T2P LFE Sub out?

I’m wondering if there us option to use the Coax out port on the Khadas Tone 2 Pro as LFE out for subwoofer?

I am currently using the T2P as. Preamp to my 2.0 amp for my bookshelf speakers. I have a active subwoofer without low level input/output. If i can send signal to it with the coax on the T2P that would be better than buying some splitters. Anyone try with success?


  • Coax out Port is the yellow balanced RCA,it can be used as a S/PDIF output by special firmware.If your subwoofer has RCA as S/PDIF input,you can have a try.And you must use our balanced RCA plug,the signal is defined as the following picture.

  • I am not sure that your subwoofer has 3.5mm Aux-in or 4.4mm Aux-in,if it has one of them,I suggest you can connect it to Tone2 Pro by 3.5mm to 3.5mm cable or 4.4mm to 4.4mm cable.

Thanks eric, that is good news to hear! I am already using the balance rca cables to my speakers.

Can you share where i can i get the special firmware to enable S/PDIF output?


  • So your subwoofer does not have 3.5mm Aux-in or 4.4mm Aux-in,you only need S/PDIF out,right?

  • And I use block diagram to decrible your demand,can you help me to make sure if it is right?

  • And I will to ask our design team how about the firmware with the S/PDIF out.

Hi Eric, that is correct. No 3.5/4.4mm in on the sub. Only RCA Left/Right in.

I guess i can but 3.5mm to RCA but i would also like to keep those available for headphones if i ever need as well.

The diagram you provide is correct in what i am trying to achieve if it is possible

OK,our hardware can support your demand,but the newly firmware does not support it.I will ask our software engineer for help to follow up it.

Sounds good. Thank you for passing my request on!

I want to ask you which version of your tone2 pro is.
You can look for it from the following window.

Hi Eric,

this is what my T2P says.



  • You should make a BAL RCA to unBAL RCA cable by yourself.
  1. Buy BAL RCA plug from this website.Notice,you should choose the plug of BAL RCA,not the jack.

  2. Buy an unBAL RCA,we have not recommended about it.

  3. Buy a single core wire with ground shield.

  4. Connect the 2nd pin of BAL RCA to the 1st pin of unBAL by the center wire,and connect the 3rd pin of BAL RCA to the 2nd pin of unBAL RCA by the ground shield.

  • Then you should upgrade the XMOS firmware which it has S/PDIF output by Khadas Tone DFU tools.
    But the firmware is for test,not official version,it may have some problems,the S/PDIF out is OK,you can have a try.

Thanks Eric and team! I will give it a try.

Can I just use a normal mono RCA cable?

No,mono RCA cable is unuseful,because the mono RCA cannot connect S/PDIF Out to your subwoofer. :grin: But you can modify it to an useful cable,you should cut down one side RCA plug and change it to BAL RCA.

Thanks Eric,

i understand, i’ll get an order for one. I tried installing the firmware, however it seemed to have bricked the device. I am getting solid light blue light and no detection. I tried other computer but it still is not be detected.

Can you help?

Oh,that is because the MCU firmware of your tone2 Pro is too old,you should update the MCU firmware by ST-Link.The method you can learn from this video.The MCU firmware you can download from here as the following picture shown.

Hi @Eric68

I tried that as I had the RCA balanced plugs since my order of the Tone2 Pro.
I went from 1.41 firmware to this one, and it worked, I had SPDIF out without problem, but I got a bug once I enter the menu.
I wanted to change to change something, and once I got on the filter menu, I saw that it not the same I had set (I had the second one before, and it was on the third or fourth, I don’t remind exactly).
I tried to change the filter and saw that some were missing, I had something like 5 choices instead of 7, and once I made a double-click to go out of the menu, the Tone2 Pro freezed.

It’s now impossible to do anything, it powers on, but the volume led are on Full and I can’t change it, and it’s not recognize by the computer anymore
It seems like the firmware has a bug, but I can’t update again.

What can I do please ? (I also have the ST-Link if needed)

I’ve been busy so haven’t been able to troubleshoot but i ran into same issue. I tried to use ST-Link to update but when i write it says OTP is locked.

Hopefully eric can help :smiling_face_with_tear:

Hi Grooved & nguykenn,
please send me the Tone2 Pro SN, will make a mcu firmware for you to do a fullly upgrade.

Thanks @kenny , I just sent it by answering to your other message first

So much thanks for your quick fix, files loaded with ST Link and everything seems OK now !

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Thanks @kenny ! I am up and running again :slight_smile: