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owners manual
Rev C all contents © Grace Design/ Lunatec LLC
owners manual
reference headphone
amplifier grace design m902
owners manual
2
Table of Contents
Important Safety Information
3
m902 Key Features
4
m902 Frontpanel
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m902 rearpanel
6
Unpacking and Installing your m902
6
Powering up the m902
7
Audio Connections
8
Operating the m902
9
About s-Locktm
10
About x-Feed
10
Accessing and Using the Submenu
11
Wireless Remote Control Operation
15
m902 Block Diagram
16
Specications
17
Cleaning and Maintenance
18
Warranty Information
18
Welcome
Thanks for purchasing the Grace Design m902 reference headphone amplier. We build all our products
to be completely reliable and easy to use, so you can concentrate on producing great sounding audio,
not struggling with complicated equipment or difcult to use product manuals.

While the m902 has been designed to be straightforward to use, we do suggest that you spend a
little time familiarizing yourself with the features and operational functions that are contained in this
manual. Doing this now will make your experience with the m902 more enjoyable.
In the event that you encounter any technical or operational difculties with this or any Grace Design
product, please feel free to contact us at 303-443-7454. Our ofce hours are from 9 to 5, Monday through
Friday, MST. Or you can e-mail your questions to: info@gracedesign.com
Also, please remember to visit our website www.gracedesign.com for the latest Grace Design product
information, owners manuals and technical documents.
Grace Design has been building audiophile quality products for the recording industry for over a
decade. The technology developed for the m902, and all of our products, has evolved through a
process of extensive listening, eld testing and careful renement.
Your new m902 amplier represents a combination of absolutely pristine audio performance, robust
mechanical construction and bombproof reliability.
Regardless of what type of work you do, your m902 will faithfully serve as an invisible link between
your source audio and your headphones or speaker systems. We sincerely hope our products help you
achieve a new level of excellence in your work! -The Grace Design Team grace design m902
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Important Safety Information
General
Indoor use only
Ordinary Protection: This equipment should not be exposed to dripping
or splashing.
Avoid placing objects lled with liquids, such as vases or glasses, on this
equipment.
Class I Equipment (grounded type)
Electrical rating: 100-120/220-240V~ 50-60Hz 25W
Mains supply voltage uctuations are not to exceed ±10% of the
nominal supply voltage.
Pollution Degree 2
Installation (Overvoltage) Category II for transient overvoltages.
Maximum Relative Humidity: <80%
Operation temperature range: 10 °C to 40 °C
Storage and transportation temperature range 40 °C to 70 °C
Maximum altitude: 3000m (9843 ft)
Equipment suitable for continuous operation
Weight: 2.3kg (5lbs)
Safety Marking Symbols
CAUTION: READ ACCOMPANYING DOCUMENTS
This symbol, located on the equipment and in this manual, refers to important instructions. Read
this manual thoroughly before operating this equipment.
Service Information
The Grace Design m902 contains no user serviceable components. Contact Grace Design for repair
and upgrade information. In the event that your Grace Design m902 needs to be returned to the
factory, contact us for a return authorization number.
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m902 Key Features
STEREO ANALOG INPUTS Balanced (+4dBu) XLR and unbalanced (-10dBv) RCA.
ULTRA-LOW DISTORTION 24-BIT /192KHZ DAC accepts stereo digital input sources in AES3,
S/PDIF and TOSLINK (Optical) formats with auto sample rate detection and digital de-emphasis
lter.
USB INPUT provides a convenient way for users to enjoy a reference quality monitoring
experience when connected to their computer. This interface supports 16-bit audio at 44.1 or
48kHz sample rates.
s-lock
tm
dual stage PLL (Phase Lock Loop) circuitry for the ultimate in low jitter digital signal
stability and sonic integrity.
UNBALANCED LINE LEVEL OUTPUTS are provided via RCA jacks on the rear panel for
connection to stereo monitors.
FRONT PANEL ROTARY ENCODER provides precision level control of both headphone and
line output levels. Level adjustments are made in 0.5dB steps within a 95dB range.
0.05dB CHANNEL LEVEL MATCHING to ensure true stereo balance at any monitoring level.
A LARGE, BLUE 7-SEGMENT DISPLAY is used to show headphone and stereo main output
levels.
CALIBRATION MODE enables left/right balance adjustment for both headphone and mains
outputs. Theres also a display dim mode that turns off all LEDs except for the main power
switch LED.
