There is a possibility that if you ask a professor, he might say no. You could try to say that it will be for strict personal use only.
Personally, the world is of the smart people, as the proverb says. If you want to shoot yourself in the foot by respecting campus regulations and copyright laws, go ahead. However, be aware that doing so, you will almost without a doubt prevent yourself from graduating and/or succeeding.
I think professors spend too little time on students and they speak too fast during lectures, which is why you would require a high quality digital dictaphone.
Try to make an informed decision.
Best of luck.