S-Video cable for Commodore 64 & Commodore 128

Since I got rid of my TV half a year ago, I only use an AverMedia USB hybrid TV dongle for vintage computer video display. I experimented with UHF RF output, with minor success, and also converted one of my C=128 monitor cables to give composite picture. However, it wasn't satisfying enough, so I decided to make an S-Video cable, that can be also attached to my USB dongle.

What is the gain in it? One would ask. Well, let's dive into a little bit of the different video formats first, and how the Commodore 64 produces those. The Commodore 64's VIC chip outputs chroma and luminance signals separately. This is the source of everything displayed, in any format. The luminance signal is essentially an old school black and white signal, which even by the oldest B&W televisions can be decoded and displayed, provided they are working with the same 50Hz mains, since their timing is closely related to that frequency source. The chroma signal in the other hand, is a PAL encoded color information, appropriately synchronized with the luminance signal. After some amplifications, and line separator circuitry, those are available as output as well. However, the amplifier module also mixes the two signals together, producing composite output. This one also can be found as output on the Commodore 64. Mixing the composite signal again with the mono sound channel data, encoded into the picture frames, and putting all these things onto a UHF carrier frequency produces the PAL RF output, which can be tuned on a TV, around UHF channel 36.

AverTV C=64 S-Video screen capture

Since S-Video is essentially a separate chroma and luminance signal carrier plug, we can see, that we would be able to ignore all of the possible distortions added with mix-matching all other signals, to ultimately produce composite, or even worse, RF output.

Quickly looking up the net for a wiring diagram, for SCART cable (which also contains the S-Video signals too), and an S-Video mini-DIN plug pin arrangement, I was ready to solder things together. Since S-Video signal doesn't contain sound, I also needed to make a separate RCA connector for that, on the receiver side, next to the S-Video connector.

The first tests showed flickering colors, even flickering screen, in fact it looked even worse than it was on the composite. At first sight I was very disappointed, but after that I recalled that I red somewhere that the Commodore 64/128 chroma signal is too strong for modern TVs, for their S-Video connection, so somebody installed 330 Ohm resistor in the way of their chroma signal cable. Looked around, and only found 200 Ohm resistor at hand. Quickly modified the cable, added that resistor into the C=64 DIN connector housing, and TADA! Works! Great! Finely detailed, vibrating colors, crystal clear display! By the way, grounding the sound input pin on the video connector really makes a difference, by significantly lowering static whoom noise.