November 24, 2015: γ24 is now released! The board and related
parts are now available at
AMB audio shop.
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
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.
The board contains the following major components:
Texas Instruments SRC4392 -
Two-channel, asynchronous sample rate
converter with integrated digital audio interface receiver and
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
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.
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
high resolution DAC via its
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
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
Up-sampling ratio status
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
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
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
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,
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