γ3 backplane board
Circuit boardThe γ3 backplane board supports the γ24 high performance DAC core, two α24 fully-differential line amplifiers (as the analog output stage), the LCDuino-1 display I/O processor (with a mated LCD display), the ζ1 Audio Widget USB-I²S module, and optionally the ε31 bridge board. With the exception of LCDuino-1, each of these modules plug directly into the backplane board without any use of wires. When using the ε31 bridge board, even the LCDuino-1 board becomes directly connected without wires.
Note: The ε31 can be used when you have the same enclosure, LCD screen location, backplane board mounting location and standoff height as AMB's reference γ3.
Additionally, the backplane provides a way to configure, at build time, each of the four (non-USB) digital inputs and one digital output to be AES/EBU (XLR), coaxial (BNC or RCA), optical (Toslink) or not used. This allows you to build the exact mix of digital input and output types you need. See the Digital input and output configuraton section for detalls.
The backplane board is made of high quality FR-4 glass epoxy, double-layer with plated-through holes as well as silkscreen and soldermask. There are ground planes on both sides of the board, with separate planes for the two galvanically isolated sections.
Note: The mounting hole adjacent to J12 (LVDD power input terminal) is directly connected to the board's ground plane. If you use metal standoffs and metal machine screws to mount the board to a metal chassis, this will automatically provide chassis ground. Thus you do not need to explicitly run a wire to the chassis.
The following diagram illustrates some important board dimensions. It can be used as a reference when you work on the chassis enclosure.
The illustration below provides essential information for cutting the USB connector and Toslink module(s) rear panel holes. Only these connectors are PCB-mount. The XLR, BNC and RCA jacks are all panel-mount. Please see the Parts list for details. Note that the Toslink module dimensions are specific to the Toshiba and Everlight units specified in the Parts list.
You must mount the backplane board such that its rear edge (where the inputs and outputs are) is against the enclosure's rear panel without any gap. This allows the USB connector and Toslink modules to protrude through their rear panel cutouts.
Note: If your rear panel is over 2mm thick, then an additional cavity should be machined around the USB and Toslink module cutouts, in order for the cable plug to seat fully. See the AMB reference γ3 rear panel design as an example.
Here are photos of the top and bottom sides of the blank γ3 backplane board (click to enlarge):
Photos of the γ3 backplane board populated with parts, and with the γ24, α24, and ζ1 modules mounted:
A PDF format file of the board silkscreen is also available (167KB).
Schematic diagramThe schematic diagram of the γ3 backplane board is shown below, spread into 5 pages (click to enlarge). See the Parts list section for details about parts selection.
Here is the γ3 backplane board schematic diagram in PDF format (188KB).
A 3D rendering of a partially-populated γ3 backplane board:
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