X-FEED is an exciting new feature that simulates the acoustics of a loudspeaker listening
environment which can signicantly improve imaging while reducing listening fatigue when
using headphones. This feature employs carefully designed signal cross-feed, ltering and
delay circuits to simulate HRTF (Head Related Transfer Functions).
HIGH CURRENT TRANSIMPEDANCE OUTPUT AMPLIFIER DESIGN drives 8 Ohm loads. The
m902 was specically designed with low impedance headphones in mind.
ONLY THE HIGHEST QUALITY 0.5% METAL FILM RESISTORS are used throughout and there
are no electrolytic capacitors in the signal path. Sealed gold contact relays are used for all
signal switching.
INFRARED REMOTE CONTROL
for level control, left/right balance, mute and more when using
the optional remote control unit.
5 YEAR LIMITED WARRANTY on parts and labor. grace design m902
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m902 Frontpanel
ILLUMINATED POWER SWITCH - illuminates green when unit is powered on.
S-LOCK INDICATOR LED - illuminates when s-lock is active.
SAMPLE RATE INDICATOR LEDS - auto sample rate detection from selected digital input
source.
ROTARY INPUT SELECTOR SWITCH - selects between all available inputs.
CROSSFEED INDICATOR LED - crossfeed circuitry is user activated in submenu.
OUTPUT LEVEL/EDIT ROTARY ENCODER - This stepped rotary encoder controls the
selected output level in .5dB increments. This encoder is also used to adjust other settings
found in the submenu.
OUTPUT LEVEL/SUBMENU DISPLAY - This blue, 2 digit display shows the current relative
output level values based on the position of the main level rotary encoder. The range of this
display is 0 to 99. Note the decimal represents a 0.5dB increment. This display is also used
to give the user information in the submenu.
OUTPUT SELECTION LEDS These LEDS indicate which output is currently selected by the
user and under interface control.
INFRARED REMOTE RECEIVER Receiver used for optional wireless remote control.
HEADPHONE OUTPUTS Two stereo headphone output jacks wired in parallel.
FEET - four custom machined removable metal feet with neoprene inserts.
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-Lock
INPUT
AES
BAL
UNBAL
S/PDIF
TOS
USB
x
feed
VOLUME
OUTPUTS
phones
line
push
reference headphone
amplifier
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m902 rearpanel
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USB TOSLINK
AES3
UNBAL IN
LINE OUT
BAL IN
S/PDIF
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PUSH
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PUSH
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PUSH
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Unpacking and Installing your m902
The m902 is shipped in one box which contains: the m902 unit, an AC power cord, a small plastic bag
containing four hand-threaded machined metal feet, a warranty registration card and some additional
Grace Design literature.
OPEN AND INSPECT THE BOX
Open all shipping boxes, carefully remove the m902 and put it aside. Before you go any further, check
to make sure the above listed components are included with your shipment. If you believe something
is missing, contact your friendly Grace Design dealer and they will make sure youre taken care of.
SAVE YOUR BOX!!
We strongly encourage you to save the box and shipping materials supplied with your m902. They are
specially designed to properly protect these valuable components, and in the unlikely event that you
need to return them for service, only these OEM shipping materials can ensure their safe return to our
factory.
REGISTER YOUR UNIT!!
Also, we strongly urge you to register your unit with Grace Design. We provide a limited 5 year warranty
on all of our products, but if you dont register your system, its hard for us to help you if and when help
becomes necessary. So please take a few minutes to complete the enclosed warranty registration card
and mail it in, or you can simply go to the warranty registration form on our web site. Thank you!
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BALANCED ANALOG INPUT
UNBALANCED ANALOG INPUT
UNBALANCED LINE OUTPUT
AES DIGITAL INPUT
TOSLINK DIGITAL INPUT
S/PDIF DIGITAL INPUT
USB DIGITAL INPUT
AC IEC INPUT MODULE
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INSTALLING THE FEET AND/ OR RACKMOUNTING
The m902 is designed to either be placed on a stable surface in your studio or listening environment,
or be rackmounted. If you dont plan to rackmount your m902, rst install the 4 supplied metal/rubber
feet. Simply thread (hand tighten only) theses supplied feet by hand into the 4 vacant threaded holes
in each corner of the underside of the m902.
For rackmount installation, the m902 chassis has a #10-32 threaded