The γ24 high performance DAC core
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News

  • November 24, 2015: γ24 is now released! The board and related parts are now available at AMB audio shop.

Overview

γ24 ("gamma 24") is a circuit that contains the essential core functonalities of a high performance digital-to-analog converter (DAC). It was developed to be the main module of the γ3 high resolution DAC, but it could also be designed into other DAC implementations. The γ24 as a standalone board does not do anything useful. Additional surrounding circuitry and a microcontroller must be added to make a working DAC.

Hardware

The board contains the following major components:
  • Texas Instruments SRC4392 - Two-channel, asynchronous sample rate converter with integrated digital audio interface receiver and transmitter.
  • Wolfson WM8741 (2 units) - 24 bit 192KHz DACs with advanced digital filtering, each wired in "differential mono" mode.
  • Crystek CCHD-957 - 24.576MHz HCMOS ultra low phase noise and ultra low jitter oscillator, for generating the master clock.
  • Texas Instruments CDCLVC1103 - Low jitter fan-out clock buffer, allowing the Crystek oscillator to drive three loads (SRC4392, two WM8741s) without incurring waveform degradation.
  • Analog Devices ADM7150 (3 units) - Ultra low noise, high PSRR LDO voltage regulators, providing super-clean power supply to the oscillator/clock buffer and the analog sections of the two WM8741s (independent regulator per stereo channenl).
  • Texas Instruments TPS793xx - High PSRR, low noise LDO voltage regulators, providing power to the SRC4392 and digital sections of the WM8741s.
  • Texas Instruments SN74ALVC244 and SN74LVC1G00 - Octal buffer/driver with 3-state outputs and single 2-input positive NAND gate, to implement a software settable switch for DSD audio functionality.
  • Microchip MCP100 or Maxim/Dallas DS1818 - Reset supervisor, for managing the reset timing of the SRC4392.
  • Passive support parts for all the above, including ferrite beads for each power branch, resistors and capacitors.

Features

As implemented on the γ24 DAC core:
  • Software control only: a microcontroller (MCU) running firmware must be used with the γ24, via the I²C bus
  • Supported on the γ3 high resolution DAC via its LCDuino-1 display I/O processor running special firmware
  • The SRC4392 provides features such as the following:
    • Digital input receiver (DIR):
      • Four fully-differential AES3, S/PDIF, IEC 60958 and EIAJ CP-1201 compliant digital inputs with PLL lock and low-jitter clock recovery
    • Digital output transmitter (DIT):
      • One CMOS-buffered single-ended digital output
      • One fully-differential AES3, S/PDIF, IEC 60958 and EIAJ CP-1201 compliant digital output with on-chip line driver
    • S/PDIF isolation transformers and optical receiver or transmitter modules are implemented off-board
    • Two synchronous digital audio serial ports
      • Input (slave) serial port (configurable as Philips I²S, left-justified, or right-justified data format), used as USB input on the γ3 DAC with the ζ1 Audio Widget USB-I²S module.
      • Output (master) serial port (configurable as Philips I²S, left-justified, or right-justified data format) connected to the two onboard WM8741 DACs
    • Asynchronous sample rate converter (ASRC) for up-sampling the input PCM data to a higher sample rate, as a way to eliminate of jitter and to optimize DAC filter operation
    • Flexible and powerful input/output signal routing between its DIR, DIT, serial ports and ASRC
    • Output volume attenuator
    • Digital mute
    • Up-sampling control
    • Up-sampling ratio status
    • De-emphasis control
    • Four programmable general purpose output ports (GPO)
  • The WM8741 DACs provides features such as the following:
    • High performance stereo DAC
    • Differential-mono mode for improved S/N ratio, dynamic range and stereo crosstalk
    • Stereo volume attenuator
    • Digital and analog mute
    • Five PCM and four DSD filter responses
    • Anti-clipping mode
    • Over-sampling rate control
    • Differential left and right channel analog voltage outputs
  • Additional direct interfaces to the SRC4392 and WM8741s for controlling or monitoring device status
  • Software switch between PCM and DSD input modes
  • All digital audio inputs and outputs support word lengths to 24 bits, and sample rates to 192KHz
  • Analog output stage and low pass filter are implemented off-board
  • Surface mount (SMD) integrated circuits for high density layout and optmized PCB signal traces
  • Passive devices are through-hole for ease of build
  • Pin header/receptacle "plug-in" to DAC main board.
  • Compact board footprint
  • Modular concept minimizes internal wiring, maximizes accessibility, serviceability, upgradability, and enhances system internal neatness/appearance
  • Open-source design with community participation
  • High quality FR-4 circuit board, with 4 copper layers, optimized ground planes, and silkscreen

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.

Why not offer a full kit

AMB is not prepared to stock all the needed parts and offer them as a full kit. It is AMB's contribution to the DIY community rather than as a for-profit product, AMB cannot assume the commercial support role that might be implicit with a full kit.

Where to get help

Be sure you read all the information at this site before building and using the γ24 DAC core.
  • If you're building an AMB project that uses the γ24 DAC core (i.e., the γ3 DAC), and you cannot find an answer to a question, or encounter a problem you cannot solve, the best place to get support is AMB DIY audio forum. Search the forums for an answer before asking a question. Your question may have already been asked and answered.
  • If the γ24 DAC core is being used on a non-AMB project, then please contact the designer or use an appropriate support channel for that project.
  • If you are a designer working to integrate the γ24 into your project, please read the Design integration section.


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