The γ3 high resolution DAC
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News

  • November 24, 2015: γ3 is now released! The board and related parts are now available at AMB audio shop.

Overview

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 ε31 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
  • α24 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 firmware
  • 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 σ22
  • 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
  • Robust ground planes
  • High quality FR-4 backplane PCB with silkscreen
  • Open-source design with community participation

See the γ3 development forum thread for discussions, a log of the design process, and the thinking behind all the details.

The γ3 DAC system

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.
γ3 backplane board
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.
γ24 high performance DAC core
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.
α24 fully-differential line amplifier
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.
ζ1 Audio Widget asynchronous USB-I²S module
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 display I/O processor
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 Arduino-compatible platform, it runs special open-source firmware which is field-upgradable with a special USB cable.
ε31 bridge board (optional)
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 β24 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 further detail. 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 and oscilloscope. 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.


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