Metra Electronics DAT Combo Instrukcja Użytkownika Pobierz pdf (Strona 52)

Layout of

the

components

the

perforated

circuit board

not

at all

critical

-but

watch ground connections

if you

take power

from amplifier.

pedance

output. Now, a preamplifier can

be designed to

straighten

the frequency -out-

put curve from

ceramic

pickup's

signal

prior to

being fed to a flat amplifier.

How it works. The schematic diagram

for

the ceramic-

pickup preamplifier

appears

be a

basic common-

emitter type

using an

npn

small

-signal transistor

-except for the

collector

-base network (resistor

R2 and ca-

pacitors

and C2).

Resistors R1 and

provide

fixed base bias. The

amplifier's input

impedance is

made smaller than

the

pickup's

impedance and Ql's

current gain is

made

vary inversely to the

velocity response

the R.I.A.A. recording characteristics.

The negative

feedback characteristics

the

collector

-base network does

the equaliz-

ing-C1 is

the effective circuit element

for

frequencies

between

30 and

500 Hz (cps);

R2 between

500

and 2000 Hz;

and

above

2000 Hz.

The large amount

of negative feedback

reduces

distortion and permits

the use of

low

operating current

in the collector cir-

cuit.

This is essential

for a

low -noise out-

put signal.

The fact

that no equalizing

net-

work

connected

series

with

the base also

helps

reduce noise.

The low input

impedance of the pre-

amplifier permits

hookup to all available

ceramic

pickups

the

market

today. Re-

member,

unlike a

vacuum -tube amplifier cir-

cuit,

this transistor preamplifier depends

A Safe Connection

When

making a

wire connection for your

projects,

cut two

one

-inch

pieces from a

half -

inch

rubber

tube. Split

these and

put one

around

EEE(WRAP

TUBE

AROUND

CONNECTION

SPLIT

TUBE

OUT

PUT

-X STAGE

FROM

CERAMIC

PICKUP

POWER LEADS

the

apparent

input impedance

proper audio equalization.

Putting

It Together.

Parts layout, shown

in photo,

closely matches

the schematic

dia-

gram.

All resistor, capacitor

and

transistor

leads terminate

at flea clips. If you prefer

not

to use

flea clips, make all

connections

passing

leads through perf

-board holes

and

soldering underneath perf-

board. Twisted

wire

leads can

be used to

connect to ceramic

pickup and amplifier

input

terminals.

Shielded cables

should be substituted

hum

level is high.

Also,

may be

necessary

connect a

10 -mf.

6 -volt electrolytic

capacitor

across

the

power

supply

leads (watch

po-

larity )

if preamp

taps

power

from phono's

power supply.

Installation

is not critical.

Keep leads

short

and locate perf

-board away from

heat.

classical recording

(with

violins)

can

serve as a

test record.

Play the

recording

before

and

after modification

-use your

amp's

AUX

input.

mismatch

for

1w,11,,,,,,,,,,,,,,,1,,,,,,,,111,,,,,,1,,,,,1,,,,,,,,,,,,,1.,1,, .,.,,,,,,,,, , 1,1111,,,1,111,1,,,,,,,.,,..,m.NN,1,11.1,.,,1MITNe.

each

wire at

the

connection

point.

Then

wrap

some

plastic electrical

tape over

all,

and it

makes

a neat, safe job.

This idea

is not suitable

for pow-

er or

lamp cords.

Polystyrene Tubing

Insulates

Chokes

To protect

the

metal

ends of

RF choke

from

accidental

con-

tacts

in a crowd-

radio chassis

saw a lengthwise

slot on one

side

length of polystyrene tubing,

and slip

it over

the RF choke.

For straight -wound

chokes,

1/2

in.

O.D.

tubing

about

right, but

for pie -wound

chokes use

larger tubing. Coil

dope or speaker-

cement applied to

wire leads

where they

enter tubing

keeps tubing from

slipping

off

choke. Or,

heat the ends of the

tubing and

pinch them

shut. Use

color

code to

indicate

value.

PoIrSTVWLNE

TJ91N4

SAW A SLOT

LENGTHWISE

CHOKE

RAnio-TV EXPERIMENTER

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