Audio Research LS28SE User manual

H I G H D E F I N I T I O N®
LS28SE

There is only One Reference®

Thank You.
Thank you for choosing the
LS28SE to be a part of your high
performance music listening
system. Since 1970, Audio Research
has been creating some of the
world’s finest 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 phono preamplifier. Once
installed, please allow an appropriate
break-in period to fully appreciate
the benefits this preamplifier
will provide to your system.
After reading the user guide, if
you have any further questions
regarding your phono preamplifier,
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
5
6
7
7
8
8
8
9
9
10
11
11
11
12
13
14
15
15
16
16
17
17
17
18
18
18
18
19
20
Warnings
Installation
Connections
Operation
Settings Menu
Maintenance
Warranty
Specifications
Before Operating the LS28SE
In Your System
A Note about Vacuum Tubes
Back Panel Connections
Input Connectors
Output Connectors
A.C. Power Connection
RS-232, IR Input, and 12v Trigger
Front Panel Controls and Display
Start Up
Shut Down
Break In
Front Panel Controls
Remote Only Functions
System Settings - Menu Tree
Settings Menu
Auto Shutdown
Processor Mode
Tube Hours
Display Brightness
Volume Reset
Input Naming
Vacuum Tubes
Service
Cleaning
Disposal and Recycling Guidelines

To prevent fire, or shock hazard, do not
expose your LS28SE to rain or moisture.
Do not place objects containing water 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 qualified
personnel.
The detachable power cord on your
LS28SE 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 LS28SE 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.
For continued protection against fire
hazard, replace the fuse only with the
same type and rating as specified at the
fuse holder
(see page 19 for fuse information).
This unit is RoHS compliant.
The LS28SE 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, amplifier failure or
speaker malfunction.
A note about packaging...
Save all packaging in a dry place away
from fire hazard. Your LS28SE preamplifier
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 other occasion
requiring shipment occurs, the original
packaging will protect your LS28SE from
unnecessary damage or delay.
Warnings
5

6
Installation
Before operating the LS28SE
Your LS28SE preamplifier 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 preamplifier.
Included are four 6H30
tubes for the analog stage. Proceed
according to the following instructions.
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. 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 top cover on the preamplifier.
V2
V4
V1
V3
right
channel
left
channel
Vacuum Tube Placement

7
In your system
To ensure normal component life and safe
operation this unit must be operated only
in an upright position. Adequate airflow
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 preamplifier 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 preamplifier must
be supported on a surface specifically
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 airflow 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 LS28SE to maintain proper
ambient operating temperature.
The ‘ambient’ operating temperature
should never exceed 120° F or 49° C.
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 preamplifier
to run quite warm, and if used for
prolonged periods, hot to the touch.
All components within are, however,
operated at safe, conservative levels and
will not be improperly aected thereby,
providing the requirements outlined
above are adhered to.
A Note about Vacuum Tubes
The vacuum tubes in your LS28SE have
been burned in, tested and electrically
matched to provide the best performance
and reliability of your preamplifier. That
said, vacuum tubes must be replaced
from time to time. The 6H30 tubes in the
LS28SE should have an expected life
of approximately 4,000 hours, while the
6550WE tube in the power supply should
have a life expectancy of approximately
2,000 hours. These life expectancies are
only approximate.

8
Connections
Record Outputs
Main Outputs
RS-232 connector
Control
connections
Fuse Holder
A.C. Mains connector
Single-ended InputsBalanced Inputs
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 amplifier(s) being
driven by the LS28SE must be greater
than or equal to 20k Ohms.
Input Connectors
The LS28SE provides eight pairs of input
connectors; four balanced and four
singleended, labeled BAL 1-4 and SE 1-4.
Back Panel Connections

9
A.C. Power Connection
It is important that the LS28SE 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 LS28SE for On/O control of the
preamplifier, 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
LS28SE 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 the
preamplifier and other linked components
such as power amplifiers having similar
capabilities.
Important
Use the best available speaker wires
and interconnects. Audio Research
cannot emphasize this enough. As better
components and systems are developed,
it becomes increasingly important to
avoid the limitations of inferior system
interconnections.
It is important sonically that your entire
system be connected so that the audio
signal arriving at the speakers has correct,
or ‘absolute’ polarity (i.e., non-inverted).

