November 24, 2015: γ3 is now released! The board and related
parts are now available at
AMB audio shop.
γ3 ("gamma 3") is a premium, full-featured
digital-to-analog converter (DAC) designed for superlative
sound quality, first class test bench performance, convenience
of use and elegant appearance.
AMB's reference γ3 DAC, equipped with the optional
bridge board (click to enlarge):
Features and Technical highlights
Twin-chassis high-end desktop DAC
USB, S/PDIF coax, Toslink, AES/EBU (5 inputs and 2 outputs)
USB input with asynchronous transfer mode
USB Audio Class 1 and 2 compliant (full speed or high speed, user-selectable)
Uses the ζ1 Audio Widget asynchronous USB-I²S module
for USB interface
All inputs support up to 24 bit, 192KHz sample rate
DSD over PCM (DoP) planned for USB, but not implemented at first release
High-end dual Wolfson WM8741 DACs in differential-mono configuration
Texas Instruments SRC4392 featuring digital audio input receiver (DIR),
digital audio output transmitter (DIT), two I²S ports and enhanced
asynchronous sample rate converter (ASRC)
Ultra low jitter, low phase noise Crystek CCHD-957 main oscillator
Ultra low jitter, low phase noise dual oscillators for USB
fully-differential, high-CMRR analog output stage & low-pass filter
Modular construction: γ3 backplane board supporting the ζ1
Audio Widget USB-I²S module, γ24 DAC core, two α24 analog output
stage modules and LCDuino-1 display I/O processor.
Galvanic isolation on all inputs and outputs: High-end Scientific Conversion SC947-02LF
S/PDIF transformers for coax and AES/EBU, high speed digital isolators
between the γ24 module and the USB and LCDuino-1 I/O processor sections
Build-time configuration of digital input and output types:
AES/EBU (XLR), coaxial (RCA or BNC), optical (Toslink) or "not used".
Software control using
LCDuino-1 display I/O processor, running special γ3
LCD information display with adjustable backlight, auto-dim mode, and selectable
standard or "big-font" modes
Handheld IR remote control for all functions. γ3 can adapt itself to
a variety of remote controls via its "Learn IR" feature
256-step digital volume attenuator with run-time configurable 0.5dB or 1.0dB steps on front panel and remote control
User-configurable minimum and maximum volume control range
The front panel volume potentiometer is a "valuation device" to the LCDuino-1
display I/O processor - the audio signal does not go through the potentiometer
When the volume is changed with the remote control, the system activates the
motorized potentiometer to keep its position synchronized
Slow (single step) or fast (user-configurable step size) volume control via
the remote control
Mute/un-mute button on front panel and remote control
Five selectable digital filters, including linear phase, minimum phase and apodizing types with soft-knee or brickwall characteristics
Selectable anti-clipping mode
Up-sampling frequency selection: 192KHz or 96KHz
Digital output routing control: up-sample or loop-out
Absolute phase control: normal or invert
Automatic de-emphasis mode, user-selectable
The displayed names of each input can be user-customized
The power-up and power-off display splash screen text are also user-customizable
DC coupled throughout: no coupling capacitors in the signal path
Three independent high performance power supplies: Two
σ11s and one
Separate ultra low noise LDO local voltage regulators for digital
and analog circuitry
Each power branch is additionally filtered by ferrite beads
Pin header/receptacle "plug-in" for various modules
γ3 is a modular design. The system is an integration of the
γ3 backplane board and the AMB projects listed below.
A brief summary of each is provided, please visit each of the project
sites for details.
The backplane board serves as the backbone of the entire system,
providing pin header connector interfaces to the other modules
listed below. It also contains the digital input receiver and
output transmitter front-end. Designed to to be configurable
at build time, each of the four (non-USB) digital inputs and
one of the digital outputs can be set up to be
coaxial (BNC or RCA), AES/EBU (XLR) or optical (Toslink).
This allows you to build the exact mix of input and output types you need.
The backplane features the two galvanically isolated areas with separate
ground planes and power supplies, and bridged only by high-speed digital
isolators ICs. This design avoids ground loops, eliminates current
loops, shields against noise/interference, and provides rock-solid
ground reference for all circuitry.
