alright, I finish half of my mod....
I only changed the OPamp
waiting for the capacitor and ERS paper
the problem is.. right after I solder them in.... the sound is very small and it crack and pops

Then after .... I test it three time, try to re solder the join every time....
finally, after removing some excess solder, I finally got the sound fixed'
wondering what cause it though
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after I changed the OPamp, I found that the highs are much more clear, and seems like there is a little more sound stage
well... the bass sounds little different.. but don't know how to describe it