Audio Research VT80 User manual

VT80
Stereo Power Amplier

Thank you for choosing theVT80 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, the
performance of this amplier will
continue to improve over time for
you to fully appreciate the benets
it will provide to your system.
After reading the user guide,
if you have any further questions
regarding your amplier, contact
your dealer who will be happy to
help you make the most of your
new component.
Good Listening!
Thank You.

4
Contents
Warnings.......................................................5
A note about packaging................................5
Before operating the VT80 ...........................5
Installation...................................................6
Top Plate ........................................................6
To remove the top cover (for VT80 units
sold outside of North America)...................... 7
In your system ............................................... 7
Connections .................................................8
Back Panel Controls and Connections.........8
Input Connectors ..........................................9
Output Connectors.......................................9
Important ......................................................9
Matching........................................................9
A.C. Power Connection............................... 10
Remote Turn-on ........................................... 11
RS-232 Control ............................................. 11
Operation ....................................................12
Front Panel Controls and Displays..............12
Start-Up........................................................13
Shut-Down ...................................................13
Hour Counter ...............................................13
Auto Shut O.............................................. 14
Break-in........................................................ 14
Auto Bias ..................................................... 14
Maintenance .............................................. 15
Vacuum Tubes ............................................. 15
Servicing ...................................................... 15
Caution ........................................................ 15
Cleaning....................................................... 15
Disposal and Recycling Guidelines............. 15
Warranty..................................................... 16
Specication ...............................................17

5
To prevent re, or shock hazard, do not
expose your VT80 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 VT80 is
equipped with a heavy gauge, 3-conductor
cable and a standard three-prong (US)
grounding plug appropriate to the country
to which it is originally shipped. For absolute
protection, do not defeat the ground power
plug. This provides power line grounding
of the VT80 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.
The VT80 shipped outside North America is
shipped with a protective, ventilated cover.
While the cover may be removed, its use is
recommended to prevent accidental contact
with the hot vacuum tubes.
For continued protection against re hazard,
replace the fuse only with the same type and
rating as specied at the fuse holder.
Warnings
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 VT80 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 VT80 from unnecessary
damage or delay.
Before operating the VT80
This unit has been shipped with the vacuum
tubes installed in protective foam in
separate boxes packed inside the shipping
carton. Included are two matched pairs of
KT120 power output tubes and two 6H30
tubes. Remove the tubes carefully from the
protective foam.

6
Installation
Top Plate
KT120
Vacuum Tubes
6H30
Vacuum Tube
6H30
Vacuum Tube
KT120
Vacuum Tubes
VT80
TOP VIEW

7
To remove the top cover (for VT80
units sold outside of North America)
Using the provided hex-head driver, loosen
the fastening screws from the front and
back edges of the tube cover. Once all of
the screws have been removed, carefully lift
the cover.
After removing the top cover and the vacuum
tubes packed in protective foam, see the Top
Plate illustration to install the tubes for your
VT80 in their proper locations in the chassis.
Note that the numbers written on each tube
correspond to a ‘V’ number etched on the
chassis next to each tube socket. Insert each
tube rmly, carefully aligning the tube pins
with the corresponding socket holes.
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.
Installation
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 or cabinet, make
certain that adequate airow above and to
each side of the unit is provided. A minimum
of 6 inches (16 cm) on top and an open back.
During operation, if there are doors on the
cabinet, they must remain open.
The ‘ambient’ operating temperature
should never exceed 86° F, 30° 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 operated at safe, conservative levels and
will not be improperly aected providing the
requirements outlined above are adhered to.

8
Connections
A.C. Mains
Connectors
Reset Button/
Hours Meter
RS-232
Connector
Fuse
12V
Trigger
Input
Balanced/Single Ended
Switch
Defeat/Auto Shut Off
Switch
Speaker Terminals
(left channel)
Speaker Terminals
(right channel)
Inputs
(right channel)
Inputs
(left channel)
VT80
REAR VIEW
Back Panel Controls and Connections

