Audio research REF 75 User Manual

Reference 75 SE

®

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 break­in 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

Thank You.

happy to help you make the

most of your new component.

Happy Listening!

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

10

5

6

7

8

9

9

9

11

Operation

12

Front Panel Controls and Displays

Maintenance

Vacuum Tubes

Service

Cleaning

Disposal and Recycling Guidelines

Warranty

Specications

15

15

15

15

16

17

13

Start-Up

13

Shut-Down

13

Break-in

13

Display Brightness Adjustment

14

Output Tube Bias Adjust

4

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.

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.

The appliance coupler (a.c. power connector)

at the rear of this unit must be accessible
for emergency power disconnect.

5

Installation

FRONT

REAR

4 KT150

V2 V1

V5 V6

TUBE LOCATIONS

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.

V4 V3

2 6H30

TOP VIEW

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.

6

Installation

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.

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.

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.

7

Connections

RISK OF ELECTRIC SHOCK

DO NOT OPEN

CAUTION

Back Panel Controls and Connections

Left and Right XLR inputs

12V remote trigger

Meter Lights on/o

REFERENCE 75

STEREO AMPLIFIER

RIGHT INPUT

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.

WARNING

WARNING

RISK OF HAZARDOUS ENERGY!

MAKE PROPER SPEAKER CONNECTIONS

SEE OWNERS MANUAL

0 4 8

5A FUSE
SLO-BLO

T4A (230V)

500W MAX 50/60 HZ

Fuse holder

PLYMOUTH, MINNESOTA

MADE IN U.S.A.

METER LIGHTS

ON

OFF

IN OUT

+12V REMOTE

TURN ON

FOR CONTINUED PROTECTION AGAINST

FIRE HAZARD REPLACE FUSE ONLY

WITH SAME TYPE AND RATING

~

A.C. Mains connector

CAUTION

VOLTS

SERIAL

LEFT INPUT

WARNING

RISK OF HAZARDOUS ENERGY!

MAKE PROPER SPEAKER CONNECTIONS

SEE OWNERS MANUAL

0 4 8

!

Speaker connections

8

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.

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., non­inverted). 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.

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.

9

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.

10

Connections

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.

11

VACUUM TUBE

REFERENCE 75

POWER

BIAS

V1RV2

POWER OUTPUT LEFT

BIAS

OPERATE

BIAS

V3V4BIAS

POWER OUTPUT RIGHT

OPERATE

OPERATE

OPERATE

Operation

Front Panel Controls and Displays

Power output and bias meters

POWER AMPLIFIER

HIGH DEFINITION

Main Power Switch

Bias/Operate Switches

12

Operation

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.

13

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.

14

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
[e-mail] 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.

15

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.

16

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

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

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)

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

17

®

3900 Annapolis Lane North

Plymouth, MN 55447

www.audioresearch.com

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.