[updated September 15, 2009]News
- The γ2 website
is now live.Introduction
γ2 (gamma2) is an extension to the γ1 full++ configuration that MisterX and I have been working on for the past few months. It builds on the "modular" idea of the γ1, and pushes the concept further into the high-end. Basically, if you take the γ1 USB and DAC boards in its original, un-broken form and then plug in the γ2 board, the whole assembly now fits into the nice and compact Box Enclosures B2-080
γ2 leverages γ1's USB and S/PDIF receiver sections and taps the I²S datastream. Then, an (optional, jumper bypass-able) SRC4192
ASRC chip upsamples to 96KHz. The resultant data stream is then sent to the top-of-the-line Wolfson WM8741
DAC chip (WM8740
The SRC4192 and WM874x DAC chips are clocked by an onboard ultra-low jitter 24.576MHz CMOS oscillator when the ASRC is installed.
If the WM8741 or WM8742 is used, γ2 allows you to select between three different digital filter responses (minimum phase, linear phase slow rolloff or linear phase brickwall), as well as enable/disable the anti-clipping mode via front panel switches. WM8740 does not have these features.
The differential analog outputs from the DAC chip is then buffered by a rail-to-rail opamp (OPA2365
) which also serves as an analog low-pass filter (fc ~= 100KHz) and balanced-to-unbalanced converter. The output is then capacitively-coupled to the output jacks (both RCA and 3.5mm jacks are provided, and could be used concurrently to drive two amps).
Separate onboard LDO voltage regulators are used for the analog and digital sections of the circuit, with extensive use of ferrite beads.
The γ1 board's WM8501 DAC section can be populated and used in conjunction with the γ2 board. The result is a compact case with two different DACs in it. You can use them both concurrently. If either of these are equipped with 470uF output capacitors (Nichicon FW or KW) then it could be used to directly drive headphones down to 32Ω impedance (You'll need to use a software volume control). On the γ2, the AD8656 is recommended for headphone drive due to its high output current capability.
The γ1 board's USB-to-S/PDIF converter section can also be fully populated, Providing front panel coax and optical S/PDIF outputs of the data stream from USB. Note that this is only possible if the γ1 is set up as a full config. Otherwise, γ2 could be plugged into a either a full or lite config γ1 board.Schematic diagram
The following is the current schematic diagram:Board layout
And here is the current PCB layout. The board has 3 copper layers, soldermask on both sides, and silkscreen on the top side. The top and bottom layers each also have a ground plane. The representative colors are: top=red, bottom=blue, inner=grey. Where the top and bottom layers overlap the color shows as lavender.3D rendering
An updated 3D rendering of the board (partially populated):Parts list
Please see the γ2 website
for the most up-to-date BOM.