Sorry, don't take it personal.
Thanks, I didn't.
But, this won't work on so many levels I hate so see someone spin their wheels.
Recorders have servos to keep the speed constant - a simple PWM does not.
I agree this could be a show-stopper. However, not all cassette decks have servos. Does his use one? I don't know.
The gap in the write head will be to big, same with the read head.
The write current will be to high.
The output from the read head will go down with the reduction in speed.
Not show-stoppers. Again, I think he understands there's going to be some degradation in quality.
Here's a thought: assuming for a minute that he
can use PWM to reduce the speed, then certainly he can build his PWM controller so the speed is adjustable, no? So try 1/2 speed first, see how that works. Then he can try reducing the speed more. Nothing to lose. I don't think he
has to have 1/4 speed; he just wants to get more stuff on a cassette, as I understand it.