This is an old rev. E1 SD2SNES cart, that I’ve bought several years ago from Krikzz.
SD2SNES did undergo some revision changes in the last couple of years. First there was Rev. F, that fixed some interference with 1CHIP units. Then there was Rev. G, that fed the DAC with +5V to improve the MSU-1 volume (and added some noise). And finally in Rev. H, the +5V change was reverted and an opamp added to fix the MSU-1 volume for good.
The old E1 revision never failed me and I never invested time to find any fixes for it. I had neither used it with an 1CHIP SNES nor did I bother much with the low MSU-1 volume – the pre-patched games and volume boost in the firmware were sufficient for me. That’s why I missed various upgrade tutorials, that have been released in the past years, and only learned about the revision changes when VideoGamePerfection announced the upgrade kit.
This is the full kit (incl. the two SMD components for upgrade to Rev. F):
Upgrade to Rev. F
This upgrade is quite easy, look here for instructions.
You need to cut a trace, scrape off 4 points of the solder mask (yellow) and solder two new components (a capacitor and a coil).
Upgrade to Rev. H
This upgrade needs more work, detailed pictured steps can be found here.
First, remove 8 components (orange). Remove one more component (JP341, red) and bridge the two solder pads.
Next add the tiny PCB with the opamp by borti4938.
And finally. wire an unused CPU pin to GND. While this step is optional right now, it adds the Rev. H HWID for future firmware versions.
A new firmware V1.8.0 has been released while I wrote this article. It doesn’t show/support the Rev. H HWID in the settings.