Audio Research GSi75 User manual

H I G H D E F I N I T I O N ®
GSi75
Stereo Integrated Amplier
User Guide

H I G H D E F I N I T I O N ®

Thank You.
Thank you for choosing the GSi75 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 integrated 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 integrated
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 GSi75
To Remove the Top Cover
In Your System
Connections
Back Panel Controls and Connections
Input Connectors
Output Connectors
IR Input
12 volt Trigger
RS-232 Control
Matching
A.C. Power Connection
5
6
6
7
9
9
9
9
9
9
9
10
Operation
Front Panel Controls and Displays
Start-Up
Shut-Down
Break-in
Front Panel Controls
Remote-only Controls
Settings Menu
Using the Headphone Output
Output Tube Bias
Using a Turntable
Using the Digital-to-Analog Converter
Windows Software Installation
Conguring the DAC for Windows
Conguring JRiver Media Center for Windows
Conguring the DAC for Mac OS
Conguring JRiver Media Center for Mac
Conguring Signalyst HQPlayer for Mac
12
13
13
13
14
15
17
20
21
22
23
24
26
28
29
30
30
Maintenance
Servicing
Cleaning
Disposal and Recycling Guidelines
Warranty
Specications
32
32
32
33
34

5
Warnings
To prevent re, or shock hazard, do not
expose your GSi75 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. Aside from the tube cover, 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 GSi75 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 GSi75 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 GSi75 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.
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 GSi75 integrated 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 GSi75 from unnecessary damage or delay.

6
Before operating the GSi75
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 KT150 power output tubes and two 6H30 tubes.
Remove the tubes carefully from the protective foam.
To remove the top cover
Use a phillips-head screwdriver to remove 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 away from the chassis making
sure not to scratch the other surfaces.
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 GSi75 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.
Installation
Note
Double damping rings are installed at the factory and
positioned on each 6H30 tube for maximum sonic
performance.

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.
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.
Do not stack components or other objects directly on top
of the GSi75.

8
Connections
Phono and
Analog Inputs
Digital
Inputs
Speaker
Terminals
(right channel)
Speaker
Terminals
(left channel)
A.C. Mains
Connector
Fuse
RS-232
Connector
IR
Input
Back Panel Connections

9
Connections
Input Connectors
The GSi75 provides four pairs of single-ended, analog input
connectors: SE1 - 3, and PHONO, and three digital input
connectors: USB, TOS, and RCA. Please note that input
SE3 can be selected as a unity gain ‘processor’ input; in
this case, SE3 should only be connected to a component
with a volume control (such as a home theater
processor). For further information about the SE3
processor mode, see the section ‘Processor’ on page 16.
Note
The phono stage of the GSi75 has two gain settings
of 45 and 62 dB; please keep this in mind when
selecting a phono cartridge to pair with your
preamplier. For further information about
connecting a turntable, please see page 22.
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 ‘0’ (black) terminal, then the
(+) lead to the ‘4’ or ‘8’ (red) terminal. Follow your
speaker manufacturer’s impedance specication to
determine if you should use the 4 - or 8 - Ohm tap.
The GSi75 puts out the same amount of power
whether the 4 or 8-ohm terminals are used.
RS-232 Connection
The RS-232 connection allows for remote control via
systems such as Creston or other automation systems.
IR Input
The IR input can be used to link the GSi75 to an IR repeater
system with a standard mono 1/8” connector.
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
Connections
A.C. Power Connection
It is important that the GSi75 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 GSi75 for On/O control of the amplier.
The AC power source for the GSi75 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 GSi75 should be connected to its own
AC power circuit branch, protected by a 15 amp
breaker. The other audio equipment should be
connected to a dierent power circuit and breaker.
The GSi75 should be turned on after the other
components of your system. If the GSi75 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 GSi75 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 GSi75
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 other AC powered equipment is used with the GSi75
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.

H I G H D E F I N I T I O N ®

12
Operation
Input
Select
Volume
Control
Power
On/O
Function
Buttons
Menu Button
side panel
Headphone
Output
DAC and Bias
Indicators
Function
Indicators
Front Panel Controls and Displays

13
Start-Up
• Secure all rear-panel connections between GSi75, input
sources, and speakers.
• Plug three-prong power cord from rear of chassis
into grounded A.C. wall outlet. The Power switch
defaults to ’o’ when the unit is plugged into a power
receptacle.
• Press power switch (either on the remote or front
panel). The amplier will begin the warm-up sequence,
which lasts approximately 45 seconds, during which
‘MUTE’ will ash on the display. After the warm-up
sequence is complete, the unit will be muted. Depress
the front panel ‘MUTE’ button or the Mute button
on the remote to initiate normal operation. You may
depress the Mute button prior to the unit completing
the warm-up cycle; ‘MUTE OFF’ will ash on the display
until the warm-up cycle is complete.
• Select input source and adjust the volume as necessary.
Shut-Down
• Activate ‘MUTE’ function.
• Press Power switch to ‘o’.
• Turn o input sources.
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 GSi75 will sound fantastic
out of the box, it will only improve with continued use.
Operation
example of display after warm-up sequence is
complete.

