The circuit I have used to produce this effect is based on one designed by RU-vidr @256byteram. The circuit is mainly the same, I have just changed the output section a bit and added a separate pot for the porch generation. The incoming video is clamped to a known DC level and buffered by an op amp. It is then split two ways, one path goes to a notch filter which removes the chroma and sends the luma to four comparators which regenerate the sync and back porch and produce one of two output voltages for the active video based on whether the input luminance is above or below a certain threshold. This is then buffered by an emitter follower. The other path is a high pass filter to extract the chroma which is fed to a common emitter amplifier, the output of which is ac coupled into the output signal. The user controls the threshold and the two output voltages over the full video range and also the amount of chroma signal added to the output. Due to the way the chroma is extracted using a simple high pass filter, the signal also contains high frequency luma detail so the chroma control also controls how much of this is present. There are also controls to set the sync and porch thresholds and the bias for the chroma amplifier. Playing with the latter can distort the choma signal and produce the multi-colour shimmering effect that is seen at certain points in the video.
For anyone interested, the circuit can be found here: drive.google.com/file/d/1Gdta...
14 окт 2022
