Constant high pitched noise from Coregrafx console audio out

[ASDR]

I have a CoreGrafx console with a THS7316 RGB mod installed. There's some buzzing and a constant high pitched whining sound on the machine's stereo audio output. I know that older consoles often have some audio noise, but this is far worse than anything I've ever heard from a SNES, Neo Geo, Mega Drive etc.

I tried the following things:

- Used a different, known-good, linear power supply to eliminate noise from a switching power supply as the source. No difference.
- Directly hooked up the audio to the console without a video cable attached to eliminate coupling between composite/RGB/stereo in the SCART cable. No difference, noise is already present on the audio output of the console.

Here's a recording:

https://soundcloud.com/user-961563879/coregrafx-whine

Volume is a bit low, might have to turn it up on your end. The noise very annoying and obvious on both my headphones and the 5.1 system I use for playing. Recorded from startup to shutdown playing the intro tune from World Circuit Racing. Recorded directly from the DIN8 jack, no video cable attached. One of the channels is more affected, the noise is even louder after the tune is finished playing. Channels might have been swapped when I wired up the audio interface to the DIN8 jack.

The console seems only silent when the sound hardware is not initialized, like when turning it on without a HuCard inserted when it just shows a white screen.

I've seen this older thread:

viewtopic.php?f=6&t=55654

Seems like a widespread problem with PC engine consoles. I wonder, does every single PC Engine, Turbografx, Coregrafx, Supergrafx, Turbo Duo etc. console have this issue? Are there models or individual machines not affected? Is there any fix (replacing caps, cutting traces, routing traces away from others etc.) that mitigates it? I never heard this constant sound when watching YouTubers that record from actual hardware (the GameSack guys etc.). and didn't find much talk about this.

Thanks!

[ApolloBoy]

They all do that, honestly I've just accepted it as one of the quirks of the PCE/TG-16 hardware.

[ASDR]

Ah well, OK. Kinda annoys the shit out of me, though. Curse you, crappy 80s consumer electronics circuit design. Tim Worthington's jailbar fix seems to work so well, I wish there was something like that for the audio. I think I'd trade jailbars for peace & quiet! Maybe I'll chain a noise gate guitar pedal between the OSSC and the PCE

This video has plenty of PCE footage, and you can actually clearly hear the whine in any moment where the game audio goes a bit quieter:

https://www.youtube.com/watch?v=ZM7aHbmo9eM

I didn't' notice it in any videos from GameSack, but I guess they just always had the game audio quite low because they talked over all the footage.

[thebeautifulones]

Bothers me too, but the right low pass filter should work fine. I don't play PCE that often, so I haven't tried any filtering yet.

[ASDR]

If I do a spectrum analysis of the noise-only part of my recording, I get this:



The most annoying / piercing part is certainly higher pitched, but it doesn't really look like something you can just LPF away.

This is a job for somebody more skilled than me, but it would be interesting to confirm if the sound chip is at fault or if there is simply poorly designed amplification / output circuitry around it or maybe some poorly routed traces. If really all revisions of the console have this issue I'd unfortunately guess the chip itself has an issue, but maybe there's hope.