10
Operation
Input Select Vacuum Fluorescent
Display Volume
Menu
Enter
(used with Menu)
Mono/Stereo
Invert Phase
Mute
Power On/O
Front Panel Controls

11
Start-Up
• Secure all rear-panel connections
between LS28SE, power amplifier(s) and
input sources.
• Plug three-prong power cord from
rear of chassis into grounded A.C. wall
outlet. The Power switch defaults to ’o’
when the unit is plugged into a power
receptacle.
• Press power switch (either on the
remote or front panel). The preamplifier
will begin the warm-up sequence,
which lasts approximately 45 seconds,
during which ‘MUTE’ will flash on the
display. After the warm-up sequence
is complete, the unit will be muted.
Depress the front panel ‘MUTE’ button
or the Mute button on the remote to
initiate normal operation. You may
depress the Mute button prior to the
unit completing the warm-up cycle;
‘MUTE OFF’ will flash on the display until
the warm-up cycle is complete. Select
input source and adjust the volume as
necessary.
Shut-Down
• Activate ‘MUTE’ function.
• Turn o power amplifier(s).
• Press Power switch to ‘o’.
• Turn o input sources.
Note
The LS28SE should be turned on before
the amplifier in your system. If the LS28SE
is turned on after the amplifier, it will am-
plify any extraneous turn-on noises the
preamplifier or other source components
might generate, which could potentially
damage the loudspeakers. Good oper-
ating practice dictates that the amplifier
should be turned on last, and turned o
first in an audio system.
Break-in
All quality stereo equipment benefits from
a break-in period; during this time, the
various components, wiring and solder
connections change as electrical signals
pass through them. While your LS28SE
will sound fantastic out of the box, it will
only improve with continued use.

12
Front Panel Controls
The LS28SE has two microprocessor-driv-
en rotary controls and six buttons (Power,
Menu, Enter, Mono, Invert, and Mute).
Left Rotary control (Input Select)
Select input by rotating the control to the
left or right. The screen displays the cur-
rent input on the left side of the display.
Right Rotary control (Volume)
Adjust volume (output level) up or down
for both L and R channels. Volume control
is also selectable via VOL UP and VOL
DN buttons on the remote control. Vol-
ume adjustment is indicated in the display
window by numeric digits on 0–103 scale.
Do not turn volume up beyond normal
listening levels when ‘mute’ is engaged to
avoid unexpected or possibly damaging
sound levels. Reduce volume level when-
ever changing input sources, even when
muted.
The right rotary control also functions to
change settings when in menu mode.
Power On/O
Supplies power from A.C. wall outlet to
preamp; indicated by active display win-
dow. The LS28SE requires approximately
45 seconds to warm up; this time is re-
quired to stabilize the vacuum tubes. See
‘Start-Up Procedure’ on page 11 for details.
Menu
The menu button enters the setup menu
of the LS28SE to allow customizing cer-
tain settings of the preamplifier. See page
15 for further details about using the setup
menu.
Enter
The enter button is used in conjunction
with the Menu button to make changes to
the systems settings of the LS28SE.
Mono
Toggle between Stereo and Mono output.
Invert
The invert button allows the absolute
phase of the recording to be switched be-
tween ‘normal’ (in-phase) and ‘invert’ (180°
inversion).
Mute
When activated, Mute electrically disables
all outputs of the preamplifier; indicated
by ‘MUTE’ in display window, beneath the
volume number. This control should be
activated before switching inputs, chang-
ing connections or shutting down your
audio system to help protect your ampli-
fier and speakers from unexpected sig-
nal pulses. When deactivated, ‘MUTE’ is
cleared from the display window allowing
normal operation.
Operation

