ADC ADDC1 User Manual
Benchmark ADC1
Instruction Manual
2-Channel 24-bit 192-kHz
Audio Analog-to-Digital Converter
ADC1 Instruction Manual Page 1
Federal Communications
Commission (FCC) Notice
(U.S. Only)
NOTICE: This equipment has been tested and
found to comply with the limits for a Class B
digital device, pursuant to Part 15 of the FCC
Rules. These limits are designed to provide
reasonable protection against harmful
interference in a residential installation. This
equipment generates, uses, and can radiate
radio frequency energy and, if not installed
and used in accordance with the instructions,
may cause harmful interference to radio
communications. However, there is no
guarantee that interference will not occur in a
particular installation. If this equipment does
cause harmful interference to radio or
television reception, which can be determined
by turning the equipment off and on, the user
is encouraged to try to correct the
interference by one or more of the following
measures:
• Reorient or relocate receiving antenna.
• Increase the separation between the
equipment and receiver.
• Connect the equipment into an outlet on a
circuit different from that to which the
receiver is connected.
• Consult the dealer or an experienced
radio/TV technician for help.
This device complies with Part 15 of the FCC
rules. Operation is subject to the following
two conditions:
1. This device may not cause harmful
interference.
2. This device must accept any interference
received including interference that may
cause undesired operation.
Instructions to Users: This equipment
complies with the requirements of FCC
(Federal Communication Commission)
equipment provided that following conditions
are met:
1. XLR Digital Output: Shielded 110-Ohm
AES/EBU digital audio cable with
connector shell bonded to shield must be
used.
2. BNC Digital Connections: Shielded 75-
Ohm coaxial cable must be used.
NOTICE: Changes or modifications not
expressly approved by the party responsible
for compliance could void the user's authority
to operate the equipment.
Safety Information
Do NOT service or repair this product unless
properly qualified. Only a qualified technician
should perform repairs.
For continued fire hazard protection, fuses
should be replaced ONLY with the exact value
and type as indicated on the rear panel.
Do NOT substitute parts or make any
modifications without the written approval of
Benchmark Media Systems, Inc. Doing so
may create safety hazards and void the
warranty.
ADC1 Instruction Manual Page 2
Contents
Overview 4
Features 6
Connections 7
Balanced Analog Line Inputs 7
Clock Reference Input 7
Digital Outputs 8
AES/EBU XLR Output 8
Optical Output 8
SPDIF/AES BNC Main and Aux Outputs 9
Word Clock Reference Output 10
AC Power Entry Connector 10
Fuse Holder 10
Operation 11
Mode Switch and Display 11
Programming the Outputs 11
Locking to an External Clock Source 11
Selecting a Fixed Frequency Using the
Internal Clock Source 12
Reading Sample Rates off of the Mode
Display 12
Programming the Aux Output 12
ADAT or AES/EBU on the Optical Output 13
Resetting the ADC1 to Factory Default
Settings 13
Meter Display 13
Adjusting Input Gain 14
First Stage Gain 14
Second Stage Gain Controls 14
Rack Mounting 15
32K B-H FFT, Idle Channel Noise 23
32K B-H FFT, -3 dBFS, 1 KHz 24
32K B-H FFT, -3 dBFS, 10 KHz 25
Specifications 26
Analog Audio Inputs 26
Clock Reference Input 26
Worldclock Reference Output 26
Digital Audio Outputs 27
Audio Performance 28
Group Delay (Latency) 29
LED Status Indicators 29
AC Power Requirements 30
Dimensions 30
Certificate of Compliance 31
Warranty 32
Extended Warranty 33
Copyright and Contact Information 34
Using ADAT S/MUX 16
UltraLock™ … What is It? 17
Performance 20
Frequency Response 20
Inter-Channel Phase Response 21
THD+N vs. Level, 1 KHz 22
ADC1 Instruction Manual Page 3
Overview
The ADC1 is a reference-quality, 2-channel
192-kHz 24-bit audio analog-to-digital
converter featuring Benchmark’s UltraLock™
technology. The ADC1 is designed for
maximum transparency. It 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 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 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 3position 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 to precise
studio reference levels. It may also be used to
optimize the gain-staging between a
microphone preamplifier and the ADC1.
