RGB to composite conversion without scaling

[ahofle]

How difficult would something like this be?  I see a ton of products out there, but they are designed to scale a higher definition signal down.  Like this:
http://www.alibaba.com/product-gs/1351388636/PC_VGA_to_TV_Composite_Video.html

What about a similar device that takes whatever signal you give it (e.g. 240p from CRT_Emudriver) and simply converts from RGB to composite.  Given that older consoles were perfectly able to send out a very clear native low res/CGA signal over composite, it seems like it should be possible.  Any electrical engineers in the house?  This would be one of the greatest innovations IMO in the arcade/emulation world, especially since TVs with composite inputs are literally everywhere and would make perfect arcade monitors.

[MonMotha]

There are a ton of single-chip analog solutions for this, actually.  Most of them also offer S-Video.

http://www.ebay.com/itm/Weiya-CV-04-RGBS-RGB-CGA-arcade-jamma-game-to-TV-composite-video-converter-MAME-/260891045027?pt=PCC_Video_TV_Cards&hash=item3cbe516ca3 is an example, but I've seen them cheaper.

Most of them use the Rohm chip, though I think the Analog Devices chip is slightly higher quality (this may just be because people who use it tend to use a higher quality supporting circuit).  Jrok sold one based on AD525 at one point.   I did a design using the AD525 a while back (no volume production) and found the results extremely good when using S-Video.  Results with composite were mediocre limited by the nature of composite video.

[ahofle]

Awesome, thank you!
I guess you would just need to hack a VGA cable to this thing and that's it.  Do you happen to know of some links with s-video connections?
Also, how can you tell if the signal is scaled or not?  For example, would this one take a CGA signal?

http://www.ebay.com/itm/VGA-to-RGBS-CGA-AV-S-video-PC-to-TV-arcade-video-game/260705997170?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D18239%26meid%3D3047640379024146001%26pid%3D100005%26prg%3D8344%26rk%3D1%26rkt%3D5%26sd%3D161153413308%26

[SailorSat]

Technically those VGA to xyz converters need to scale the image down somehow.
Go with the Wei-Ya CV-04 as suggested

[MonMotha]

The popular Weiya linked above has an S-Video output, as does the JROK.

[Brian74]

I have one of theses and it works great!
27" crt tv going from vga to s-video
http://m.ebay.com/itm/380651416783?nav=SEARCH&sbk=1

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