

up

to

500

or

1kHz

thereafter.

Check

that

the

response

is

within

4_2dB

of

the

1kHz

reference

set

over

the

full

range.

Variation

greater

than

+2dB

can

only

be

rectified

at

the

top

end

of

the

bandwidth,

above

6kHz.

As

with

the

replay

top

adjustment

the

control

will

vary

the

level

by

up

to

+1.5dB.

Adjustment

is

best

carried

out

at

frequencies

between

15kHz

and

20kHz.

8.3

Repeat

the

above

procedure

for

remaining

channels.

9.

ADJUSTING

THE

RECORD

LEVEL

9.1

Connect

an

audio

signal

generator

to

the

input

of

channel

one

9.2

Set

the

generator

to

a

frequency

of

1kHz

at

an

output

level

of

approximately

OdBm.

9.3

Set

the

line

in

level

control,

with

the

monitor

switch

set

to

INPUT,

to

give

a

level

of

OdB

on

the

VU

meter.

9.4

Start

the

deck

in

the

RECORD

mode

and

switch

the

channel

unit

to

record

on.