Benchmark ADC1 USB User manual

Benchmark ADC1 USB
Instruction Manual
2-Channel 24-bit 192-kHz
Audio Analog-to-Digital Converter

ADC1 USB Instruction Manual Page 2
Contents
Overview 3
Features 5
Front Panel Descriptions 6
1) Mode Switch 6
2) Mode Display 6
3) Meter Switch 8
4) Meter Display 8
5) First Stage Gain Switches 9
6) Second Stage Gain Switches 9
7) Second Stage Gain Knobs 9
8) Second Stage Gain Trim Pots 9
Back Panel Descriptions 10
1) Balanced Analog Line Inputs 11
2) Aux BNC Output 11
3) Main BNC Output 11
4) TOSLINK Optical Output 11
5) AES/EBU XLR Output 12
6) Clock Reference Input 12
7) Word Clock Reference Output 12
8) Fuse Holder 12
9) AC Power Entry Connector 13
10) USB Computer Interface Output 13
Rack Mounting 14
Rack Mount Coupler 14
Blank Rack Panel 14
Performance 15
Frequency Response 15
Inter-Channel Phase Response 16
THD+N vs. Level, 1 KHz 17
32K B-H FFT, Idle Channel Noise 18
32K B-H FFT, -3 dBFS, 1 KHz 19
32K B-H FFT, -3 dBFS, 10 KHz 20
Specifications 21
Analog Audio Inputs 21
Clock Reference Input 21
World Clock Reference Output 21
Digital Audio Outputs 22
Audio Performance 23
Group Delay (Latency) 24
LED Status Indicators 24
AC Power Requirements 25
Dimensions 25
Weight 25
ADAT S/MUX 26
UltraLock™ … What Is It? 27
Regulatory Compliance 30
CE Certificate of Conformity 30
RoHS Compliance 31
Warranty Information 31
1 Year Warranty 31
Extended 5 Year Warranty 31
Extended 2 Year International Warranty 32
Warranty Repair Procedure 32

ADC1 USB Instruction Manual Page 3
Overview
The ADC1 USB is a reference-quality, 2-
channel, 192-kHz, 24-bit, analog-to-digital
converter featuring Benchmark's Advanced
USB Audio™ technology, phase-accurate
UltraLock™ clock system with multi-function
clock input and word clock output, and
Benchmark’s 9-segment dual-range digital
LED metering. The ADC1 USB is designed for
maximum transparency and is well suited for
the most demanding applications in studios
and mastering facilities. A rugged and
compact half-wide 1 RU enclosure also makes
the ADC1 USB an excellent choice for location
recording, broadcast facilities, and mobile
rigs. The internal power supply supports all
international voltages and has generous
margins for over and under voltage
conditions.
The ADC1 USB achieves outstanding
performance over a wide range of input
levels. Each channel has a 41-detent variable
gain control, a 10-turn calibration trimmer,
and a 3-position first-stage gain switch (0,
10, and 20 dB). Each channel has a two-
position toggle switch that selects either the
41-detent pot or the 10-turn trimmer. Both
the pot and the trimmer have a 20 dB
adjustment range. In combination with the
first-stage gain switch, these controls provide
exceptional SNR and THD+N performance
over a 40 dB adjustment range. The 10-turn
calibration trimmer may be used to calibrate
the ADC1 USB to precise studio reference
levels. It may also be used to optimize the
gain-staging between a microphone
preamplifier and the ADC1 USB.
The ADC1 USB has a total of 5 digital outputs
(1 XLR, 2 coaxial, 1 optical and 1 USB) which
can operate simultaneously at up to three
independent sample rates. One of the five
outputs can be configured for 16-bit TPDF
dithered output. This unique flexibility allows
simultaneous recording to a CDR, a high-
resolution digital recorder, and a high
resolution DAW. For example the CDR may
operate at 44.1/16 while the DAW operates at
88.2/24 while the digital recorder operates at
192/24. The optical output supports AES or
ADAT formats at resolutions up to 192/24.
In ADAT mode, high sample rates are
supported using SMUX2 and SMUX4. Backup
and/or demo recordings can be created with
ease while high-resolution outputs are fed to
primary recording devices.
The ADC1 USB has a Word Clock output that
follows the sample rate of the Main Outputs
and Word Clock output is active in all modes
of operation.
A multi-format clock input automatically
recognizes AES/EBU, SPDIF, Word Clock, or
Super Clock signals. This clock input is used
to synchronize the Main Outputs. If desired,
the Main Outputs may be driven from internal
sources. The ADC1 USB will automatically
revert to an internal clock source when the
external clock is lost.
The ADC1 USB has two clock modes: Auto
and Internal. Both modes support 44.1, 48,
88.2, 96, 176.4 and 192 kHz.
The Auto mode allows the ADC1 USB to lock
to an external clock reference. In Auto mode,
the ADC1 USB will follow changes in sample
rate, and/or changes in the type of reference
signal (AES, SPDIF, word clock, or super
clock).
When a clock reference is not available, the
Internal mode must be used, and a sample-
rate must be selected (44.1, 48, 88.2, 96,
176.4, or 192 kHz). When the Internal mode
is active, the ADC1 USB is acting as clock
master, will only operate at the selected
sample rate, and will ignore any signal at the
clock reference input. If Internal mode is
used, all devices connected to the ADC1 USB
digital outputs will need to be configured to
lock to the ADC1 USB. Use the clock output
on the back of the ADC1 USB if the connected
devices require word clock.
The Benchmark UltraLock system is 100%
jitter immune. The A/D conversion clock is
totally isolated from the AES/EBU, SPDIF,
ADAT, WC, and super clock interfaces. This
topology outperforms two-stage PLL designs.