9
Input Connectors
The VT80 uses a fully balanced circuit
topology and has a pair of balanced XLR
input connectors along with a pair of single-
ended RCA input connectors. The rear panel
switch must be in the appropriate position
for either Single-Ended or Balanced use.
Connect your preamplier’s output to the
VT80 before turning on the amplier. Do not
connect the balanced XLR input connectors
and the single-ended RCA connectors at the
same time – connect one pair or the other.
Output Connectors
Proprietary, 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
( 0 Ω black banded) terminal, then the
(+) lead to the matching (4 or 8 Ω red
banded) terminal. Follow your speaker
manufacturer’s impedance specication.
The VT80 puts out the same amount of
power whether the 4 or 8-ohm terminals
are used.
Note: The 4 Ω tap is grounded. Avoid
wiring and speaker switching systems that
have a common ground wiring or switching
of the amplier output. Some headphone
switching systems have a common ground.
Special connections must be made to use
such systems. Contact Audio Research
customer support for more information.
Connections
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 VT80. Connect the red or ‘+’ speaker
terminal to the wire that connects to the
‘4’ or ‘8’ terminal on the VT80 and tighten
the speaker terminals securely to ensure
best sonic results. Use a 7/16” (12mm)
hex- end screwdriver to tighten the output
terminals. Avoid using a wrench as this can
lead to overtightened, stripped or broken
output terminals.
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.

10
VT80 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 VT80 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 VT80
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.
Connections
Connect the VT80 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.
Note: The VT80 will not be damaged
by improper impedance match to the
speakers, but maximum power delivered
into the speakers may be aected.
A.C. Power Connection
It is important that the VT80 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 theVT80
for On/O control of the amplier, or the
12V start-up trigger for remote installations.
The AC power source for the VT80 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 VT80 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 VT80 should be turned on after the
other components of your system. If the

11
If electronic crossovers or other AC powered
equipment is used with the VT80 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.
Remote Turn-on
The VT80 has a built-in 12VDC 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
mini plug to connect to the +12V TRIGGER IN
jack on the rear of the VT80.
The +12V TRIGGER IN jack should be
connected to the +12VDC output of the
master control system, using a continuous
+12VDC signal at 12mA per VT80 for the
duration of amplier on-time. Do not use a
momentary or data pulse control signal.
The +12VDC remote jacks have polarity
protection, so they will not operate if a
-12VDC signal is accidentally connected, or if
the control wires are reversed.
Connections
RS-232 Control
The VT80 has an RS-232 connector on the
back panel, in the event the amplier is
incorporated into an automated or two-way
remote communication system. Please see
your dealer or contact customer service at
Audio Research to acquire the specic codes
relative to the RS-232 control.

12
Operation
POWER
Power
On/Off On/Off L.E.D.
VT80
FRONT VIEW
Front Panel Controls and Displays

13
Operation
Hour Counter
An LCD hour meter of elapsed tube operating
time can be viewed on the back panel, located
nexttotheIEC powerconnector.Thisdisplays
accumulated hours of vacuum tube service
life. If the amplier is unplugged from the
mains supply, the total accumulated hours
are retained. The hour counter may be reset
by inserting a small, pointed object in the
hole directly to the left of the LCD counter.
The KT120 power vacuum tubes in your VT80
have an average life span of approximately
2000 hours. The smaller 6H30 vacuum tubes
have a life span of approximately 4000
hours. Actual tube life will vary depending
on the frequency and manner of usage of the
amplier.
Note: Once the hour counter has been
reset, the total accumulated hours cannot
be recalled.
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 VT80 front panel control switch.
Green power LED will light.
• The VT80 has an automatic 30 second
mute circuit which allows the amplier to
stabilize before becoming active.
• Unmute preamplier output, initiate
source component signal, and adjust gain
as appropriate.
Shut-Down
• Mute preamplier output.
• Press VT80 front panel power switch.
• Turn o preamplier and then the
associated input source components.
Note: When the VT80 is shut o,
avoid restarting the unit for a minimum of 5
minutes to allow the vacuum tubes to cool.

