The γ2 compact high performance DAC
 

News

  • Sep 17, 2009: γ2 circuit boards and precision CNC-machined and engraved aluminum front and rear panel sets are now available.
  • Custom-built, ready-to-use γ2 DACs are available exclusively from MisterX (Marshall Wyant). Please contact him directly for details.

Overview

γ2 (gamma2) is an extension and upgrade to the γ1 DIY stereo digital-to-analog converter (DAC). It builds on γ1's modular idea, and pushes the concept far into the high-end. Designed for the compact, attractive and sturdy Box Enclosures B2-080 series extruded aluminum casing, γ2's tightly integrated packaging makes it ideal for home and portable use, such as computer audio, CD/DVD players and digital media players.

The γ1 and γ2 boards plug into each other to form a two-board "sandwich". γ1 provides USB and S/PDIF receiver functionality and feeds the I²S digital audio datastream to the γ2. γ1 also supplies the raw 5V DC power to the γ2, which is then regulated locally on the γ2 board.

The γ1 Full++ (F) configuration is most easily upgraded to γ2, as it uses the same enclosure. The γ1 Full (A), Lite (B), USB-to-I²S (D) and S/PDIF-only (E) configurations may also be upgraded to γ2 by joining the two γ1 board sections back together and changing the enclosure. The only incompatible γ1 configuration is USB-to-S/PDIF (C), because it does not produce an I²S output. See the γ1 website about its various configurations and options.

γ2 could also used standalone as an upgrade DAC for any device that already has an I²S bus (e.g., A CD player or digital media player). Simply connect the I²S bus to the γ2 board and hook up a 5V DC power supply. See the instructions section for details.

On the γ2 board, the digital audio stream is upsampled to 24-bit 96KHz by an asynchronous sample rate converter (ASRC) and then converted to analog with Wolfson's top-of-the-line ΔΣ oversampling DAC chip. An onboard ultra-low jitter oscillator provides the master clock for the ASRC and DAC chips. A high-performance analog output stage serves as a balanced-unbalanced converter, low-pass filter and line-drive buffer.

For the cost-conscious builder, the ASRC chip and onboard oscillator may be omitted and bypassed with jumpers. They can be populated later (and jumpers removed) as funds allow. Without the ASRC, no upsampling will occur.

A front panel switch selects between linear phase brickwall, minimum phase slow-rolloff, and linear phase slow-rolloff digital filter modes, allowing the user to choose the performance characteristics on-the-fly. Another front panel switch enables an anti-clipping mode.

A rail-to-rail, low-noise, precision CMOS dual opamp implements balanced-to-unbalanced conversion, 100KHz analog low pass filtration and output buffering. The low output impedance and high output current capability allows a long interconnect cable to be used without degradation. It could even directly drive low-impedance headphones (AD8656).

With an off-the-shelf enclosure solution and wire-free board mounting of all components, γ2 is relatively easy and inexpensive to build. The only surface-mount parts are the integrated circuits, all other parts are through-hole. See the Tech highlights and Parts list sections for details.

γ2 is designed by AMB and MisterX with community input. See the History section for details.

Basic feature set

  • Designed for the Box Enclosures B2-080 series extruded aluminum case, available in various colors.
  • 24-bit 192KHz top-of-the-line Wolfson WM8741, WM8742 or WM8740 DAC chips.
  • Texas Instruments/Burr-Brown SRC4192 or Analog Devices AD1896 ASRC.
  • Ultra-low jitter onboard CMOS oscillator for I²S master clock.
  • The upsampling process eliminates jitter, and optimizes the DAC chip's digital filter performance.
  • ASRC chip and oscillator may be omitted and bypassed with jumpers.
  • Plugs into γ1 for USB and S/PDIF (coax and optical) inputs and power. γ1's onboard WM8501 DAC is retained for two DACs sharing one enclosure.
  • Unbalanced-to-balanced converter, analog 100KHz low-pass filter, output buffer based on the Texas Instruments/Burr-Brown OPA2365 or Analog Devices AD8656 CMOS rail-to-rail dual opamp.
  • Analog line outputs (RCA jacks and 3.5mm stereo mini jack), with high output current and low output impedance.
  • Onboard power supply voltage regulation (separate LDO voltage regulators for the digital and analog sections), with extensive use of ferrite beads for noise rejection.
  • Through-hole resistors, capacitors, ferrites and other parts to reduce build difficulty. The only SMD parts are the various ICs and voltage regulators.
  • In default configuration, all parts (including jacks) are PCB-mounted. No internal wiring necessary.
  • The printed circuit board has three copper layers, two of which contain largely contiguous, low-impedance ground planes which are tightly-coupled with a matrix of vias. This minimizes current loops. Traces are carefully routed to assure maximum signal integrity and minimum jitter.
Some photos of γ2 with γ1 Full++ (click to enlarge)

What skills and tools are needed

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 (with a fine tip) and accessories, screw drivers, needle nose plier, diagonal cutter, a sharp tweezer (for positioning the SMD integrated circuits), etc. For the front and rear panels, you will also need to be able to accurately drill the holes needed for the input, output and DC power jacks, etc (unless you opted for the AMB CNC-machined and engraved panel set).

To obtain the blank printed circuit board and some related parts, visit the AMB audio shop. Other parts are available from online vendors. See the Parts list section.

Please be sure to read every section of this site carefully before attempting to build the γ1 DAC. If you don't thoroughly understand everything, please consider having someone more experienced to build the DAC for you.

The scope of the γ2 project

The γ2 project is primarily centered around the γ2 board. You will also need to build a γ1 to use with the γ2. You also need a Box Enclosures B2-080 series case. The γ2 and γ1 circuit board assembly is designed to slide into this case without additional mounting hardware.

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 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 the finished product

This is intended to be a project for DIYers, and AMB is not set up to manufacture completed units.

Professional builder

Inquire with the follow professional builder if they would build you a completed γ2 DAC, in case you cannot build one yourself.

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 forums for an answer before asking a question. Your question may have already been asked and answered.


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