14
Front Panel Controls
The GSi75 has two microprocessor-driven rotary controls
and ve buttons (Power, Menu, Mono, Speaker O, and
Mute).
Left Rotary control (Input Select)
Select input by rotating the control to the left or right. The
screen displays the current input at the top left.
Right Rotary control (Volume)
Adjust volume (output level) up or down for both L
and R channels. Volume control is also selectable via
VOL UP and VOL DN buttons on the remote control.
Volume adjustment is indicated in the display window by
numeric digits on 0–103 scale.
Do not turn volume up beyond normal listening levels
when ‘mute’ is engaged to avoid unexpected or possibly
damaging sound levels. Reduce volume level whenever
changing input sources, even when muted.
Power On/O
Supplies power from A.C. wall outlet to the GSi75;
indicated by active display window. The GSi75 requires
approximately 45 seconds to warm up; this time is
required to stabilize the vacuum tubes. See ‘Start-Up
Procedure’ on page 11 for details.
Menu
The menu button enters the setup menu of the GSi75 to
allow customizing certain settings of the integrated
amplier. See page 15 for further details about using the
setup menu.
Mono
Toggle between Stereo and Mono output.
Speaker O
Toggle between the speaker outputs and the headphone
jack, located on the right side of the unit. Please note
that the GSi75 maintains individual volume settings for
the speaker and headphone outputs.
Mute
When activated, Mute electrically disables all output of
the GSi75; indicated by ‘MUTE’ in display window. This
control should be activated before switching inputs,
changing connections or shutting down your audio
system to help protect your amplier and speakers from
unexpected signal pulses. When deactivated, ‘MUTE’
disappears from the display window allowing normal
operation.
Operation

15
Operation
Cartridge Impedance
The load button allows you to change the input
impedance associated with the ‘Phono’ input; this
feature only operates when the ‘Phono’ input is selected.
To match the impedance of the GSi75 with your
cartridge, refer to the specications included
with your phono cartridge. If no impedance
is indicated, contact the manufacturer.
If your cartridge impedance is dierent from the ve
settings oered on the GSi75, select the number
which is closest to that of your cartridge.
Gain
The gain button allows you to change the gain
for the ‘Phono’ input; this feature only operates
when the ‘Phono’ input is selected.
Note
Because it oers an additional gain stage, the Phono
input should only be used with a turntable. Connecting
another source, such as a CD player or TV to this
input, may cause signicant distortion which can
cause serious damage to your amplier or speakers.
Both the gain and cartridge impedance functions are
only operable when the Phono input is selected.
Remote Only Functions
In addition to the controls found on the front
panel, the remote control oers access to the
following additional features of the GSi75.
Display Brightness Adjustment
The front panel display has six brightness settings, as
well as the ability to dim the display completely. To
change the brightness, use the ‘DSP UP’ or ‘DSP DN’
buttons on the remote. Note that when the display
is completely dimmed, a small illuminated square
in the middle of the display appears after 6 seconds
of inactivity to indicate the unit is powered on.
Hours
Pressing the ‘HOURS’ button will display the total
accumulated hours of operation for the GSi75. This
is useful to determine the approximate number
of hours the vacuum tubes have been in use.
After ve seconds, the display will revert to the
normal operation screen. After replacing vacuum
tubes, the hours counter should be reset (see
instructions under ‘Settings Menu’ on page 17).

16
Operation
Remote Only Functions, continued
Sample
The sample button will switch the DAC in the GSi75
between native rate sampling (whatever the bit rate
of the original signal is) and upsampling when using
the digital inputs. The upsampling feature will use an
integer multiplier (with no quantization) to a sampling
frequency of 352.8 kHz (all multiples of 44.1 kHz) or 384
kHz (all multiples of 48 kHz). The upsampling circuit
will not upsample to DSD. An LED to the left of the
display indicates whether upsampling is on or not.
Filter
The DAC in the GSi75 has two dierent lter settings
- fast and slow. These two settings represent the
lter curves available for playback. While there
is not a single ‘correct’ setting for the lter, you
may nd you prefer the sound of one lter over
the other on dierent recordings. LEDs on the left
of the display indicate which lter is selected.
Bias
The bias button enters the GSi75 into bias adjust
mode; for further details on how to properly
check and adjust bias, please see page 21.
Balance
The Balance control adjusts the output from center
position to the left or right channels, which in
turn will shift the center point of the sonic image.
This is useful in the event the main listening
position is not centered between the speakers,
or can help with certain room anomalies.
To adjust the balance, press the ‘BAL L’ or ‘BAL
R’ button on the remote. The balance scale will
appear at the bottom the display, and the indicator
block will move in the selected direction:
After ve seconds of inactivity, the balance scale
will disappear from the screen. If the balance
has been shifted to the right or left, ‘R+’ or
‘L+’ will appear at the bottom left corner.
Balance scale in center position
Balance scale shifted left

