Some users are reporting that when the Tone Board is connected via USB-C cable to a Raspberry Pi, the Rpi’s HDMI-port will emit high-frequency audio noise (which for some people is really annoying).
According to our audio engineer, @Edison:
“The power supply for the Tone Board comes from your Raspberry Pi, and this current draw is always at a constant 350mA (independent of music playing, or not). We tested the USB-5V power supply of a Raspberry Pi with the equivalent load, and we found that the ripple interference voltage became very large: greater than 380mV. The source of the high frequency noise is the Raspberry Pi’s power chip. The good news is that our Tone Board has a filtering circuit, therefore despite the noise coming from the Pi’s power chip, the audio produced by the Tone Board is very clean.”
So this only affects other devices connected to the Rpi (not the Tone Board), that don’t have a filtering circuit. That said, if you wish to avoid using the Rpi as a power source, you can power your Tone Board via the 5V / GND pins on the GPIO, here’s how:
WARNING: DIY experience is required to perform this hack.
Tone Board works best when the input voltage is kept between 5-5.5V. Do NOT exceed 6.5V, lest you will see the magic smoke (and void your warranty).