The ADC1 has four digital outputs (1 balanced
XLR, 2 coaxial, and 1 optical). The optical
output supports AES, ADAT, and ADAT
S/MUX. The two coaxial outputs (Main and
Aux) can operate simultaneously at different
word lengths and even at different sample
rates. The ADC1 has the flexibility to allow
simultaneous high-resolution and lowresolution recordings. For example, the main
outputs of the ADC1 can be set to 192 kHz
24-bits while the auxiliary output is set to
44.1 kHz 16-bits for a safety backup or CDR
demo recording. Both the Main and Aux
Outputs originate from the same A/D
converter. All outputs are professional format.
The ADC1 has a Word Clock output that
follows the sample rate of the Main Outputs.
The 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 will automatically revert to
an internal clock source when the external
clock is lost.
The ADC1 has two clock modes: Auto and
Internal. Both modes support 44.1, 48, 88.2,
96, 176.4 and 192 kHz.
ADC1 Instruction Manual Page 4
The Auto mode allows the ADC1 to lock to an
external clock reference. In Auto mode, the
ADC1 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 samplerate must be selected (44.1, 48, 88.2, 96,
176.4, or 192 kHz). When the Internal mode
is active, the ADC1 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 digital outputs
will need to be configured to lock to the
ADC1. Use the clock output on the back of the
ADC1 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.
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.
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 is phase accurate between
channels, and between other ADC1 boxes
when locked to AES/EBU or word clock
reference signals. The word clock output from
one ADC1 may be connected to the clock
input on another ADC1 to expand the number
of phase-accurate conversion channels.
The ADC1 is designed to perform gracefully in
the presence of errors and interruptions at
the clock reference input. The ADC1 follows
an audio-always design philosophy. Audio is
present at the outputs shortly after applying
power to the unit. The ADC1 will even lock to
and AES/EBU signal that has its sample-rate
status bits set incorrectly. 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.
ADC1 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, 10dB, 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 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
• Four digital outputs (1 XLR, 2 Coax, 1 optical)
• 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 Instruction Manual Page 6
p
Connections
Balanced Analog
Line Inputs (XLR)
Left Right
Analog Line In
Main Digital Output,
BNC (SPDIF/AES)
TOSLINK Optical (ADAT /SPDIF)
Auxiliary Digital Output,
BNC (AES)
Aux 24 or 16-Bit
Digital Output
SPDIF,
AES
Main 24-Bit Digital Outputs
Main Digital Output,
ADAT/SPDIF
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)
Clock Reference Input,
BNC (AES, Wordclock, Superclock)
AES/EBU
Main Digital Output,
XLR (AES /EBU)
AES,
WC,
SC
Ref In
WC
Out
Wordclock Reference
Out
ut, BNC
2. Connect ground (sleeve on ¼” phone
plug, case on RCA plug) to XLR pins 3 and
1.
Note it is best to used balanced wiring (“+”,
“-“, “shield”) and to tie the “-“and “shield” at
the unbalanced connector.
Clock Reference Input
This 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 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 even when
very high levels of jitter are present on the
clock reference.
To adapt to unbalanced sources
1. Connect “+” or hot (tip on ¼ phone plug,
center pin on RCA plug) to XLR pin 2.
ADC1 Instruction Manual Page 7
Digital Outputs
The ADC1 has four digital audio outputs:
three Main Outputs and one Aux Output.
designed to drive standard 4 Vpp AES signals
into a 110 Ohm load. Use 110 Ohm digital
cable when connecting this output to other
devices. The use of analog audio cables may
cause data transmission errors.
