There are many many hardware versions of the S3, not all of them support variable voltage AFAIK.
@dogie and @BITMAIN can you please tell us witch versions of S3 support voltage setting? Is it depending on hardware, PIC-firmware or software?
So please inform us about different hardware, PIC-firmware and cgminer versions. I notice changes to the files in the different firmwares.
regards Tomten
Its not firmware or cgminer based, I believe its DC/DC based. There are a few variants of DC/DC. There's no real way to track them seeing as they were/are sold under S3 or S3+, and may or may not span batches.