SD2SNES DAC Upgrade
UPDATE: User borti4938 on the krikzz forum has created a PCB to simplify this mod (see here). PCB's can be ordered at OSHPark (select 0.8mm thickness).
SD2SNES hardware revision H added a unity-gain op-amp to the DAC output in order to properly solve the low output volume experienced in previous revisions. Firmware v0.1.7 included a volume boost option that helped resolve this, but there was still an impedance mismatch on the output, resulting in less than optimal output, even with the volume boost enabled. It is possible to add this op-amp to the older revision boards to match the latest revision (this guide is based on revision F, I'm not sure if there were any changes to this section of the PCB in earlier revisions than that, YMMV).
With this mod, you will NOT NEED THE VOLUME BOOST ENABLED.
Also, THIS MOD SHOULD NOT BE COMBINED WITH THE +5V MOD, IF YOU HAVE REWIRED YOUR DAC TO +5V, REINSTALL FB341 TO ITS ORIGINAL POSITION.
First, remove R341, R342, R343, R344, C346, C347, C348, and C349
Replace R341 and R343 with 10ohm, 0805 resistors
Solder in a TS922 or equivalent op-amp (be sure to verify the pinout if using a different chip)
(Click to enlarge image)
Pin 1: LOUT
Pin 2: LFB
Pin 3: LIN
Pin 4: GND
Pin 5: RIN
Pin 6: RFB
Pin 7: ROUT
Pin 8: +3V3 (Connect to the left side of FB341, do NOT remove FB341)