Demag tapes don't excist. Well I mean there is no tape inside. If you want to demagnetise, the power of the recorder should always be powered of. Else you would do exactly the opposite of what you intended.
The use of Cleaning Tape should be avoided, because it will bring physical dammmage to your tape heads afer a while.
Use cotton cleaning sticks(for cleaning ears and keyboards) and alcohol based solutions, for tape head cleaning. The products they provide with this tapehead cleaner should do fine.
Go and see a technician, and explain him what you did. He can measure the amount of Gauss on your tape-heads, and see if he can still reverse the problems you have created.
Maybe you have not checked all the routings of your recorder, and it all is maybe still working fine. Check the levels and the pan/pot knob situation again. See if you haven't forgotten some switch....
Usually the problem is solved by something simple.
Good luck. Hope things go well in the future.
Enjoy the music.
[This message has been edited by Hano (edited 07-24-2000).]