I remember when i wanted to make something like a chromecast audio with volumio and spotify connect on my Pi 2. I had to buy an audio DAC (~30€) because I could not get the 3.5 Jack to work correctly. It just sounded bad when cranked up to a volume you could actually hear something. You almost couldn't understand lyrics in songs due to the static noise. I read that this was due to being badly shielded from the power source.

The Audio jack on the Pi 3 I have is ok, but still not that good compared to the Audio DAC of course. But then again, the audio DAC i bought for 30€ was said to be on par with 1000€ standalone audio interfaces lol.

It was some hacked-together sound output that was terrible quality compared to a real sound card output, AFAIK. You could make it make sounds, but if you care at all about quality it was a non-starter, which is one reason a whole lot of audio hats exist.

Connectors seemed low quality and so did the audio. Crackling and sounding... sort of like a broken toy for kids.

The sound quality sucks.