Main Outputs
• XLR connector, balanced, AES/EBU
professional format, 24-bits
• BNC connector, un-balanced, AES/EBU
professional format, 24-bits, compatible
with most SPDIF inputs
• Optical TOSLINK connector, multi-format
(AES professional, ADAT, ADAT S/MUX II
& IV), 24-bits
Aux Output
• BNC connector, AES Professional format,
16 or 24-bits
All of the outputs are controlled by the frontpanel 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/MUX
S/MUX
4
2
(88.2 and 96 kHz), and ADAT
(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 lowresolution function is not needed, the Aux
Output can be set to mirror the highresolution Main Outputs.
AES/EBU XLR Output
This output uses a gold-pin Neutrik™ male
XLR connector. The output is balanced and
has an output impedance of 110 Ohms. This
output is DC-isolated, transformer-coupled,
current-limited, and diode-protected. It is
• 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
Optical Output
The Optical Output has four modes of
operation; AES/EBU, ADAT, ADAT S/MUX
and ADAT S/MUX
front panel is illuminated whenever any of the
ADAT Modes are active. S/MUX
4
. The ADAT LED on the
2
and S/MUX4
are automatically enabled if required to
support the selected sample rate. S/MUX
active at 88.2 or 96 kHz, S/MUX
4
is 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 uses a special highbandwidth version that supports AES/EBU
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/MUX
ADAT S/MUX
4
.
2
, or even
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
2
2
,
is
ADC1 Instruction Manual Page 8
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/MUX2 Optical 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
interfaces. The ADC1 ships with BNC-to-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-Ω 1 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-Ω 0.5 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.
ADAT S/MUX4 Optical 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
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 75Ω source impedances. Outputs are DCisolated, transformer-coupled, currentlimited, and diode-protected. Use 75 Ohm
coaxial cable when connecting these outputs
to other devices. The use of 50 Ω coax is not
recommended and may cause data
transmission errors.
Many customers are more familiar with
consumer-style RCA-equipped SPDIF digital
Main BNC Output
This digital data at this 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
Aux Output
This BNC digital output has two signals
available to it. 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 at
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
ADC1 Instruction Manual Page 9
Word Clock Reference Output
This output provides a Word Clock signal for
use with downstream components.
AC Power Entry Connector
The AC power input uses a standard IEC type
connector. Within the USA and Canada, the
ADC1 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).
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
The drawer includes a voltage selection switch
with two settings: 110 and 220. Both settings
use a 0.5 Amp fuse.
®
Type fuses.
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 will
operate normally over a range of 95 to 140
VAC. At 220, the ADC1 will operate normally
over a range of 190 to 285 VAC.
CAUTION: ALWAYS REPLACE THE FUSES
WITH THE CORRECT SIZE AND TYPE.
ADC1 Instruction Manual Page 10
Operation
Mode Display
Mode Switch Meter Display
Meter Switch
Left
First Stage Gain
Right
First Stage Gain
Mode Switch and Display
The ADC1 can be programmed to function in
a variety of conversion modes, including
sample rates, bit depths, and output formats,
using internal and/or external clock sources.
This programming is all done through the
Mode Switch. The Mode Display shows the
selected mode in a concise format.
The Mode Switch is a momentary toggle
switch. There are two ways of operating the
mode switch:
1. Press
2. Press and Hold
Pressing the Mode Switch momentarily and
then releasing it results in a particular change
to the ADC1 conversion mode, while pressing
and holding the switch results in a different
change.
Left Gain
Preset
Right Gain
Preset
Variable/Calibrated
Left
Gain Switch
Right
Variable/Calibrated
Gain Switch
Left Gain
Right Gain
• 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 to Factory Default settings.
Details about all of these actions follow.
Programming the Outputs
Pressing up repeatedly on the mode switch
cycles 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.
Locking to an External Clock
Source
To program the conversion mode
The ADC1 can sync to a variety of external
clock sources, including Word Clock, Super
• Press the Mode Switch up repeatedly to
cycle through the clock source and sample
rate options for the Main Outputs.
Clock, AES, and SPDIF. Once the ADC1
acquires sync, it will perform conversion at
the sample rate of the external clock.
• Press the Mode Switch down repeatedly to
to cycle through the sample rate and bit
depth options for the Aux Output.
ADC1 Instruction Manual Page 11
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