Audio Research LS27 User manual

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Owner’s Manual
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Model
LS27
Stereo Preamplifier
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audio research
H I G H D E F I N I T I O N®

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Contents
Model LS27 Stereo Amplifier
Illustrations 4
Remote functions 5
Preface 6
Warnings 6
Packaging 6
Installation of Vacuum Tubes 6 – 7
Description of Controls 7 – 9
Connections 9
Installation Instructions 9
Operation Procedure 9
Tape Recording Procedure 9 – 10
Troubleshooting 10
Servicing 10
Cleaning 10
Disposal and Recycling Guidelines 11
Limited Warranty 11
Specifications 12

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DEFINITION SERIES
0
DISPLAY
0
VOLUME INPUT
POWER MONO BAL / SE PROC MONITOR MUTE
MODEL LS27 HIGH DEFINITION .
TUNER PHONO CO VIDEO AUX 1 AUX 2 MONITOR PROCESSOR RECORD OUT MAIN OUT 1 MAIN OUT 2
RIGHT@ @) @) @) @) @) @) @) @) @) @)
[Q][Q)[Q][Q)[Q][Q][Q][Q)[Q][Q][Q]
MODEL LS27
STE REO PREAMPLIFIER
audio research
PLYMOUTH, MINNESOTA
MADE
IN U.S.A.
I A. • 1ix,:; •AI
WAANING

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Note: All LS27 functions are
available on the LS27R hand
held remote controller. All
functions are indicated in the
display window as they are
selected. See ‘Description of
Controls’ in this manual for
more information.
Adjusts balance left . Bar graph
indicates balance in display window .
Mutes output of the LS27 .
Adjusts
volume down . Visible as 1-------1- •
numeric readout in display window.
Select as appropriate for Balanced (BAL) 1------.-1--
or Single-Ended (SE) input for each source.
Inverts
absolute phase of all outputs.
Selects
low, medium or high output gain
settings for each input source.
Turns
power on/off.
Select one of six available audio inputs.
Routes the
monitor input signal to
the
main outputs.
---1---a------1 Adjusts balance right . Bar graph
indicates balance in display window.
• Adjusts
volume up . Visible as numeric
readout in display window.
r---------1 Sums Land R input for mono output
from any source selected.
Displays number of operating hours
vacuum tubes have been in service.
Input for external A-V processor.
Provides unity
gain, disabling volume
controls. NA appears in display window.

Preface
Please take time to carefully read and
understand the following instructions
before you install or attempt to operate
your Audio Research LS27 preamplifier.
Becoming familiar with the product and
its correct operating procedures will help
assure you of maximum musical
enjoyment and reliable operation. The
effort you invest now will be well
rewarded in the years ahead.
Warnings
1.To prevent fire or shock hazard, do not
expose this product to rain or moisture.
2.This unit operates on voltages which
can cause serious injury or death. Do
not operate with covers removed.
Any necessary servicing should be
carried out by your authorized Audio
Research dealer or other qualified
electronics technician.
3.The power cord supplied with this unit
is safety tested and is equipped with a
proper grounding plug. If used
normally, it will provide a safe earth
ground connection of the chassis.
Defeat of the grounding plug or use of
a power cord without a grounding
plug, or any unauthorized modification
of the active circuitry or controls of this
unit, automatically voids warranty
coverage, and could cause injury or
death.
4.For safe operation and protection
against fire hazard, replace fuses only
with those of the same type and rating
as those supplied with this unit.
Packaging
Save all packaging accompanying this
product. You have purchased a
precision electronic instrument, and it
should be properly cartoned any time
shipment becomes necessary. It is very
possible that this unit could be
damaged during shipment if
repackaged in cartoning other than
that designed for it. The original
packaging materials help protect your
investment from unnecessary damage,
delay and added expense whenever
shipment of this unit is required.
Installation of Vacuum Tubes
Note: This unit has been shipped with the
vacuum tubes installed in a protective
foam block under the top cover. Using a
phillips-head screwdriver to loosen the
fastening screws, remove the top cover
and set aside. Remove the tubes
carefully from the protective foam block
and store the foam block with the
carton.
Warning! Do not attempt to install or
replace vacuum tubes unless this unit is
first turned off and disconnected from
A.C. power outlet. Unit should be
connected to A.C. outlet and turned on
only after all vacuum tubes have been
installed and appropriate panels
replaced and fastened. See owner's
manual for installation details.
Before replacing vacuum tubes, turn off
unit, disconnect from A.C. outlet and
allow existing tubes to cool before
attempting to remove and replace with
new tubes. Hot tubes may cause burns
or other injury if not first allowed to cool.
When replacing tubes, do not touch
other components, as the circuit may
retain sufficient levels of voltage and
current to cause injury or death.
Contact Audio Research Customer
Service (763.577.9700) if you have any
questions about installing or replacing
tubes in this unit.
Do not attempt to operate
this equipment before
installing the numbered
vacuum tubes in their
respective sockets.

