之前的問題 is solved. it is because of the unstable output of the +12v and -12v. When i measured the output of the VR500Rs, it can't stabilize at (+/-) 12.00v, it changes to 12.01v and 11.99v from time to time. After turning the VRs from 11.00v to 13.00v three to four times, it comes to stabilize at 12.00 finally. Any one have the same experience of mine?
Now my DAC is working fine with 39uf and 33uf Cap.