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LXP-5

Service

Manual

Circuit

Description

Separate

output

hold

circuits

are

provided

for

reconstructing

the

left

and

right

audio

signals.

This

circuitry

includes

dual

amp

(U37)

and

two

analog

switches

(U3S).

DEGO

and

DEG1

command

signals

from

the

Lexichip

termi¬

nate

respectively

pins

and

U38,

providing

separate

control

the

right

and

left

output

hold

switches.

During

the

digital

analog

conversion

cycle,

either

the

DEGO

DEG1

signal

goes

high

when

the

DAC

ready

output

the

respective

right

left

analog

voltage.

This

permits

capacitors

C80

C85

charge

the

corresponding

voltage

level

for

the

audio

waveform.

When

the

DEGO

DEG1

signal

goes

low,

the

capacitor

will

remain

the

current

signal

level

until

the

conversion

cycle.

The

left

and

right

signals

from

the

output

hold

circuitry

are

applied

separate

pole

passive

kHz

filters

(U35

and

U36).

De-emphasis

circuitry

incor¬

porated

into

the

signal

path

compensate

for

the

pre-emphasis

function

performed

before

the

conversion

process.

dual

amp

(U34)

with

its

associated

circuitry

provides

the

de-emphasis

function.

The

outputs

U34

are

applied

one

end

the

stereo

Mix

control,

R41.

The

other

end

this

potentiometer

connected

the

outputs

the

input

preamplifier.

adjusting

the

wiper

the

Mix

control,

the

ratio

wet

(processed)

dry

(unprocessed)

signal

can

controlled.

The

wipers

R41

are

connected

one

end

the

Output

level

control,

R32.

R32

adjusts

the

signal

level

being

applied

the

output

amplifier,

U33.

This

dual

amp

provides

unity

gain

and

buffers

the

left

and

right

signals

separately.

impedance

600

ohms

developed

resistors

R33,

R34

for

the

right

output,

and

R25,

R26

for

the

left

output.

These

resistors

also

provide

current

limiting

protection.

Bipolar

coupling

capacitors

(C62

and

C63)

and

pulldown

resistors

(R37

and

R38)

are

installed

prevent

offset

voltages

from

appearing

the

outputs

the

LXP-5.

Two

discrete

JFETs,

and

Q8,

provide

muting

function

creating

low

impedance

path

ground

along

the

output

signal

path.

this

case,

R26

and

R34

serve

current

limiting

resistors

preventing

the

outputs

amp

U33

from

shorting

directly

ground.

The

mute

function

under

software

control.

The

Mute/

command

signal

emanates

from

and

applied

the

base

transistor

through

R30.

When

Mute/

low,

on,

which

provides

positive

voltage

the

gates

and

Q8.

The

JFETs

turn

and

enable

mute.

When

Mute/

high,

turns

off

which

allows

negative

voltage

applied

the

JFETs.

and

turn

off

and

disable

mute.

C50

insures

quiet

transition

between

mute

and

unmute

ramping

the

gate

voltages.

Mute

enabled

during

power

down

conditions,

and

some

program

change

sequences.

The

output

jacks

(J5

and

J6)

are

located

the

input

jacks

the

rear

panel.

The

1/4”

unbalanced

phone

jacks

are

configured

such

away

that

the

left

and

right

output

signals

are

summed

together

only

one

plug

connected.

However,

both

output

jacks

should

utilized

for

the

full

stereo

effect

attained.

Static

protection

provided

for

the

output

circuitry

diodes

CRM,

CR15,

CR17

and

CR18.

Ferrite

beads

FB6

and

FB7

and

capacitors

C48

and

C51

prevent

unwanted

high

frequency

interference

from

entering

leaving

the

LXP-5

through

the

output

cables.

Output

Hold

Output

Circuitry

Mix

and

Output

Level

Controls

Output

Buffer

and

Mute

Circuitry

3-7

Brand	Lexicon
Model	LXP-5
Category	Recording Equipment
Language	English

Lexicon LXP-5 Service Manual

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Questions and Answers:

Lexicon LXP-5 Specifications

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