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Diagram indicates relative positions of two
6H30 tubes located on circuit board as
viewed from the front and looking down from
above the preamplifier.
Description of Controls
Front Panel Rotary Controls
The LS27 has two microprocessor-driven
rotary controls.
The rotary control on the left adjusts
Volume (output level) up or down for
both R and L channels. Volume control
is also selectable via Vol DN and Vol UP
buttons on the remote control. Volume
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 whenever changing input
sources, even when muted.
The rotary control on the right selects
any of six input sources connected to
the preamp: CD, Video, Aux 1, Aux 2,
tuner and phono. Each of these sources
may also be selected via direct access
buttons on the remote control. The
selected source is indicated in the
display window.
Front Panel and LS27R Remote Control
Buttons
Power On/Off: Supplies power from A.C.
wall outlet to preamp; indicated by
active display window. Function also on
remote control.
For approximately 50 seconds after start
up, ‘Mute’ appears in the display
window and flashes until the automatic
muting cycle is completed. This also
occurs in the event of power
interruption. Upon completing the cycle,
“Mute” will cease flashing. The preamp
will remain muted until normal operation
is selected by pressing the “Mute”
button.
Mute: When activated, electrically
mutes all output of the preamplifier;
indicated by “Mute” in display window.
This control should be activated before
switching inputs, changing connections
or shutting down your audio system to
help protect your amplifier and speakers
from unexpected signal pulses. When
deactivated, “Mute” disappears from
the display window allowing normal
operation. Function also on remote
control.
The LS27 also has automatic muting to
help protect system components during
A.C. power interruptions or low line
voltage. When sensing these conditions,
the preamp automatically goes into
‘Mute’ and disables all outputs. The 50-
second warm-up timer will restart and
‘Mute’ will flash in the display window
when normal power conditions have
been restored.
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.
Processor (PROC): May be selected by
button on front panel or on remote
control. Selects external A-V (home
theater) processor as input source and
controller of volume level for R and L
channels. LS27 provides Unity Gain
when this input is selected.
When engaged, ‘PROC’ and ‘UNITY
GAIN’ will appear in the display, and the
volume control is not adjustable
because gain is fixed. The preamp will
also mute the input after ‘PROC’ is
engaged.
TUBE LOCATIONS
TOP VIEW
REAR
FRONT
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Warning
Before unmuting the
‘PROC’ input, be sure to
turn the volume down on
the home theater processor. Never
connect a source with a fixed level
output (DVD player, tuner, CD, etc.) to
the PROC input or the amplifier(s) and
speaker system could be damaged
when the LS27 is unmuted.
Volume Up/Down: Increases/decreases
overall volume level of both channels
equally for whichever input has been
selected. Caution: do not turn up
volume beyond normal listening levels
when “Mute” is engaged to avoid
unexpected or possibly damaging
sound levels. It is a good idea to reduce
volume whenever changing program
sources, even when muted. Function
available on remote control buttons and
front panel rotary control on left. .
Bal/SE: Select as appropriate for each
input. For source components having
balanced (XLR) connections to the LS27,
select BAL. For single-ended (RCA)
sources, select SE. Once selected for an
input source, the setting is memorized.
Mono: Sums L and R input for mono
output from any source selected.
Remembers setting for each input.
Monitor: Selecting Monitor (MONITOR
appears on display) routes Monitor input
signal to the Main outputs.
The Input Selector indicates what is
routed to the Record out. To exit the
monitor position and return to program
source controlled by input selector (CD,
Tuner, Phono, etc.), press monitor switch
again.
Note: The gain of the LS27 through the
monitor input is not adjustable by gain
selector button (on the remote), and is
fixed at ‘High’ gain (the gain setting on
the display is unlit in the “Monitor”
position).
LS27R Remote Only
Display: Selects one of nine display
illumination levels, including off. When
off, the display can be reactivated for
10 seconds at a low level by pressing
any button (except Power) on remote or
control on front panel.
Bal L/Bal R: Adjusts balance left or right.
Adjustment appears in display window
as movable marker on bar graph. Useful
for compensating for uneven speaker
placement or imbalanced output from
a phono cartridge.
Hours: When pressed, displays number
of operating hours vacuum tubes have
been in service.
WARNING: after replacing tubes, this
function should be reset to “0” only by a
qualified technician. Hours display can
be reset to “0” by pressing black button
labeled “Reset Hours” located on lower
right corner of circuit board directly
behind display window. The preamp
must be “On” to reset function–the
service technician must be careful to
avoid any contact with other circuit
components during reset operation.
Contact Audio Research customer
service (763.577.9700) for information
regarding this procedure.
Gain: The Gain selector limits the input
level to the LS27, with resulting Low,
Medium and High labeled gain option
settings to the outputs. Note that the
gain to the single ended outputs at
each of the three settings is half of the
gain to the balanced outputs at the
same setting. The gain options allow
limiting the output of “hot” high-gain
signal sources to the preamplifier's input
circuitry and prevents potential
overloading. Properly used, this results in
extremely wide signal input range
capability while preserving optimum use
of the Volume control. For each input
source, simply set the Gain selector at
the highest of the three gain settings
viewed on the display that allows you to
use the Volume control over the desired
range without audible distortion on peak
levels from your program source. Once
you have selected the optimum gain
setting for a given input, the LS27 will
“memorize” it and return to that gain
setting each time you select that input.
Note that the Gain selector defaults to
the “High” setting for each input unless

