DAR 18 – Very High Performance Compact S/PDIF to I2S Converter

Excellent S/PDIF performance
- W-DAC v2 “golden units” show no measurable degradation compared to direct I2S input, meaning at least -117dB THD+N
Two galvanically isolated S/PDIF inputs onboard: RCA and Optical Toslink
- XLR AES/EBU can be wired out (connector not provided), input circuit included onboard
- Alternatively, XLR and BNC inputs can be added with DAR 18 XLR/BNC addon board
PCM/I2S input (bypass) for external modules, for example USB to I2S
Up to 192 kHz / 24-bit S/PDIF input
- It is not recommended to use Toslink over 96 kHz due to performance degradation and potential unreliability
- PCM input does not have a sample rate limitation as it bypasses S/PDIF circuitry
I2S output via U.FL connectors
Mute output to hard-mute the DAC (e.g. W-DAC v2) when S/PDIF input is unlocked or not PCM audio
AK4118A S/PDIF receiver
Compact size at 70 mm x 50 mm

Requires following supplies:

5V, max 30 mA
Supply via 2-pin Molex Micro-Fit (or solder your own wires)

Features

Common features for both HW and I2C variant:

Identical performance
- I2C variant needs configuration tweaks for the best performance, see DAR 18 Guide
Mute output
- HW-variant Mutes with S/PDIF unlock and non-PCM audio
- In I2C-variant mute conditions can be changed via registers
Support for XLR/BNC addon, see photo below.

DAR 18 and XLR/BNC addon.

HW-variant features

Easy to use, no microcontroller needed
Input selection with jumper link, or use your own input switch/logic
- See more in DAR 18 Guide

I2C-variant features

Needs an I2C host, for example microcontroller
Input selection and all other settings done via registers
S/PDIF output via U.FL, provides option to re-clock S/PDIF input to S/PDIF output
- The output is also functional in HW-variant but fixed to XLR input as it cannot be changed without registers
We do not provide a control firmware but there are example register writes in DAR 18 Guide to get started

Important information on order

All SMD components are soldered down and the board is fully tested, connectors and headers are soldered if selected.
Please ensure you have the skills to solder the remaining components and wires to connect the board in your system – and most of all understand what you are doing. Especially pay attention you have the correct power supplies and signal levels.
Be careful with supply polarity and level, incorrect connections may damage the board and/or your power supply.
If you need help prior to purchase, please contact us.

Order contents

List of what is included in the order.

HW-version:

Fully tested board with all SMD components populated
Toslink receiver
Mono RCA connector
PCB to back panel mounting terminal
2-pin Molex power connector
2×3 male pinheader + two jumper links for input selection
2×4 male pinheader for PCM input

By default, connectors and headers are delivered unsoldered.

I2C-version:

Fully tested board with all SMD components populated
Toslink receiver
Mono RCA connector
PCB to back panel mounting terminal
2-pin Molex power connector
2×4 male pinheader for PCM input

More information

For more information on using the board, see DAR 18 guide. There is also a post on how to connect DAR 18 and W-DAC.

For measurement results and version history, see the tab above.

Files

Schematics
Component placement (including board dimensions)

Control	HW, I2C

Measurements and Version History

See board version history at the bottom of the page.

Measurement results

This is a digital board so you would think measurements are not that important. And we did fall into that trap when designing the first iteration of this board using PCM9211. While everything else worked perfectly, audio measurements when connected to DAC weren't excellent. Therefore, the performance of DAR 18 was verified with a W-DAC v2 "golden unit" achieving under -117dB THD+N.

997 Hz FFT, 48 kHz sample rate, RCA input.

12 kHz tone in the same use case:

12 kHz, 48 kHz sample rate, RCA input.

RCA, BNC, and XLR input at 48 kHz, 96 kHz, and 192 kHz sample rates

The spectrum looks almost identical to above in all RCA, BNC, and XLR inputs and sample rates from 48 kHz to 192 kHz, except 44.1 kHz family of sample rates have slight differences. However, the level of any spikes is very low.

Toslink at sample rates over 48 kHz

However, Toslink input is different, especially when going up in sample rate. It is commonly known that Toslink does not have as good performance, it has higher jitter and so on. Not sure how much the source, cable, etc. matters but we always recommend using other cable options if possible.

Below examples are 10 kHz signal and show how Toslink deteriorates with increasing sample rate. First RCA for reference.

10 kHz FFT, 48 kHz sample rate, RCA input.

10 kHz FFT, 48 kHz sample rate, OPT input.

10 kHz FFT, 96 kHz sample rate, OPT input.

10 kHz FFT, 192 kHz sample rate, OPT input.

The level of these harmonics and interference is still low and likely inaudible. However, with this significant difference in measurements we should avoid them if possible. Moreover, at 192 kHz the optical connection may become unreliable as well; it is usually specified only up to 96 kHz.

I2C-variant performance tweak

To get the best performance out of the I2C-variant, see DAR 18 guide for a register setting tweak.

Board version history

Current version and the first released version is v1.2.

This is a new design. It is based on nihtila.com W-Input (and W-Input S) which had similar functionality and performance. Unfortunately the main IC AK4115 used was discontinued and it took a few iterations to design a board that functions and behaves similarly. Although this is a complete re-design, the biggest change to the user are the U.FL connectors used for PCM signals for better signal integrity.

DAR 18 – Very High Performance Compact S/PDIF to I2S Converter