Featuring the Texas Instruments SRC4392, two Wolfson WM8741 DACs
configured in differential-mono mode, an ultra low jitter,
low phase noise oscillator and ultra low noise LDO local voltage
regulators. This module is the core of the γ3 system.
A pair of α24s are used as the analog output stage and
low pass filter. It offers ultra low noise and distortion,
high common mode rejection ratio (CMRR), high input impedance,
low output impedance characteristics, and provides balanced
and unbalanced outputs.
This module provides USB audio functionality. It supports both
USB audio class 1 (UAC1) and USB audio class 2 (UAC2) operating
modes, both with low-jitter asynchronous transfer mode.
This module comes as a pre-assembled and tested unit.
LCDuino-1 integrates a front-panel LCD display to show
input selection, volume attenuation settings
with a bargraph and a numeric dB readout, input sample rate
display, and other operating information including
many configurable display options and modes. LCDuino-1 also
serves as the main processor that controls the operation of
the SRC4392, WM8741 and other circuitry on the γ3 and
γ24 boards. A wide array of off-the-shelf infrared
remote controls are supported for all γ3 DAC functions.
Based on an
platform, it runs special open-source firmware which is field-upgradable
with a special USB cable.
The ε31 bridge board is used in lieu of wires and
Molex connectors to connect LCDuino-1 to the γ3 backplane board,
making for a cleaner and neater internal appearance.
It can be used when you have the same enclosure,
LCD screen location, backplane board mounting location and
standoff height as AMB's reference γ3.
The backplane board and plug-in modules concept minimizes
internal wiring, maximizes accessibility, serviceability,
upgradability, and greatly enhances neatness and appearance.
The result is an elegant desktop stereo DAC with an uncluttered
front panel, tidy and modular interior, ample digital and analog
input and output connectivity, convenience of IR remote control,
excellent test-bench performance, and great sound.
γ3 can be used as a DAC/pre-amplifier in a system with all-digital
sources, driving a power amplifier directly. Using its balanced analog
outputs, γ3 is particularly suited to to drive the
power amplifier, as the signal will remain fully-differential
through the entire audio chain to the speakers.
γ3 can also be used as a traditional digital source, connected
to the line input of an analog pre-amplifier or a headphone amplifier.
In this application, the γ3's volume control should be set to
maximum. Use the volume control on the pre-amplifier or
headphone amplifier instead.
The scope of the γ3 project
The γ3 project is primarily centered around the γ3
backplane board and each of the plug-in modules listed above.
To build a working DAC, you will also need three
power supplies of appropriate specifications,
as well as select and/or build enclosures to house everything.
While it's possible to place the power supplies in a single large
enclosure shared with the γ3 backplane board and its plug-in modules,
a twin-chassis setup for the DAC and the power supplies is recommended
for optimum enclosure internal layouts and maximum isolation from
magnetic field interference. The information in this website assumes
that you have separate enclosures.
WARNING: Building the power supply
for the γ3 would require that you work with AC line voltage,
which is a lethal shock hazard. If you don't know what you are doing,
please ask someone who is experienced to help you.
(See the disclaimer).
What skills and tools are needed
This is a fairly advanced project requiring you to solder small
surface-mount devices (SMD) with very close pin pitch. Please
see the Instructions section for
You should know how to read a schematic diagram and correlate it
to the circuit board layout, identify electronic parts and their pin-outs,
have decent soldering skill, and be proficient with a multimeter
You need at least a basic set of tools for electronics work, such as a
good soldering iron and accessories, screw drivers, needle nose plier,
diagonal wire cutter, sharp tweezers, etc. For the chassis case, you
will also need to be familiar with using the tools that are necessary,
such as an electric drill, bits, center punch and others.
Why not offer a full kit
AMB is not prepared to stock all the needed parts and offer them as a
full kit. This DAC also provides a number of customizable
options that makes it unwieldy for such a kit. Lastly, this DAC is
AMB's contribution to the DIY community rather than a for-profit
product, AMB cannot assume the commercial support role that
might be implicit with a full kit.
Why not offer completed DACs
This is intended to be a project for DIYers, and
AMB is not set up to manufacture completed DACs.
Where to get help
Be sure you read all the information at this site. If you cannot find
an answer to a question, or encounter a problem you cannot solve,
the best place to get support is the
AMB DIY audio forum.
Search the forum for an answer before asking a question. Your
question may have already been asked and answered.