Khadas Tone Board 2 - linear power supply

@Pedro_TL yes you can :slightly_smiling_face:
mobile phone charger wouldn’t be the most optimal (due to noise)
something like a powerbank would be a bit more optimal
and a linear power supply is best.

Thank you very much! If using a power bank, there is some special specs that you recommend?

well I just studied the internal spec of the Tone2pro, and it seems that it consumes atleast 570mA nominal (just the USB decoder, not considering the internal audio/heaphone jack amp)
hence it shows the reason why your phone drained quickly…

I suggest something like 10,000 mAh to provide enough power for atleast 16+ hours of continuous listening, its purely your convenience, just choose something that can output atleast 5w of power steadily.

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If it can help, I’ve measured the USB draw between power supply and the I2S port and while playing and headphones, it’s more or less 450 mA (tested with 24 and also 60 Ohm headphones.
It was done with Tone2 Pro set on High gain, and full MQA decoding+rendering at 352.8kHz (3 unfolds), so the almost the biggest load you can put on the XU216 chip.

Found something strange, if I connect the Tone2 Pro to the computer via a powered USB 3.0 hub set to power the USB port, it’s priorities and the Tone2 Pro has no current draw on the power supply via I2S port.
If let it on the USB hub but stop powering this port (it has a switch for each port), then the Tone2 Pro get it’s power from the power supply again.


Thanks a lot it worked just fine.

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To Khadas Team : I’ve found a strange thing regarding the power drawn from the USB port of the Tone2 Pro when using a power supply on the I2S port at the same time.

It’s like my Tone2 Pro looses its power priority in some cases. I’ve measured the drawn current between the power supply and the the Tone2 Pro, and this is what I get :
0.35A from power supply (plugged in the I2S port)

  • USB port plugged on USB 2.0 port Windows : 0.30A (0.05A drawn from the computer port)
  • USB port plugged on USB 3.0 port Windows : 0.27A (0.08A drawn from the computer port)
  • USB port plugged on Powered USB 3.0 Hub with own Power ON : 0.00A (all current comes from USB Hub)
  • USB port plugged on Powered USB 3.0 Hub with own Power OFF : 0.35A (perfect)
  • USB port plugged on micro-USB 2.0 port Android : 0.15A (0.2A drawn from the smartphone)

Pluging the I2S port to a power supply or a battery gives the same results.

The same here: when I plug the I2S to an external 5V power supply, the power is taken from it and not from the USB input anymore.
However, if I connect both I2S and USB to my PC ports then the power is always taken from USB input, the I2S input is therefore unused at all… (even if the LED stays white).
Not a normal behavior I believe, it needs to be fixed.

Thanks for you feedback! USB port still have 50mA and 80mA output is normal,when you use I2S port for KTB2 power.Because I2S port Power PIN have two fuctions, INPUT and OUTPUT. The define of the I2S port is shown below.

So when you use the standard USB type C plug,the INPUT pin and OUTPUT are connected together.So that will cause the extra current from USB Port.
I will take a test as you did,and give you an explain for your problem as soon as possible.


@Eric68 Great if you can check it

@Mikymax , I may have not explained it correctly, but I never plugged both cables to the computer, all my measurements was done with the I2S port linked to a USB power supply or USB portable battery

Hi,I advise you can try to use USB type C cable which PINs A4/B4 and PINs A9/B9 are separated.
I have used this cable for your test.The following pictures are shown.

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Hi @Eric68, i’ve 0 eletronic bakcground, i just want to make my KT2 Pro “portable” using my phone. So, with this in mind i’m unable to choose the correct cable with USB type C cable which PINs A4/B4 and PINs A9/B9 are separated… how can i overcome this? what type of cable should i be looking for?


Hi,@Pedro_TL,I think you do not care the electric leakage,that will not affect the DAC fuction and performance,you can also the standard USB type cable. If you insist to supply power completely from
I2S Port, we will produce a adaptive cable for our I2S port.

Thanks for your answer. I’m not sure but I think it’s what I had at the beginning, as soon as I plugged a cable between “I2S” port and a power supply, I had 0A on the “USB” port, but not anymore. But I’m not sure, I may have this since the first use.
Or is it possible that I changed something in the settings creating it ?

The only possibility for me to get 0A is to connect the cable from the “USB” port to a USB Hub able to cut the power on each port, and not directly into the computer (and I have 0.36A from the power supply on idle, and 0.45A on playing)
If I turn the power on for this Hub port, it send 0.14A on idle to the Tone2 Pro and 0.16A on playing (so 0.22A from the power supply connect to the “I2S” port on idle, and 0.29A on playing).

If I connect the “USB” port of the Tone2 Pro directly to a USB port of my computer, the power supply send 0.30A to the Tone2 Pro on the “I2S” port on idle (so 0.06A from the computer), and 0.35A while playing (so 0.10A from the computer)

So the only solution to plug it to any computer and get 0A coming from the computer (with a power supply on I2S port) would be :

  • using the USB Hub and cut power on the port used
  • connecting it to a computer with a special USB cable

More important, if I use an Android smartphone, there’s only 0.17A on idle and 0.20A while playing coming from the power supply, so the smartphone is still sending 0.19A (0.36 - 0.17) on idle and 0.25A (0.45 - 0.20) while playing, instead of 0A

Hi,thanks for your meticulous tests.Our “USB” Port is standard usb port,but “I2S” Port is defined by ourselves,as to support both our external bluetooth module and linear power supply, and external bluetooth module needs Tone2 Pro to supply power, Linear power can supply power for Tone2 Pro, then the usb power pins A4/B4/A9/B9 have two functions,input and output, so we separate the A4/B4 and A9/B9, A4/B4 are for outputs,A9/B9 are for inputs.However, the standard usb type C cable connects these four PINs, so if you use this cable to supply power for “I2S” port, the power management of our Tone2 Pro will work unnormally. I hope you can understand my explanation. :grin:

Hi Eric,

yes, I understand, thank you. Will try to find a different cable.

Hello! I understand a little about electronics, can you show in detail which PINs you’ve connected the wires to?
In the KTB was easier :slight_smile:

I can’t understand
“which PINs A4/B4 and PINs A9/B9 are separated”

Thank you!

Hi,normal USB C plug has 16PINs,PINs A4/B4 and PINs A9/B9 are conected together. Such as the picture showing blew.

And our I2S port has 24PINs,we defined the A4/B4 as the output PINs,and A9/B9 as the input PINs.


can anyone recommend a cable where PINs A4/B4 and PINs A9/B9 are separated?

This should be very helpfull

So this is a custom solution. I’m enjoying my T2P with my smartphone, but it drains the battery really quick. @Eric68 @Gouwa do you plan to offer the cables for connecting external power supplies? It would be a great addition to the device!

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