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
amplier. Once installed, please
allow an appropriate break-
in period to fully appreciate
the benets this amplier will
provide to your system.
After reading the user guide, if
you have any further questions
regarding your ampli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!

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
Specications
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 qualied 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 specied 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
ampli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 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 amplier is shipped
with the vacuum tubes packed in foam
blocks. These must be unpacked and
installed before you attempt to operate
the amplier. 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 amplier.
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
airow and proper cooling can occur only
if there are no restrictions above and
behind the unit and on either side. Be sure
that airow 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 ampli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 ampli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.
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 power
amplier 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.
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 preamplier
output, as provided by most Audio
Research preampliers. Connect your
preamplier’s output to the Reference
250 SE before turning on the amplier.
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 specication.
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 amplier
and speaker for optimum transfer of
power to the speaker with minimum
distortion. In the case of speaker systems
with signicant 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 preamplier 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 amplier 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.

11
A.C. Power Connection
It is important that the Reference 250 SE
be connected via its supplied 20 amp IEC
12-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 Reference 250 SE for On/
O control of the amplier, or the 12V
start-up trigger for remote installations.
The AC power source for the Reference 250
SE amplier should be capable of supplying
10 amperes for 100 or 120 volt units, or
5 amperes for 220 or 240 volt units.
For the very best performance on 100
or 120 volt circuits, the Reference 250
SE should be connected to its own AC
power circuit branch, protected by a 15
amp breaker. The preamplier and other
audio equipment should be connected
to a dierent power circuit and breaker.
The Reference 250 SE should be turned
on after the other components of your
system. If the Reference 250 SE is turned
on before other components, the amplier
will amplify any extraneous turn-on noises
those components might generate, which
could potentially damage the loudspeakers.
Good operating practice dictates that
the amplier should be turned on last,
and turned o rst in an audio system.
The Reference 250 SE uses a grounding
system that does not require a ground-
lifter adapter plug on the A.C. power cord
to minimize hum. The power cord supplied
with the Reference 250 SE has a standard
grounding plug to provide maximum safety
when properly connected to a grounded
wall receptacle. If there is any question
regarding proper grounding procedures in
your installation, seek help from a qualied
technician. Caution should be taken before
using custom after-market power cords:
they must be at least 12-gauge and have a
standard grounding plug properly installed.
These power cords are to be used with
caution, at the sole risk of the owner.
If electronic crossovers or other AC powered
equipment is used with the Reference
250 SE it may be necessary to use ‘ground
lifter’ adapters on the power plugs of
that equipment to minimize system
hum. Generally, the lowest hum is
achieved when the only direct connection
between audio common ‘ground’ and true
earth ground occurs in the preamplier,
through its grounded power cord.
Other equipment in the system should
have some form of isolation to prevent
ground loops and associated hum.
Connections

12
VACUUM TUBE
POWER AMPLIFIER
REFERENCE 250
HIGH DEFINITION
FAN LIGHT POWER BIAS METER
V1 V3 V5 V6 V4 V2
SET SET
CHECK CHECK
R
Panel output and bias meter
Main Power Switch
Fan
Speed
Operation
Front Panel Controls and Displays
Display
Brightness
Bias/
Operate
Meter
On/O
Bias Adjust
V1/V3/V5
Bias Adjust
V2/V4/V6

13
Start-Up
• Secure interconnects between the amplier
and your preamplier; attach speaker leads
to the appropriate output terminals.
• Attach supplied power cord to rear IEC
inlet of amplier, and plug other end
into grounded A.C. power receptacle.
• Turn on preamp and all other
components; mute preamp output.
• Press Reference 250 SE front panel control
switch. Green power LED will light.
• The Reference 250 SE has an automatic
mute circuit which lasts approximately
45 seconds to allows the amplier to
stabilize voltage before becoming active.
• Unmute preamplier output,
initiate source component signal,
and adjust gain as appropriate.
Shut-Down
• Mute preamplier output.
• Turn o Reference 250 SE front
panel power switch.
• Turn o preamplier and then the
associated input source components.
Display Brightness Adjustment
The front panel meter display is illuminated
with ultra low-noise, low voltage LED
lighting which has no impact on sound
quality when turned on. The display
brightness has three settings: high, low,
and o. To change the brightness of the
display, locate the front panel button
labeled ‘Light’. Press this button to toggle
through the three available settings.
Fan
Press the fan switch to select low
(dim Power LED) or high (bright
Power LED) for fan speed setting.
Meter
Press meter button to turn on or o the
power level monitoring meter function.
Note
The light, fan, and meter settings
at turn o are retained each time
the amplier is turned on.
Break-in
All quality stereo equipment benets from
a break-in period; during this time, the
various components, wiring and solder
connections change as electrical signals
pass through them. While your Reference
250 SE will sound fantastic out of the box,
it will only improve with continued use.
Important!
After the Reference 250 SE is turned
o, wait at least ve minutes before
turning it on again. This allows the large
bank of storage capacitors to drain
energy. Not allowing enough time for
this process can result in blown fuses
or other damage to your amplier.
Operation

