Wee DAC baseboards

Wee DAC is a flexible modular system and there are several different baseboards for different configurations depending on the system requirements:

DAC with S/PDIF inputs or only I2S-input
Two channel DAC or four channel (2x stereo) I2S DAC
Number of S/PDIF inputs
Vertical or horizontal stack of boards

Configuration options

There are four different boards and larger dual boards can be configured in two different ways.

With flexibility comes also complexity so the number of options may be overwhelming. Following photos show examples of different configurations. And always feel free to ask if you’re unsure what board you need.

Let’s first have a look at the narrower boards, called vertical stack here.

Vertical stack

These boards are

W-BB Breakout
W-BB PSU

Breakout board just breaks out power supply connections to screw terminals and provides a bit of extra capacitance and very simple protection. Thus, all four supplies (5 VD, 7.2 VA, +15 V, -15 V) must be provided externally.

W-BB PSU has voltage regulators for all four supplies on board and only requires dual input of ±18 V or similar to operate.

These boards can be used for

W-DAC (and optional W-Output XLR addon)
W-Input (and optional W-Input+ addon)
W-Input and W-DAC (and optional W-Output XLR addon)

See examples below.

W-BB Breakout and W-DAC with W-Output XLR

W-BB Breakout and W-Input with W-Input+ Combo XLR

W-BB Breakout, W-Input, and W-DAC with W-Output XLR

Downside of the last option is height. For lower stack, larger baseboards can be chosen for horizontal stack.

Horizontal stack

Similarly, there is a breakout board and a PSU board available:

W-BB Dual Breakout
W-BB Dual PSU

In these boards W-Input and W-DAC can be mounted next to one another, making the stack lower. Moreover, it is possible to use both W-Input+ addon and W-Output XLR at the same time.

W-BB Dual Breakout, W-Input, and W-DAC

W-BB Dual Breakout, W-Input with W-Input+ Combo XLR, and W-DAC with W-Output XLR

4-channel I2S DAC

Things get a bit more complicated as I wanted to make support for two W-DACs for 4-channel setup. This is with I2S input only though, no W-Input can be used in this configuration.

W-BB Dual Breakout and 2x W-DAC with W-Output XLRs

No baseboard at all?

Baseboard is not needed to use W-Input or W-DAC, you can always just wire supplies to the edge connectors if you want to save space or money. This may be useful if enclosure height is limited as baseboard always adds height. W-Input and W-DAC boards have screw holes so baseboards are not needed for mechanical reasons either.

Just make sure wiring is correct as there is no protection on overvoltage or reverse voltage on W-Input and W-DAC!

Design

Here are schematics and brief design description of all baseboards. Basically the idea is as follows:

Breakout boards only route supplies to screw terminals and provide a bit of capacitance, LEDs and very basic protection
PSU boards provide voltage regulators for all supplies

Voltage protection

Supply protection here is very basic, just TVS on supply lines. TVS works like a zener diode, limiting the voltage across it. However, as other diodes, it cannot offer very steep transition from working voltage to breakdown. For example, SMA4F5A TVS used here has specified working voltage is 5 V but it breaks down at around 6.7 V. That may be enough to damage 5 V circuits. Therefore, take care to avoid overvoltage. But if it happens, TVS can limit it to at least a more reasonable value.

TVS also works as reverse voltage protection for a circuit after it – but not to a circuit supplying it. In reverse voltage condition, TVS shorts the supply which may cause damage to the external power supply.

TVSs used here are small so they cannot withstand heavy loading condition for a long period of time. It is always highly recommended to use fuses somewhere in the power supply.

W-BB Breakout

Very simple breakout board to route supplies to screw terminals (or optionally to pinheaders).

W-BB Breakout

W-BB PSU

Power supplies are basic circuits using robust LM317/LM337 regulators. These are in D2PAK-3 case soldered directly on board.

Maximum input voltage to ±15 V circuit here is ±30 V and to VD and VA circuits +15 V. Please note that using high voltages may overheat regulators and board if load is high.

Default configuration is to supply VA and VD regulators from +15 V VCC supply. In this case the whole board just needs a dual supply of around ±20-25 V However, these can be taken elsewhere, for example from separate transformer, by removing jumper links and using those pinheaders as input.

W-BB PSU

W-BB Dual Breakout

Dual slot version of breakout board. Two population options make it slightly more complicated.

There are two population options where A-version is for 4-channel dual-DAC setup, and B-channel is for 2-channel W-Input and W-DAC setup.

In stereo B-version I2S signals are routed directly from W-Input slot to W-DAC slot.
In 4-channel A-version external I2S is brought to J8 where all clocks are split and buffered to each slot, and data signals taken separately. In this case W-Input cannot be used; it’s just 4-channel I2S to two stereo DACs.

W-BB Dual Breakout B-version (2-channel)

W-BB Dual Breakout A-version (4-channel)

W-BB Dual PSU

Power supply version of dual board baseboard.

As in Dual Breakout board, there are two population options where A-version is for 4-channel dual-DAC setup, and B-channel is for W-Input and W-DAC setup.

In stereo B-version I2S signals are routed directly from W-Input slot to W-DAC slot.
In 4-channel A-version external I2S is brought to J8 where all clocks are split and buffered to each slot, and data signals taken separately. In this case W-Input cannot be used; it’s just 4-channel I2S to two stereo DACs.

Otherwise power supply circuits are very basic using robust LM317/LM337 regulators. These are in D2PAK-3 case soldered directly on board.

Maximum input voltage to ±15 V circuit here is ±30 V and to VD and VA circuits +15 V. Please note that using high voltages may overheat regulators and board if load is high.

Default configuration is to supply VA and VD regulators from +15 V VCC supply. In this case the whole board just needs a dual supply around ±20-25 V However, these can be taken elsewhere, for example from separate transformer, by removing jumper links and using those pinheaders as input.

W-BB Dual PSU (2-channel B-version)