First impressions are WOW! :) The treble response is a lot better, the midrange has opened up and sounds absolutely spacious with deep bass, and a very extended treble. The Head Box Mk II plus this upgrade is highly recommended.
There were a few changes from the standard values which were made, here is what you need to do to replicate:
- 1000uF caps were upgraded from 16V to 25V. This is more of a longevity issue than sound.
- Input caps C13, 14, 16 and 17 were upgraded from 4.7uF to 22uF. For two reasons. First, they are almost the smallest FM caps I could find. Second, I wanted to beef up the bass response.
- Output caps C8 and C10 were upgraded from 470uF to 1,000uF. Again, to improve the bass response at the headphones.
- Op-Amp replaced with an NE5532. I know I dissed it as old, but it was a good old op-amp and I have them lying around.
The one problem is that it's picking up all the noise coming from my PC, which it masked before. I guess the next step is going to be an outboard DAC for it. :)
One tip, make sure you put the 1,000uF caps as close to the board as you possibly can. It's going to be a tight squeeze.