Metra Electronics DAT Combo Manual de usuario descargar pdf (Pagina 51)

Flat

amplifiers

are

great

but

you

must have

a flat

in-

put signal.

Here's

how

to

match

that pickup.

One of the

problems

with

home -made

phono

amplifiers is that they are invariably

flat -good

circuit design can

make

even the

cheapest transistor

audio amplifier flat

to

within

±3

db

throughout the

usable portion

of its frequency

curve.

You would

think

this

feature would

be desirable, but its not

necessarily

so

when

you

take

a

hard look

at the signal supplied by the

phono

pickup.

The unequalized output voltage

curve

for

a

typical

ceramic cartridge extends from

50

to 10,000

cps. peaks

at about 300 cps,

and

falls about 6

db per octave at 50 cps and

15

db

per

octave

at

10,000

cps. Also,

the

impedance

of

a ceramic pickup

decreases

as the frequency

is increased.

On

top of

this

non

-linear characteristic the

signal

is

Ceramic

Pickup

EQUALIZING

PREAMP

by

Jay

Copeland

further

complicated

by the record

manu-

facturers.

Recordings

are

deliberately

made

with

reduced amplitudes

at low frequencies,

a

relatively

flat middle

frequency range, and

increased amplitudes

at high frequencies due

to

manufacturing

difficulties in the prepara-

tion of

plastic platters.

Therefore, a care-

fully

designed

preamplifier circuit is needed

to boost the

low- frequency

signals,

reduce

the highs and match the ceramic pickup's

impedance

before passing

an equalized audio

signal to the

frequency -flat amplifier.

Fortunately, the

recording industry

had

decided on a recording

equalization

standard

(R.I.A.A.)

and the

characteristics

of cer-

amic pickups

are almost universally identical

with respect

to

frequency

response

and im-

PARTS

LIST

FOR

EQUALIZING

C1-

.01 -mf. disc

capacitor

(voltage not critical)

C2- .0033 -mf. disc capacitor (voltage

not

critical)

C3- 10 -mf., 6 -WVDC

electrolytic

capacitor

Q1-

2N1091

npn

transistor,

RCA (Alternates

are

2N440, 440A,

635,

636, 636A,

1005,

1006)

R1- 220,000

-ohm,

1/2 -watt resistor

5

R2-

33,000 -ohm, 1/2 -watt resistor 5%

R3- 10.000

-ohm, 1/2

-watt

resistor

5%

R4 -4,700

-ohm,

l/2

-watt

resistor 10

1 -Pert -board

cut to 22/4" x 21/2"

approx.

Misc.

-Flea clips, bare

and

insulated wire,

solder, etc.

Estimated

cost: $3.50

Construction time: 11/2

hours.

FEBRUARY

-MARCH, 1967

Cl

.01MF

PREAMP

0033

MF

C2

R2

33K

RI

220K

bl

BASE

2N1091

e

2N1091

R4

47K

CERAMIC

PICKUP

} 45VDC

Equalized output

is

taken across C3 and

the

negative

lead of

the

DC power input.

t

1 2 ... 46 47 48 49 50 51 52 53 54 55 56 ... 113 114

Comentarios a estos manuales

Sin comentarios