Audio Research LS28 Manuel utilisateur

LS28

Thank You.

Thank you for choosing the LS28

as part of your high performance

music system. Since 1970, Audio

Research has been creating

some of the world’s nest

audio equipment. Each piece is

handcrafted in Minnesota, and has

been designed to provide many

years of listening enjoyment.

We understand you are eager

to begin listening; however,

please take a few minutes to

read through this guide for

useful information concerning

the operation of your new

preamplier. Once installed,

please allow an appropriate

break-in period to fully appreciate

the benets this preamplier

will provide to your system.

After reading the user guide, if

you have any further questions

regarding your preamplier,

contact your dealer or Audio

Research customer service - they

will be happy to help you make the

most of your new component.

Happy Listening!

Contents

Warnings

Installation

Before Operating the LS28

In Your System

A Note about Vacuum Tubes

Connections

Back Panel Connections

Input Connectors

Output Connectors

Record Output

A.C. Power Connection

RS-232, IR Input and 12 V trigger

Operation

Front Panel Controls and Display

Start-Up

Shut-Down

Break-in

Front Panel Controls

Remote Only Functions

Settings Menu

System Settings - Menu Tree

Settings Menu

Auto Shutdown

Processor Mode

Tube Hours

Display Brightness

Volume Reset

Input Naming

Maintenance

Vacuum Tubes

Service

Cleaning

Disposal and Recycling Guidelines

Warranty

Specications

Warnings

• To prevent re, or shock hazard, do not

expose your LS28 to rain or moisture.

• Do not place objects containing

liquids on top of this unit.

• This unit contains voltages which can cause

serious injury or death. Do not operate

with covers removed. Refer servicing

to your authorized Audio Research

dealer or other qualied personnel.

• The detachable power cord on your

LS28 is equipped with a heavy gauge,

3-conductor cable and a standard three-

prong grounding plug. For absolute

protection, do not defeat the ground

power plug. This provides power line

grounding of the LS28 chassis to provide

absolute protection from electrical shock.

• The appliance coupler (a.c. power

connector) at the rear of this unit must be

accessible for emergency power disconnect.

• The power button on the front of this

unit, when o, does not disconnect

all power from this unit. This unit is

in sleep mode when not on. (In sleep

mode, the tubes and audio circuit are

powered o; the microprocessor that

operates the LS28 remains on).

• For continued protection against re

hazard, replace the fuse only with the same

type and rating as specied at the fuse

holder (see page 19 for fuse information).

• This unit is RoHS compliant.

• The LS28 has automatic muting to help

protect system components in the event

of low line voltage. When sensing low line

voltage, the preamp displays ‘Low Line’

and automatically goes into ‘Mute’. This

condition will persist until the line voltage

returns to a safe operating level; please

note the unit will remain in ‘Mute’ even

after ‘Low Line’ no longer appears.

• Note that automatic muting is only

designed to protect against power line

interruptions or severe voltage drop. It

will not mute in the event of subsonic

transmissions from a faulty input source,

amplier failure or speaker malfunction.

A note about packaging...

Save all packaging in a dry place away from

re hazard. Your LS28 preamplier is a

precision electronic instrument and should

be properly cartoned any time shipment is

made. You may not have occasion to return

your unit to the factory for service, but if

that should prove necessary, or another

occasion requiring shipment occurs, the

original packaging will protect your LS28

from unnecessary damage or delay.

Before operating the LS28

Your LS28 preamplier is shipped with the

vacuum tubes packed in a separate foam-

lined carton. These must be unpacked and

installed before you attempt to operate

the preamplier. Included are four 6H30

tubes for the analog stage. Proceed

according to the following instructions.

Installation

Remove all screws fastening the top cover.

Carefully remove each vacuum tube

from its protective foam and match its

location ‘V’ number (written on the base

of the tube) to the ‘V’ number printed

next to each socket on the circuit board.

Firmly seat each tube in its matching

socket, taking care to ‘key’ the tube pins

to the socket holes. Retain the tube

carton with other packing materials

for possible future use. Refasten the

top cover on the preamplier.

right

channel

left

channel

Installation

In your system

• To ensure normal component life and

safe operation this unit must be operated

only in an upright position. Adequate

airow and proper cooling can occur

only if there is no restriction above and

behind the unit and on either side.

• The special non-marring elastomer feet

provide adequate spacing and stability

only on a smooth, hard surface, and also

assist to isolate the preamplier from

spurious vibrations. For upright stability

and best performance, never operate

the unit while it is sitting on a soft

surface such as a thick rug or carpet.

• Due to its weight, this preamplier must

be supported on a surface specically

rated for such a load. Check with the

manufacturer of your support system to

be sure it is rated to handle this weight.

• If the unit is to be operated in an

enclosure such as an equipment rack,

make certain that adequate airow

above and to each side of the unit is

provided. Audio Research recommends

a minimum of 6-8 inches (15-20 cm) of

clearance above the LS28 to maintain

proper ambient operating temperature.

• The ‘ambient’ operating temperature

should never exceed 30° C, 86° F.

Improper installation will cause premature

tube failure and will aect your warranty,

as well as the service life of the unit.

• It is normal for a vacuum tube preamplier

to run quite warm, and if used for

prolonged periods, hot to the touch. All

components within are operated at safe,

conservative levels well within tolerances.

A Note about Vacuum Tubes

The vacuum tubes in your LS28 have

been burned in, tested and electrically

matched to provide the best performance

and reliability of your preamplier. That

said, vacuum tubes must be replaced

from time to time. The 6H30 tubes in

the LS28 should have an expected life

of approximately 4,000 hours. This

life expectancy is only approximate.

Connections

Back Panel Connections

Record Outputs

Main Outputs

RS-232 connector

Control

connections

Fuse Holder

A.C. Mains connector

Single-ended InputsBalanced Inputs

Connections

Input Connectors

The LS28 provides eight pairs of input

connectors; four balanced and four single-

ended, labeled BAL 1-4 and SE 1-4.

Output Connectors

Two pairs of BAL/SE main outputs are

provided. The outputs are connected

in parallel. If using both outputs

simultaneously, the combined input

impedance of the amplier(s) being

driven by the LS28 must be greater

than or equal to 20k Ohms.

Record Output

The record output should be connected to

your recorder’s ‘Record’ or ‘Line’ inputs.

These outputs provide a xed-level two-

channel signal (left and right) to your

recorder from whichever input is selected.

The non-variable output level will be the

same as the output of the selected source.

It is possible to dub or copy from one

recorder to another by connecting the

output of the source recorder to an unused

set of stereo inputs. The signal will then

be routed to the Record Out connectors

when that input source is selected.

Warning

Do not connect the record output directly to

an amplier. This will send full output (with

no volume attenuation) to the amplier(s),

and could cause serious serious damage

to the amplier(s) or loudspeakers.

A.C. Power Connection

It is important that the LS28 be connected

via its supplied 15 amp IEC 14-gauge

power cord to a secure, dedicated A.C.

power receptacle. Never connect to

convenience power receptacles on

other equipment. Only use the power

switch on the front of the LS28 for On/

O control of the preamplier, or the

IR input, RS232 or remote control.

RS-232 Input

The RS-232 input allows connection of

a control or automation system.

IR Input

The IR input allows a remote IR sensor

or repeater system to be connected to

the LS28 for control purposes, utilizing

a standard mono 1/8” connector.

12V Trigger Out

The +12V DC trigger out jack provides

the ability to remotely turn on and o

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