14
Auto Shut O
The VT80 is equipped with an auto shut o
feature, designed to turn the amplier o
after two hours of no signal being present at
the output of the amplier.
In the event that quiet music is listened
to at very low volumes, there may not be
adequate signal for the auto shut o circuit,
resulting in the amplier turning itself o. If
this is the case, please disengage the auto
shut o feature. The auto shut o feature
control switch is located on the back panel
of the VT80. Toggling the switch allows you
to turn the feature on or o.
Note: The auto shut o feature is not
in the signal path of the amplier and has no
deleterious sonic eect on music playback.
Break-in
All quality stereo equipment benets from
a break-in period; during this time, various
components change as electrical signals
pass through them. While your VT80 will
sound excellent out of the box, it will only
improve with continued use.
Auto Bias
The VT80 incorporates a highly sophisticated
auto-bias circuit for each individual output
tube. There are no user-adjustable bias
controls. Each tube will auto-bias upon initial
turn-on of the amplier. There should never
be a need to check or adjust the auto-bias
circuit, once it is factory set, no additional
adjustment is required. The auto bias circuit
Operation
compensates to maintain the proper bias as
the tubes age. Auto-bias sets idle current at
65ma per tube.
It is always recommended owners purchase
replacement tubes from Audio Research
Corp. It is still recommended that matched
sets of output tubes be installed. While
auto-bias will correct for mismatches, sonic
benets still apply with matched tubes.
The auto bias circuit will not accommodate
output tubes with extremely high or low
plate current readings. Aftermarket tubes
may not be tested to the same rigorous
standards as Audio Research tests, so
care must be exercised when installing
aftermarket tubes. If uncertain about
aftermarket tube requirements, please
contact Audio Research Customer Service
for recommendations.

15
Maintenance
the Customer Support Department of
Audio Research Corporation at service
@audioresearch.com. You may also initiate
a service request by visiting the Audio
Research website (www.audioresearch.com)
and selecting ‘Service Repair’.
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 when the
unit is powered o. 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 and the
acrylic insert of the front panel. A small, soft
paintbrush is eective in removing dust from
bevels 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,
visit audioresearch.com for the name of your
importing distributor and how to contact
them. Packing and shipping materials may
be disposed of in a normal manner.
Vacuum Tubes
It is recommended that you replace the
vacuum tubes of your VT80 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. Audio Research
recommends replacing output tubes after
2,000 hours of operation.
Servicing
Because of its careful design and exacting
standards of manufacture, your VT80
amplier should normally require only
minimal service to maintain its high level
of performance. Your VT80 is equipped with
individual fuses for each output tube. This
is to prevent circuit board damage should a
tube arc occur. These fuses are accessed on
the underside of the circuit board adjacent to
each tube. In the event a fuse opens, consult
a qualied service technician or Audio
Research Customer Service. High voltages
can exist long after the unit is turned o.
Use extreme caution.
Caution
Your VT80 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 another
qualied technician. Additional questions
regarding the operation, maintenance or
servicing of your amplier, please contact

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 from 20Hz to 20kHz. 1kHz total harmonic
distortion typically 1% at 75 watts, below 0.05% at 1 watt. (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 80kHz.
INPUT SENSITIVITY: 1.4V RMS BAL for rated output. (25dB Bal gain into 8 ohms.)
INPUT IMPEDANCE: 300K ohms Balanced (150K ohms SE).
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 CIRUCIT
(Damping factor approximately 8).
OVERALL NEGATIVE FEEDBACK: 15dB
SLEW RATE: 10 volts/microsecond
RISE TIME: 4.0 microseconds
CHANNEL SEPARATION: 112dB
HUM & NOISE: –84dBV weighted, 8 ohms tap
SIGNAL TO NOISE: 112dB
CONTROLS: Power on/o, auto shut-o on/defeat, Input BAL/SE, RS232, 12V trigger
AMBIENT AIR TEMPERATURE: 30° C (86° F) maximum ambient air temperature
POWER SUPPLY ENERGY STORAGE: Approximately 350 joules
POWER REQUIREMENTS: 100-125VAC 60Hz (200-250VAC 50Hz) 410 watts at rated output,
500 watts maximum, 230 watts idle. Sleep power < 1 watt
TUBES REQUIRED: 2 – Matched pair KT120 – Power Output; 2 – 6H30 Driver
DIMENSIONS:
width 19” (48.3 cm)
height 10.33” (26.2 cm)
depth 18.45” (46.8 cm) to chassis , 19.40” (49.3 cm) to terminals
WEIGHT: 45.7lbs. (20.7 kg) Net; 60.5 lbs. (27.4 kg)

Specications subject to change without notice.
©2016 Audio Research Corporation. Reproduction of this document in part or whole is expressly forbidden without written
consent from Audio Research Corporation.
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