OSSC Pro Gain Voltage / ISL51002

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  • November 12, 2025 at 12:06 AM #67692
    M3Patterns
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      I just got the OSSC Pro plus the Extra AV Out. I am using it in passthrough mode to go from component video into my VGA 240p monitor.

      I’m trying to figure out what the component gain units are in actual volts. (The default gain unit is 324 in the OSSC Pro.)

      I also see that the picture is not as bright as what I normally see when using either a component to RGB adapter (LMH1251) or the Retrotink2x Pro in passthrough.

      Looking at the ISL51002 spec sheet, it lists the gain as spanning from +/-6dB (just about 50% to 200%) and again says specifically that the nominal gain voltage range goes from 0.5V to 2.0V.

      The transfer function is stated to be 0.5V + (GainCode / 170). For 1.0V (which is 0.7V Peak to Peak) it’s stated that the GainCode value should be 85.

      In 8-bit, 85 / 255 = 1/3

      1/3 of 1.5V = 0.5V

      So, 0.5V + 0.5V = 1.0V

      That means that a GainCode value of 0 is 0.5V and the rest of the 1.5V is added in a proportion of 1.5V / 255.

      That’s appears to match what I see on the OSSC Pro: a gain value of 0 is dim, but not zero contrast.

      However, I think that also means that the default Y / R-Y / B-Y gain values of 324 in the OSSC Pro may be wrong.

      If I want 1.0V of output (0.7 p-p) in the 10-bit numbers that are listed in the menu, that would mean I would want a gain value of 341. (341/1023 = 1/3.)

      The math would be 0.5V + (341/1023)*1.5V = 1.0V (0.7p-p).

      If this is not correct, does anyone know what the actual gain value units are in volts?

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