17
Operation
Settings Menu
The GSi75 has been designed with a simple, intuitive
menu to allow you adjustment of several features of
the amplier. To enter the menu, press the ‘MENU’
button on the remote or front panel. If no further
interaction with the amplier or remote is taken for ve
seconds, the GSi75 reverts back to its normal operation
screen. Continuing to press the ‘Menu’ button will
toggle you through the dierent setting options:
Pressing the ‘Menu’ button will enter the GSi75
into the Settings Menu. Pressing repeatedly will
toggle through the menu options.
While a menu item is displayed, rotating the volume
knob on the front panel, or using the volume up/down
buttons on the remote, will adjust the settings of that
particular selection. After making the appropriate
change, pressing the ‘MUTE’ button will conrm the new
setting, and the display will show ‘OKAY’ for ve seconds
before reverting back to the normal operation screen.
For example:
Press ‘MENU’ until desired menu item is
displayed
Turn volume knob or use volume up/down
buttons on remote to make change
Press ‘MUTE’ button to conrm change
After ve seconds, display reverts to normal
operation screen

18
Operation
Settings Menu continued...
Auto Shutdown
The GSi75 is equipped with an auto shut-o feature,
designed to turn the integrated amplier o after a
period of time during which it is not used. The auto shut
o feature senses any interaction with the GSi75, such as
button presses, changing the volume, remote usage, etc.
To change/disengage the auto shutdown feature, press
the ‘MENU’ button until the ‘AUTO SHUTDOWN’
screen is displayed. Using the volume knob on the
front panel, or the volume up/down buttons on the
remote control, you have the option for ‘o’ (no auto
shutdown) or 1-8 hours. Once you have made a selection,
press ‘MUTE’ to conrm. The display will show ‘OKAY’
before reverting back to the normal operation screen.
Note
The auto shutdown feature is not in the audio signal path
and has no deleterious sonic eect on music playback.
Processor On/O
The SE3 input of the GSi75 can be selected as a standard,
volume-controlled input like the other inputs, or it
can be set as a ‘unity gain’ processor input. This is
useful when combining the GSi75 with a multichannel
surround sound processor to maintain the same
speaker/amplier system for left and right channels.
To use SE3 as a processor input, connect the left and
right output channels from your surround sound
processor to the left and right SE3 inputs. Press the
‘MENU’ button until ‘PROCESSOR’ is displayed:
Turn the front panel volume knob, or press the
volume up/down buttons on the remote to
change the setting to ‘PROCESSOR ON’:

19
Operation
Conrm the setting by pressing the ‘MUTE’ button,
and the display will show ‘OKAY’ before reverting
back to the normal operation screen. Now when
SE3 is selected, it will display ‘PROCESSOR’ and
the volume control will be disengaged:
Tube Hours
The tube hours display shows the accumulated
time the GSi75 has been powered on. This is useful
for determining the number of usage hours of
the installed vacuum tubes. After approximately
3,000 hours for the KT150, or 4,000 hours for the
6H30, the vacuum tubes should be replaced and
the tube hours counter should be reset to zero.
To reset the tube hours counter, press the ‘MENU’
button until ‘TUBE HOURS’ is shown.
Turn the front panel volume knob, or press the
volume up/down buttons on the remote until
the display reads ‘TUBE HOURS RESET’:
Press the ‘MUTE’ button to conrm, and
the display will read ‘CONFIRM?’:
Then press ‘MUTE’ a second time to reset the counter.
The display will show ‘OKAY’ for ve seconds before
returning to the normal operation screen.
Note
Once the hour counter has been reset, the total
accumulated hours can not be recalled.

20
Operation
Settings Menu continued...
Volume Reset
The GSi75 has been designed to remember the individual
volume settings for each input, and it will also remember
them after a power cycle. You can choose to turn o this
feature in the event you are concerned about accidental
excessive volumes from a previous listening session.
To change the status of the volume reset feature, press the
menu button until the display reads ‘VOLUME RESET’:
Using the volume knob, or up and down volume buttons
on the remote control, change the status to On or O:
After selecting your desired setting, press the Mute
button to conrm the selection. ‘OKAY’ will be
displayed for ve seconds and your setting is saved.
Using the Headphone Output
The headphone output of the GSi75 has been
designed to accommodate a wide range of
headphone designs and should provide excellent
results with most any headphone.
To use the headphone output, locate the ¼” headphone
jack on the right side of the GSi75 (when looking at
the front panel). Connect headphones, and on the
front panel, press the speaker/headphone button, or
press the ‘SPKR OFF’ button on the remote control. An
LED to the right of the display window will illuminate
when the headphones are selected. Sound from
the main speaker outputs is muted. You may leave
your headphones connected and use the speaker/
headphone button to toggle between the two.