ADC1 USB Instruction Manual Page 4
In fact, no jitter-induced artifacts can be
detected using an Audio Precision System 2
Cascade test set. Measurement limits include
detection of artifacts as low as -140 dBFS,
application of jitter amplitudes as high as
12.75 unit intervals (UI) and application of
jitter over a frequency range of 2 Hz to 200
kHz. A poor-quality clock reference will not
degrade the jitter performance of the ADC1
USB. In addition, the AES/EBU receiver IC has
been selected for its ability to decode signals
in the presence of very high levels of jitter.
The Benchmark UltraLock system delivers
consistent performance under all operating
conditions.
The ADC1 USB is designed to perform
gracefully in the presence of errors and
interruptions at the clock reference input. The
ADC1 USB will even lock to an AES/EBU
signal that has its sample-rate bit status set
incorrectly since the sample rate is
determined by measuring the incoming
signal. Lack of sample rate status bits or
incorrectly set status bits will not cause loss
of audio.
The ADC1 USB is phase accurate between
channels, and between other ADC1 USB
boxes when locked to AES/EBU or word clock
reference signals. The word clock output from
one ADC1 USB may be connected to the clock
input on another ADC1 USB to expand the
number of phase-accurate conversion
channels.

ADC1 USB Instruction Manual Page 5
Features
•Two analog-to-digital conversion channels
•Two XLR balanced analog inputs providing high-performance over a 43 dB range
•-14 dBu to +29 dBu input sensitivity range (at 0 dBFS)
•Two 0 dB, 10 dB and 20 dB first-stage gain switches (1 per channel)
•Two 41-detent gain controls with a 20 dB range (1 per channel)
•Two 10-turn gain calibration controls with a 20 dB range (1 per channel)
•Benchmark’s 9-segment dual-range digital LED meters
•Sample Rate LED indicators
•Conversion at 44.1, 48, 88.2, 96, 176.4, and 192 kHz
•Versatile Auto and Internal clock modes
•Multifunction clock input with auto-recognition of AES, SPDIF, Word Clock, or Super Clock
•Word Clock output
•Total jitter immunity with Benchmark’s, phase-accurate UltraLock™ technology
•Simultaneous output at two different sample rates
•Simultaneous 16 and 24-bit outputs
•Five digital outputs (1 XLR, 2 Coax, 1 Optical, 1 USB)
•AES/EBU, ADAT, and ADAT S/MUX2, and ADAT S/MUX4 output formats
•THD+N = -104 dB, 0.00063% @ -3 dBFS input, SNR 121 dB A-weighted
•Reliable and consistent performance under all operating conditions
•Internal 115 V, 230 V, 50-60 Hz international power supply with very wide operating range
•Low radiation toroidal power transformer significantly reduces hum and line related
interference
•Meets FCC Class B and CE emissions requirements

