Dac attack

DAC Attack!

A small S/PDIF to line-level audio adapter design. The intended use case is with some versions of ZuluSCSI, though the design should work with any S/PDIF compatible output source generating a TTL-compatible signal.

Used with a compatible board, and the appropriate firmware, this allows sending audio to a retro computer. See later sections for usage information.

As of this writing, only some ZuluSCSI variants offer audio output. This list may change in the future. Refer to the ZuluSCSI project page for details about audio output support.

License and Disclaimer

This project is made available under the CERN Open Hardware Licence strongly-reciprocal variant version 2, available at LICENSE.

This source is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE. Please see the CERN-OHL-S v2 for applicable conditions.

ZuluSCSI™ is a registered trademark of Rabbit Hole Computing™, used with permission.

Assembly

The author has had JLCPCB assemble these boards as prototypes. The files dac-attack-bom.csv and dac-attack-top-pos.csv files were used successfully, though caution should still be excercised: other open-source hardware projects have reported some inconsistency in individual orders using files like these.

Adding through-hole components to assembled boards is relatively straightforward. The choice of what connectors to solder is up to the user:

• 'analog' provides standard line-level output for sending to a sound card.
• 'digital' provides TTL-level S/PDIF from the CS8416 chip, which should theoretically be suitable for sending to a sound card with a digital-in connector, those this use case is NOT TESTED florian3 on Vogons reports this is working fine, thanks for testing!
• 'ext button' provides a place to attach a button for the B_READ line.
• 'user' is connected to the U pin of the CS8416. This feature is not tested and this pad can be left vacant.
• The four pads for G, 3V, D_IN, and B_READ are available if you do not want to use the modular connector. See the later section for hookup information.

Part numbers for through-hole parts are in bom-full.csv.

Installation

The screw holes on the board are spaced to match a 2.5" hard drive, which is the same pattern on most ZuluSCSI boards. Use standoffs to prevent shorting connections. An example mount is shown below. The full BOM has some options, which you can probably also find at your local hardware store or a convenient online retailer.

Most parent boards use either a 0.1" holes or a matching 4-pin modular connector. Instructions vary between these two board types.

Important note: DAC Attack uses a 4-pin connector that matches common hobbyist I2C formats; however, the board is not compatible with I2C.

0.1 Connectors

Carefully solder a socket on the parent board. Most will need either a 2x2 or 1x4 connector for this. Example parts to order are in the BOM. You only need to solder to points labeled GND, 3V0, SCL, and SDA on the bottom of the board. Again, use great care during this process to avoid damaging anything.

Once soldered, connect a suitable cable from the socket to the DAC's modular connector. Potential options are listed in the BOM. If the DAC's modular connector is not populated, or you would prefer not to use it, the separate labeled points on the DAC may be used instead.

If using the modular cable pin breakout version, colors should correspond as follows:

• Black: GND
• Red: VCC (3V)
• Blue: B_READ ('SDA' label)
• Yellow: D_IN ('SCL' label)

Modular Connector

If your parent board is equipped with a 1x4 modular connector, you're all set: just connect the board to the DAC.

If the parent board does not have a modular connector, the most straightforward option is to add the modular connector, likely part BM04B-SRSS-TB(LF)(SN).

Cabling

Once you have installed the board and applied correct firmware (if needed), all that remains is connecting the 'analog' port to a suitable target. Most period- correct sound cards will use either a 3-pin or 4-pin cable for connecting a CD drive. This pinout is also compatible with the one used on retro Mac computers.

It is recommended to test your configuration to determine if stereo audio is being handled appropriately. If it is not, rotate the cable in the socket.