USB interface board Mark 3

It is two years since we offered the third version of the USB interface board, but the parts shortage and mediocre interest resulted in postponing it.

Now, with parts (almost) normally available, and that kind of problem hopefully behind us, we would like to know if such an undertaking could be finally feasible.

Everything about this board design will remain as discussed before. So, it would be an asynchronous USB stage, outputting up to 4 channels up to 384 kHz Philips simultaneous data, or up to 8 channel 192 kHz I2S protocol, with all the features you know from recent Audial DACs, such as low jitter clocks, galvanic decoupling from the source (PC), etc, as discussed in the original topic at Audial blog from 2021.

So, now the USB board Mk3 release really depends only on the interest. This would be a limited series, so if you are (still) interested, please confirm that in this poll.

Apr 17, 2023, update:

The interest was sufficient, and you can place an order during the next ten days. Then we will start the manufacturing process. ETA: the end of May.

The main USB interface board Mk3 features are:

• Asynchronous USB operation
• Two low jitter XO clocks, no PLL
• Audio clocks and outputs are galvanically isolated from the source PC
• All local supplies (the board takes two transformer voltages)
• TDA1541A simultaneous data or I2S output (the future firmware update for I2S will add the DSD support)
• Up to 4 channels in simultaneous data, or up to 8 channels in I2S mode (stereo operation works straightforward)
• A-link (HDMI connector) and U.FL outputs
• Optional inverted data U.FL outputs support balanced DACs architecture

For further information, please see the third post below.

May 24, 2023, update:

The manufacturing process is underway. Ordering is not possible anymore.

  Instruction manual (Revision 0)

Windows USB driver download is available to the USB interface board Mk3 users, and requires login with the customer account.

17 thoughts on “USB interface board Mark 3”

  1. Thanks, Joao, it is taken into account.

    Generally, the interest looks fine, and this time we’ll proceed and release this board.

    I will come up with an actual proposal next week.

  2. As we announced two weeks ago, the USB interface board version 3 is coming. The interest was sufficient, and the design is finished, so now we can start the manufacturing process.

    I will however have to correct the initially proposed price of 200 EUR. I looked more closely at the current suppliers’ prices, and the cost of the parts used in this board actually almost doubled since the previous USB board Mk2 release (2017), which was sold for 150 EUR. So the initially announced price of 200 EUR must be corrected, and taking into account all the circumstances, it will be compromisingly set to 240 EUR, so I hope it will be still acceptable. And we will skip another poll in this regard (there were already too many polls), and proceed with the actual offer.

    So, the ordering form is above. You can place an order during the next 10 days, and then we will start the manufacturing process. Previous year we’ve been struggling with lead times and delays, but now the process is stable again, so once started, everything will be finished and shipping will begin in somewhat more than one month.

    At this time, there are two options. The one is TDA1541A simultaneous data output format – I must say that I am proud of how this format became popular since I brought it back to life with the Model S USB in 2011 – and the other is more universal I2S. We do plan to add DSD support to this I2S option – there is no exact time frame for now, but once it will be available as a firmware upgrade. Migration between these two options might be also generally possible at one point (the firmware is the only difference), but for now, it is recommended to order the option you actually need.

    We will discuss further some aspects of this design (questions are welcome), for now just to note that I accepted the suggestions of adding DIP14 clock footprints (optional U.FL clocks inputs are also here, as in the AYA 5), and I also increased the clocks’ supply current capabilities.

    So, other than aiming at the highest quality, it should be also quite a versatile “platform” at the same time.



  3. Board looks great, is it switchable between I2S and simultaneous mode?

    What frequency oscillators would we need to run our own clocks?

  4. The migration between two output formats will be possible by installing the migration file, from the Windows control panel. Reverting is also possible. This is how it was already done in the USB board Mk2.

    By default, this Mk3 board uses 22.5792 / 24.576 MHz clocks. You can replace them or use the external clocks with the same frequency, with no other changes.

    Using different frequencies would require firmware change, i.e. appropriate migration file as above. Necessary code changes are not huge, so I could try to address requests for some other frequencies, however, I am not sure if I will be able to test and verify them all too, and in that regard, they might be provided only as beta versions. But let’s see if there will be actual interest in this first.

  5. The S5 uses practically the same circuit and practically the same software.

    There are only some practical differences. For instance, the S5 has all linear regulators, while this USB interface board includes one buck regulator, so here the USB processor stage takes about 100 mA current, while in the S5 it takes 300 mA, which might be not DIY friendly. Please see:

    On the other hand, this board is more DIY oriented and has more features (so one can experiment with different clocks, it supports more channels, etc.).

  6. Could you give an update on when shipping might start as I am due to go
    on vacation shortly.

  7. There is a certain delay with this project, as I am still working on the prototype, but the series will be made relatively quickly once it is finished. I will post more details in the next few days.

    As for the shipping, I will notify everyone by email once the items are ready, and they will be dispatched only after I receive your confirmation.

  8. The series is currently in production, and here is what the protoboard looks like.

    The instruction manual will be online in the next few days and will include much more information on this board’s features and use than what is posted on this page by now.

    More pics to come, too.


  9. There are many details (hiding many devils) around, but this is the core: USB (XMOS) processor, digital isolators, reclocker flip-flops, and 22.5792 MHz clock below.



  10. Is it possible to configure the processor to output data in sign magnitude format? I’m aware this requires 2 TDA1541’s if you were to do it this way.

  11. Frankly, I have not thought about this by now, but it could be an interesting proposal and challenge.

    I would also guess that the data split into positive and negative parts would be more desirable than the real signed magnitude format, as it would still require some glue logic, to be actually used with TDA1541(A) (?).

    Also, regarding the current state of this project, at this moment practically all the boards with Philips simultaneous data output protocol are shipped, and next week the boards with I2S output will ship too.

  12. @ Joao, if you are watching this:

    I tried mailing you several times, but emails bounced back. Can you look at this and possibly fix it, or send me another email address?


  13. I have my board and it works great in simultaneous mode. Is the migration file available for moving from simultaneous to i2s?



  14. Hello Greg,

    Such a file is not available at the moment, but I will try to add it in the next few days.

    Speaking about the firmware change, in the previous weeks we added the migration file for the S5 DAC, which reduces its USB stage channel count from 4 to 2. While with Windows or with Mac you won’t need to do this, it turned out that some streamers can’t support more than 2-channel operation. The file we provided for S5 works also for this USB Mk3 board, and for the AYA 5, so in case anyone needs it, it will be soon in the download area for these two items too.


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