ADC1 USB Instruction Manual Page 6
Front Panel Descriptions
1) Mode Switch
The Mode Switch is a non-locking toggle
switch which controls the conversion modes
of the ADC1 USB.
Mode Switch Operation
The ADC1 USB can be programmed to
function in a variety of conversion modes.
These include multiple sample rates, bit
depths, and output formats using internal
and/or external clock sources. This
programming is accomplished by pressing or
pressing and holding the Mode Switch.
Factory Default Settings
The ADC1 USB can be easily reset to Factory
Default settings by pressing and holding the
Mode Switch up for approximately 3 seconds.
2) Mode Display
The Mode Display shows what bit depth and
sample rate the Main and Aux outputs are set
to.
Conversion Mode Programming
•Press the Mode Switch up to cycle
through the clock source and sample
rate options for the Main Outputs.
•Press the Mode Switch down to cycle
through the sample rate and bit depth
options for the Aux Output.
•Press and hold the Mode Switch down
for approximately 3 seconds to switch
between AES/EBU and ADAT mode for
the Optical Output.
•Press and hold the Mode Switch up for
approximately 3 seconds to reset the
ADC1 USB to Factory Default settings.
Output Programming
Pressing up on the mode switch will cycle
through the clock source and sample rate
options for the Main Outputs. The Main
Outputs can be set to operate at a fixed
frequency using the internal clock source or
they can be set to follow and lock to an
external clock source.
External Clock Source Locking
The ADC1 USB can sync to a variety of
external clock sources, including Word Clock,
Super Clock, AES, and SPDIF. Once the ADC1

ADC1 USB Instruction Manual Page 7
USB acquires sync, it will perform conversion
at the sample rate of the external clock.
Off = Internal Sync
On = Locked to External Sync
Flashing = External Sync is
Selected, Not Locked
The bottom left LED in the Mode Display is
the Ext Indicator. If the Ext LED is off, then
the ADC1 USB is set to operate at a fixed
sample rate using the internal clock source.
If this LED is illuminated then the ADC1 USB
is locked to an external clock source. When
locked, the Mode Display will indicate the
sample rate.
If the reference sample rate is changed, the
ADC1 USB will automatically switch sample
rates to match the change in the reference
sample rate. If the Ext LED is flashing, the
ADC1 USB is set to sync to an external clock
source and is locking to that source. The
ADC1 USB should lock in less than 5 seconds
and if a lock doesn’t occur within a 5 second
window then there’s a problem with the clock
it’s trying to sync to. If a sync error occurs,
verify a secure connection is present between
the ADC1 USB and the external clock source.
The ADC1 USB will lock to AES, SPDIF, WC, or
Super Clock and is very tolerant of low-level
low-quality reference signals.
External Clock Source
Synchronization
•Press up repeatedly on the Mode
Switch and cycle through the Main
Output modes until the lower left Ext
LED is either on or flashing.
Fixed Frequency Conversion
The ADC1 USB can be programmed to
convert at a fixed frequency using an internal
clock source. The following sample rate
frequencies are available: 44.1, 48, 88.2, 96,
176.4, and 192 kHz. The ADC1 USB External
Clock Input is ignored when the internal clock
source is selected.
Selection of a fixed sample
frequency on the Main Outputs
•Press up repeatedly on the Mode
Switch to cycle through the available
sample frequencies until the four LEDs
in the upper left of the Mode Display
match one of the diagrams below.
Black = Lit
White = Not Lit
Gray = Irrelevant
44.1kHz 48 kHz 88.2 kHz
96 kHz 176.4 kHz 192 kHz
Sample Rate Display
Column one of the Mode Display has a “44”
LED and a “48” LED. These indicate sample
rates of 44.1 kHz and 48 kHz respectively.
Column two has an “X2” LED and an “X4”
LED. These indicate 2x or 4x multipliers.
Multiply the sample rate shown in column one
by the multiplier shown in column two. For
example, if the 44 and X2 LEDs are on, the
sample rate is 88.2 kHz (44.1 x 2 = 88.2).
Aux Output
The Aux Output can be programmed to mirror
the Main Outputs (bit for bit), or it can

