It could be for speed control. Like you said autostop could be another possibility. I have seen on here Walkmans in which an optical disk is used to check if the hubs are still rotating.
hey, the previously released CR124 was in 1971 the smallest portable stereo cassette recorder and featured besides hifi-recording allready autoreverse (looks very similar to the 134 but features a silver coloured fascia, there were versions with round eject-button, too.
Photo sensitive usually means that when the clear leader at the "end of tape" goes through the transport, a light switch activates and stops the motor. For those still confused, most cassette tapes start with clear plastic and then the brown recording tape starts. The clear tape is called the leader tape. autoreverser, do you have a photo of the CR124?
...and „photo-sensitive“ was meant for optical sensor controlled speed. those units actually have extreme low wow and flutter
Wow, that's nice and that case is beautiful, there was a lot of love put into that. I'm guessing the Walkman wins because it had a 3.5 mm jack? I always thought the Walkman also had the miniature headphones that were the first of their kind, so you didn't look like a dork with big cans on your head. Judging by the size and date this was way ahead of the Walkman, they didn't have the killer headphones to seal the deal.
that case is solid leather and heavier than the most walkmen the unit wasn't thought to be used for personal entertainment, the purpose was to replace the heavier broadcast/reporter reel-to-reels. they did well, the unit was great, but not using 3.5 / 6.3 or rca-jacks (instead of that they had a confusing amount of different "tuchel" / DIN jacks, so they hardly made it out of germany.
My JBR Microcassette Deck has a military grade photo sensor that can control speed instantly with very little wow and flutter but they paid a ton for the technology for each unit. I don't know much about all of the technologies but I would think a hall effect sensor would be a less costly alternative but it might not have the same sensitivity.
My memory is shot but I think it reads off the hub or motor shaft while it rotates. The rotating piece would have markings that the sensor picks up through light and dark and keeps supplying power to the motor at a constant rate. I found an article for Legos, but it explains how Legos uses it. This is probably similar to the early tape decks that used this technology. https://www.sciencedirect.com/topics/computer-science/rotation-sensor
I've seen the same done by Accel Automotive Performance on a "breakerless" distributor they made in the late-60s, and also by Mitsubishi later on. Both employed a simple arrangement of a light source, a shutter wheel and a photoelectric sensor. Accel used an ordinary 12v filament bulb in theirs, while Mitsubishi used not one... but TWO LEDS, for separate functions inside the same housing! Because they're enclosed inside the distributor housing, a shield between the works and what happens inside the distributor cap was used to prevent a misreading.
Yea, if I had been looking at one of my turntables, I would have said that.... Sometimes the answer is right in front of us!