Audio Noise and Distortion from IO Board

[SuperSpongo]

Hey guys,

I have a problem with the analog audio output from my MiSTer IO board (I think it may be rev 5.5 or 5.6).
Recently, the output has developed some kind of distortion, I can also hear SD access very clearly.
I googled and found a hint that it might have to to with i2s and the four switches on the DE10 board, but the switches are all in the off position (i also have my MiSTer in a case so it was unlikely to begin with).

I had a look at the schematics of the analog audio out, it goes something like "GPIO pin --> RC filter --> RC filter --> coupling cap --> headphone jack" for each stereo channel.
The distortion sounds like a cap charging up in my tests, so it might be the the cap? But the problem occurs on both channels so I kinda ruled this out.

Also, when I screw with the volume settings and custom audio filters in software, the distortion is affected. So I kind of hope it is something software related. I plan on disabling "volumectl" in the ini and see what that does.

Does anybody have a clue what this could be? Did I fry my GPIO pins (that would suck in this market..)? Any input is appreciated!

[FPGA64]

The audio from the 3,5 mm jack is bad. Much better to use a miniTos cable and connect to an external dac

[SuperSpongo]

Yeah, I read as much, but it's never been THIS bad. I setup the MiSTer pretty early and have always used it with the analog output without problems.
Also, the MiSTer has enough cables sticking out of it from all sides as it is, I really want to avoid adding yet another dongle with its own power supply if I can.
I have a workaround with an HDMI to VGA adapter which breaks out the audio, but it's another device. The Tendak dongle introduces pops and crackles itself on the Super Nintendo core, by the way. I have to use my HD Fury2.

[SuperSpongo]

I did some more testing yesterday. I swapped the coupling caps for 10uF without any change. Then I remembered reading somewhere that some core builds affect the analog audio differently because of the way the circuits are arranged in the fpga (don't know whether this is true or not).
I tested other cores and it seems to be a problem of the SNES core. Genesis, Neogeo and NES are fine.

I tested with the 240p test suite sound test on the SNES (Mario jump sound) vs the NES core's jump sound on Mario 1.

I think I'll try a couple of older SNES core versions and see if they perform better.

[antoniovillena]

Not all MiSTer have sigma-delta DACs. You can buy one with I2S DAC that has better sound quality

[wellbow]

I built my MiSTer a year ago (maybe?) and I am using the 3.5mm jack on the analog board just because the spare monitor I am using doesn't do audio. I haven't noticed too much of a difference with the audio than emulator, or what I remember from the original systems. How can I tell which DAC I have? I have been curious about this