ADC1 USB Instruction Manual Page 8
provide an independent low-resolution copy of
the converted signal, at an independent
sample rate. Column three of the Mode
Indicator displays the Aux Output mode
setting.
Note that no matter how the Aux Output is
programmed it does not affect the Main
Outputs in any way.
Aux Output Programming
Press down on the Mode Switch repeatedly to
cycle through the Aux Output mode settings
until the right-hand column of LEDs in the
Mode Display matches the desired mode
based on the diagrams below.
Exact Copy of
Main Outputs
(24-bit)
44.1 kHz
16-bit
48 kHz
16-bit
ADAT or AES/EBU on the Optical
Output
The Optical Output (one of the three Main
Outputs) can provide either AES/EBU or ADAT
format. The bottom LED in the middle column
of LEDs indicates what mode the Optical
Output is in.
When ADAT is active, S/MUX is automatically
enabled at all 2X and 4X sample rates (88.2
kHz, 96 kHz, 176.4 kHz, and 192 kHz).
ADAT or AES/EBU Selection on the
Optical Output
Press and hold the Mode Switch down until
the Optical Output mode LED matches the
desired mode based on the diagram below.
Off = AES/EBU on Optical
Output
On – ADAT on Optical Output
3) Meter Switch
The Meter Switch selects what scale the Meter
Display uses during operation.
Meter Scale and Peak Hold
Function Selection
•Set the Meter Switch to “H” (top) to
enable the Peak Hold function and set
the scale to a 1 dB step.
•Set the Meter Switch to “1” (center) to
disable the Peak Hold function and set
the scale to 1 dB step.
•Set the Meter Switch to “6” (down) to
disable the Peak Hold function and set
the scale to a 6 dB step.
4) Meter Display
The ADC1 USB is equipped with a multi-
function 9-segment LED meter. The Meter
Switch selects either a 6 dB step or 1 dB step
scale and controls the peak-hold function.
Metering is fully-digital and is post conversion
for absolute accuracy. The units are dBFS (dB
below the level of a full-scale sine wave, or
more simply, dB below digital clip).

