Audio Research GS150 User manual

H I G H D E F I N I T I O N ®
GS150
Stereo Power Amplier
User Guide

Thank You.
Thank you for choosing the GS150 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 GS150
In Your System
Connections
Input Connectors
Output Connectors
Matching
A.C. Power Connection
Remote Turn-on
RS-232 Control
5
6
7
8
8
8
9
10
10
Operation
Front Panel Controls and Displays
Back Panel Controls and Connections
Start-Up
Shut-Down
Cooling Fan Speed Adjustment
Display Brightness Adjustment
Hour Counter
Auto Shut O
Break-in
Output Tube Bias Adjust
11
12
13
13
13
14
14
14
14
15
Maintenance
Servicing
Cleaning
Disposal and Recycling
Guidelines
Warranty
Specications
16
16
16
17
18

5
Warnings
To prevent re, or shock hazard, do not
expose your GS150 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 GS150 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 GS150 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 GS150 is shipped with a protective, power-
ventilated cover. While the cover may be removed,
its use is recommended to prevent accidental
contact with the hot vacuum tubes. The protective
cover is also recommended to provide powered
ventilation if the amplier is mounted in shelving.
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 GS150 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 GS150 from unnecessary damage or delay.

6
Before operating the GS150
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
quads of KT150 power output tubes and four 6H30 tubes.
Remove the tubes carefully from the protective foam.
To remove the top cover
Using a phillips-head screwdriver to loosen the fastening
screws from the front and back edges of the tube cover
(you do not need to remove any screws from the side
panels of the cover). Note that the screws between
the tube cover and transformer cover can be dicult
to reach; the included screwdriver will reach them as
well as provide a magnetic tip to remove the screws.
Once all of the screws have been removed, carefully
lift the cover and detach the ventilation fan
power plug located at the back of the unit/cover.
Note that the plug has a screw-type securing
connector; turn counter-clockwise to loosen.
Installation
After removing the top cover and the vacuum tubes
packed in protective foam, see the accompanying
illustration for instructions on installing the tubes for
your GS150 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.

7
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. Be sure that airow to the 12V D. C.
cooling fans 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.

8
Connections
Input Connectors
The GS150 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 GS150 before turning on the amplier.
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 (black) terminal,
then the (+) lead to the matching (red) terminal. Follow
your speaker manufacturer’s impedance specication.
The GS150 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.,
non-inverted). Connect the black or ‘–‘ speaker
terminal to the wire that connects to the ‘0’ terminal
on the GS150. Connect the red or ‘+’ speaker
terminal to the wire that connects to the ‘4’ or ‘8’
terminal on the GS150 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 GS150 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
A.C. Power Connection
It is important that the GS150 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 GS150 for On/O control of the amplier, or
the 12V start-up trigger for remote installations.
The AC power source for the GS150 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 GS150 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 GS150 should be turned on after the other
components of your system. If the GS150 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 GS150 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 GS150
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 GS150 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.

10
Connections
Remote Turn-on
The GS150 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 mono mini plug to connect
to the +12V IN jack on the rear of the GS150.
The +12V IN jack should be connected to the +12VDC
output of the master control system, using a
continuous +12VDC signal at 12mA per GS150 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.
RS-232 Control
The GS150 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.

11
Operation
Left Channel
Output Meter
Right Channel
Output Meter
Voltage Meter
Power On/O Display
Brightness
Bias/Operate
V1-V4
Bias/Operate
V5-V8
Front Panel Controls and Displays
Power Indicator

12
Operation
Back Panel Controls and Connections
side panel
Bias Adjust
V5-V8
side panel
Bias Adjust
V1-V4
Fan SpeedAuto
Shut O Hour Counter
RS-23212 Volt
Remote Turn On
Ventilation
Fans

13
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 GS150 front panel control switch.
Green power LED will light.
• The GS150 has an automatic mute circuit which 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.
• Press GS150 front panel control switch.
• Turn o preamplier and then the
associated input source components.
Important!
After the GS150 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.
Cooling Fan Speed Adjustment
The protective vacuum tube cover of the GS150 has
two low-noise fans installed against the back panel
to provide ventilation when the cover is installed on
the amplier. Depending on your amplier installation
location, you may wish to change the speed of the fans
for adequate cooling. As a guideline, if the amplier is
sitting in the open with a minimum six inch clearance
on all sides of the tube cover, the low setting is
sucient. If you are placing the amplier in a rack or
cabinet, the high setting will be preferable to keep the
vacuum tubes within a comfortable operating range.
To change the fan speed, nd the fan speed switch
located on the back panel, on the far right side of
the unit. Select between high and low speeds.
When removing or installing the protective vacuum
tube cover, be sure to rst turn o and unplug the
amplifer from its power receptacle. At the back of
the amplier, make sure to connect or disconnect the
power cable for the cooling fans. When reinstalling the
cover, be certain the threaded collar is secured before
replacing and screwing on the vacuum tube cover.
Note
Do not operate the GS150 with the protective
vacuum tube cover installed and the cooling
fans disabled. This could result in damage
to your amplier due to overheating.

14
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 ‘Lights’. Press this button
to toggle through the three available settings.
Hour Counter
An LCD hour meter of elapsed tube operating time
can be viewed on the back panel, located in the
center above the IEC power connector. This displays
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 KT150 power vacuum tubes in your GS150
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 dependant on the frequency
and manner of usage of the amplier.
Note
Once the hour counter has been reset, the total
accumulated hours can not be recalled.
Operation
Auto Shut O
The GS150 is equipped with an auto shut o feature,
designed to turn the amplier o after a period of time
during which it is not used. The auto shut o feature
is comprised of a signal-sensing circuit designed to
detect any incoming signals from your preampli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 going into standby mode. 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 GS150 at the far left side. 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 to music playback.
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 GS150 will sound fantastic
out of the box, it will only improve with continued use.

15
Operation
Output Tube Bias Adjust
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 70 watt
rating. This point of operation provides ‘enriched’
Class AB1, and will satisfy the most critical listener.
For best results, operate and adjust the GS150 at the
voltage specied for your unit. Adjustment must be
made under zero-signal conditions after at least 15-
20 minutes of uninterrupted stabilization time.
The GS150 operates with paired vacuum tubes; one
tube provides adjustment for a second ‘slave’
tube. For example, V1 provides adjustment for
both V1 and V2, V3 provides adjustment for both
V3 and V4, and so on. When making adjustments,
understand that one adjustment pot aects
the bias of two power output tubes.
To adjust bias, turn one of the ‘Bias/Operate’ knobs
on the front panel to a vacuum tube position. Using
the supplied plastic bias adjustment tool, locate
the appropriate adjustment pot on the side of the
amplier, immediately behind the front panel. Insert
the adjustment tool into the pot corresponding to
the ‘V’ number selected with the ‘Bias/Operate’
knob. Slowly turn the adjustment tool, watching
the front panel meter of the selected vacuum tube.
Continue to adjust the bias until the needle of the
meter is within the bias area on the output meter
(see green area in illustration), with the black ‘Bias’
triangle on the meter being the center of the bias
point. Once you have made the adjustment, switch
the ‘Bias/Operate’ knob to the next tube to check
that the bias of the slaved tube is also within the
acceptable bias region on the meter. Continue to the
next adjustment tube, and repeat the operation.
Please note there may be slight variances between
paired tubes; this is normal. Though the output
tubes of your amplier are carefully matched
before installation at the factory, small changes
can occur over the life span of the vacuum tubes.
Remember that one tube is slaved to the adjustment
of another tube; readjusting the bias for the rst
tube will change the bias of the paired slave tube.
If the bias dierence between the two output tubes can
not be maintained within the acceptable range on the
panel meter, one or more of the output tubes may need
replacement. Contact your dealer or email the Audio
Research service department at service@audioresearch.
com for a replacement set of output tubes.
safe
operating
bias
range

16
Vacuum Tubes
It is recommended that you replace the vacuum
tubes of your GS150 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.
Servicing
Because of its careful design and exacting
standards of manufacture, your GS150 amplier
should normally require only minimal service
to maintain its high level of performance.
Caution
Your GS150 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.
Maintenance

17
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.

18
Specications
Power Output 155 watts per channel continuous from20Hz to
20kHz. 1kHz total harmonic distortion typically 0.6% at 155 watts,
below 0.03% at 1 watt. Approximate actual power available at
‘clipping’ 160 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 80kHz.
Frequency Response (-3dB points at 1 watt) 0.5Hz to 120 kHz.
Input Sensitivity 2.0V RMS BAL for rated
output. (24 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.
Overall Negative Feedback 14dB.
Slew Rate 13 volts/microsecond.
Rise Time 2.0 microseconds.
Hum & Noise Less than 0.1mV RMS – 114dB below
rated output (IHF weighted, input shorted).
Controls Rotary selector for tube bias, Power on/o, fan
speed, auto shut-o on/defeat, RS232, 12V trigger
Power Supply Enery Storage Approximately 1040 joules.
Power Requirements 105-125VAC 60Hz (210-250VAC 50Hz) 730
watts at rated output, 900 watts maximum, 420 watts idle.
Tubes Required 4 – Matched pair KT150 –
Power Output; 4 – 6H30 Driver.
Dimensions
width 19” (483 mm)
height 9 ⅞” (251 mm)
depth 22 ½” (572 mm)
Weight 87 lbs. (39.5 kg)

Specications subject to change without notice.
©2014 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