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another is selected.
Invert: Inverts absolute phase of the
output signal.
Connections
Input Connectors: Remembers setting
for each input. The LS27 provides eight
pairs of BAL/SE input connectors: CD,
Tuner, Phono, Video, Aux 1, Aux 2,
Monitor and Processor. The BAL/SE
selector button (front panel and on
remote) should be selected to match
the type of connection used (BAL or SE)
on each input.
Connect either the BAL or SE connectors
for each input. Never connect the BAL
and SE connectors simultaneously for
any input.
Output Connectors: Two pairs of BAL/SE
main outputs are provided.
Record Output: The BAL/SE tape outputs
should be connected to your recorder's
“Record” or “Line” inputs. These outputs
provide a fixed-level two channel signal
(R, L) 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 (Aux 1, Aux
2). The signal will then be routed to the
Record Out connectors when that input
source is selected.
12V In/Out Remote Power Jacks: The
+12V DC input/output jacks provide the
ability to remotely turn on and off other
linked components such as power
amplifiers having similar capabilities.
Installation Instructions
While the LS27 does not dissipate an
unusual amount of heat, it is important
that it be provided with reasonable
airflow to assure long, trouble-free
operation. In addition, the following
installation guidelines will help insure
maximum sonic performance as well as
reliable service:
1.Operate unit in upright and horizontal
position, preferably on solid, non-metal
shelving.
2.Do not stack the preamp on top of a
power amplifier: not only could this
cause overheating, but hum may be
introduced into the preamp from the
proximity of the amplifier's power
transformer. Do not stack components
or other objects directly on top of the
LS27.
3.Do not place or operate your preamp
on a soft or irregular surface such as a
rug. This will prevent proper ventilation.
4.Do not operate your preamp without
the top and bottom covers installed.
These are required both for safety as
well as shielding from interference
(except in service operations by
qualified personnel).
Operating Procedure
Start Up
1.Secure all rear-panel connections
between LS27, power amplifier(s) and
input sources.
2.Plug three-prong power cord from rear
of chassis into grounded AC wall
outlet. The Power switch defaults to
‘off’ when the unit is plugged into a
power receptacle.
3.Press power switch (either remote or
front panel). ‘Mute’ will will flash in the
display window for approximately 50
seconds, then cease flashing and
remain in the display. Press ‘Mute’ to
initiate operation.
4.Select input source, then BAL or SE as
necessary.
Shut Down
1.Activate ‘Mute’ function.
2.Set Volume level to ‘0’.
3.Turn off power amplifier(s).
4.Press Power switch to ‘off ‘.
5.Turn off input sources.
Tape Recording Procedure
When using the LS27 as a control center
for recording, the program source to be
recorded must be connected to one of
the six inputs controlled by the Input
selector switch or to the Processor input.
This routes the selected program to the
Record output.