ADC1 USB Instruction Manual Page 9
Time constants are built into the meters so all
transient peaks can be observed easily. If a
transient peak has a duration as short as one
digital sample occurs, an LED will be
illuminated, and will stay illuminated long
enough to be observed by the human eye.
A peak indication mimics the action of the
needle on a peak-reading analog meter, while
the remaining LEDs will follow the
instantaneous level of the audio.
The red 0 LED indicates that a full-scale
digital code has been reached and that digital
clipping has occurred. Full-scale events as
short as one digital sample, will light the 0
LED. Short single-sample digital clipping
events are often audible, and all 0 dBFS
events should be avoided.
The ADC1 USB has a very large dynamic
range (especially when operating at 24-bit
output word lengths). It is wise to use some
of this dynamic range to provide more
headroom as insurance against clipping.
Leave some extra headroom between your
highest anticipated peak and the red 0 dBFS
LED.
Input Gain Adjustment
Input Gain Stages
First Stage Gain Switches
Each channel on the ADC1 USB is equipped
with a 3-position first-stage gain switch. The
first gain stage provides exceptional noise
performance at gains of 0 dB, +10 dB, or +20
dB. This stage is followed by a second-stage
having a continuously variable gain range of
-1.3 dB to +22 dB. This gain structure
provides ultra-high performance at any gain
setting between -1.3 dB and +42 dB. The
higher gain settings will allow direct
connections from many instrument pickups
(no DI box required).
5) First Stage Gain Switches
The First Stage Gain Switches select the three
different amounts of gain (0, 10, 20 dB) that
can be applied to the left and right channel.
Both channels have their own dedicated
switches.
To select the first stage gain
•Set the Gain Switch to “0” (center) to
select 0 dB gain (unity gain) for the
first-stage.
•Set the Gain Switch to “10” (down) to
select 10 dB gain for the first-stage.
•Set the Gain Switch to “20” (up) to
select 20 dB gain for the first-stage.
6) Second Stage Gain Switches
The second stage gain switches (one for each
channel) can be set to either Variable or
Calibrated. When the switch is set to Variable
the Second Stage Gain Knob for that
respective channel is active and when the
switch is set to Calibrated, the Gain
Calibration Trimmer for that respective
channel is used to fine tune the gain.
7) Second Stage Gain Knobs
The Second Stage Gain Knobs are 41-detent
adjustable dials with a usable range of
approximately -1.3 dB to +22 dB. In order to
use the knobs the Second Stage Gain Switch
must be set to Variable (up).
8) Second Stage Gain Trim Pots
The Second Stage Gain Trim Pots are 10-turn
gain calibration trimmers with a useable
range of approximately -1.3 dB to +22 dB. In
order to use the trim pots the Second Stage
Gain Switch must be set to Calibrated (down).

ADC1 USB Instruction Manual Page 10
Back Panel Descriptions
All of the outputs are controlled by the front-
panel Mode Switch. The status of these
outputs is shown in the Mode Display
adjacent to the Mode Switch.
Three of the outputs are Main Outputs and
always operate at 24-bits. The Main Outputs
may be synchronized to an external clock
reference or may be controlled by the internal
clock. The Optical Output has two modes of
operation; AES/EBU and ADAT. The ADAT
mode supports ADAT (44.1 and 48 kHz),
ADAT S/MUX2(88.2 and 96 kHz), and ADAT
S/MUX4(176.4 and 192 kHz).
The Aux Output can operate asynchronously
at 44.1 or 48 kHz with a TPDF-dithered 16-bit
word length. The Aux Output is provided as a
convenience for making safety backups or
demo recordings to low-resolution 16-bit
recorders (i.e. CDR or DAT). If this low-
resolution function is not needed, the Aux
Output can be set to mirror the high-
resolution Main Outputs.
•XLR connector, balanced, AES/EBU
professional format, 24-bits
•Aux BNC connector, un-balanced,
AES/EBU professional format, 24-bit or
16-bit compatible with most SPDIF
inputs
•Main BNC connector, un-balanced,
AES/EBU professional format, 24-bit
compatible with most SPDIF inputs
•Optical TOSLINK connector, multi-
format (AES professional, ADAT, ADAT
S/MUX II & IV), 24-bits
•USB Computer Interface
SPDIF/AES BNC Main and Aux
Outputs
The two BNC coaxial digital outputs use
female BNC connectors. These connectors are
securely mounted directly to the rear panel.
These are 1 Vpp unbalanced outputs with 75-
Ωsource impedances. Outputs are DC-
isolated, transformer-coupled, current-
limited, and diode-protected. Use 75 Ohm
coaxial cable when connecting these outputs
to other devices. The use of 50 Ωcoax is not
recommended and may cause data
transmission errors.
Many customers are more familiar with
consumer-style RCA-equipped SPDIF digital
interfaces. The ADC1 USB ships with BNC-to-

