Interesting. We have a modded Technics 1/4" deck that was done by Super 8 Sound back in the day, to play fullcoat S8 mag tape. This is Super 8 film that has no picture, it’s all audio, used for double system editing of picture and sound. They made two or three portable systems, based on different decks (some Uher, some Sony), and the track position varies from portable to portable. And then they made some larger studio machines that can take big reels, like ours. The technics allows you to choose which head you want, and has adjustments to fine-tune the head position to maximize coverage.
To keep sync, they added a perf sensor, which presumably sends a pulse to an external resolver. That in turn sends signals to the servos in the deck to adjust speed. This is similar to what’s done on a Nagra and other 1/4" decks, but instead of a perf sensor, they use a recorded 50Hz or 60Hz pilot tone signal on a separate track (or with Nagra’s Neopilot, two out of phase pilot tones that cancel each other out on playback). In any case, the basic idea is the same - a resolver detects the speed variation using the reference signal, and adjusts the playback speed on the fly to correct for speed changes.
We don’t have the resolver for ours and there is no documentation available. Most of the people who designed these machines are long gone, and I’ve been unable to get good information from the folks who sold them, so I’m very curious how you go about doing this. Eventually I want to start probing the mystery “Sync” port on the back of the machine to see if I can figure out which pin does what. But controlling the servos like this is well beyond my skill set…
Front:
Back:
Inside, back side of the Sync connector. Haven’t traced these yet because the inside of the deck is like spaghetti:
