Purpose:
We can achieve a superior digital to analog signal conversion by removing USB power-noise from the Tone Board. Eliminating power-noise allows us to achieve an even higher signal-to-noise ratio, thus creating an extremely pristine listening experience.
Problem:
This power-noise is generated by a PC or SBC’s USB hub, and is unavoidable in ordinary situations involving connections between the Tone Board and a computer.
To get around this issue, users of our Tone Board community decided to supply their Tone 1 DAC with clean-power from a 5V linear power supply. To their dismay however, they discovered that when power is supplied via the Tone Board’s GPIO header instead of the USB-C port, the Tone Board automatically switches USB data-input to the header, ignoring the USB-C port.
The Tone 1 DAC’s circuit diagram shows us this USB-switch in greater detail:
The automatic USB input-switching frustrated our users who wished to use their 5V linear power supplies with the Tone 1 DAC, whilst still maintaining data-input from the USB-C port (PC / SBC).
Aim:
This blog article aims to equip you with three solutions for dealing with this problem, one of which will void your Tone Board’s warranty. Let’s begin.
Solution 1 (warranty valid):
Our first solution involves the destruction of two USB-cables, but not the Tone Board itself. Buy two USB-C to USB-A cables and slice them in-half along the cable length. Next re-solder them such that the data-pins and power-pins are separated and routed to each USB-A plug, respectively. The 3 ground-lines need to be connected together.
This cable is also known as a Y-Splitter:
Connect one USB-A plug to your 5V linear power supply, and the other USB-A plug to your PC or SBC, respectively. This is the simplest solution that does not involve potential damage to your Tone Board, and we recommend it for beginners as your warranty will remain intact.
Solution 2 (warranty valid):
The second solution would be to “go with the flow”. We know that when the Tone 1 DAC is powered via it’s GPIO, it will only accept USB data-input from the GPIO header. Conversely, when powered via the USB-C port, it will only accept data-input from the USB-C port.
Thus, the logical thing to do would be to re-route our USB data to the GPIO header. In the diagram below, I will show you how to connect your 5V linear power supply and your USB-C cable to your Tone 1's GPIO header:
Looking at the diagram above, connect your 5V linear power supply to either ground (GND), and either 5-volt pin (5V). The other two pins (USB DM, USB DP) are for the USB-data connection. If you’re using the “Generic Edition” Tone Board, soldering wires to the board directly will void your warranty.
From the picture above, the USB-power-cable has two wires, black (closer to the camera), and red (further from the camera). The USB-data-cable has two wires, USB DM is the white wire (on the left), whilst USB DP is the green wire (on the right). The colors may be different for your USB cable, however usually black is ground and white is USB DM. It is a reversible mistake to plugin the data-cable in reverse, it is an irreversible mistake to plug the power cable in reverse!
For solution 2, it is best to purchase the “VIM Edition” Tone Board with the female GPIO header already attached; this will allow you to use a breakaway GPIO header (sold separately), which is cheap and easily replaceable. This route will keep your warranty intact.
Solution 3 (void warranty):
For our more adventurous users, you may want to retain usage of the Tone 1 DAC’s USB-C port for data-input from a PC or SBC, whilst pushing linear 5V power into the GPIO header. In other words, we want to use the 20-pin GPIO for power, and the USB-C port for data.
To do this, we must disable the automatic USB-switching. This can be done within 3 steps, (1) removal of the diode D2 from the upper-side, (2) removal of resistors R28 and R29 on the underside, and (3) bridging the left-pad of R29 with the right-pad of C67. You may refer to the Tone 1 schematic for details, or just follow the pictures below:
Once you've performed the above 3 steps, you can then connect your Tone Board as shown in the picture below:
Note that 5V power is being fed from the black and red wires connected to the 20-pin female GPIO header (on the left), whilst data is being fed from USB-C (on the right). Because of steps 1 to 3, USB-C power has been cut-off from your Tone Board. Again remember that the black wire (ground), is closer to the front of your Tone Board (picture: left), and the red wire (5V) is closer to the back (picture: right) - do NOT reverse the power polarity!
Please remember that solution 3 will void your warranty.
Conclusion:
That's it for this blog post guys! We hope that these 3 methods will enable you to get super-clean 5V linear power into your Tone Board, or enable you to integrate it into other products / DIY projects using a combination of the GPIO header and USB-C port.
Happy Tinkering!
Khadas Team