ADC1 USB Instruction Manual Page 11
RCA adapters. These adapters allow easy
interfacing with consumer-style digital
interfaces. BNC to RCA coaxial cords are also
available from Benchmark.
BNC connectors are specified by the AES3-id
and SMPTE 276M standards for 75-Ω1 Vpp
digital audio signals and are commonly used
in video production facilities and other
professional audio applications. RCA
connectors are specified by IEC 609588-3 for
75-Ω0.5 Vpp consumer-format digital audio
signals (commonly known as SPDIF). We
have chosen to comply with the professional
standards because the BNC connectors lock
and are generally more reliable than RCA
connectors. Compliance with the 1 Vpp digital
audio standards increases the reliability of
digital connections, and often allows
increased transmission distances.
1) Balanced Analog Line Inputs
Left and Right balanced inputs use locking
Neutrik™ gold-pin female XLR jacks. These
inputs have a wide operating range. The input
sensitivity (at 0 dBFS) ranges from -20 dBu
(at maximum gain) to +29 dBu (at minimum
gain). The input impedance is 200k Ohms
balanced, and 100k Ohms unbalanced. The
high input impedance and input sensitivity,
allow direct connections from many
instrument pickups (adapter cable required).
Direct connection of piezo pickups is not
recommended as these pickups require higher
input impedances (to prevent low-frequency
roll-off problems).
•XLR pin 2 = + Audio In
•XLR pin 3 = - Audio In
•XLR pin 1 = Cable Shield (grounded
directly to the chassis to prevent
internal ground loops)
Unbalanced Source Adaptation
1. Connect “+” or hot (tip on ¼ phone plug,
center pin on RCA plug) to XLR pin 2.
2. Connect ground (sleeve on ¼” phone
plug, case on RCA plug) to XLR pins 3 and
1.
Note: It’s best to used balanced wiring (“+”,
“-“, “shield”) and to tie the “-“and “shield” at
the unbalanced connector.
2) Aux BNC Output
This Aux BNC digital output has the unique
ability to output two different bit rates. The
first is a 16 bit TPDF auxiliary output for use
with low-resolution devices. The second signal
is the Main digital output and is identical to
the data available to the other Main digital
outputs.
•Data Format = AES/EBU professional
format
•Word Length = 16 bits TPDF dithered,
or 24 bits
•Sample Rate = 44.1 or 48 at 16 bits,
44.1, 48, 88.2, 96, 176.4, or 192 kHz
at 24-bits
•Clock Source = Internal at 16 bits,
internal or external at 24 bits
3) Main BNC Output
The digital data output from the Main BNC
Output is identical to that of the Main XLR
Digital Output.
•Data Format = AES/EBU professional
format
•Word Length = 24 bits
•Sample Rate = 44.1, 48, 88.2, 96,
176.4, or 192 kHz
•Clock Source = Internal or external
4) TOSLINK Optical Output
The Optical Output has four modes of
operation; AES/EBU, ADAT, ADAT S/MUX2,
and ADAT S/MUX4. The ADAT LED on the
front panel is illuminated whenever any of the
ADAT Modes are active. S/MUX2and S/MUX4
are automatically enabled if required to
support the selected sample rate. S/MUX2is
active at 88.2 or 96 kHz, S/MUX4is active at
176.4 or 192 kHz.
The Optical Output uses what is often called a
TOSLINK, Type FO5, or 5 mm optical
connector. The ADC1 USB uses a special high-
bandwidth version that supports AES/EBU

