Introduction
The Khadas Tone Board has become very popular due to its great balance of high quality sound at an affordable price. Owing to the ever-growing diversity of users, the Tone Board has become used in an ever-wider variety of listening environments.
We understand that different people have different ears, and some are more acutely sensitive than others, to even the very low-level noise generated by a USB power source.
This blog article will discuss a few methods we can employ to reduce, but not completely eliminate, electrical noise emitted by your USB audio source.
1. USB Noise Filter
Compatible Audio Sources:
PC / Mac
Khadas VIMs
Raspberry Pi
Power Sources:
USB Audio Source doubles as a power supply
Noise-Reducing Device:
USB Signal Purifier
How-It-Works:
The USB Signal Purifier is a special device designed to filter out USB noise. It should be attached between the USB audio source and the Tone Board, and will reduce the power noise emitted by the USB source.
Do note that your noise-reduction is heavily dependent on how noisy (or what type of noise, e.g jitter, ground-loop) your USB audio source emits.
2. USB Y-Splitter
Compatible Audio Sources:
PC / Mac
Khadas VIMs
Raspberry Pi
Mobile Device
Power Sources:
Linear Power Supply
5V USB Power Supply
Noise-Reducing Device:
USB Y-Splitter
How-It-Works:
The USB Y-Splitter will allow you to split the USB power from the data signal. In this way, your Tone Board will receive data from your USB audio source, and power can be supplied by a Linear Power Supply, or other clean 5V sources.
This solution will also allow you to also use your Tone Board with a mobile device, without depleting its batteries.
Some DIY modification of the Y-splitter is required, see this website for more information: https://www.tnt-audio.com/clinica/221_diy_usb_e.html
3. Linear Power Supply
Compatible Audio Sources:
PC / Mac
Khadas VIMs
Raspberry Pi
Mobile Device
CD Player
...
Noise-Reducing Device:
Linear Power Supply
How-It-Works:
A 5V linear power supply connected to GPIO pins 1 and 21, or the USB-C input via a USB-Y-splitter, will provide superior power-noise reduction and better sound, as compared to a switching power supply. Instead of a USB-Y-splitter, you can also solder a secondary USB connector onto the Tone Board for the linear power supply.
Note that when an external power source is connected via pins 1 and 21, USB power input is automatically cut-off; however the USB-data-signal is still permitted.
4. SPDIF Input
Audio Sources:
CD Player
Other devices that support SPDIF output
Noise-Reducing Device:
SPDIF Input (Black RCA Plug)
How-It-Works:
By using the SPDIF (Sony-Philips Digital Interface) input, which is the black RCA plug on your Tone Board, you can avoid USB noise altogether. At the same time, you will still need to provide power from a clean source such as a linear power supply, to GPIO pins 1 and 21 or to the USB-C port.
5. Faraday Cages
Noise-Reducing Device:
Metal Casing
How-It-Works:
A Faraday Cage is simply a sealed metal box that will block-out external electromagnetic interference (EMI), that could introduce noise into the Tone Board.
EMI can come from many sources such as microwaves and even ceiling lights. Building a cage is simple, and instructions can be found on the web.
GPIO Pinout Diagram
This picture shows you the appropriate GPIO pins for connecting a linear power supply, or for soldering an extra USB port to receive power input! For more information, refer to: https://docs.khadas.com/toneboard/UserManual.html
Thanks for Reading!
Ideas for this blog post were taken from these forum threads:
Warmly,
Khadas Team