Fixing analog audio on the $2.58 HDMI-to-VGA adapter | nyanpasu64's blog
Fixing analog audio on the $2.58 HDMI-to-VGA adapter
Written by nyanpasu64
on July 4, 2026
I recently purchased an ultra-cheap HDMI-to-VGA DAC to hook up my Nintendo Switch to my CRT monitor and external speakers. Unfortunately its audio out jack produced serious noise problems on my audio mixer, as well as my PC's mic jack. I spent several days diagnosing impedance issues, prototyping filtering for the delta-sigma audio DAC, and reworking PCB components to produce the best quality audio achievable with the hardware.
🔗<br>Prequel: Repairing my old HDMI DAC
Before buying the audio DAC, my initial plan for video was to plug my Switch dock into my ICY-Box HDMI-to-VGA DAC. While reworking my I2C bodge, I damaged several traces and lost components on the board, and had to reconstruct them by tracing the I2C lines in GIMP to learn their functionality. (The DAC's HDMI input is an I2C slave/peripheral, the SDA/SCL lines had high-impedance pull-up resistors to 5V which I omitted, and low-impedance resistors to the chip to pull the bus to ground.)
I took this as an opportunity to practice microsoldering with NH's recommended magnet wire and 3 second solder mask, before I used them for Switch modchip installation. The 36-gauge wire was helpful, as the enamel insulation was less prone to melting than Kynar, and the wire was thick enough to not snap easily while also thin enough to largely avoid ripping pads. The solder mask could cover exposed pads I didn't want to solder onto; I also used it to pin "finished" solder joints and wires in place while working nearby, though it proved to have poor adhesion to the PCB. Perhaps I needed to clean and roughen the surface more, or try YCS's 3 second mask instead of Relife?
While tracing the PCB in my photos, I messed up several times by reading the PCB with the wrong orientation while flipping between the top and bottom. Next time I may use KiCad's reference photo functionality to model the PCB symbolically, rather than tracing traces with the GIMP pencil tool.
🔗<br>Hooking my Switch to my audio mixer
Surprisingly the hardest part of my setup was connecting my console to my external speakers. The ICY-Box DAC does not have audio out (as far as I can tell, the ITE IT6892FN chip does not output analog audio), while the Switch's headphone jack output annoying interference to my audio mixer and speakers. After hours of troubleshooting by unplugging and swapping out various cables and components, I eventually concluded that when the Switch is connected to a ground loop and not in sleep mode, its audio circuitry picks up 60hz hum and amplifies it into the output.
Asking online, I received a large number of suggestions, of varying levels of viability.
Ground loop isolators use transformers to pass voltage offsets between circuit segments with separated grounds.
I read that small ones tend to attenuate bass and other low-frequency signals, and large ones were expensive. Perhaps a cheap ground loop isolator is still worth considering?
Converting my audio equipment to balanced differential audio can avoid ground loops; this is the approach taken by professional audio mixing consoles.
However the equipment seemed expensive, and DI boxes often lower voltages to mic level (which seems counterproductive since it raises susceptibility to noise).
Another option was HDMI audio extractors, but chaos (👋) told me every AliExpress HDMI-to-3.5mm or TOSLINK extractor it tried was poor quality, while audiophile products were expensive.
In my research, most HDMI audio extractors are part of full bitstream receivers that also process the video signal. Perhaps it's just as expensive to only extract data islands and convert to analog or S/PDIF audio?
Negative-feedback audio optoisolators have two receivers, and the LED is driven so both receivers' voltage matches the input voltage.
I was dissuaded from using them by the 1BitSquared Discord server, but don't know why.
I researched processing the ground and two audio signals as inputs to a differential amplifier. I abandoned the idea since I didn't know how to make it work with inputs outside the amp's supply rails, and it could have poor common-mode noise rejection.
The easiest workaround I found was to turn my Switch's volume jack to max (with the headphone volume limiter off) so game audio would be louder than ground loop hum, then turn down audio in my mixer. However I still had to plug and unplug the headphone jack every time I put my console in or out of the dock, and I worried about long-term damage to the console's audio amplifiers. I also tested an Apple USB-C audio dongle, but did not get audio out of it.
(I also experienced the same audio buzz with a "friend's" Switch 2 hooked up to my mixer, but at the time attributed it to my third-party HDMI dongle. As a sidenote, I will never buy a new Nintendo console after they sued Switch emulator developers,...