Marantz 5220 Manuel d'utilisateur télécharger pdf (Page 42)

MODEM

AUDIO

OUT

E3¢

E4¢

AUDIO

OUT

GND

AUDIO IN

(A)

9DAA

60011

ç DR

VOLTAGE HERE IS

EQUAL

TO AUDIO

OUT

IOK

VOLTAGE,BUT

OPPOSITE

POLARITY

IOK

600f1

IF ALL IMPEDANCES

ARE

EQUAL,

VOLTAGE PRODUCED BY

AUDIO

OUT

IS ZERO

(B)

transmitter

oscillator

IC7

via

R59.

The

TRANSMIT

switch (Si)

has a section

that simulates a received carrier to

turn

the

oscillator.

Data is

"looped

back" from the transmitter to the re-

ceiver when DUPLEX

switch

is in the

HALF duplex position. This

provides

echo

data originated at the

terminal

without

requiring

that the data travel

to the

other

end

and

return. Some

time

-share services

require half -

duplex

operation, which

one

reason

for including this feature in the Pen -

nywhistle. Another is that it provides

self

-test

capability for the terminal and

modem.

The

transmitter

built around /C7, a

555

timer

chip.

The

output of IC7

is fed

the output

filter (half

of IC8),

which

smooths

out

the waveform to

reduce

harmonics

and provides enough

power

drive a

small

speaker or

the

telephone

line.

The frequency

at which

IC7 oper-

ates

determined

by Q5,

Q6,

and Q7,

which form

a symmetrical current

source

that

keeps the

"on" and "off"

periods of

the

oscillator equal,

regard-

less

the

operating

frequency.

Potentiometers

R77

and

R75

set the

mark frequency, while

R76

and R78

determine

the

space

frequency.

The

-Q4

Schmitt

trigger

circuit

accepts

data from

either

the EIA data

input (positive

negative levels) or

from

optoisolator /C6,

which can be

tied into

a standard

20 -mA teleprinter

current

loop. Mark data has a negative

voltage level

the EIA input or a cur-

rent

15 mA

more at

the

current

loop input.

Space

data

a positive

voltage level at the EIA data

input or no

60011

IMPEDANCE

DRS

Fig...

Direct line

connection

between the modem and the

phone

-company supplied

DAA is

shown at (A).

Use of

the

active hybrid connection

between

the ,parlent

and DAA is shoran

(B).

current at the current -loop

input. With

nothing

connected to either

input,

the

modem "sees" a

space.

TRANSMIT

Switch

used to

select

either the high-

the low -tone

band.

Normally

left in the Low position, for

tape recording

or unit

-to

-unit

trans-

mission, it is

switched

HIGH.

Construction.

The modem lends it-

self equally

well to

either

printed -

circuit or

perforated -board wiring.

Since

the design of

the

system

pro-

vides for maximum flexibility, both

current

-loop and EIA circuits are pro-

vided. However, you can omit either of

these

circuits,

depending on the

needs

your

system.

Capacitors

C2, C7, C8, C10, C12,

and

C22

must

operate

with a relatively

high degree of stability

in the

circuit.

So,

it is important that you use only

Mylar,

polystyrene,

or other

high -

stability capacitors

where these are

called out.

Do not use

wire

-wound poten-

tiometers. They can be difficult

ad-

just with a high enough degree of ac-

curacy.

Transistor types are not criti-

cal, but

it is

good

policy to use only

complementary

pnp

and

npn types for

and Q6.

All transistors in the

sys-

tem must

be good

-quality silicon

switching

types.

Any 741 -type

operational

amplifier

will operate

in the modem's circuit.

The

only

restriction here is that the op

amp

you select

must

be able

to oper-

ate with a short

-circuited

output

indef-

initely with ±18 volts do applied

to the

positive

and

negative

pins

of the

IC.

Not

all op amps

can

meet this re-

quirement;

check this

out on

the IC

specifications

sheet before you

buy.

Most

quad op

amps

will not meet

the

requirement.

Type 3900

op amps will

not work in this

circuit because

the

radical

design

changes

required.

After wiring

the circuit board

as-

sembly, mount

the two

soft

-rubber

acoustic "muffs"

the

cover of the

enclosure. Note that

all parts,

except

the muffs

and

J1, J2,

and

J3,

mount

the

pc board.

The

case

supplied

with

the

kit has

a stepped area through

which the toggles

of the

switches

protrude

and holes through which

the

LED's

are

visible.

Connector

fits

along the edge

the

board and is held

in place

soldering

its

pins to the foil

pads.

The

connector is

then

secured

the

metal

base plate that forms the

bottom

the

enclosure with machine

hardware

through

its

tabs. Mount

J1,

J2,

and

in holes in

the base plate

near

P1 and

wire them

to the

board.

Secure the power cord with

a strain

relief

after soldering its conductors to

the

appropriate

points

in the

circuit.

If you

buy your

parts

locally, you'll

have

to fabricate

your own acoustic

coupler from

a pair of

small

loudspeakers

(see

Parts

List) and

some

commonly available materials.

do this, apply

thin

bead of

silicone adhesive

/sealing

compound

around the

entire

front

edge of one of

the

speakers. Make

sure

the

bead

is no

than 1/8"

(3.2

-mm) thick

and

doesn't bleed

onto

the

cone.

Place

this

speaker, front down,

on a square

of wax paper

atop a

flat, level

surface.

Gently press the

speaker so

that

the

silicone cement

bead spreads out.

Allow the

speaker

to remain like this

for at least 24 hours

to permit the

silicone cement to cure. At the end of

this time,

slowly and

gently peel

away

the

wax paper. Trim the

silicone ce-

ment flush with

the outside perimeter

of the

speaker and check that

the

sili-

cone provides a tight seal to the

microphone

of a

telephone handset.

From

a piece

resilient

polyurethane

foam,

cut a "donut"

fit

over the rear

this loudspeaker.

Solder

lengths

stranded

hookup

wire to the

speaker's

lugs. Route

the

wires through the hole in the

plastic

foam,

and cement the latter to the rear

the

speaker

with

silicone adhesive.

Two 25

/e" (6.7

-cm)

diameter tin cans

can be used as "wells"

in which to

mount

the

speakers

to make good

contact with

the telephone handset.

The

cans should

be mounted 53/4"

(14.6)

apart, center

to center, and

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Marantz 5220 Manuel d'utilisateur Page 42

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