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Is there an off the shelf converter / adapter from C128 RGBI to VGA that will work with modern-ish low voltage VGA?

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  • Not that I'm aware of. Typically this requires using chained RGBI -> RGBA and RGBA -> VGA converters.
    – mnem
    Mar 21, 2021 at 3:11

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RGBI to RGB only needs a couple of diodes and resistors, see e.g. here, and that will work with VGA-RGB. I am not aware off-the-shelf ones for that are available, OTOH they are not exactly difficult to make yourself.

I have no idea what @mnem means by "RGBA", usually this is an abbreviation for red-green-blue-alpha, and refers to how image data is stored on memory. There is no alpha channel when outputting this.

Here's the RGBI to VGA RGB conversion circuit:

Schematic
Credit: Alex Hajnal based on circuit by Frank Buß

The circuit above was based on the one shown below (from this page). Personally1 I'd go with the former circuit.

Alternate schematic
Credit: Alex Hajnal based on circuit by H2Obsession

1 Personally == @AlexHajnal's opinion

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  • A as in analog, as opposed to digital RGBI. RGBA is a common abbreviation used in arcade circles, which is what a lot of the common inexpensive RGB to VGA adapters were originally made for.
    – mnem
    Mar 21, 2021 at 9:01
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    Interesting, but for me analog RGB is still just RGB... and "digital" RGB is just RGB with two analog levels. RGBI is RGBI.
    – dirkt
    Mar 21, 2021 at 11:36

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