ADC1 USB Instruction Manual Page 12
digital audio at sample rates up to 192 kHz.
Please note that many optical inputs cannot
support AES/EBU or SPDIF digital audio at
sample rates above 48 kHz, others are limited
to 96 kHz. A few products (such as the
Benchmark DAC1) support 192 kHz optical
inputs. Please note that high-bandwidth
optical transmitters and receivers are not
required for ADAT, ADAT S/MUX2, or even
ADAT S/MUX4.
AES/EBU Optical Output Mode
•Data Format = AES/EBU professional
format
•Word Length = 24 bits
•Sample Rate = 44.1, 48, 88.2, 96,
176.4, or 192 kHz
•Clock Source = Internal or external
ADAT Optical Output Mode
•Data Format = ADAT
•Word Length = 24 bits
•Sample Rate = 44.1 or 48 kHz
•Clock Source = Internal or external
•ADAT channel assignments: 1 = Left,
2 = Right, 3-8 = muted
ADAT S/MUX2Optical Output
Mode
•Data Format = ADAT
•Word Length = 24 bits
•Sample Rate = 88.2 or 96 kHz
•Clock Source = Internal or external
•ADAT channel assignments *: 1 = Left
a, 2 = Left b, 3 = Right a, 4 = Right b,
5-8 = muted
* a, and b are successive samples
ADAT S/MUX4Optical Output
Mode
•Data Format = ADAT
•Word Length = 24 bits
•Sample Rate = 176.4 or 192 kHz
•Clock Source = Internal or external
•ADAT channel assignments **: 1 =
Left a, 2 = Left b, 3 = Left c, 4 = Left
d, 5 = Right a, 6 = Right b, 7 = Right
c, 8 = Right d
•** a, b, c, and d are successive
samples
5) AES/EBU XLR Output
The balanced AES/EBU XLR output uses a
gold-pin Neutrik™ male XLR connector. It
has an output impedance of 110 Ohms as well
as DC-isolation, transformer-coupling,
current-limiting, and diode-protection. It’s
designed to drive standard 4 Vpp AES signals
into a 110 Ohm load. 110 Ohm digital cables
are recommended when connecting this
output to other devices because analog audio
cables may cause data transmission errors.
•Data Format = AES/EBU professional
format
•Word Length = 24 bits
•Sample Rate = 44.1, 48, 88.2, 96,
176.4, or 192 kHz
•Clock Source = Internal or external
6) Clock Reference Input
The Clock Reference Input auto-detects
AES/EBU, SPDIF, Word Clock, or Super Clock
signals, and automatically follows changes in
sample-rate. When Auto mode is active the
ADC1 USB will lock to the external clock
source. Benchmark’s UltraLock™ circuitry
isolates the conversion clock from any jitter
present on the clock reference. Auto Mode will
not degrade the conversion quality of the
ADC1 USB even when very high levels of
jitter are present on the clock reference.
7) Word Clock Reference
Output
This output provides a Word Clock signal
which can be passed to downstream
components.
8) Fuse Holder
The fuse holder is built into a drawer next to
the IEC power connector. The drawer
requires two 5 x 20 mm 250 V Slo-Blo®Type
fuses. The drawer includes a voltage
selection switch with two settings: 110 and

ADC1 USB Instruction Manual Page 13
220. The fuse rating for all voltage settings is
0.50 Amps.
The AC input has a very wide input voltage
range and can operate over a frequency
range of 50 to 60 Hz. At 110, the ADC1 USB
will operate normally over a range of 90 to
140 VAC. At 220, the DAC1 USB will operate
normally over a range of 175 to 285 VAC.
Caution: Always install the correct fuses.
Always insure that the voltage setting is
correct for your locality.
9) AC Power Entry Connector
The AC power input uses a standard IEC type
connector. Within the USA and Canada, the
ADC1 USB ships with a power cord. In other
locations, a location-specific IEC style power
cord may be purchased from a local source
(including a local Benchmark dealer).
10) USB Computer Interface
Output
The USB input accepts a ‘B-type’ male USB
1.1 or USB 2.0 connector. An ‘A-B type’ USB
cable is provided with the ADC1 USB. The
USB cable connects the ADC1 USB directly to
a computer’s USB output. The USB interface
utilizes USB 1.1 protocol, and is compatible
with both USB 1.1 and USB 2.0 ports.
The USB input supports 44.1, 48, 88.2 and 96
kHz sample rates at word lengths up to 24-
bits. The USB interface acts as a ‘native’ USB
audio device and does not require the
installation of any custom drivers.
Benchmark’s Advanced USB Audio technology
achieves bit-transparent operation without
special drivers and without changing system
settings.
The Benchmark USB interface is truly a plug-
and-play solution. The ADC1 USB can begin
streaming high resolution audio bit-
transparently within seconds after being
plugged into a computer for the first time. No
software or hardware configuration is
required.
The ADC1 USB is designed, tested and proven
compatible with the following four operating
systems:
•Windows Vista
•Windows XP
•Windows 2000
•Mac OS X *
* When using OS X the system sample rate
should be set to match the sample rate of the
files being played. Also, we do not
recommend using the OS X system volume
control – set it to 100%.

