Audio Research Reference 75 SE User manual

Reference 75 SE
H I G H D E F I N I T I O N ®

Thank You.
Thank you for choosing the
Reference 75 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 75 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
Break-in
Display Brightness Adjustment
Output Tube Bias Adjust
12
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
75 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 75 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 75 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.
This unit is RoHS compliant.
A note about packaging...
Save all packaging in a dry place away from
re hazard. Your Reference 75 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 75
SE from unnecessary damage or delay.

6
Before operating the Reference 75 SE
Your Reference 75 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 two matched pair
of KT150 output tubes, and two 6H30 dual
triodes used in the input 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. 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.
V2 V1 V4 V3
V5 V6
FRONT
REAR
TUBE LOCATIONS
TOP VIEW
4 KT150
2 6H30

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 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 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
5A FUSE
SLO-BLO
T4A (230V)
IN OUT
+12V REMOTE
TURN ON
REFERENCE 75
STEREO AMPLIFIER
VOLTS
SERIAL
048
LEFT INPUT
PLYMOUTH, MINNESOTA
MADE IN U.S.A.
500W MAX 50/60 HZ ~
RIGHT INPUT
048
RISK OF ELECTRIC SHOCK
DO NOT OPEN
CAUTION
!
METER LIGHTS
OFF
ON
WARNING
RISK OF HAZARDOUS ENERGY!
MAKE PROPER SPEAKER CONNECTIONS
SEE OWNERS MANUAL
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
Left and Right XLR inputs
Meter Lights on/o
12V remote trigger
Speaker connections
Fuse holder
A.C. Mains connector
Back Panel Controls and Connections

9
Connections
Input Connectors
The Reference 75 SE uses a fully balanced
circuit topology and has a pair of balanced
XLR input connectors 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
75 SE before turning on the amplier.
Output Connectors
Heavy-duty output terminals are provided
on the rear panel for 4 or 8-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 75 SE puts out the
same amount of power whether the
4 or 8-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 75 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
75 SE. Connect the red or ‘+’ speaker
terminal to the wire that connects to
the ‘4’ or ‘8’ terminal on the Reference
75 SE and tighten the speaker terminals
securely to ensure best sonic results.

10
Connections
Remote Turn-on
The Reference 75 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 75 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 75 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.
When the 12V DC remote turn-on/o
circuit is used, the power switch on the
front panel should be turned o.

11
A.C. Power Connection
It is important that the Reference 75 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 75 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 75 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 75
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 75 SE should be turned
on after the other components of your
system. If the Reference 75 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 75 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 75 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
75 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 75
HIGH DEFINITION
POWER
BIAS
V1
R
V2
POWER OUTPUT LEFT
BIAS
OPERATE
BIAS
V3
V4
BIAS
POWER OUTPUT RIGHT
OPERATE
OPERATE
OPERATE
Power output and bias meters
Main Power Switch
Bias/Operate Switches
Operation
Front Panel Controls and Displays

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 75 SE front panel control
switch. Green power LED will light.
• Unmute preamplier output,
initiate source component signal,
and adjust gain as appropriate.
Shut-Down
• Mute preamplier output.
• Switch Reference 75 SE front
panel control switch to o.
• Turn o preamplier and then the
associated input source components.
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
75 SE will sound fantastic out of the box,
it will only improve with continued use.
Display Illumination
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
illumination can be turned on or o. To
change the brightness of the display, locate
the switch on the back panel labeled ‘Meter
Lights’. Select the on or o position.
Important!
After the Reference 75 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 60
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 75 at 117.5 VAC (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, switch the rotary knob to
one of the ‘V’ settings. Insert only the
supplied non-conductive bias adjustment
tool into the appropriate bias adjustment
holes. Slowly turn the bias adjustment
potentiometer in each of the holes
marked with the output tube ‘V’ number
position only when the bias switch is set
to that associated ‘V’ number position.
The meter should be set to read in the
center of the tube bias arc (@65mA)
for each of the four output tubes V1 –
V4 for optimum sonic performance.

15
Maintenance
Vacuum Tubes
It is recommended that you replace the
vacuum tubes of your Reference 75 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 ordering a new tube.
Servicing
Because of its careful design and
exacting standards of manufacture,
your Reference 75 SE amplier should
normally require only minimal service to
maintain its high level of performance.
Caution
Your Reference 75 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: 75 watts per channel
continuous from20Hz to 20kHz. 1kHz
total harmonic distortion typically 0.6%
at 75 watts, below 0.05% at 1 watt.
Approximate actual power available at
‘clipping’ 76 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)
7Hz to 60kHz
Frequency Response: (-3dB points
at 1 watt) 0.7Hz to 75 kHz
Input Sensitivity: 1.4V RMS BAL for rated
output. (25 dB Bal gain into 8 ohms)
Input Impedance: 300K ohms Balanced
Output Polarity: Non-inverting.
Balanced input pin 2+ (IEC-268)
Output Taps: 8 ohms, 4 ohms
Output Regulation: Approximately
1.0dB 8 ohm load to open circuit
(Damping factor approximately 8)
Overall Negative Feedback: 15dB
Slew Rate: 10 volts/microsecond
Rise Time: 4.0 microseconds
Hum & Noise: Less than 0.06mV
RMS – 112dB below rated output
(IHF weighted, input shorted)
Power Supply Energy Storage:
Approximately 520 joules
Power Requirements: 105-125VAC
60Hz (210-250VAC 50Hz)
410 watts at rated output, 500
watts maximum, 230 watts idle
Tubes Required:
2 – Matched pair KT150 – Power Output
2 – 6H30 Driver
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 ®
3900 Annapolis Lane North
Plymouth, MN 55447
www.audioresearch.com