Marantz 5220 Manuel d'utilisateur télécharger pdf (Page 41)

D5 to

D8,D11

D14- 1N4001 rectifier

diode

F 1 -3AG, 1/2- ampere slow -blow fuse

with

pigtails

LED1, LED2-Light- emitting diode (one

red. one amber)

J1,J3- Two- conductor, closed- circuit

miniature phone

jack

J2-Two- conductor, open

-circuit minia-

ture

phone

jack

-No.

DB25S connector plug

Q I ,Q2,Q4,Q5-2N2907 transistor

Q3,Q6,Q7-

2N2222 transistor

Following resistors are 1/4-watt,

5% toler-

ance,

except

as noted:

R I ,R51,R80-6800

ohms

R2, R3, R9,

R17, R18, R19, R45, R47,

R54, R55,

R59,

R60, R61, R63-

10,000

ohms

R4,R5-

150,000 ohms

R6,R25,R26- 330,000 ohms

R7- 20,000 ohms

R8,R14-

18,000

ohms

R11,R70 -2200 ohms

R12,R13,R53 -4700

ohms

R 15,R 16,R22,R57,R64

R69

-1000

ohms

R20,R21

-5100 ohms

R23,R24,R33-

15,000 ohms

R27,R40,R46,R48,R58

-3300 ohms

R28,R41,R42 -1000 ohms

(1/2-watt)

R29,R30,R31 -680 ohms

-watt)

R32 -680 ohms

R34 68,000 ohms

R35,R72,R73-

220,000

ohms

R36 -4300

ohms

R37

-1.5 megohms

R38- 24,000

ohms

R39-

180,000 ohms

R43 -8200 ohms

R44,R56-

100,000 ohms

R49,R50 -82

ohms (1/2-watt)

R52-

22,000 ohms

R62 -620

ohms

R71-

470,000 ohms

R74-47 ohms

R10,R77-

5000 -ohm

trimmer

potentiome-

ter (CTS

No. 360S502B

or similar)

R75-

20,000 -ohm

trimmer

potentiometer

(CTS

No. 360S2038

or similar)

R76,R78-

100,000

-ohm trimmer

poten-

tiometer

(CTS

No. 360S

104B or

similar)

R79

-1000 -ohm

trimmer

potentiometer

(CTS

No.

360S102B

or similar)

Sl,S2,S3

-PC -type

dpdt

toggle switch

-24

-volt center -tapped,

600-mA power

transformer

ZI,Z2 -12

-volt,

I -watt zener

diode

(1N4742 or similar)

Misc. -Printed

circuit

or perforated

board

and

solder clips;

sockets

for

IC's (op-

tional);

21/4"-diameter,

8 -ohm

loudspeakers

(2); suitable

enclosure;

three -conductor

line cord

with

plug;

line

cord

strain

relief;

metal spacers;

hookup

wire; machine

hardware;

solder;

etc.

Note: A complete

kit of all Pennywhistle

modem parts,

including

cabinet,

av-

ailable

for $97.50

from

Enter-

prises, P.O.

Box

1011,

Sunnyvale,

94088.

Add $1.50

if ordering

from Cana-

da. California

residents,

please add

sales

tax.

Allow

15 days

for delivery

after

receipt

of order.

Send SASE

above address

for

free copies (8"

1I ")

of schematic,

etching

and drilling guide,

and

component

layout guide.

tion.

Modems that

transmit on

the

low

and

receive

the

high band

are

termed "originate-

mode"

devices,

since

they are

usually used

by a

local

terminal

to call

into a

remote central

computer.

either

band,

digital

data

is trans-

lated

from 1's and

0's (marks

and

spaces)

to high and

low

frequencies.

Don't confuse

this

with high and

low

band terminology.

The receiving

modem

translates

the tones

back

1's

and

0's. Note that

the

high and

low

frequencies used

in FSK are only

200

apart.

Most originate

modems,

including

the

Pennywhistle, employ

acoustic

coupling

to the

telephone

line

via the

telephone

handset.

(Some

modems

are,

however, designed

to be

directly

wired into

the

phone

line.)

