Nugent Spdif "Float" ModI am an advocate of everything in the Spdif input circuit path does nothing but add jitter, and yes that's everything, right down to a RCA jack.
However I hate to say this but if are going to be using the Upsampling/Re-Clocking (USR) card, the gains from this sort of thing will be minimal. To confirm this I ran the Pace Car into the Spdif input with USR card installed and I hear very little difference compared to the USB input. This means the USR card is creating a common denominator dragging the Pace Car's superior jitter reduction down to its level. Same would be true with any other Spdif input improvements.
Ok where does that leave us, well if you pull the USR card then all bets are back on again. Here I can clearly "hear" every little thing I do to improve the Spdif path. On that note I had Steve Nugent look at the Chameleon wiring diagram. This is "his" recommendations.
Bill - I prefer to wire the RCA directly to the primary, no grounding. Float it. Then put the 75 ohm resistor on the secondary and ground one side of the secondary. Secondary feeds the receiver chip through a .1uFd cap.
Thanks Steve! Interesting "floating" the + Spdif input. OK if you do the direct wire of the Spdif + input all you need to do is lift the Spdif RCA jack ground wire. Pat's picture on page 4 clearly shows the direct wire mod and existing green .1uf cap to Wolfson receiver chip. The only question is; what side of the Pulse transformer is that 75 ohm surface mount resistor. The wiring diagram shows it on the input side. However if its actually on the secondary like Krisno suggests then Nugents Spdif "Float" Mod is already complete.
Humm ... anyone care to check this out, I am out of town until Monday.