Audio Research Reference 250 SE User manual
Reference 250 SE
H I G H D E F I N I T I O N ®
Thank You.
Thank you for choosing the
Reference 250 SE to be a part of
your high performance music
listening 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
amplier. Once installed, please
allow an appropriate break-
in period to fully appreciate
the benets this amplier will
provide to your system.
After reading the user guide, if
you have any further questions
regarding your amplier, contact
your dealer or Audio Research
customer service - they will be
happy to help you make the
most of your new component.
Happy Listening!
4
Contents
Warnings
Installation
Before Operating the Reference 250 SE
In Your System
Connections
Back Panel Controls and Connections
Input Connectors
Output Connectors
Matching
Remote Turn-on
A.C. Power Connection
5
6
7
8
9
9
9
10
11
Operation
Front Panel Controls and Displays
Start-Up
Shut-Down
Display Brightness Adjustment
Fan
Meter
Break-in
Output Tube Bias Adjust
12
13
13
13
13
13
13
14
Maintenance
Vacuum Tubes
Service
Cleaning
Disposal and Recycling Guidelines
Warranty
Specications
15
15
15
15
16
17
5
Warnings
To prevent re, or shock hazard,
do not expose your Reference
250 SE 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 qualied personnel.
The detachable power cord on your
Reference 250 SE 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 Reference 250 SE 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.
For continued protection against re hazard,
replace the fuse only with the same type
and rating as specied at the fuse holder.
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.
This unit is RoHS compliant.
A note about packaging...
Save all packaging in a dry place away from
re hazard. Your Reference 250 SE
amplier 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 Reference 250 SE
from unnecessary damage or delay.
6
Before operating the Reference 250 SE
Your Reference 250 SE amplier is shipped
with the vacuum tubes packed in foam
blocks. These must be unpacked and
installed before you attempt to operate
the amplier. Included are a matched
sextet of KT150 output tubes, a matched
pair of KT150 driver tubes, 2 6H30 dual
triode used in the input and regulator
stages, and a 6550WE for the power
supply regulator. 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. Firmly seat each
tube in its matching socket, taking care
to ‘key’ the tube pins to the socket holes.
Retain the foam blocks with other packing
materials for possible future use.
Refasten top cover on amplier.
V1 V2
V3 V4
V11
FRONT
REAR
TUBE LOCATIONS
TOP VIEW
V5 V6
V7 V8
V10
V9
output
tubes
driver
tubes
power
supply
tubes
7
In your system
To insure normal component life and safe
operation this unit must be operated
only in an upright position. Adequate
airow and proper cooling can occur only
if there are no restrictions above and
behind the unit and on either side. Be sure
that airow to the 12V D. C. cooling fan
located on the rear panel is not blocked.
The special non-marring elastomer feet
provide adequate spacing and stability
only on a smooth, hard surface, and
also assist to isolate the amplier 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 amplier must
be supported on a surface specically
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 airow above and to
each side of the unit is provided.
The ‘ambient’ operating temperature should
never exceed 120° F or 49° C. Improper
installation will cause premature tube
failure and will aect your warranty,
as well as the service life of the unit.
It is normal for a vacuum tube power
amplier 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 aected
thereby, providing the requirements
outlined above are adhered to.
Installation
8
Connections
7A FUSE
SLO-BLO
T4A (230V) IN OUT
+12V REMOTE
TURN ON
REFERENCE 250
MONAURAL AMPLIFIER
VOLTS
SERIAL
0 4 8 16
INPUT
200K BAL
PLYMOUTH, MINNESOTA
MADE IN U.S.A.
900W MAX 50/60 HZ ~
RISK OF ELECTRIC SHOCK
DO NOT OPEN
CAUTION !
WARNING
RISK OF HAZARDOUS ENERGY!
MAKE PROPER SPEAKER CONNECTIONS
SEE OWNERS MANUAL
WARNING
TO PREVENT FIRE AND SHOCK HAZARD, DO NOT
EXPOSE THIS DEVICE TO RAIN OR MOISTURE.
UNIT MUST BE OPERATED IN A HORIZONTAL POSITION.
-DO NOT OPERATE WITH COVERS REMOVED-
UNIT CONTAINS VOLTAGES WHICH MAY BE HAZARDOUS.
CAUTION
FOR CONTINUED PROTECTION AGAINST
FIRE HAZARD REPLACE FUSE ONLY
WITH SAME TYPE AND RATING
XLR input
12V remote trigger
Speaker connections
Fuse holder
A.C. Mains connector
Back Panel Controls and Connections
9
Connections
Input Connectors
The Reference 250 SE uses a fully balanced
circuit topology and has a balanced XLR
input connector on the rear panel. It
therefore requires a balanced preamplier
output, as provided by most Audio
Research preampliers. Connect your
preamplier’s output to the Reference
250 SE before turning on the amplier.
Output Connectors
Heavy-duty output terminals are provided
on the rear panel for 4, 8, or 16-ohm
speaker impedance loads. Using high-
quality speaker cables, securely fasten the
(-) speaker lead to the appropriate (black)
terminal, then the (+) lead to the matching
(red) terminal. Follow your speaker
manufacturer’s impedance specication.
The Reference 250 SE puts out the
same amount of power whether the
4, 8, or 16-ohm terminals are used.
Matching
It is important to use as close as possible an
impedance match between the amplier
and speaker for optimum transfer of
power to the speaker with minimum
distortion. In the case of speaker systems
with signicant variations in impedance
throughout the frequency spectrum,
such as most electrostatic types,
determine the best impedance match
empirically for best overall sonic results.
Connect the Reference 250 SE input
to the preamplier or electronic
crossover, using only the highest
grade of audio interconnect cables.
To avoid sonic degradation use the
shortest practical length of cables.
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). Connect the black or ‘–‘ speaker
terminal to the wire that connects to
the 0 terminal on the Reference 250 SE.
Connect the red or ‘+’ speaker terminal
to the wire that connects to the 4, 8, or
16 ohm terminal on the Reference 250
SE and tighten the speaker terminals
securely to ensure best sonic results.
10
Connections
Remote Turn-on
The Reference 250 SE has a built-in 12V DC
remote turn-on/o circuit for operation
by a master control system in a home
theater or large audio system. Use a
3.5mm (.140”) diameter mono mini
plug to connect to the +12V IN jack on
the rear of the Reference 250 SE.
The +12V IN jack should be connected to
the +12V DC output of the master control
system, using a continuous +12V DC signal
at 12mA per Reference 250 SE for the
duration of amplier on-time. Do not use
a momentary or data pulse control signal.
The +12V DC remote jacks have polarity
protection, so they will not operate if a
-12V DC signal is accidentally connected,
or if the control wires are reversed.
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