Custom RGBHV cable for Saturn to Audio Authority 9A60

I don't think 5V is necessary bc the 9A60 already has it's own separate power source.

 

I thought 5V is used for something else. Why is it present in some VGA cables/devices anyway?

 

Leave 5v alone. It's used only on PC video cards to supply power for the EDID EEPROM (EDID is the memory with display capabilities information for the video card).

The card supplies 5V so it can read EDID information even when the monitor is not powered.

 

Oh ok. I always wondered what it was for. Now I know why. Thank you!

 

Oh well. A later 3rd-party extension at best then.

 

The Saturn doesn't output a logic level sync to use directly with a VGA input.

Using a sync splitter on the TV-level sync directly from the Saturn, then having the transcoder re-combine the syncs (yeah, it most likely is a naive XNOR function) might "work", but the sync signal will not have the integrity of a true composite sync signal so could mean display incompatibility.

The best solution would be to take the Saturn's TV-level sync and amplify it to logic level, then feed that to the VGA H-sync input, and connect V-sync to VDD. You could do this either with a sync splitter (using it only for sync "slicing", as most people do, by taking its logic-level C-sync output) or you could build a discrete amplifier from two 74HCU04 inverter gates.

http://www.sbprojects.com/projects/irtoslink/coax2ir.png

This circuit should work if you increase input resistor from 75 ohm to 1k, increase the coupling capacitor to 1 uF and increase the feedback resistor to 100k. A discrete amplifier will only work with C-sync though, not composite video. A sync splitter would work with composite video too if you include the chroma filter at the input, but it costs significantly more and has slightly worse performance.

 

Audio Authority 9A60 internal tear down inside

 

From those pics it can be concluded the AA 9A60 does indeed use a very naive sync "combiner". Two of the '86's gates probably serve as sync polarity detection since VGA modes may use either polarity, and the other two make an XNOR gate for component's negative-sync.

It's pretty certain that you'll need a sync amplifier--it can be assumed all 6 op amps are enlisted for transcoding and there wouldn't normally be any need for a robust sync input when used with VGA. If you installed a LM1881 (sync slicer as amplification) with chroma filter circuit into the 9A60 you could possibly* use it with most passive RGB cables and adapters.

*The last complication may be that the 9A60 requires dc-coupled RGB signals because VGA is also dc-couped. This would require either a complicated reworking of the 9A60's input circuitry, or you could install a THS RGB amp in series with the input in order to use its internal clamp circuitry.

 

Sounds like a lot of work for nothing, if all that is involved. A decent SCART to component will have the same effect without sorting out technical mumbo jumbo.

 

That's true, but on the other hand a SCART transcoder probably will have much lower performance, and can't directly interface with VGA. The 9A60 has enough bandwidth for high resolution PC graphics. If you want to be practical, it's most practical to go with neither since analog video is obsolete.

 

Why not just use an RGB SCART cable and a SCART to HDMI converter or an RGB JP-21 cable and an XRGB mini?

 

Yeah that'd be fun to investigate. See how SCART transcoders handle RGBS at 480p and above.

 

You can try testing it with the GCVideo lite GameCube mod. It can output 480p 31KHz RGBS via SCART/JP-21.

 

Oh. Already have a component cable.

 

Then you could temporarily solder a SCART connector onto the component cable's pcb. You will have to enable RGB mode though. There are plenty of tutorials online on how to do it but avoid cutting up the actual cable part and just solder a SCART cable to the necessary pins. This way, you can remove the SCART cable when testing is complete and still have the cable intact.

 

Any simple, solderless option to temporarily test between connections?

 

Most likely not.

 

Wouldn't it be better to have a modder merge h-sync and v-sync on a Dreamcast VGA cable? GC component cables shouldn't be hacked up in such ways.

 

I think that's what the Toro VGA box does on it's SCART connector. That would be a much better option than risking a rare and ridiculously expensive cable.

 

True, but nevermind I guess. Nothing for me to gain from it.