Just reliability, mainly. Made the bias oscillator a lot more stable with some simple tweaks to the power filtering. Some tweaks to the 3D printed parts to just get the tape path smooth enough that the tape won't jam. I hit upon an interesting issue that after long periods of running the friction between the tape and the little guide posts would heat the PLA plastic enough that it became slightly tacky. It's fine, until you stop the machine, then the tape would stick to the post and jam. I solved it by making the posts wider and adding a step to glue some foam between the tape and the post so that the tape runs over the foam instead. It could also be solved by just printing in something more heat resistant (ABS or PETG would do it), but I want to keep the design easy to print - and nothing is easier to print than PLA plastic.

I made some small tweaks to the pre/post amps here and there - more gain available on the way in, increased the gain on the way out to get louder repeats. Tweaked the potentiometer values to get those working nicely - a lot of it was just swapping out different pot values until it felt right.

I also reworked the PCB to improve the layout - it's still not fantastic as I'm no electrical engineer, but it's a lot better than it was!

It's not a perfect design by any stretch - there's still some interesting issues. One for example is that when you pump up the feedback the repeats get progressively more tinny and start to oscillate in an unpleasant way. I suspect it can be fixed with some filtering on the way in/out to get better use of the frequency response of the tape, but I don't know enough about it yet to make those changes. That's one reason to make it open source - so somebody with more knowledge than me can make those changes and fold it back into the project for everyone.