there is a thread on c.d. burners..
i have a Marantz / Superscope unit.
one (cdr 300?) is capable of running off of the battery pack.

so it is portable. the other next model up in price has these
interesting features......
1. it has 2 c.d. decks so can copy/dub.
2. it can change the speed and not change the pitch--slower or faster
3. it can change the pitch and not change the speed-
   -up to an octave above or below.
4. you can select small passages to repeat for studying
    a complicated riff or passage...