Something you may want to consider and think about. If you look at a few financial institution cards like credit cards for example the magnetic strip positions are all the same. The magnetic strips are all about .223" down from the tops of the cards. The strips all occupy about the same height also and that should be about .330". Financial cards are all formatted the same to a standard. Within that .330" top to bottom there are 3 tracks of data, each track being .110". What this means is that when reading data on a two or three track card your read head must remain in or on the track you are reading. Not for example like using a wand to read a bar code where we can just swipe the wand over the code. If you look back at the German in the early link reading the card note how he used a straight edge and worked along that edge. Readers that read strips on credit cards actually have three read heads in a single package.
All this really means if we use a hacked read head (from for example a cassette player) is that we can only read a single track and in the case of a multi track strip we need to remain within that track. Everything depends on the type strip you are reading.
Ron