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Note: If the Processor input is activated
by selecting the ‘Processor’ switch
position, all other inputs will be
deactivated. When recording from the
Processor input to the Record out of the
LS27, the level of the recording will be
dependent on the level setting of the
processor.
If you own a three-head tape deck, and
wish to monitor the actual tape while
making a recording (for a true ‘A-B’
comparison of signals before and after
recording), connect the tape deck
output to the Monitor input.
It is also possible to dub from one tape
deck to another. Simply connect the
output from one tape deck to an
unused set of inputs controlled by the
Input selector (Tuner, Phono, CD, etc.)
on the LS27. This signal will then be
routed to the second tape deck through
the Record output when the
appropriate input is selected on the
Input selector.
Troubleshooting
It is possible for a static discharge to
temporarily disable the microprocessor
that allows the controls to function. If
this should occur, depress the ‘Mute’
button, then turn off the preamp and
unplug the preamp from the A.C.
receptacle for 60 seconds. Reconnect
the A.C. plug and turn the preamp back
on, along with other components. The
controls should resume normal
operation. If the problem persists,
contact your dealer or Audio Research
Customer Service at 763.577.9700.
Servicing
Because of its careful design and
exacting standards of manufacture,
your LS27 should require no routine
maintenance. The remote control's
batteries (AAA) should be replaced
once a year.
Caution
Your LS27 contains sufficient
levels of voltage and
current to be lethal. Do not
tamper with a component
or part inside the unit. Refer any needed
service to your authorized Audio
Research dealer or other qualified
technician.
The vacuum tubes inside your LS27 are
quality 6H30 dual triode tubes and with
normal use should not need to be
changed for approximately 4,000 hours
of use. Replacement tubes should be of
equivalent quality and are available
from Audio Research.
Note that tube numbers (V1 and V2)
match printed numbers next to tube
sockets on circuit board.
Should service be necessary, please
contact your Audio Research dealer, or
Audio Research Customer Service at
763.577.9700.
Cleaning
To maintain the new appearance of this
unit, 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 effective in
removing dust from bevels, the recessed
nameplate and other features of the
front panel.

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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 effective 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.
Limited 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, or may be
obtained from the authorized retailer or
from the Audio Research Customer
Service Department. 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.
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Specifications
Frequency Response: +0-3dB, 0.2Hz to
160kHz at rated output (Balanced, 200k
ohms load)
Distortion: Less than .01% at 2V RMS BAL
output.
Gain: Main output: Selectable for each
input: 24dB, 18dB, 12dB Balanced output.
(18dB, 12dB, 6dB SE output.) Record
output: 0dB (Processor input: 0dB
balanced).
Input Impedance: 120K ohms Balanced, 60K
ohms SE. Inputs (8): Tuner, Phono, CD,
Video, Aux 1, Aux 2, Monitor, Processor
(XLR and RCA connectors).
Output Impedance: 700 ohms Balanced, 350
ohms SE Main (2), 20K ohms minimum load
and 2000pF maximum capacitance.
Outputs (3): 2 Main, 1 Record (XLR and
RCA connectors).
Output Polarity: Non-inverting.
Maximum Input: Low Gain: 48V RMS BAL,
24V RMS SE, Medium Gain: 24V RMS BAL,
12V RMS SE, High Gain: 12V RMS BAL, 6V
RMS SE.
Rated Outputs: 2V RMS 1Hz to 100kHz into
200K ohm balanced load (maximum
balanced output capability is 15V RMS at
less than 0.5% THD at 1kHz).
Controls: Rotary volume selector (104 steps)
and rotary input selector.
Push buttons: Power, Mono, BAL/SE, Proc,
Monitor, Mute. Also remote buttons:
Display, Bal L, Bal R, Hours, Invert, Gain.
Power Supplies: Electronically regulated low
and high voltage supplies. Automatic 50
sec. warm-up/brown-out mute. Line
regulation better than .01%.
Noise: 1.3uV RMS residual IHF weighted
balanced equivalent input noise with
volume at 1 (100dB below 2V RMS output).
Tube Complement: 2-6H30P dual triode,
(Hybrid JFET/ tube audio circuit, solid-state
power supply).
Power Requirements: 105-130VAC 60Hz (210-
260VAC 50/60Hz) 50 watts maximum.
Dimensions: 19" (48 cm) W x 5.25" (13.4 cm)
H (standard rack panel) x 13.3" (33.8 cm) D.
Handles extend 1.50" (3.8 cm) forward of
the front panel.
Weight: 16.3 lbs. (7.4 kg) Net; 23 lbs. (10.5 kg)
Shipping.
Specifications subject to change without notice.
©2010 Audio Research Corporation.
3900 Annapolis Lane North
Plymouth, MN 55447
763.577.9700
www.audioresearch.com
audio research