Acoustic

couplers

obviate

the

need for the user

pay

installation and

rental charges

for the devices

the

telephone com-

pany

requires

for direct

-line hookups.

The

main disadvantage of

the acoustic

coupler

is that

can

cause an

increase

distortion

problems

that

can

in-

crease

the

error

rate.

It is

important that you bear

in mind

that

modems do

not process

the data

passed

through

them.

They

merely

a stream

of serial

bits

at one

end and

deliver

the

same

bit

informa-

tion at

the

other

end.

The translation

that takes place

between

merely

makes it possible

have remote

point communication.

Also,

modems

not generally

have UART's

built

into them;

they are

designed

to be

connected

to outboard

UART's,

such

as those

designed

into computers.

Circuit

Operation.

block

diagram

the

modem

shown

in Fig.

which

will use

to explain

system

opera-

tion.

(The schematic

diagram

and

etching

and

drilling

and

component

placement

guides

are

too large

fit

these pages.

They

are

available

FREE by

sending

a stamped,

self

addressed

x 11"

envelope

to the

source

given

in the

Parts

List.)

The

audio

input

to the

modem

is first

applied

three -stage

filter consist-

ing

both

parts of IC1

and

half of IC2.

This

prevents

most

noise and

har-

monics

from passing

through

the sys-

tem.

The filtered

signal

is then

passed

to the IC3 phase

-locked

loop,

which

contains

variable-

frequency

oscil-

lator

and comparator.

The

PLL

always

attempts

to lock

the

frequency of

its

internal oscillator

the

incoming

signal

frequency.

The correction

vol-

tage supplied

the comparator

the

oscillator

provides

measure of

how

far

off

the

incoming signal

frequency

is from a preset

center

frequency.

It is

difficult

for a

PLL

to discrimi-

nate

between

input signal

the

proper

frequency and

one of

its

har-

monics

subharmonics.

Since

the

high -band

frequencies

are almost

twice those

the low band,

this can

present

a problem

for

some

modems,

which

is the

reason

for preceding

the

PLL with

the three

-stage

active

filter in

the

Pennywhistle.

Potentiometer

R10

is used

to set

the

PLL's center

fre-

quency.

The PLL

itself delivers

two

outputs:

one

is a

fixed

reference

volt-

age

from the

internal

voltage

divider,

and

the other

is the actual

output

the stage.

One of

the lesser

problems

as-

sociated

with a

loop

is that

voltages

drift

with changes

in temperature.

The

Pennywhistle

tackles

this problem

with

the

floating

reference

circuit

made up of

half of IC2

and

Q1.

This

circuit

takes advantage

the

fact that

in asynchronous

data

transmission,

the serial

data

signal

returns

to the

"mark"

condition

between

every

character

sent.

The

floating

reference

circuit

detects

the

mark and

resets

its

voltage accordingly.

If the data goes

and

remains

at a "space"

condition,

the circuit

slowly

readjusts

itself

and,

in about

seconds,

will claim

the

new

level as

a "mark."

It readjusts

much

faster in

the opposite

direction

to cor-

rect

such

mistaken

impression

quite

rapidly.

The

floating reference

is fed to IC5,

a Schmitt

trigger,

while

the data

is fed

to the other

input.

The

output

of IC5

EIA

data output

which,

turn,

drives Q2

to deliver a

20 -mA

current

output.

The

IC4

circuit

is used

to detect

the

presence

of an

adequate

signal

level

for

reliable

loop operation.

The

output

of IC4

provides

a positive

EIA -type

"carrier

present"

signal

to turn

ex-

ternal

terminals

and

hold

the

data

output

to the

terminal

mark condi-

tion

when

insufficient

carrier

is pres-

ent.

Indicators

LED1

and LED2

are

driven

by IC5.

A positive

output

from

the

IC turns

on LED2,

while

negative

output

turns on LED1.

When

no car-

rier

is present,

the

output

IC5

normally

negative.

With

a carrier

pres-

ent,

positive.

Hence,

the

LED's

will

alternately

light

when

data

is being

re-

ceived,

providing

a useful

indication

modem

operation.

The carrier

detect

signal

turns on

MARCH

1976

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Marantz 5220 Manuel d'utilisateur Page 41

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