Due to the different expansion ports, my C64 A/V adapter (with a 5 pin DIN plug) does not really fit well to teh VIC-20. Since the VIC-20 got into my focus, end of 2020, it was sooner or later required to make a dedicated A/V adapter for it. It had to be much narrower, than the one for the C64.
VIC-20 A/V adapters (Rev. 0)
The A/V adapter does not contain any magic parts, that will improve the picture quality, but... it does not ontain anything, that will make it worse and it allows you to use standard cables of the quality, that you want to pay for and the desired length. And all that is better than any badly soldered DIY cables made from the cheapest possible of the shelf cables. So, this is the cause of the picture improvement, that was reported about the C64 A/V adapters by some users.
The PCB (rev. 0) and 3D-printed case
I have already stated, that the special DIN connector (the Lumberg SV-50) is a necessity. The cylindric flange of it provides a secure fit in the VIC-20's A/V-jack. Other (cheaper) DIN connectors, which don't have this flange, will cause weight of the adapter and the cable(s) apply force on the terminals of your VIC-20. Not a good idea! If I wouldn't have found this (not exactly cheap) connector series, I would not have developed an A/V-adapter!
Backside of the A/V adapter with teh Lumberg SV-50 DIN connector
The VIC-20 A/V adapter fits on the C64 as well (but is just providing composite video) and also on the Atari 800XL.
Testing the adapter with my original (2 prong) VIC-20
Fitting the A/V-Adapter on an Atari 800 XL
After reading about the S-Video mod of the VIC-20 - the VIC chip provides Luma and Chroma - I was thinking of upgrading a further revision (Rev. 1) of the VIC-20 A/V adapter. Also Fredric QJ Blåholtz mentioned the free space on the PCB that might be suitable for a version with a mini-DIN connector (for S-Video).
I had to make the PCB slightly bigger (1mm in each X- and Y-direction), which should not be a problem. It requires a new case, anyways.
Eagle layout of the Rev. 1 PCB
The revision 1 is now tested, documented and released on github.
Test fitting the Rev. 1 on a VIC-20
The PCBs arrived a couple of days ago. I have made a resesign of the (3D printed) case and first tried to fit it on a VIC20, which works well.
The yellow RCA jack is composite video with unmodified VIC-20s. On modified VIC-20, it will be Luma only, so the picture is black and white.
The Composite video was tested successfully on an unmodified VIC-20.
One VickyTwenty (that new build clone) was then modified with the S-Video mod. and the S-Video jack was tested successfully. The S-Video image quality is way better than the composite video quality, which is traditionally not so great for some color combinations (= checker board). Check it out here.
BASIC screen after S-Video mod (photography)
The feather like effects on the previous image are matter of photography (Moiré pattern).
NOTE: The VIC-20 A/V-Adapter is NOT the S-Video Mod. This has to be done inside the VIC-20. But the adapter allows to connect an off the shelf S-Video Cable.
The VIC-20 A/V-adapter is open hardware, please find the complete set of files and documentation for Rev. 0 and Rev. 1 on github.