AF-1 used with Bayou Jumper
As a followup to what I posted just a bit ago, quoted at the end...
You can get away with using the AF-1 without the extra capacitor because it has its own on-board battery supply. So the AF-1 ground is floating with respect to the Bayou Jumper ground. But if the AF-1 ground ever got connected to the BJ's power supply common, the U1 audio amp in the BJ would be only a memory.
"The AF-1's audio input jack "sleeve" is grounded. So care is needed...
You have to be sure the neither side of the Bayou Jumper's audio lines ever sees a DC ground, lest U1 buy the farm.
Since the AF-1 already has a DC blocking cap on the "hot" side, that line is accounted for.
You should still put a DC blocking cap in series with the "ground" lead to the AF-1
There's a note in the BJ manual APPENDIX about that.
Also, there are pads provided on the main PC board (JP-2 and JP-3) that can be used to install caps (a cuttable trace is provided) but the downside of that is the caps will now be in line with headphones, which can reduce the headphone level somewhat."