13
Remote Only Functions
In addition to the controls found on the
front panel, the remote control oers
access to the following additional
features of the LS28SE.
Hours
Pressing the ‘HOURS’ button will display
the total accumulated hours of operation
for the LS28SE. This is useful to determine
the approximate number of hours the
vacuum tubes have been in use. After
five seconds, the display will revert to the
normal operation screen. After replacing
vacuum tubes, the hours counter should
be reset (see instructions under ‘Settings
Menu’ on page 16).
Note
The installed 6H30 vacuum tubes have an
average life span of approximately 4,000
hours. After this time, we recommend
replacing them to maintain the best
performance of your preamplifier.
Input Select Buttons
The input buttons labeled BAL 1-4 and
SE 1-4 allow direct selection of each of the
eight inputs available on the LS28SE.
Display Brightness Adjustment
The front panel display has six brightness
settings, as well as the ability to dim
the display completely. To change the
brightness, use the ‘DSP UP’ or ‘DSP DN’
buttons on the remote. Note that when
the display is completely dimmed, a
small square appears in the middle of the
display to indicate the unit is powered on.
Balance
The Balance control adjusts the output
from center position to the left or right
channels, which in turn will shift the center
point of the sonic image. This is useful in
the event the main listening position is not
centered between the speakers, or can
help with certain room anomalies.
To adjust the balance, press the ‘BAL
L’ or ‘BAL R’ button on the remote. The
balance scale will appear in the middle of
the display, and the indicator will move in
the selected direction:
After five seconds of inactivity, the
balance scale will disappear from the
screen. If the balance has been shifted to
the right or left, ‘R+’ or ‘L+’ will appear at
the bottom left corner.

14
Settings Menu
Menu Tree
Tube Hours
Processor Mode
Auto Shutdown
Volume Reset
Display Brightness
Input Naming

15
Settings Menu
The LS28SE has been designed with a
simple, intuitive menu to allow adjustment
of the various features of the preamplifier.
To adjust the settings, press the ‘MENU’
button on the remote or front panel.
If no further action is taken with the
preamplifier or remote for five seconds,
the LS28SE reverts back to its normal
operation screen. Continuing to press the
‘Menu’ button will toggle you through the
dierent setting options:
While a menu item is displayed, press
‘ENTER’, followed by rotating the volume
knob on the front panel, or using the
volume up/down buttons on the remote
to adjust the settings of that particular
selecton. After making the appropriate
change, pressing the ‘ENTER’ button will
confirm the new setting, and the display
will show ‘OKAY’ for five seconds before
reverting back to the normal operation
screen.
Note
For the following menu settings, please
refer to the menu tree on page 14 for
examples of the front panel display.
Both the ‘MENU’ and ‘ENTER’ buttons
(found on the front panel and remote), as
well as the volume knob (or the up/down
volume buttons on the remote) are used
to make changes to the menu settings.
Note that the ‘MENU’ button can also be
used to back out of a menu selection,
returning to the main settings options.
Auto Shutdown
The LS28SE is equipped with an auto
shut o feature, designed to turn the
preamplifier o after a period of time
during which it is not used. The auto shut
o feature senses any interaction with
the preamplifier, such as button presses,
changing the volume, remote usage, etc.
To change/disengage the auto shutdown
feature, press the ‘MENU’ button until the
‘AUTO SHUTDOWN’ screen is displayed.
Using the volume knob on the front
panel, or the volume up/ down buttons
on the remote, you have the option for
‘o’ (no auto shutdown) or 1-8 hours.
Once you have made a selection, press
‘ENTER’ to confirm. The display will show
‘OKAY’ before reverting back to the
normal operation screen.
Note
The auto shutdown feature is not in the
signal path of the preamplifier and has
no deleterious sonic eect on music
playback.

16
Settings Menu
Processor Mode
The LS28SE has the ability to assign unity
gain (also called ‘pass through’) to one
of the eight inputs available in the event
it will be integrated into a system with
a secondary control device, such as a
surround sound processor. When an input
is assigned as the processor input, the
volume control on the LS28SE is disabled
so that the processor’s volume is the only
control used.
To set up a processor input, connect
the left and right output channels from
your surround sound processor to the
left and right inputs of your choice on
the LS28SE. Press the ‘MENU’ button
until ‘PROCESSOR MODE’ is displayed,
and press ‘ENTER’. With ‘PROCESSOR’
displayed, turn the volume knob, or
use the up/down volume buttons on
the remote, to select the desired input
for processor mode. Press the ‘ENTER’
button to select the input, and ‘ENTER’
once again to confirm the selection. The
LS28SE will display ‘OKAY’ and show the
selected input on the bottom line.
When using the input selected for
processor mode, note that in place of the
volume number on the operation screen,
a ‘pass through’ symbol will be shown.
Warning
When processor mode is assigned to an
input, do NOT connect a source (such as
a CD player or phono stage) to that input.
This will send full output from the source
to your amplifier(s), and could cause
serious damage to your loudspeakers or
amplifier(s) - not to mention your ears!
Tube Hours
The tube hours display shows the
accumulated time the LS28SE has been
powered on. This is useful for determining
the number of usage hours of the installed
vacuum tubes. See A Note about Vacuum
Tubes on page 7 for specific information
regarding the tubes in the LS28SE. To
reset the tube hours counter, press the
‘MENU’ button until ‘TUBE HOURS’ is
shown. Press the ‘ENTER’ button to
display ‘ENTER TO RESET’. Press ‘ENTER’
again and the display will read ‘ENTER TO
CONFIRM’. A final press of the ‘ENTER’
button will reset the tube hour counter to
0 and the display will show ‘OKAY’.
Note
Once the hour counter has been reset,
the total accumulated hours cannot be
recalled.

