VGA - Eurorack interface project (I'm looking for feedback)

Hi, it’s my first euro project and I don’t know if I did anything wrong.

KiCad project file

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I think you should definitely build this on breadboard first, to confirm the design works the way you think it will. For example the R_IN circuit is currently configured as a 10K/750R voltage divider, giving you only 7% of the input signal being passed through - very likely not what you want. Also I’m not sure the voltage dividers/non-inverting mixers will work quite the way you would typically want them to (two signals with variable resistors into a non-inverting op-amp input doesn’t give you summing or a linear response like an inverting op-amp summer circuit would). Always a good idea to prototype!

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VGA operates on 0.7Vpp and I dont expect input voltage to be higher than 10Vpp, so that’s exactly what I want

Fair enough, that makes sense - and I should have seen that in your block diagram. I’m used to LZX standards, where voltages are typically 0-1V for video synthesis.

Cool idea. I wish VGA was more supported in the video modular world.

Is this intended for use with an LZX system? Will it sync to other modules?

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nah, they’re too expensive

if you’re just doing stuff with vga, i’ve had good luck mixing the rgb channels with dirty mixers to get different colors combinations.

If you’re just mixing the color channels from a VGA signal, the mixer circuit in the “dirty mixer” is just a passive mixer… nothing dirty about it since there’s no sync involved.

I originally started trying to build a VGA based system. I built a couple or basic ramp based oscillators and I injected images from a camera, through an old box that I had for video gaming (Composite > VGA). When I used that box, it would generate the timing signals, which would be passed through. Otherwise, timing would be generated by a CHA/V.
It seemed like the monitors started displaying horizontal imagery as soon as they detected a signal even if it was outside the display window that the incoming video was being displayed in.
This meant that when I added an oscillator into a signal path that also contained an incoming camera image, that image was displayed in a smaller ‘window’ that was disconnected from the left of the screen.
Remove the oscillator and it went back to full screen. At that point, I realised that I was going to have to add a lot more circuitry and add a more complex output stage. When I looked into the number of op-amps that I would need to use, the Cadets didn’t look so expensive after all, so I went LZX.
Best of luck with this!

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yeah, but I don’t want to make full video system. Only this module and maybe sync generator.
Thanks for reply!