[k00zk0]

I got this older SB card that can use kX drivers. The default and recommended method is to use the rear output jack since it uses the I2C codec instead of AC97 which is apparently the better choice as AC97 adds noise in.
 
The problem with this is that there is a weak amp on the I2C output and driving 24 ohm phones gets the amp to clip very easily. It is definitely made to be an unloaded output... The AC97 jack is very loud in comparison and pushes 5hz without distortion at max volume easily into the phones making the drivers visibly wobble.
 
The question is whether it kills to use the weaker opamp with better codec, or if the huge headroom offered by the louder amp makes up for the distortion or noise the worse codec introduces, whatever that may be. I just took a listen in silence and with zero output, it seems the AC97 makes ticks or hisses/buzzes and this may be interference from the nearby pc components. Will wrapping it in foil fix this? Alternatively I guess I can solder a new opamp in place of the one on this I2C output, or does it clip another reason? The normal listening value is probably about 1/8 of the audible loudness as the level where it clips.
 
Why does the AC97 operate worse?

 

[cladisch]

AC'97 was designed only for onboard integrated audio, so all chips ever made were optimized for price.
 
Foil will not help if the noise comes over the signal or power lines.
Changing the output's characteristics is not as easy as replacing a chip.
 
I'd suggest using an external headphone amp, or replacing the card.