17
Display Brightness
The display brightness feature oers
six dierent settings (including o) for
the vacuum fluorescent display on the
front panel. When the lowest setting
(o) is selected, the display will remain
on for five seconds after any button is
pushed, after which it will revert to a
black screen with a small, illuminated
square in the center to indicate the unit
is powered on. To change the display
brightness, press the ‘MENU’ button
until ‘DISPLAY BRIGHTNESS’ appears.
Press the enter button. Using the volume
knob on the front panel, or the up/down
volume buttons on the remote, change
the display brightness to your preference.
Once you have selected the appropriate
brightness, there is no need to press
‘ENTER’ or any further buttons.
Note
The remote control oers direct control
of the display brightness via two buttons
labeled ‘DISP UP’ and ‘DISP DN’. You
can choose to use these buttons as an
alternate to the settings menu.
Volume Reset
The volume reset feature tells the LS28SE
to either remember the volume settings
for each individual input, or to reset them
to zero after a power o cycle. When
volume reset is set to ‘OFF’, the LS28SE
will also remember settings after a power
cycle. To change the status of the volume
reset, press the ‘MENU’ button until the
display reads ‘VOLUME RESET’. Press
‘ENTER’, and use the volume knob on
the front panel, or the up/down volume
buttons on the remote, to select ‘ON’
or ‘OFF’. Press ‘ENTER’ to choose the
appropriate setting, and ‘ENTER’ once
again to confirm. The display will read
‘OKAY’ and show the current setting for
volume reset.
Input Naming
The LS28SE is pre-loaded with a selection
of names which can be assigned to the
eight inputs of the preamplifier, allowing
for easier identification of the various
inputs. When selected, the chosen input
name will display above the default name
(BAL 1, SE 3, etc.) on the normal operation
screen. To select an input name for any of
the inputs, press the ‘MENU’ button until
‘INPUT NAMING’ is displayed. Press the
‘ENTER’ button, and use the volume knob
on the front panel, or the up/down volume
buttons on the remote, to select the
desired input for naming. Press ‘ENTER’ to
engage the naming utility, and using the
volume knob or up/down volume buttons,
select the appropriate name for the input.
Press ‘ENTER’ a final time to confirm the
input name. The display will show ‘OKAY’.

18
Maintenance
Vacuum Tubes
It is recommended that you replace the
6H30 vacuum tubes of your LS28SE in
sets. All of the tubes in your preamplifier
have been matched to have similar
operating characteristics, to provide the
best sound quality and reliability.
Servicing
Because of its careful design and exacting
standards of manufacture, your LS28SE
preamplifier should normally require only
minimal maintenance to maintain its high
level of performance.
Should you need service, please contact
your authorized Audio Research dealer
or other qualified technician. Additional
questions regarding the operation,
maintenance or servicing of your
preamplifier, please contact the Customer
Support Department of Audio Research
Corporation at service@audioresearch.
com or call 763-577-9700. You may
also initiate a service request by visiting
the Audio Research website (www.
audioresearch.com) and selecting ‘Service
Repair’ at the top right of the home page.
Caution
Your LS28SE preamplifier contains
sucient levels of voltage and current
to be lethal. Do not tamper with a
component or part inside the unit. Even
with the power turned o, a charge
remains in the energy storage capacitors
for some time.
Cleaning
To maintain the new appearance of this
preamplifier, occasionally wipe the front
panel and top cover with a soft, damp
(not wet) cloth to remove dust. A mild,
non-alkaline soap solution may be used
to remove fingerprints or similar smudges.
Cleaners containing abrasives should
not be used as they will damage the
anodized finish of the front panel. A small,
soft paintbrush is eective in removing
dust from bevels, and other features of
the front panel.
Disposal and Recycling Guidelines
To dispose of this electronic product, do
not place in landfill. In accordance with
the European Union Waste Electrical and
Electronic Equipment (WEEE) directive
eective August 2005, this product
may contain regulated materials which
upon disposal require special reuse and
recycling processing.
Please contact your dealer or importing
distributor for instructions on proper
disposal of this product in your country.
Or, contact Audio Research Corporation
(763.577.9700) for the name of your
importing distributor and how to contact
them. Packing and shipping materials may
be disposed of in a normal manner.