14
Operation
Output Tube Bias Adjustment
As shipped from the factory, the output
‘bias’ adjustments are set for a nominal
65mA per KT150 tube. Under these idle
conditions the tubes are each dissipating
approximately 27 watts of their 75
watt rating. This point of operation
provides ‘enriched’ Class AB1, and will
satisfy the most critical listener.
For best results, operate and adjust
the Reference 250 SE at 117.5 VAC
(or 230 VAC). Adjustment must be
made under zero-signal conditions
after at least 15-20 minutes of
uninterrupted stabilization time.
With the amplier warmed up and signal
set to zero, press BIAS switch once and
the V1 output tube LED is illuminated with
its bias level indicated on the front panel
meter. Adjust V1 tube bias level with the
plastic at-bladed bias tool (provided),
inserted in the V1 SET hole in the front
panel so the meter reading is in the center
of the labeled bias range. Press BIAS
switch again to check V3 tube bias level
which should be within the bias range
arc. Press the BIAS switch again and check
the V5 tube bias level in the same way.
Note that the V3 and V5 tube bias levels
are controlled by the V1 bias setting.
Press the BIAS switch once more to read
and adjust V2 tube bias level with the
bias tool in the V2 SET hole in the front
panel in same way the V1 tube bias level
is adjusted. Press BIAS switch again
to check V4 tube bias level, and once
again to check the V6 tube bias level.
Note that the corresponding V number LED
is illuminated for each output tube as
you proceed through the bias adjustment
and monitoring sequence. Press BIAS
switch a nal time to exit the bias status
function and return the meter to the
power level monitoring function.
The Reference 250 SE is shipped from the
factory with all tubes properly biased and
ready to use. It is not necessary to check
bias each time the amplier is turned on.
Under typical circumstances, most owners
will nd that checking the bias level once
a month or so will insure proper operation
and good service life of the output tubes.

15
Maintenance
Vacuum Tubes
It is recommended that you replace the
vacuum tubes of your Reference 250 SE
in sets. All of the tubes in your amplier
have been matched to have similar
operating characteristics, to provide the
best sound quality and reliability. In the
event you need to replace a single output
tube, please refer to the numbers written
on the silver base at the bottom of the
vacuum tube when placing an order.
Servicing
Because of its careful design and
exacting standards of manufacture,
your Reference 250 SE amplier should
normally require only minimal service to
maintain its high level of performance.
Caution
Your Reference 250 SE amplier 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. Refer any
needed service to your authorized Audio
Research dealer or other
qualied technician. Additional questions
regarding the operation, maintenance or
servicing of your amplier, please contact
the Customer Support Department of
Audio Research Corporation at
[email protected] 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.
Cleaning
To maintain the new appearance of this
amplier, 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 ngerprints or similar smudges.
Cleaners containing abrasives should not
be used as they will damage the anodized
nish of the front panel. A small, soft
paintbrush is eective in removing dust
from bevels, the recessed nameplate
and other features of the front panel.
Disposal and Recycling Guidelines
To dispose of this electronic
product, do not place in landll. 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.

16
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 specic terms,
conditions and remedies for fulllment
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 specic terms and remedies for
fulllment 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 fulll 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.

17
Specications
Power Output: 250 watts per channel
continuous from 20Hz to 20kHz. 1kHz total
harmonic distortion typically 0.5% at 250
watts, below .04% at 1 watt. Approximate
actual power available at “clipping” 270
watts (1kHz). (Note that actual power
output is dependent upon both line
voltage and “condition” i.e.: if power line
has high distortion, maximum power will
be aected adversely, although from a
listening standpoint this is not very critical)
Power Bandwidth: (-3dB points)
5Hz to 70kHz
Frequency Response: (-3dB points
at 1 watt) 0.5Hz to 110 kHz
Input Sensitivity: 2.4V RMS Balanced for
rated output. (25.5 dB gain into 8 ohms)
Input Impedance: 200K ohms Balanced
Output Polarity: Non-inverting.
Balanced input pin 2+ (IEC-268)
Output Taps: 16 ohms, 8 ohms, 4 ohms
Output Regulation: Approximately
0.9dB 16 ohm load to open circuit
(Damping factor approximately 10)
Overall Negative Feedback: 8.8dB
Slew Rate: 20 volts/microsecond
Rise Time: 1.5 microseconds
Hum & Noise: Less than 0.2mV RMS –
110dB below rated output (IHF A-weighted,
input shorted, 16 ohm output)
Power Supply Energy Storage:
Approximately 900 joules
Power Requirements: 105-130VAC
60Hz (210-250VAC 50Hz) 770 watts at
rated output, 1000 watts maximum,
380 watts at “idle,” 1 watt o
Tubes required: 3 Matched pair KT150
(Power output V1-6); 1 Matched
pair KT150 (Driver V7-8); 2 6H30
(Gain stage V9 and Regulator Driver
V11); 1 6550C (Regulator V10)
Dimensions:
width 19” (48.3 cm)
height 8.75” (22.2 cm)
depth 19.5” (49.5 cm)
Handles extend 1.5” (3.8 cm) forward
Weight:
47 lbs. (21.3 kg) Net
63 lbs. (28.6 kg) Shipping

Specications subject to change without notice.
©2015 Audio Research Corporation. Reproduction of this document in part or whole is expressly forbidden without written
consent from Audio Research Corporation.
H I G H D E F I N I T I O N ®
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Plymouth, MN 55447
www.audioresearch.com