Prefiltered S-video to composite for better pics on vintage color TVs

[wa2ise]

On a vintage color TV, they didn't have comb filters, but only "notch" bandstop and bandpass filters for chroma-luma separation. This assumed that anything above 3 MHz on the demodulated composite video signal belonged to the chroma subcarrier. Problem is that any fine detail in the luma ends up as crawling rainbow colors on the CRT.

But, if I have a source of S-video (separate luma and chroma, like on a better CECB or cable box), I can prefilter the luma (bandstop) and prefilter the chroma (bandpass) so no fine detail luma exists anymore, and thus won't become crawling rainbows on a vintage, or a later production notch filter TV set.


The circuit:
The values of the parts are not that critical. The resulting prefiltered composite video then feeds a TV modulator to send to your vintage color TV set. Your set will present better looking pictures.

[DavGoodlin]

Thanks for the great idea.
My Allied catalog shows that Bourns and API Delevan both make 5.6 uh inductors for a buck or two.

[wa2ise]

I used a combo composite and Svideo jack I salvaged out of a dead DVD player to build this filter on. The cap lead with the red sleeve is the chroma.

[Findm-Keepm]

Originally Posted by DavGoodlin

Thanks for the great idea.
My Allied catalog shows that Bourns and API Delevan both make 5.6 uh inductors for a buck or two.

Aside from the salvaged connector, I got the coils and caps for less than $1. Thanks! Can't wait to try it!
I used a TDK inductor, SPT0203A-5R6.

[wa2ise]

An update, here I acquired a modulator that includes an S-video input jack. So I installed the above circuit to it.

And a snap of a notch filter TV fed by this s-video modulator mod:
Notch filter TVs usually have color crawlies on sharp luma edges, but as I filtered those out in the luma before it became composite video, these are way down or not visible.

This modulator uses a LA7161 chip, and it can be configured to do Japan channels 1 and 2, which happen to be identical to American CATV channels 95 and 96. Because I can. And this allows me to have multiple modulators running at the same time.