ADC1 USB Instruction Manual Page 14
Rack Mounting
The ADC1 USB is part of Benchmark’s ½-wide
System1™ product family. Each is one rack
unit high and is exactly ½ the width of a
standard 19” rack panel. The front panels on
System1™ products have rack-mount holes
that are machined to conform to standard
rack-mount dimensions. Two ½-wide
System1™ units may be joined together to
form a single rigid 19” panel that can be
installed in any standard 19” rack.
Either ear of a ½-wide System1™ device can
be mounted directly to a standard 19” rack.
A Rack Mount Coupler connects the other ear
to a ½-wide Blank Rack Panel or another ½-
width System1™ product
Tip: Use the rack-mount screws supplied with
the DAC1 USB (or screws with plastic
washers) to avoid scratching the surface of
the faceplate.
The Rack Mount Coupler and Blank Rack
Panel are available from Benchmark.
Call us, visit our website:
http://www.benchmarkmedia.com or contact
your dealer to purchase these accessories.
Rack Mount Coupler
The Rack Mount Coupler is a machined
aluminum junction block that joins any two
½-wide System1™ devices for rack mounting.
It is also used to join a Blank Rack Panel to
a single ½-wide System1™ device.
Blank Rack Panel
The Blank Rack Panel is a ½-wide 1-RU
aluminum panel for mounting a single ½-wide
System1™ device in a standard 19” rack.
Installation requires one Rack Mount Coupler.

ADC1 USB Instruction Manual Page 15
Performance
Frequency Response
The above graphs show the frequency response of the ADC1 USB when it is operating at a 192-kHz
sample rate. Note that the amplitude response is down by less than 0.05 dB at 10 Hz and 80 kHz.
The bass response extends well below the 10-Hz limitation of the measurement equipment, and
the high-frequency analog response extends well above the 96 kHz bandwidth of 192 kHz digital
audio.

ADC1 USB Instruction Manual Page 16
Inter-Channel Phase Response
This graph shows that the differential phase is significantly better than ± 0.25º from 10 Hz to 20
kHz.

ADC1 USB Instruction Manual Page 17
THD+N vs. Level, 1 KHz
w/20 kHz LPF unweighted
Below –4 dBFS, distortion is lower than the noise floor of the converter. Above –3 dBFS, distortion
reaches a maximum value of only –107 dBFS.

ADC1 USB Instruction Manual Page 18
32K B-H FFT, Idle Channel Noise
The above graph demonstrates that the ADC1 USB is free from idle tones and clock crosstalk. The
highest spurious tone measures –128 dBFS and is AC line related hum. The highest non-line
related tone measures –135 dBFS.

ADC1 USB Instruction Manual Page 19
32K B-H FFT, -3 dBFS, 1 KHz
The above FFT plot shows that the ADC1 USB has very little harmonic distortion. Distortion is
exceptionally low and is dominated by 2nd harmonic distortion. Note the near absence of spurious
tones.

ADC1 USB Instruction Manual Page 20
32K B-H FFT, -3 dBFS, 10 KHz
The above FFT plot shows that the ADC1 USB is free from jitter-induced sidebands. Any jitter
present at the conversion sampling circuit would produce sidebands equally spaced above and
below the 10 kHz test tone. The tone at 20 kHz is due to second harmonic distortion, and measures
almost 120 dB below full scale. Note the near absence of spurious tones.