19
Warranty
Audio Research Corporation products
are covered by a 3-Year Limited Warranty
or a 90-Day Limited Warranty (vacuum
tubes). This Limited Warranty initiates
from the date of purchase, and is limited
to the original purchaser, or in the case
of demonstration equipment, limited
to the balance of warranty remaining
after original shipment to the retailer or
importer.
In the United States, the specific terms,
conditions and remedies for fulfillment
of this Limited Warranty are listed on the
warranty card accompanying the product
in its shipping carton. The warranty terms
are also available on the internet at www.
audioresearch.com/en-us/company/
warranty-statement. Outside the United
States, the authorized importing retailer or
distributor has accepted the responsibility
for warranty of Audio Research products
sold by them.
The specific terms and remedies for
fulfillment of the Limited Warranty may
vary from country to country. Warranty
service should normally be obtained from
the importing retailer or distributor from
whom the product was purchased.
In the unlikely event that technical service
beyond the ability of the importer is
required, Audio Research will fulfill the
terms and conditions of the Limited
Warranty. Such product must be returned
at the purchaser’s expense to the
Audio Research factory, along with a
photocopy of the dated purchase receipt
for the product, a written description of
the problem(s) encountered, and any
information necessary for return shipment.
The cost of return shipment is the
responsibility of the purchaser.
Audio Research Corporation does not
warrant compatibility of Audio Research
products with future operating systems
and/or hardware of other manufacturers.

20
Specifications
Frequency Response: +0-3dB, 0.4Hz to 200kHz at rated output (Balanced, 200k ohms load).
THD + noise: Less than .007% at 2V RMS BAL output.
Dynamic Range: >122 dB (AES17)
Gain: Main output: 18.7dB Balanced output, 9.3dB SE output. Record out: 0dB (Processor input: 0dB
BAL output).
Input Impedance: 100K ohms Balanced, 50K ohms SE. Inputs: 4 balanced, 4 single-ended. Assign-
able processor passthrough.
Output Impedance: 600 ohms Balanced, 300 ohms SE Main (2). 20K ohms minimum load and
2000pF maximum capacitance. Outputs (3): 2 main, 1 record out (XLR and RCA connectors).
Output Polarity: Non-inverting.
Maximum Input: 16V RMS BAL, 8V RMS SE.
Rated Outputs: 2V RMS (1V RMS SE) into 200K ohm balanced load (maximum balanced output ca-
pability is 17V RMS at less than 0.5% THD at 1kHz).
Crosstalk: -105dB or better at 1kHz.
Controls: Rotary encoders: Volume (103 steps), Select Input. Push Buttons: Power, Menu, Enter,
Mono, Invert, Mute.
Power Supplies: Electronically regulated low and high voltage supplies. Automatic 45 sec. warm-up/
brown-out mute. Line regulation better than .01%.
Noise: Less than -100 dBv at maximum volume (103).
Tube Complement: (4)-6H30P dual triodes.
Power Requirements: 100-125VAC 60Hz (200-250VAC 50/60Hz) 130 watts. Standby: 2 watts.
Dimensions:
Width 19” (48 cm)
Height 6.5” (13.7 cm)
Depth 13.7” (34.8 cm)
Handles extend 1.6” (4 cm) forward of the front panel.
Weight: 15.9 lbs. (7.2 kg) Net; 24 lbs. (10.9 kg) Shipping.